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wally8
02-15-2005, 07:00 PM
Hey Guys,

What roll center height should I be shooting for here. Again I'm drawing from my dirt oval background here.

We normally shoot for 3.5 to 4 inches static from a geometry standpoint. This is for an A body or G body front stub on dirt. Typically if you were going to put the same car on asphalt it's recommended you go lower, like 2 inches but I've never actually put one on asphalt so I wouldn't know the validity of that number.

How about road racing? What is typical for say an American Iron car?

The numbers I'm working through look best with an Impala spindle (8.75in.), stock BJ's, a level LCA and relocating the UCA inner pivot up about 3/4 inch or so. This moves my IC out to about 2.5 times the track (77in.) and gives me the lowest RC migration, from 3 static to about 1.4 with roll. Not sure where it's going side to side. This seems to give me a minimal jacking effect as well. This is for an A body BTW.

I haven't checked what this will do to my camber gain, however, but I'm assuming nothing too bad. Not too worried about bumpsteer at this point either. I'll do whatever I need to do to shim it out. Having the IC out there like that should make that part fairly easy.

Am I working in the right ballpark on this? Am I way off the mark? I've run too many numbers right now and I'm losing track. Any opinions are appreciated.


Wally

wendell
02-16-2005, 11:32 AM
WOW, can't believe that no one is touching this. Possibly the most substative post in months. Guess everybody is busy discusing how to tuck 24inch spinners under their first gen.(I'M KIDDING!)

All kidding asside, quite a few people hang out here that can answer this question in spades.

With out any paved or dirt experience and after studying for the last 6 months, this week I started to design a front end with a static front RC @+2inches. I too am looking at maximizing the length of the ICs and minimizing RC migration then clean up bump steer. This is for my first gen Fbody.

The book "Paved Track Stock Car Technology" has been a great resource for me and would be a very quick read for someone with dirt track experience. Also, try to get as much info as possible from the Bush North guys. Heavy, fairly narrow track, high CG... I'm hoping to get some face time with a American Irion racer in the next few weeks. I'll pass along anything I can extract. :ssst:

wally8
02-16-2005, 12:15 PM
Thanks for the input Wendell.

As I expected my dirt experience is only good for the fundamentals.

I thought about 2" as a baseline also since that's the recommendation for an asphalt modified but I was worried that it might venture below ground dynamically. I don't think that sort of migration would be any good (+ to -).

My thoughts on AI are that it's a fairly similar app to what I'm shooting for although my wheelbase is probably longer.

I might try tuning it down to 2.5" and see what I get from there. My CG should be a little lower than stock since the car will be lowered but I'll have a big ol' steel headed big block in there so my F/R balance is not going to be good.

Sounds like we're designing along similar lines though.

Let me know what you find out, if anything.


Wally

dennis68
02-16-2005, 12:15 PM
Typical??? nothing is typical on asphalt. it depends on who you talk to. There are a bunch of guys out there running whatever advertising has determined to be the latest and greatest. You would be surprised how few folks are actually out there have a basic understanding of suspension geometry....evn fewer understand what works, what doesn't and why.

here is a link to the spindles I designed for my A body, it's the last image of text. link (http://www.onrails.net/suspension101.html)

FRCH came in at 3" with RC migration at less than 4" throughout range of travel. I also got bump to near 0.

You seem to have a good grasp on dirt geometry...not much different. Minimize the difference between RCH and CoG without inducing any unpleasant jacking effects. On the A body I have found it is pretty difficult to put RCH and FVSA where you want it and limit RC migration without lengthening the upper and lower arms.

Also watch scrub radius, it has a little more importance on asphalt.

wally8
02-16-2005, 12:56 PM
Hey Denny,

I've raced for a lot of years now so I'm not surprised at all by how many people have no clue what they're doing with their cars :-)

I don't want to be derogatory or offend anyone but road racing I'm sure has a higher average education level than dirt track racing by far......

Most people are into the "trick of the week" rather than solid theory. I guess that's why we have won more than they have :-)

I was curious to ask you some more questions about your spindle since it seems you're going the opposite of what Wendell and I are thinking about.

Seems you'll have a very close IC (short FVSA) with the spindle you're contemplating thus the reason for your high rate of RCH migration. Are you comfortable with that or is it more a compromise you're making due to not relocating the UCA pivot point? It's pretty common to move that point up from stock on all the race cars I've seen.

I don't care much about correcting the bumpsteer with the spindle directly. I can shim it out easy enough other ways.

How much taller is your spindle than an Impala (8.75in.)? Did you figure in using tall BJ's too? Also, you wouldn't happen to have the KPI spec for an Impala spindle would you?

I'm interested in your thought process for the design, particularly since you've had the Impala spindle on yours (still do?)


Wally

C4Bird
02-16-2005, 01:12 PM
Not trying to go too far off subject here, but other than "Paved Track Stock Car Technology", what other books do you guys recommend reading to learn about this? I am very interested in learning suspension design and theory, but don't have the time to go to school for it. I would rather spend time reading what the knowledged on the board suggest rather than as Wally stated "the trick of the week". Thanks
-Nate

wendell
02-16-2005, 01:20 PM
Wally,

I agree with looking at the AI cars. The Bush North cars are also a good fit. I'm guessimating my CG @ my cam height.

dennis,

I've been reading your posts for a while. If I could do it all over again I'd be a mechanical engineer. I think this stuff is as fun as it gets!
Not to hijack this post but what is the most universal format to share suspension info? When everything is fleshed out I'd like to solicit oppinions. So much fun!
J

Salt Racer
02-16-2005, 02:08 PM
Dennis,
Did you change something from what we did? I thought FRCH was 1.78".

Wally,
I helped Dennis design his spindles based on his measurements. It's 2.5" taller (UBJ center to LBJ center) than what he currently has (B-body spindles?). FVSA came out to be about 110".

Anyway...What numbers to shoot for really depends on what your main objective is. What works good on slow, twisty road courses may not be the best for high-speed open road racing, for example.

77" FVSA may be bit too short for OE type short knuckles, as short knuckles tend to increase the rate of FVSA length change. Check the FVSA length and IC height at 3" bump. I'd say instanteneous camber gain is -0.8* or so with 77" FVSA. If you plan to do more than one type of racing, I'd make the FVSA adjustable.

I normally shoot for RC height anywhere from 1.5" to 3" depending on application. I wouldn't go much higher than 2" with short FVSA.

Vertical RC migration isn't necessarily a bad thing. The goal is to maintain the roll moment as close to constant as possible. So RC should drop 1" down from static when suspension is at 1" bump position. This usually happens on SLA suspension w/o trying. You do want to minimize lateral migration under roll, however.

Both side scrub and scrub radius play a big role in stability on pavement, especially if you intend to run wide rims. Keep LCAs close to level. Getting small scrub radius may be tough with OE GM style knuckles, since most of them wouldn't even fit inside 18" rims. Either steering arm or UBJ will hit the rim.

dennis68
02-16-2005, 02:33 PM
I figured the master would check in soon. :worship:

Yeah Katz, I don't remember why now but I did make a small change that bumped FRCH to 3". It was a worthwhile compromise, maybe to further reduce RC migration, it's been awhile. Looks like I'll have my spindles this time next month :fingersx: .

Wendell, I've been playing with Performance Trends, as long as you understand basic design theroy and know the x,y,z measurements it's a pretty good peice of software.

Wally, I did not figure in tall ball joints, I left them out so I can later add them if nesessary. The Impala spindles are the same height as the "b" spindle so mine would be a couple inches taller. Total height is 10.50". KPI is 13*ish. I made quite a few compromises playing with getting scrub as low as possible without lengthening the arms. You are correct in that I did not want to relocate the arm mounts.

Mean 69
02-16-2005, 03:04 PM
Total height is 10.25". KPI is 13*ish.

With ball joints? With a few degrees static camber too, or is this the static design? I have to say, I STILL have not studied the stuff you sent me, though the numbers you show look darned good.

I'd shoot for as low a roll center as possible, but, as Den and Katz very most likely did, let it float a bit to minimize migration. If it moves all over the place, well, things won't be "linear" in roll, etc. As you probably know, from the dirt track deal (which we are very eager to learn from by the way!!!!), the longer the control arms, the slower things like scrub, IC, etc move around in bump and roll. My personal feeling is that the roll center height, scrub, and migration characteristics far outweigh the need to have a cool "camber gain" figure. Everyone is different though, we all have our preferences.

I'll advertise what I think is an excellent book on suspension, once again, it is called Race Car Suspension Design, or something really close to that, from Allan Staniforth. It is a terrific read, and has an absolutley wonderful section on weight transfer. A great third book to Herb's (first), and a number of the others (Carroll Smith, Van Valkenberg, etc).

Great stuff, keep it coming.

Mark

Salt Racer
02-16-2005, 03:53 PM
...it's been awhile. Looks like I'll have my spindles this time next month :fingersx:

Yeah, it's been a while plus I've been so freakin busy. I forgot exactly what we did. It'd be cool if you show up at Buttonwillow with new spindles on!


...My personal feeling is that the roll center height, scrub, and migration characteristics far outweigh the need to have a cool "camber gain" figure...

Couldn't agree more. I actually use long FVSA and short SVSA when I design suspension from scratch for a dual-purpose car.

As for Dennis' numbers, I belive 10.25" from UBJ center to LBJ center. The vertical span between UCA and LCA inner pivots was like 9.625" average. My computer shows 11.9* KPI with -1.5* camber, so he must have increased it for reduction in scrub radius.

All this tech talk is really making me want to fix the front end of my car...

Mean 69
02-16-2005, 04:43 PM
All this tech talk is really making me want to fix the front end of my car...

Me too. But at this point, I'd really just like brakes, and for my new headers to fit. And to beat the poop out of the car on the track. Aye-aye-aye.

So the spindle you guys came up with is a one-off? I know that HRP, Coleman, SCP, etc offer a 9" unit, with a ~10 degree KPI, and a ~3" or so pin height. Hoerr has used this on their T/A cars in the past, though they wouldn't give me the exact, or even close goodies, other than to say that scrub is minimized even with a really deep set wheel (or is that especially because of a deep set wheel?).

I could be in my new shop as early as next week, and I'll tell you, one of the first darned things I am buying is a car lift. I am getting too old to crawl under the car trying to fit big tube headers, bleed brakes, bla bla.
M

MrQuick
02-16-2005, 06:15 PM
I can't wait to see what Den and Katz came up with as a spindle. Im also looking into the SED units too.
Den how much is a pair going to run you. I was pondering several ideas over the years and how improvments can one make to pivot points on a stock frame to improve geometry but using a tall GM F, G body,or any other production spindle? I guess what im trying to ask is, Is a new spindle design really necassary?
Mark, I have seen the circle track spindles and they look basic and do improve geometry but are they designed to sit with in a certain guide line as per rules and regulations of the race class? Congrats on your new shop, Im going through the same thing now, hey if your rack hunting, go with a drive on type with center point lifts,with all of the suspension work you have infront of you. Trust me you will not regret it. Your brakes still giving you problems? I had the same thing happen to me, turned out to be a bad master cylinder...I guess new don't mean sheet!
Thanks for the info guys :bicycle:

wally8
02-16-2005, 06:21 PM
Okay. Thanks for all the input so far.

I'm down with the low roll center and I'll start shooting for 2".

I agree with the order of priority for the design principles as well. We just adjust static camber with tire temps and work on it until they come out even. If everything else is close then it's pretty easy.

Now for some questions:

1. Maybe I'm missing something but how do you raise spindle height, maintain stock UCA pivot point and come up with an FVSA of 110"? I must be doing something wrong here. I'm using A-body numbers as well and they are very similar to Denny's (mine's a 65 for reference) I assume that you're using stock length LCA's as well? (15.5in) This would seem to shorten FVSA substantially.

2. I'm trying to get a handle on actual spindle measurements and I don't have any sitting in from of me yet so it's been a little tough. Are the heights you're talking about from UBJ pivot point to LBJ pivot point? I see that's the case with Salt Racer's numbers. From my research that would be pretty close to a B-body with tall UBJ's and LBJ's. Of course, I could be way off since I don't have one physically present.

3. If so, Denny, do you have numbers for a B-body spindle with stock BJ's? I was under the impression that B-body spindles were about an 1.5in taller than my stock spindle which would make it about 8.75 in. tall (no BJ's, just the spindle measurement)

4. I was actually getting some decent numbers with my stock spindles and tall UBJ's and LBJ's. Comments?

5. I thought an FVSA of 77 was pretty good given the recommendation of 2 to 3 times track (1/2 track actually which is 29 in this case). 77 is about 2.5 times. This is a Van Valkenburgh reference IIRC (<--- thanks Denny, I got to use that reference <---)


Admittedly I'm handicapping myself by sticking with stock spindles but I haven't found a big enough reason to pursue something different yet. This won't be an all out track car so there are some compromises (weight being the biggest one).

Good discussion so far.



Wally

dennis68
02-16-2005, 06:28 PM
OK, here is the scoop. As many know I am on....limited funds (limited by my kids and wife, my W2 shows I should be a damn millionaire-where the hell is all the money)? I thought about this a long time and evaluated all the different possibilities. Buying a pair of 1 off custom spindles built exactly to my spec for under 500 bucks is a way better use of funds than trying to cobble together something that may or may not work.

The only problem is that the steering arm and ball joint tapers are not negotiable, they have a jig and it cuts the taper and you have to find ball joints to fit; small trade off in my opinion.

After enough hours in front of this damn LCD to make my eyes jump out of my head I came to a few conclusions;
1) No matter what you do to the stock spindle it will never be ideal
2) No matter what you do an F or B spindle it is even worse than stock
3) Relocating control arms is feasible but spindles require much less work and with relocating all of the pivot points that leaves a great deal of room for error.
4) Katz is a great guy and I'm grateful for his advice and time over the last month.
5) My elco is gonna whoop ass at the track……let the smack talkin’ commence!!!

Wally, I'm pretty sure the B spindles are only an inch taller, maybe 1.25". Mine are 10.50, that’s about 3" taller than stock.
110", I wish. My FVSA is under the magic 70" mark but scrub is under 2" and bump steer is almost 0 (.026" at 2.00" of dive) so I'm not terribly worried about the violent change, again a trade off for something else. I suppose if I were going to do a lot of high speed runs (ala Nevada style) I would be more concerned running that short of an FVSA but for street driving I don't mind the stiffness and most of tracks i will visit are nicely paved.

If I had to do this all over again I might have just gone with tall ball joints upper and lower, no on second thought I wouldn’t only because I like to be different. Using the stock spindles with tall ball joints is a huge improvement over the typical “tall” spindle conversion.

Good luck, I’ll post pics of my spindles when they show up.

MrQuick
02-16-2005, 06:42 PM
ok but why? We had so much better handeling (as it seemed till now) with a GW upper and a tall spindle. There has to be something other than having a spindle made. How about other production ones? C4, C5, Mustang, 4th gen Camaro...I know strut style but hey I though i'd throw it out there.
I hope your Elco kicks something,it better! The only thing I usually wanna kick (down) is my previous lap time. Remember the only thing tha hauls more trash (talk) would be a garbage truck, and they would benifit from a lower roll center too.
Wally sorry for high jacking your thread. :drive2:

dennis68
02-16-2005, 06:49 PM
ok but why? We had so much better handeling (as it seemed till now) with a GW upper and a tall spindle. There has to be something other than having a spindle made. How about other production ones? C4, C5, Mustang, 4th gen Camaro...I know strut style but hey I though i'd throw it out there.
I hope your Elco kicks something,it better! The only thing I usually wanna kick (down) is my previous lap time. Remember the only thing tha hauls more trash (talk) would be a garbage truck, and they would benifit from a lower roll center too.
Wally sorry for high jacking your thread. :drive2:
Vince, you find a spindle with all the correct number and I’ll try it out. I honestly don't think one exists.

I'm gonna save my trash talk for the GG show.

wally8
02-16-2005, 06:51 PM
Hey Denny,

Man! Ain't that the truth!

Would you care to expand on a couple of your points?

Specifically

1. I'm not looking for ideal, not that it's not a good idea, obviously. This is one of my compromises. What area do you think the stock spindle falls shortest?

2. This is clearly no where near the case in the dirt world. B-spindle geometry is considered far superior to any other stock spindle (stock spindle classes being the assumption here) What makes it worse than stock for a road racing app, in your opinion?

3. This may raise the skill level but I see it as something that has to be done. What sort of compromises have you found by leaving it stock?

4. No explanation needed :-)

5. I wish I was in a position to get mine on a track soon but it'll be awhile. I'm sure it will be faster than yours though ;-)

I know you're pretty passionate about your setup so don't think that I'm hacking on you. I'm just trying to figure some stuff out given different compromises. You've picked a different set of parameters than I have so I'm genuinely interested.


Wally

dennis68
02-16-2005, 07:07 PM
Hey Denny,

Man! Ain't that the truth!

Would you care to expand on a couple of your points?

Specifically

1. I'm not looking for ideal, not that it's not a good idea, obviously. This is one of my compromises. What area do you think the stock spindle falls shortest?BIggest gripe is spindle pin height. By the time you drop the spring height down to a reasonable level the whole front geomtery looks like hell. Mine had a FRCH of like -12.00 or something with stock spindles and a pretty big spring drop



2. This is clearly no where near the case in the dirt world. B-spindle geometry is considered far superior to any other stock spindle (stock spindle classes being the assumption here) What makes it worse than stock for a road racing app, in your opinion?
They aren't even great for dirt track, you guys just don't notice it in that controlled 4 wheel slide you call racing (looks like drifting on dirt, albeit fun as hell looking). Bumpsteer is friken crazy once you add some spring drop, FRCH is still down in hell somewhere, steering ratio drops to like 25:1 as well as losing 5-8 feet from your turning circle (try steering out of oversteer conditions with a real crappy steering ratio) and they are way heavy.


3. This may raise the skill level but I see it as something that has to be done. What sort of compromises have you found by leaving it stock?with or without the tall ball joints? With tall ball joints they work pretty well. Without tall ball joints, see #1



4. No explanation needed :-)
we agree :cheers:


5. I wish I was in a position to get mine on a track soon but it'll be awhile. I'm sure it will be faster than yours though ;-)dream on dirt boy.



I know you're pretty passionate about your setup so don't think that I'm hacking on you. I'm just trying to figure some stuff out given different compromises. You've picked a different set of parameters than I have so I'm genuinely interested.


Wally
Can't hack on me....I'm Superman.

zbugger
02-16-2005, 07:15 PM
Someone needed to rate this thread, so I did.

And Dennis, you're not superman. You're Underdog.

Salt Racer
02-16-2005, 07:24 PM
...I could be in my new shop as early as next week...

:headbang:

I inquired some specs of HRP's version 2 knuckles with centerlock hubs. There's fair amount of offset from hub face to steering axis, like 8" at spindle centerline. KPI is 10 degrees. This obviously ain't gonna work with rim width we're most likely using on street cars, but with 12~13" wide rims they use on front of T/A cars, it's possible to get near zero scrub radius. I think I'll stick with C5 or S10 4x4 hubs for my Riv. I doubt I can fit anything wider than 10" rims up front, unless I want to live with turning diameter of a semi truck.


OK guys, just to clarify some things...

The primary reason why Dennis and I started his spindle revision was his very low ride height. LCAs had excessive angle, causing 0.5" side scrub at 2" bump! :eek: Spindles only had to be slightly taller than what he had in terms of FVSA length, but both UBJ and LBJ had to be lowered. Then the project snow-balled, just like any other projects of this nature.

We kept raising the UBJ in an effort to decrease RC lateral migration and bumpsteer (FVSA length was too long relative to tie rod length). My final design had 110" FVSA, which I felt was good compromise for many purposes, but I guess Dennis made it even shorter for further reduction in RC migration and bumpsteer.

I don't know how we are getting so much descrepancies in FVSA length. Unless Dennis screwed up the measurements, the numbers we came up are correct for what he has.

BTW Wally, 77" FVSA is normal for road race cars. But unless arms are really long, there'll be more side scrub than a similar suspension with longer FVSA. Thus my comment "depends on what your object is". You can drive it w/o any problem whatsoever, but it could be better for certain other applications. Whatever you do, I'd still recommend making the FVSA adjustable (multiple UCA chassis mount holes, slots with offset bushings, etc).

Blown353
02-16-2005, 07:51 PM
Hey Dennis, what's your front tire OD and the distance from the bottom of your x-member to the ground? I'm trying to compare ride height / suspension working angle between our two cars, with those two numbers I should be able to get a good grasp comparing how our two cars sit up front. If things are similar I would be inclined to give a set of your spindles a whirl. Right now I'm at 26.1" tire OD and my x-member is 5" off the pavement. I should probably take a measurement to get a difference from the inner LCA pivot point to lower balljoint, that would be a better comparison.

What UCA's are you going to run? Are you going to keep your Pole Positions? I'm wondering if I would be able to get away with my current GW's with the different spindles. My guess is with the revised KPI and the limited adjustability provided by the factory "shim-n-pray" method I probably can't shim them nowhere near enough to get things to work.

I think I've got a lead on a good Elky frame, if it pans out I'm going to pick it up and start on a rear 3-link...

Troy

wally8
02-16-2005, 08:36 PM
Denny,

#5 almost made me spit water through my nose :-)


1. I agree with that. That's a real problem.

2. It is a lot of fun. We cure all those problems though. The RCH is actually 4" since we relocate the UCA pivots. The steering ratio is moot since we use a quick box (2:1 quickener) and bumpsteer is easily fixed by lowering the steering box and idler arm mounting points and shimming the outer tie rod with a heim stud adapter.

Salt Racer,

I'm still missing how raising the UCA BJ pivot point by virtue of a taller spindle while maintaining the stock UCA inner pivot would lengthen the FVSA. Again, this could be because I'm completely missing something and it's getting late but from a geometric standpoint it doesn't make sense to me. What sort of angle are you talking about for the LCA? Maybe that's the issue. Mine is level at normal ride height.

Talk to me about side scrub as well if you would. I'm drawing a blank on what that is. Maybe it's a difference in terms between the two worlds.

Oh yeah, one more thing: You said FVSA was too long compared to tie rod length. What's the problem with that? You just have to find the right location for the tie rods so that they follow the same arc as FVSA, right? This is something that I'm recalling from a book so that could be wrong too. It's not clear to me right now. Good thing to add to the discussion though.

Wally

dennis68
02-16-2005, 09:12 PM
Katz, I'll have to recheck some things, I may have transposed some numbers wrong.


Troy, Right now front tire OD is 25.75 but will be 25.00 in the end. Right now crossmember height is 4.5" but will wind up at about 2" all said and done. The new spindles are basically 3" drop spindles plus whatever spring drop I dial in.

I don't run Pole Position arms, they are Speedway and yes I will stick with them. If they neded be shorter or longer that is easy enough to order new arms.

Blown353
02-16-2005, 09:24 PM
2" crossmember height?!?!? Egads, man! Youse crazy! :bananna2:

I'd love to slam my car that low but that's too low to be safe and practical out here in my opinion. Potholes and road irregularities would eat me alive! That, and I'd get tired of buying new headers every 3 days as I scrape them to oblivion getting into and out of my own driveway.

Guess I need to get to work on my own spindles as our parameters are quite a bit different. I definately want to improve on my current B-body spindles but I'm going to have to make some geometry changes and some compromises to keep the car road "friendly" at least by my definition (aka, higher ride height.) Custom spindles for less than $500, as you said, is a very worthwhile deal.

Have you thought about a custom, longer LCA so you can run a wheel with more backspacing for a better scrub radius? Or have you managed to find a solution that works well with stock length LCAs?

Sorry guys for semi "thread-jacking" and introducing another subject. If it gets too disruptive, I'll start another thread.

Troy

dennis68
02-16-2005, 09:41 PM
The spindles Katz and I have designed will work fine for you, my ride height is going to be a result of spring drop.

I was able to acheive 1 3/4" of scrub radius as is so I am not going to invest in building new lower control arms altough it would be nice to get under an inch of scrub by simply adding an inch to the LCA's.

Hmmmm good job Troy, now I'm thinking again.

Blown353
02-16-2005, 09:49 PM
LOL, sorry Denny. Guess I need to stop thinking, it appears to be contagious. :icon_razz

1.75" scrub radius isn't too shabby at all given you're working within the limits of the stock LCA. I personally think it will handle quite well. But you're right, there is the possibility for improvement with longer LCA's. Is it worth the extra cost and effort? That's up to you. My gut is saying you'll be fine with the 1.75", but sometimes it's worth the extra effort (and cash outlay) just to get rid of that gremlin in the back of your head which constantly nags "I know it works as-is, but don't you wish you would have done it that other way?" I HATE THAT LITTLE GUY!

I think I could live with the extra 1.5" drop your spindles would give me over the current 1.5" drop in the B-body spindles. If not, I could just stuff some slightly longer springs in there to raise things back up. Or use this as a good excuse to switch to coilovers up front. LOL.

I was going to ask what lower balljoint taper you were going to have them made for (standard or B-body lower taper), but I suppose if I ordered a set I could get them with whatever taper I wanted.

Troy

dennis68
02-16-2005, 10:04 PM
The ball joint taper is Chrysler screw-in design. I'm not sure what taper it is. Anybody know what the taper is of the Chrysler screw-in design?

zbugger
02-16-2005, 10:20 PM
The ball joint taper is Chrysler screw-in design. I'm not sure what taper it is. Anybody know what the taper is of the Chrysler screw-in design?

It's what ever chrysler made it to be.


Ok, that's the last outta me..... :injured:

dennis68
02-16-2005, 10:42 PM
:slap:

yody
02-16-2005, 10:42 PM
underdog!

Salt Racer
02-17-2005, 07:01 AM
Katz, I'll have to recheck some things, I may have transposed some numbers wrong...

Den,
I had you triple-check the numbers so I don't think there's an error, but it's still a good idea to re-check everything before you order the spindles. One-off custom parts are too expensive to make mistakes on.


Wally,
Dennis initially had 858" FVSA length (yes, eight-hundred fifty eight). IC was still towards the chassis side. LCA inner pivots were 7.5" off the ground, now it's 7.0". LCAs were pointing up towards LBJs by 13 degrees. So I dropped LBJ down to 7.0" so LCAs are level, and adjusted UBJ height for 110" FVSA.

There is something wrong here. Maybe (big maybe) there is some differences in chassis pickup points between '64-'67 and '68-'72 A-bodies. Could you do us a favor and post your height measurements? Dennis had LCA inner pivot height of 7.5" (front & rear), and 17.75"/16.50" UCA pivots, front/rear respectively.

Side scrub is track width change at the contact patch when suspension moves up and down. Maybe it isn't a big deal on dirt track, but you definetely want to minimize it on pavement.

Last but not least... Incorrect tie rod height is not the only thing that can cause bumpsteer. Let's say you got zero bumpsteer on suspension. Imagine what would happen if you swap in a wider drag link and 5" center-to-center tie rods. This causes toe-in bumpsteer (on front steer) on both bump and rebound even though the tie rod height is correct. This is what I was talking about. It is rarely talked about b/c most OE suspension have reasonably close-to-ideal tie rod length, and it's not quite as sensitive as the tie rod height. For example, my car currently has 1/16" toe-out bumpsteer at 2.25" bump and rebound. This is an indication of correct tie rod height but incorrect tie rod length. It's rear steer, so tie rods are too short. To get rid of this last 1/16" (actually 1/32" in GM's language), I need to extend each tie rod by 2"!! The car has good Ackermann, and tie rods are right against the pan at full lock, so I'll live with 1/32" bumpsteer for a while.

wendell
02-17-2005, 07:36 AM
HA. Some days I love this web site!

Dennis,
Performance Trends it is.

Dennis, Katz et.al,
I'm presently doing 2D sketches in Solidworks to get my design started. My figuring is that eventually I can flesh out the structural design in 3D. Is this a good idea? I'm mostly conserned with being able to share information effiecently. Thanks for your time. I'm enjoying this conversation.
J

dennis68
02-17-2005, 08:54 AM
Katz, I think in the last evaluation I added the tall ball joints and lowered the chassis height an additional inch just for kicks. It improved RC migration and camber curve but at the expense of FVSA. It shows how little change change to x,y,z numbers results in substantial change of different angles. IE, just an inch of chassis drop can totally change the handling characteristics.

wally8
02-17-2005, 11:27 AM
Salt Racer,

Looks like we have the same type of measurements. Currently my LCA inner pivot is 7 3/8" and my LCA BJ is 8" with stock spindles and the tire size that I anticipate. I'm using different figures though since I'm anticipating a higher pin height on the B- body spindle (+1in I think) and I'm going to use a taller LBJ as well. When it's all said and done I should be level on my LCA at about 7 3/8 or 7 1/2.

My UCA inner pivots are very similar to Denny's as well. Slightly lower just like the LCA.

So in my case, using the numbers I have which could be off due to not having the exact spindle, I have to move the UCA inner pivot up to get a longer FVSA. Raising the spindle more and more will shorten it. This would be the general trend for any setup given this case, no?

You're right that the A bodies start out with an atrocious number.

Thanks for the side scrub explanation. I remembered what it was as I was going to sleep last night. And you're right, it's not that big of deal on dirt with this particular suspension combo. The left front is rarely on the ground and the overall load transfer is very radical already.

In fact, I once saw one of the nationally ranked mod drivers lose his left front tire due to loose lugnuts. He completed the entire heat (10 laps on a 1/2 mile) and kicked everyone's butt doing it. Yeah, he's good. He had some dirt packed in his LCA though :-)

Very good point on the bumpsteer also. I take that for granted because we all "know" which drag link to use and where to relocate the mounting points. That's the advantage of working within the parameters of a highly developed combo versus starting from scratch I guess. Another important note is that we don't get to 0 bumpsteer, just tolerable limits.


Wally

Mean 69
02-17-2005, 11:40 AM
In fact, I once saw one of the nationally ranked mod drivers lose his left front tire due to loose lugnuts. He completed the entire heat (10 laps on a 1/2 mile) and kicked everyone's butt doing it. Yeah, he's good. He had some dirt packed in his LCA though :-)

Oh, that's cool! I saw a guy run a practice session in AI with no brakes once!!! How's that for needing new underwear?!

Den, you slay me. Great humor!

I think there was a question of KAI for a typical AI car previously. The overwhelming majority of AI/X cars are late model Mustangs, which use mac strut front suspension. As such, it really isn't too relevent to compare. AI/X is a pain from the rules standpoint, as I have gone off on before. Basically they are forced into making consessions for the whining Mustang crowd that makes up the majority of the field. Everytime they suggest that they may open up the rules and allow thing like aftermarket subframes, etc, a bunch of guy pee and moan and they retract the idea. It is really frustrating. They may come around eventually, but you'd be nuts to build an AI specific car, in that the rules will probably bite you sooner or later. Eh, Sean?

Mark

CoryM
02-17-2005, 12:50 PM
Good thread guys.
Spindle reamers for chyrsler screw in balljoints are 1.5inch/ft and GM are 2inch/ft so the actual taper will be close to that.
When you guys talk about RC migration how much do you personally like to see on a full body car?

dennis68
02-17-2005, 01:28 PM
OK, the Chrysler uppers share the same taper and size as the GM truck, which is what most of the round-round arms run. The lower is off by itself, I think Howe will build a precision ball joint with a GM body and Chrysler stud reasonable enough.

The less RC migration the better, no compromise here. RC migration evolves to unpredictable handling very quickily. I don't know that there is a "number" that could be assigned as a reasonable amount. Each chassis is going to respond differently to change.

Mean 69
02-17-2005, 04:08 PM
Good point on the migration issue, hard to put a number on it, but I'd say anything more than a few inches is something that I'd tend to look a bit deeper into (how many is a few?? I dunno, four, five?). As importantly, and it would be hard to imagine if the absolute numbers were pretty small to begin with, is the rate of change. If it goes ballistic at some specific point, I'd be alarmed.

Again, to reinforce, the migration is probably more important for folks that are doing higher speed stuff, such as open track/road racing. I just feel very strongly that you don't want any funny business going on when you are really moving out. Imagine being loaded laterally in a fast turn, and having to chase the car due to erratic behavior over small bumps/reises, etc, it would seem to me to be a bit unsettling.

Great thread folks, nice to get the brain working once in a while!

Mark

David Pozzi
02-17-2005, 05:26 PM
chrysler and GM up to 1969 used 7 deg tapers, GM 1970 up with cast knuckle, used 10 deg tapers. Nova and it's cousins with forged knuckle and bolt on caliper brackets, used the 7 deg thru 1974.

Salt Racer
02-18-2005, 08:21 AM
...I'm presently doing 2D sketches in Solidworks to get my design started. My figuring is that eventually I can flesh out the structural design in 3D. Is this a good idea?....

Yes, but think of it as only a part of suspension design. When I design scratch-built suspension, I constantly go back and forth between suspension program and drafting or solid modeling software once basic parameters are set (tire size, rim offset, LCA length, etc). Watch for John Parsons' article in May issue of PHR.


...It shows how little change change to x,y,z numbers results in substantial change of different angles. IE, just an inch of chassis drop can totally change the handling characteristics...

Yup, that's why it's important to evaluate the modification on geometry before you actually make the physical change. It's so easy to overdo something.



...I'm using different figures though since I'm anticipating a higher pin height on the B- body spindle (+1in I think)...

This may or may not be the case. I don't know exactly what kind of spindles Dennis had, but it needed 3.0~3.5" drop to make LCAs level. I doubt you're planning to use 23" tall tires. Better get the parts in your hand before you finalize the design.


...Raising the spindle more and more will shorten it. This would be the general trend for any setup given this case, no?...

Assuming you're talking about raising UBJ, then yes. If you're talking about raising the whole spindle (w/o changing its height) relative to the chassis pickup points, that would be generally yes also.


...In fact, I once saw one of the nationally ranked mod drivers lose his left front tire due to loose lugnuts. He completed the entire heat (10 laps on a 1/2 mile) and kicked everyone's butt doing it. Yeah, he's good. He had some dirt packed in his LCA though :-)...

That is just too cool!! Having good suspension helps, but it all comes down to driver's ability in the end.


...Another important note is that we don't get to 0 bumpsteer, just tolerable limits...

That's what I do too when I'm just modifying what exists.



...When you guys talk about RC migration how much do you personally like to see on a full body car?

No more than a couple of inches. Less than that on paper or computer b/c more than likely the finished product isn't as dimensionally precise as what you intended.

wendell
02-18-2005, 08:52 AM
Thanks Saltracer,
Thats what I'm planning to do. Right now I'm crawling around with a tape measure trying to get dimesions and entering them in Solidworks. I'm sure everybody is going to be interested in John's article. Might have to break down and buy the may issue.

Salt Racer
02-18-2005, 09:18 AM
...Might have to break down and buy the may issue.

Tell me about it. The price of magazines are outragous these days. There's not enough tech articles to justify subscription, and it's tough for me to spend $6 for an issue of one of those magazines when I can buy an issue of Racecar Engineering for $2 more.

No offense to magazine editors. It's just an opinion coming from a non-typical occasional reader. I don't enjoy reading about pampered hot rods with loud barks and weak bites. I modify my cars to go faster on tracks, not to get attention from people like most "hot rodders" seem to do.

yody
02-18-2005, 12:26 PM
:offtopic: I have a question, in reality when on the track, how much of an actual difference do all the small details make? What would be the difference between a well thought out suspension consisitng of decent wheels and tires, mostly bolt on parts, like tubular control arms, del a lum everything, matching spring rates, matching valved shocks, matching sway bars, decent weight balance, etc.... compared to something where all the calculations have been made, like unsprung weight, scrub radius, backspacing, custom spindles, spline swaybars, everything measured out, and all that other crap. I would assume it also depend on what type of car we are talking as some had better geomety from the factory. I mean If dennis gets $700 custom spindles how much better are they really going to be? Dennis, are you going to take the car to the track first to get a baseline, are you an experienced enough driver to actaully get a consistent baseline:wrc:? I ask because if you got enough data, you could sell the custom spindles. I wish i understood what you guys are talking about with all this top secret code and such, I just dont really have a mathematical geometry brain. I would like to do the research but I have been so busy trying to finish my car, which was a huge project for me. I stuck with a pretty basic combo which should work pretty good. Everything is proven or is based on a pretty strong foundation like i listed above. I am wondering if i re engineered my entire setup if i would really gain much? Dennis are you teaching classes:wedgie:? I get pretty lost reading the books.....they need a "suspension for dummies"! :rolleyes5

wally8
02-18-2005, 01:11 PM
Salt Racer,

Yes, that is by far my biggest problem. Time to order some parts. I'm comfortable enough now to start that process so maybe in another week or so. I think I can end up with something that will work for this application. I'm saving all the really custom stuff for the next car.


Yody,

To answer your question very simply, it's the difference beteen 1st place or some other much less meaningful finishing position, at least in my experience anyway.

Which book are you reading right now? I would recommend one by Don Alexander (ISBN:0760309485) that really starts at the basics and gives you a comprehensive definition of everything and the basics of traction circle theory for the tires. Don is a writer first and a suspension / driving guy second so his stuff is more readable IMO. From there you can pick up any of the other books and get into the math. It's mostly straight forward high school geometry and physics so it's not too bad but then again, I'm an engineer by trade.

Other than that, ask questions to get the answers. Anytime I'm around some fast guy I give them the interview to see what they know that I don't. There's always something to pick up. Some relationship you haven't thought about yet. If there's some abbreviation like FVSA that you don't know what it means, just ask. I've been around this stuff to this level for years and I've found several things that these guys mention that are different from how I refer to them. Different schools as it were.

Obviously there are some knowledgable people here who would be glad to explain things.

Careful though or you'll end up saving for that perfect uber spindle that you have designed to be within 0.0001% perfect :-) There is a reason they compare racing to crack.


Wally

dennis68
02-18-2005, 02:34 PM
Yodi, a nicely refurbished suspension (which is what you have) will be a nice car to learn in. "Matched" springs and "matched" sta-bars are questionable. Without hours of track time it is impossible to determine if they are matched. Matched says who, and by what criteria?

If you pay attention to pit strategies this weekend you will see crew chiefs "add a wedge", this a small amount of change, maybe the difference between 1300lbs springs and 1350lbs, it will make a drastic difference in the way the car feels. So, to answer part of your question...Yes, small changes make a big difference.

Setting the chassis up is not a universal setting to begin with, all drivers have different likes/dislikes. Some drivers prefer the chassis be a little loose, some like it a little tight (I'll stop the jokes right here!). So while you may set your car up the way you like, a different driver may not feel comfortable in it.

There are some chassis design criteria that are universal however. Limited scrub radius, negative camber gain, limited RC migration, limited bump steer and a reasonable FVSA are the same regardless of driver or chassis. If any of these criteria are not met you will be stuck with a car that will never handle the way it could or should.

Will the investment I made in having spindles built pay off....I'd be willing to bet with rubber bushings and all OE control arms it would run circles around a "bolt-on" car.

Tires are the deciding factor in lap times, if you can keep the tires in traction with track and have enough HP to push the car around the track you will have the fastest car (actually it will be a truck :woot: ) out there.

The trick is to keep the tires perpendicular to the track and the chassis flat, that is where suspension geometry comes in.

Yes, I do not see the new spindles being on the car by April so I will have a good day of baseline runs to compare against.

Do I do classes.....sure, on how to be a dumb ass. I know nothing compared to most of these guys, I just have more time to play at work so my post count is real high

Salt Racer
02-18-2005, 03:38 PM
...What would be the difference between a well thought out suspension consisitng of decent wheels and tires, mostly bolt on parts, like tubular control arms, del a lum everything, matching spring rates, matching valved shocks, matching sway bars, decent weight balance, etc.... compared to something where all the calculations have been made, like unsprung weight, scrub radius, backspacing, custom spindles, spline swaybars, everything measured out, and all that other crap...

It depends on many things, like baseline, type of tracks, etc.

It's possible to go fast in a well-sorted bolt-on car with somewhat crappy geometry. Shock tuning, roll rate distribution, and driver ability go a long way. But how long can you keep going? And what would happen if you go over the limit a little while going through a 100+mph sweeper? Would the car remain predictable or go completely haywire? How about transitions?

That's where good geometry makes difference. It makes a car easier to drive fast and consistently, which takes a tremendous amount of load off the driver. This is somewhat irrelevant for casual track users like us, but it makes a big difference in real wheel-to-wheel racing - the difference between 1st place and also-runs as Wally pointed out.

Some of what we talk about, namely scrub radius, side scrub and bumpsteer, also make the car easier to drive even on street. Some even have significant affect on ride quality. Equally-sprung, identical cars would have totally different ride quality depending on geometry.

As for Dennis' spindles, I'd say the return of his investment will be significant, judging from where he started from. In terms of lap time, the new spindles may not pick up 3 seconds, but he will be able to tell the difference (ease of driving) and his lap times will be more consistent. As a secondary effect, this will probably results in slightly better lap time in many cases (more concentration, confidence, maybe faster exit speed, etc). It's guaranteed to make ride quality better. Tire will wear better also.

wally8
02-18-2005, 03:47 PM
Denny makes a good point. Putting it on the track is the only way to figure out anything. All of the computational stuff gets you in the ballpark and keeps your waste of time and dollars to a minimum but you can't put a theoretically perfect car on a track and have it be fast out of the gate.

BTW, Wedge is preloading, not an actual change in rate. If I put more wedge in (or bite as we call it) I'm jacking weight into the left rear tire.

And again, not to pick apart what Denny was saying but all of the design really depends on what you're doing. Another circle track example that doesn't apply here is that late models favor a tremendous RCH migration in the rear mainly because they actually desire the jacking component of that action. Denny's example definitely applies to roadracing though.

Collectively this is a fairly high level forum that you should be able to learn anything you want from. There's enough people here to figure it out.


Wally

yody
02-18-2005, 06:37 PM
eh good info. BTW i like to think of my suspension as a little more than a "refurbished suspension" alright smart guy? I mean just because you have "race" parts doesn't make a "race car" :slap: . It will be interesting at the least to see Denny on the track for the first time. I know my first time was a real eye opening experience! Also riding along with a professional driver is fun too. Those guys really push it. Makes you kinda scared to take your "baby around some of those turns at 80mph(which is a LOT faster than it sounds) especially on a track like infineon. Dennis sounds like your car is going to eventually be pretty radical and handle very well if you don't crash it, are you going to join a racing class(i.e. racing organization, not school)? Wally that is some good info. Once this car is done, I think i will devote some time to studying this stuff, so i can at least follow along without getting lost in these conversations, one of the books i have is the herb adams book. I read most of it, which included skimming a lot, and seemed to get lost pretty easily. I think it would pay off better to hang around soem people that i can talk too better.

dennis68
02-18-2005, 10:00 PM
Sorry Yodi but in the opinion of most, bolting on tube arms and Teflon bushings is not doing anything to improve upon the inferior geometry which leads to classifications like "refurbished suspension".

BTW, not my first time on the track....just the 1st time in a decade and the 1st time in this chassis.

Sorry Wally, wrong use of verbage. Meant to say "add a rubber", ot "take a turn".

No competetive racing for me, just for fun. I can't afford to compete.

yody
02-18-2005, 10:33 PM
okay, sort of like your refurbished body work? :) I think you could join NASA, kinda expensive but much cheaper than really trying to compete, with NASA i believe you can just enjoy the car at track days.

dennis68
02-18-2005, 11:21 PM
:offtopic:

Or, I could just go out without joining any group and run whenever I want anyway.

BTW, the body work is hack, not refurbished. Then again I'm not about bling-bling or how good it looks sitting still.

wendell
02-19-2005, 04:09 AM
Looks like this thread is starting to head south.

Katz,
"Racecar Engineering"?
I took it easy on PHR in my post. My first urge was to say that its nother more than a catalog to look at when American Hot Rod isn't on.


It should be noted that the fact that Denis has "custom" spindles in and of it self means nothing. What he has of value is a KPI that will minimize scrub and a height that will get him the FVSA he's after. Thats the important difference between his spindles and a pair of tubular UCAs.

It interesting to hear about the addative effects of the different design parameters and how they will play out on a street and on a track.

Can any one get a "deal" on performance trends? I can get a "deal" on Solidworks. :ssst:

dennis68
02-19-2005, 09:36 AM
I'm up for a deal on Performance Trends. I use the free trials as needed but I'm running out of computers to put in on.

796spdbu
02-19-2005, 04:39 PM
Hey guys
This thread is a real eye opener for me,cause when i started my 79 mali project iwas like damn i got real trick stuff here.Now its like oh....it just looks better than stock stampings.I've always like to tryand engineer stuff but i didnt take any college coarses for it,i took business management.Now i'm looking into ITT tech for C.A.D and some kind of mechanical engineering.You guys have any suggestions as to where i can learn more.wheredo i get this computer software at.How about these books how bout BORDERS.I'm thinking about building some kinda of race car/streetcar.You guys have helped me out in getting me motavated.I've built and helped build some street rods and trucks and know I've been doing it on my own for a year,but nothing in the wat of performance handling,no one has come to the shop looking for any thing like that.I do mostly air bag and conventional drops.Know if i get better at suspension design and theory,maybe i can apply it to my shop.I dont think there are an tracks in lower ohio for road caorse racing that i'm awhere of? Mainly drag racing and dirt track.Speaking of dirt track...Do you guys think that if i get into dirt circle track racing it would give me a hands on with suspension tuning,friend has offered to lert me drive his old street stock car.Thanks for any input. :jump: :jawdrop:

dennis68
02-19-2005, 05:45 PM
Check out the racing section of this forum, there is a list of different clubs who put on events all over the place.

As far as I know Performance Trends is only available from them on the web, books are available everywhere.

CoryM
02-19-2005, 06:49 PM
No more than a couple of inches. Less than that on paper or computer b/c more than likely the finished product isn't as dimensionally precise as what you intended.

Good to hear. The setup I have been poking at is 30mm (1.2inch) of movement. Just designing it for the learning experience and I have had a hard time finding out what you usually expect to see for allowable movement.
Cheers.

Mean 69
02-19-2005, 06:58 PM
Good to hear. The setup I have been poking at is 30mm (1.2inch) of movement.

In which direction, and in what circumstances? Better yet, what does it do in 2" bump and 2 degrees roll? Them's good numbers, but it depends upon the input critera.

M

wally8
02-19-2005, 07:27 PM
CoryM,

Those are good numbers. Give us some pivot locations if you would.....

796spdbu,

Racing of any sort will put you far ahead of the average guy especially if you read a few books along with it. Worked for me anyway :-)

Whatever you do put something on a some kind of track somewhere. You don't want to be one of those lawn chair racers at the car show......

Wally

CoryM
02-19-2005, 08:17 PM
Sorry. I should have mentioned that the theoretical setup is not GM based and is for a (at this point also theoretical) very small car. Also I am pretty green at this stuff so its possible (probable?) that I am missing something important. That was at 3degrees of roll 3" of bump. I will need to buy a real program when I start buying parts for the car and can measure the spindles I want. Hopefully I will know enough by then to figure it out.
Cheers.

Marcus SC&C
02-20-2005, 08:53 PM
How did I miss this thread until now? Anyway,Dennis and Katz I`m curious,what kind of camber gain are you looking at with such a huge gain in spindle height?

Yody,the suspension on a car like your Formula is quite a bit better than that of a `64-`72 A body (or for that matter a 1st gen F body or G body) so bolt ons and tweaking the factory parts yields a pretty decent overall package. On the more geometry challenged vehicles you can either put bandaids on it and fight the geometry (and the car) or fix the geometry,then tune it and have a car that works with you instead of against you. That means better and more predictable performance over a wider range of circumstances. Correcting poor geometry makes a huge difference in performance and drivability. Driving an otherwise totally stock car before and after underscores that more dramatically than on a car with lots of bolt ons to mask it`s behavior. Marcus SC&C

dennis68
02-20-2005, 11:09 PM
Marcus, the added spindle height has much less to do with increased negative camber gain and more to do with overall improvement. You must have missed the last time we discussed the spindles we designed. You seem pretty in touch with the poor geomtery the early "A" suffers from so this should actually mean something to you.

FVSA ~100"
FRCH 3.00"
RC migration >2" at over 2" of bump 3* roll
Negative camber gain over 1* per 1" of bump
Bump steer .02" @2" of bump
Steering ratio increased ~10%

That is why we went with new spindles vs. a bolt on cover up. After hundreds of hours in front of the screen there is no combination of bolt on parts that come even close to offering the same results.

Salt Racer
02-21-2005, 12:53 PM
This is camber gain with the geometry where I left off...

Static -1.5*

-2.16* at 1" bump
-3.10* at 2" bump
-4.33* at 3" bump

As you can see it's progressive, due to very short spindle height. It's much taller than OE knuckles, but it's still pretty short by today's standard. Camber gain is a bit more aggressive than I normally use for a street car especially at 3" bump. That said, I've driven a car with FVSA shorter than 70", and it isn't terrible (the car has taller knuckles and longer arms, however).

Overall this was a very good compromise with factory chassis pickup points untouched (one of criteria).

harshman
02-21-2005, 01:22 PM
So this is why companies hire engineers!!! LOL. Beins you guys seem to know your stuff, what are some simple tests that the basic guy can perform in order to tune and get a good definition of how well your car handles? My car was tested at Cal. Motor Speedway. 200’ skid pad, 420’ slalom, 0-60, 60’, ¼ mile, 60-0 were the tests (a G-tech and a stopwatch are all that are needed). Are there any others that would help?

dennis68
02-21-2005, 02:34 PM
I think track times (same track and same conditions) and feel are the 2 best tuning tools out there. Only you know if feels better, loose, tight or whatever. Track times will confirm how you feel the car is responding.

There is a story circulating about Dales kid Kerry not being able to qual for a past event and blaming the set-up, little "E" jumped in it as is and turned damn near track record in a car he had never driven.
Stewart picked up a used sprint and took it out to a local track (never been to), took podium finish first time out against veteran drivers (familiar with the track).

Point being only you can determine how the car is responding to your abilities. While it may seem slow to you a more experienced driver may be able to turn quicker times. Maybe see if after you feel it is OK if a veteran driver is willing to take it out for a hotlap and offer some input.

Marcus SC&C
02-21-2005, 06:23 PM
I posted some stuff here but after going over some of the older posts I decided to edit it out and reread it all when I get time. I entered most of what was discussed and I can`t seem to get anywhere near the quoted numbers with just a bolt on spindle and ride height change. I`m sure I just missed something. I`ve been doing a lot of A body geometry work lately,maybe I`m getting burned out on em. :hammer: Marcus SC&C

wally8
02-21-2005, 06:54 PM
I'll give my two cents.

Denny is right, the track is the final frontier. The tests you've done should give you an idea of being in the ball park.

It is all about your feel in the car, though. I wouldn't recommend going on someone else's feel. If the other driver is really good you won't like the car most likely. Loose to a fast guy is no where near the same as loose to an amateur.

Just make it feel the way you like. Learn what loose and tight really are and think about how it feels in all the different parts of the corner (entry, middle, exit) and how your transitions feel (since this is road racing). If you can think in terms of those 3 areas for every corner you can make the proper adjustments.

My Tony Stewart story is watching him race (several times) in a WoO Sprint and WDRL Late Model. He showed up at the track, jumped in a house prepared car and ran 2nd against the top guys in the nation in that class and would have won were it not for a severe bit of contact by the leader (Bloomquist) to keep him back. He put on an equally impressive show in the Sprint car. He was just as pi$$ed about being smacked in a dirt late model as he gets in Nextel Cup.

Oh yeah, we've been passed very quickly by Kenny Schrader in a dirt modified too :-) I could say we raced against him but that wouldn't quite be accurate......

(BTW, "we" in this case would be our driver. I'm more crew chief than driver. I've resigned myself to the fact that I am somewhat sucky in that respect.)

Wally

wally8
02-21-2005, 06:57 PM
Marcus,

Let's hear what you've got. I don't have spindles in front of me so my info is somewhat suspect. I'd like to hear what your measurements are for a B-body spindle with or without tall BJ's if you have them.

Anything would be great.

Wally

Salt Racer
02-22-2005, 06:29 AM
...what are some simple tests that the basic guy can perform in order to tune and get a good definition of how well your car handles?....Are there any others that would help?

Like others have said, go to the track. You'll never find the limit on street, and only at the limit you can really tell how your car really handles.

Looking at pics would help as well. There is a current issue of PHR floating around in office, and I think it's the pic of your car on the page of bumpsteer article. Look at the front tire - lots of positive camber and fair amount of sidewall deflection. Deflection could be either due to insufficient pressure and/or the construction of the tire itself, or the rims are too narrow for your tires. Excessive positive camber suggests you need more static neg. camber and/or revised geometry. Increased caster will help as well.


Marcus,
Please post the numbers you're getting. You can also get Dennis' pickup point numbers somewhere in his website, so try them on your software (Dennis uses freebie Perf Trend, and I use WinGeo3). I should also note that Dennis has SCP UCAs. Length may be different from OE arms, and UBJ offset is different for sure. He initially had like +14* caster.

harshman
02-22-2005, 09:22 AM
I haven’t seen the article yet (subscription ran out) but I can tell you that at the time I didn’t know my butt from a hole in the ground. At the time my car was tested my air pressure was around 10 psi in front and back and the only “mods” that I had (and still have yet to amend) were 650 lb springs and a sway bar. I did learn a very good lesson through all this though. The biggest factor (bone stock ’94 Z28) that spanked me was where the rubber meats the road. I have now switched to the Nitto DR sticky tires and will soon be changing the suspension around a bit (thanks to you guys). Again I am very grateful for all the information you have divulged to me.

dennis68
02-22-2005, 10:20 AM
Nooo, only 9*. :icon996:

The SCP arms are 8.5" I beleive. I have made so many changes to plans lately I can't remember where I started anymore... :banghead:

Link to tech print-outs analysis (http://www.onrails.net/suspension101.html)

Salt Racer
02-22-2005, 04:59 PM
Hmmm, my WinGeo file shows +14* caster and so did your Perf Trend analysis... Better recheck your measurements!

Harshman,
Yes, tires are one of the single biggest improvements you can make but obviously there is more to it as you're aware.

Check out this video clip. This is what you can expect from old cars when things come together. You've seen Super Chevy's slalom sessions in person, so you'll probably have a perception to tell how fast this car's going through the cones.
http://www.artmorrison.com/albums/GT55testing/seg3.wmv

Also, bunch of us will be doing OT event at Buttonwillow on April 15th. Come on out if you can.

dennis68
02-22-2005, 05:09 PM
You know what they say....garbage in, garbage out. I must be off on my ball joint to centerline measurements; I'll bet my centerline to mount number is off a little too.

We'll see when I get the new spindles on and get real "precise" with measurements how far off I was. The 9* was on a freshly calibrated HunterP611 so I think it's pretty accurate.

harshman
02-22-2005, 05:47 PM
Check out this video clip. This is what you can expect from old cars when things come together. You've seen Super Chevy's slalom sessions in person, so you'll probably have a perception to tell how fast this car's going through the cones.
:jawdrop: :hail: Yup, that pretty much sums it up!

Mean 69
02-22-2005, 07:00 PM
You know, I really wonder how terribly important lots of positive caster is. I run a smooch over 6 degrees on the Camaro, which is what Global designed into the UCA. I really wonder if it needs that much. I always thought it was cool to have the steering wheel snap back to center after a turn, but the drawback is the wheel lift associated with lots of postive caster in a tight turn. I didn't study what the design target was on D's bad boy ride, but I can tell you, 9 degrees sounds like a ton. I am guessing that you guys are not trying to get anywhere near that. Anyway, the power steering masks the bad stuff with lots of positive caster, but it would be interesting to see how sensitive a car would be to this, for instance, 4 degrees versus 6 degrees. For those of you that run lots of caster, go turn the wheel lock to lock in your garage and see how much the front end moves vertically, more than you'd think. Hmm. Given, you don't normally use that much steering input on a typical course, but, well, you get my point.

Harshman, nice looking car in the magazine, good to see that you drive it. Awesome. I am not so sure I could agree with Tony's comment on Karl Chicca's car during the Pony Express. It certainly "could" have been a bump/toe issue, but also could have *merely* been a scrub issue, or something else. A buck-fifty is moving out, than you very much, doesn't take much road irregularity to show nasties on a setup. Anyway, Tony's comments were well put, this is a fundamental aspect of car setup (bump steer). Oh, and by the way, you have to be careful how many of those "praying" smilies you put towards Katz, he'll get a big head.

Mark

Norm Peterson
02-23-2005, 04:42 AM
Lots of +caster does lift the front end, but it's the inside tire that's doing all of the lifting (and gaining load in the process). Meanwhile, the outside tire is being lifted, and loses load. Since this effect opposes the lateral weight transfer due to lateral acceleration at the front end and improves its overall lateral grip, it's a "loosening" effect. A secondary effect involving rear LWT that occurs due to chassis stiffness, roll stiffnesses, and tire vertical spring rates is also in the "loosening" direction. Not necessarily a bad thing, but it could perhaps result in different hardware choices relative to an otherwise similar car running only a couple degrees of +caster.

I'd guess that this effect occurs even more immediately than LWT through the roll centers, since you first need a steer angle before lateral acceleration can be developed, and that sounds like more responsive "turn-in" to me. As you unwind the wheel on corner exit, this effect diminishes, for a tendency toward "push".

Norm

Salt Racer
02-23-2005, 07:36 AM
...Oh, and by the way, you have to be careful how many of those "praying" smilies you put towards Katz, he'll get a big head...

My head is physically big (7-3/8" Simpson helmet is tight), so I need to match the mental size. ;-)

My decision on design static caster angle is based on intended use, King pin angle, scrub radius, the rest of suspension geometry, weight bias, etc.

Like Norm pointed out, the effect can be used as advantage especially on nose-heavy cars. But as with many other things, there is a point of diminishing return. I don't exactly know what this point is, but 89* caster obviously won't do any good (if that's physically possible).

Greater scrub radius (for a given tire size) will result in greater rise/fall effect caused by steering axis inclination. Earlier in this thread, Wally stated that roundy-round racers use different rim offset on left front and right front to tune handling. Because of this and other ill effects of scrub radius, I tend to stay conservative on caster when there is much more than 2" scrub radius.

IIRC, Mercedes uses over +10* caster.

Marcus SC&C
02-23-2005, 07:04 PM
Thanks for the link to the specs. I`ll plug them in as soon as I get a chance and compare them to my numbers. It may be a little while. I`ve got so many projects (customer and R&D) going right now I`m going (gone?) nuts. BTW one is a C-5/C-6 based suspension package for A body. Does anyone know for sure if there are any dimensional differences between `64-`67 and `68-`72? Our test car is a `65. I`ve been told the earlier frames are slightly more narrow but that they`re otherwise identical. This might explain some of the differences in #s too.

On the caster issue... I`ve done a great deal of on road testing with our different suspension packages,much of it determining the best alignment specs for each. The adj. upper arms made it easy to try a really wide range of specs. I tried as much as +12* caster with my Stg.2 equipped Monte. There was very little difference in "centering" vs. say +6* and the car became much more vague and sluggish in transitions (S turns and such). It also picked up an odd twitchyness at times on rougher surfaces. For that car and combination +4.5* ended up giving the best overall results (only 1* more than stock specs). The car`s handling is nice and crisp,turn in is good and it`s still stable and well centered. Initially I would have thought +6* or so would have worked better but it wasn`t the case. Our G-5 package test car feels a little bit better at +5.5*,which may have to do with it`s much faster steering ratio,spring rates etc.
One note about track testing. It`s great fun and I`m going to get a lot more time in doing it..but..we should keep in mind that the track is not the street and we`re dealing with street cars here. Some combinations we`ve tried that worked very well on nice smooth track like roads have been lousy (even scary) on rough roads with potholes,ripples and off camber turns and such. Of couse you lucky stiffs that live in the southwest or California etc. can pretty much disregard this. ;) Marcus

Mean 69
02-23-2005, 08:36 PM
we should keep in mind that the track is not the street and we`re dealing with street cars here.

Err, who is "we?" Not me!? Just kidding. 'course, I never thought I'd need rain tires either!

M

dennis68
02-23-2005, 08:59 PM
Who has a street car here??? My wife drives a street car (or SUV). I would be happy with Said's car from Sunday and some headlights and license plates.

Salt Racer
02-24-2005, 06:59 AM
...It also picked up an odd twitchyness at times on rougher surfaces...Our G-5 package test car feels a little bit better at +5.5*....

I'm almost certain that difference in scrub radius has a lot to do with it as well. GM did a fantastic job designing C5 knuckles and hubs.

I'm currently running +6.0* on my Riviera. Feels better on street compared to stock +4.0* Never ran it at track with stock alignment so I have no comparable result. Scrub radius is currently 2.38", which isn't terrible for a '60s car. I might try +7.0* at Buttonwillow just to aid camber angle a little.


Dennis,
The spindles you currently have must be a lot taller than what we thought. But I'm pretty sure you'll be getting the new ones made anyway, so just be sure to take accurate measurements on chassis pickup points. Those are what determines new UBJ/LBJ locations. You can still re-measure your existing spindles for academic purpose.

If you still have access to Perf Trend, try backing out a little on KPI. 14* is very steep. Its drawbacks may not be worth the small gain in scrub radius.

I don't know what your long term plan is with your car, but scrub radius can be reduced later when you can afford new rims and longer A-arms. If you have the slightest intention of doing this somewhere in your head, plan ahead and redesign spindles accordingly so you wouldn't have to have two sets of custom spindles made.

kmracer
03-24-2006, 09:38 PM
wow. you guys rock.

David Pozzi
03-24-2006, 10:26 PM
I think I'll move this thread to the Tech section. Thanks for finding this one!

kmracer
03-24-2006, 10:52 PM
yea, there was actually a link to it on lat-g. great stuff. this is the reason i love this site.