Reducing scrub radius vs. track width

[baz67]

I just ordered my front wheels and I gave up some track width in order to reduce scrub radius. Both were small reductions. One of my goals was to increase the overall stability of the front end. I am curious what everyone elses opinion would be on what I did. Any and all are welcome.

Brian

[zbugger]

What exactly did you do? Did you just get narrower wheels? What's the balance gonna be between front and rear tires?

[Salt Racer]

[Devil's voice]...Build longer A-arms and revised knuckles. You shall have both small scrub radius and widest track possible....[/Devil's voice]

[baz67]

Damn Allen with the hard questions. 17x8.5 with 5.375 BS. There is a .250 overall track reduction(.125 per side), but also it reduces scrub. I am putting a 255/40 17 tire on it. That has a 25" diameter compared to a 25.7 on a 245/40 17. The shorter tire increases scrub, but I should be able to tuck it in more with the deeper BS and not lose turning radius or have clearance issues. My rears are 315/35 17 so that is one of the reasons why I wanted to widen the fronts. I looked into fitting 275s, however there was too many trade offs to fit them.

Fikse could not get me the 5.250 BS I was looking for. I only had the choice of 5.125 or 5.375. The 5.125 widened track, but also increased scrub radius. I chose the 5.375 for the reduction of scrub radius and the option of putting a .125 spacer in to achieve the original BS I wanted.

I guess I am just curious on what everyones opinion in loosing track to gain a recuction of scrub radius.

Brian

Brian

[Salt Racer]

On a typical Camaro (3600-lb running weight, 53/47 distribution, 59" front track) setup for very slight understeering, 0.25" less track width results in 3 lbs increase in lateral load transfer @ 1.0G cornering load.

I'd take reduced scrub radius anyday.

[wally8]

Salt Racer,

Could you expound a bit on your penchant for decreasing scrub radius?

I know we talked about it a bit in another thread and I said we use it for a jacking effect on circle track cars but: We're talking rims with only 1 to 2 inches of backspacing, lots of steering angle, quite a bit of caster and it's still only a very minimal effect overall. It really falls under the optimization heading not a mandatory setting in circle track.

I've read others who say that as long as you're not parallel parking, who cares about scrub radius. It seems many would say that you need at least some scrub radius to get the proper "feel". It would seem then that there might be other things that are more important, like increasing the track (that would have been my choice).

I don't want to highjack the thread, I'm just curious.....


Wally

[Salt Racer]

Well, I guess I should have been more specific. Sorry about that.

For track-only cars that never see bumpy surface at super high speed (like circle track cars), then my answer would have been the opposite. I may go with even shallower BS so track would increase at least an inch overall.

For other applications, I'm concerned more about steering stability. I strongly believe one of the reasons why late model vehicles drive so nice is b/c of small scrub radius.

1/8" reduction in scrub radius is very small and has minimal effects, but so is 3-lb change in lateral load transfer @ 1.0G load. Old cars typically have 3~4" scrub radius, and generally accepted max. number for cars driven on street is 2.0". I'd like to see smaller number on cars with wide front tires, like 0.5~1.25".

My car originally came with wheels with -0.3" offset, and crappy brakes. Somebody packed the drum on one side full of grease, and the car pulled to one side quite badly under braking. I cleaned it up, bled the wheel cylinder, and adjusted the shoes - it got better but the problem never went away for some reason under panic stops. It was nerve wrecking to drive the car on highway.

Then I swapped in my current wheels with +0.5" offset. The tires are shorter than original by 1.3" or so, so I'd say the reduction in scrub radius was 0.7" or so with KPI I have. The car was much more manageable under hard braking. The difference was greater than I had expected, to be honest. I would think shorter sidewall, grippy tires would compound the problem like this if the scrub radius was kept the same. Now that was with over-boosted power steering. I can't imagine what it would have felt like doing panic stops with original wheels and manual steering. I have also experienced similar things with my Jeep.

So that's my reasoning. For what Brian's trying to do with his car (driven regularly on street, frequent track visits), I'd go for smaller scrub radius.

[Steve1968LS2]

I just got done polishing a story on scrub radius.. learned a few things I will employ the next time I buy wheels..

Should be in the June issue..

[Steve1968LS2]

I strongly believe one of the reasons why late model vehicles drive so nice is b/c of small scrub radius.



Yep, you don't want zero SR because that would leave you with very little feedback. I must admit it is something I didn't consider when doing cars before. Modern cars run less than 2" of SR I believe.

[Salt Racer]

I just got done polishing a story on scrub radius...

So you probably saw pics of rusty undercarriage of Riviera and my fine artwork on a piece of cardboard then.

Modern ABS-equipped cars have much smaller scrub radius, actually. C5, for example, has +0.275" up front. FWD and AWD cars, as well as IRS-equipped RWD cars, have small amount negative scrub radius for similar but different reasons. It would have been nice to include those info, but I guess that would be somewhat beyond the scope of the article.

For visual effect, I recommend watching movie Lethal Weapon 4. There's a scene where bad dudes in a 4WD SUV pushing some poor guy's car on rail road track. You can see the front wheels of SUV swivelling back & forth. That's happening due to scrub radius.

[David Pozzi]

Salt Racer,
I believe my Camaro had a little over 2" scrub radius, it wasn't too bad considering but the power steering probably covered up some of the kick back. I'd like to have less SR when I put it back together. I think it's great for straight line stability. When you corner hard, the tire contact patch moves inward the most just as you lose traction. The driver feels the steering getting light and knows he's at the limit. Some drivers need to feel this to know what the front tires are doing. I learned to drive with overboosted PS so it isn't such a big deal to me.

[wally8]

Salt Racer,

Thanks for the extra info. I'm inclined to agree with the 1 to 2 inch numbers. I would think something around 1.5 would be quite tolerable on the street to the average enthusiast. 4 is way out there and those kind of numbers can jack as much as 30lbs onto the left rear with enough steering angle.

I agree with David that driver feel is a really important consideration, so in the end it should be whatever you feel the most comfortable with (within reason).

I would stilll trade out scrub radius for track width any day though (again, within reason). Of course this is SOP for circle track.

David,

Good point about CP deformation. That could be a good case to have at least a little scrub radius.



Wally

[David Pozzi]

I should correct myself, the tire contact patch moves inward when cornering hard, the rear part of the contact patch moves forward when the tire begins to lose traction. So there is less tire trail, it is felt as lighter steering.

another thing is if you have lots of scrub radius, the tire moves more front to rear and it takes a lot more room for clearance.

[USAZR1]

I am putting a 255/40 17 tire on it. That has a 25" diameter compared to a 25.7" on a 245/40 17.
Brian

Huh? That sounds like a typo,Brian. A 255/40 is taller than a 245/40.
Strange but my 275/40/17's are listed at 25.7".

[baz67]

Clint it is not a typo. You are correct. I just worded it funny. It says what you think is correct.

Brian

[Steve1968LS2]

So you probably saw pics of rusty undercarriage of Riviera and my fine artwork on a piece of cardboard then.



No, we photoshopped all that out.. you now have a chromed out undercarriage ;)

Actully it was cool, shows the car is actually DRIVEN. Good pics by the way and I feel the story will teach a lot of people something new. It is definetly an ignored aspect of suspension and handling :)

[Salt Racer]

...a 25.7 on a 245/40 17....

It's a typo - should have read 245/45 17.


David & Wally,
I agree about the steering feedback. Personally I think C5's 0.275" is bit too small. I think the production car can get by with it b/c of Magnasteer.

My car currently has 2.375" scrub radius. It drives good, but it can be further improved. Once I relocate and get back on my feet financially, I'm planning to build new knuckles and long A-arms. 275/40R18s on Kinesis 18x10s up front. I'm shooting for 0.75" scrub radius.


No, we photoshopped all that out.. you now have a chromed out undercarriage ;)

Ouch! People would think I'm a closet show car freak!

The car wasn't that rusty until last August. Bonneville flooded last year and I had to drive my car in 2-inch deep salt water. Oh well, at least I had a good time out there.

[USAZR1]

How do you figure scrub radius?

[Steve1968LS2]

How do you figure scrub radius?

Wait till the June PHR and find out ( :secret: )

Craig Morrison and Katz Tsubai did a great story with diagrams and lots of pictures and in this case a picture (or diagram) IS worth a thousand words..

A quote that sums it up:

Scrub radius is the measured distance at the road surface between the Steering Axis and the centerline of the tire

[dennis68]

Imaginary line running through both the ball joints and where the center of the tread on the front tires intersects at the ground...the difference is scrub radius. Did you guys just say that?

I miss all the good stuff.

[baz67]

Damnit I hate it when that happens. Thanks Katz. He is correct. That is what I get for using only my brain cells and not checking.

Brian

[MarkM66]

Here's a good article. It tood defines scrub radius.

http://www.rodandcustommagazine.com/techarticles/135_0401_ifs/index.html

Not sure on the credibility of this Mr. Tsubai though, :poke: .

[Salt Racer]

...Not sure on the credibility of this Mr. Tsubai though, :poke: .

No *****. Who the hell is this guy? I've never heard of him.

:jump:

[baz67]

He sounds like a dork who wishes he could design suspension like Katz.

Brian

[airrj1]

like a dork who wishes he could design suspension like Katz.

Isn't that a desciption of several of us? :hmm:

[Salt Racer]

Nah, I'm sure you guys are better than this Tsubai guy. No doubt he's a dork, but I bet he's a good looking guy.

;-)

[airrj1]

So, for someone like myself that has OEM C5 rims with allot of offset, it would be advantageous to work towards a longer upper and lower A-arms instead of spacing the rim out with an adaptor. I would need to confirm that I can fit the knuckle inside the rim without interference. But the scrub radius and side scrub would be reduced.

I believe that my adaptor is 1.75" thick, so my other question would be if I moved the knuckle out that amount would this significantly affect the motion ratio of my spring and shocks if they remain in the stock location?

[David Pozzi]

It might be a good thing but you need to draw it all out and see what amount of scrub radius you would have when done.
Also watch out for wheel clearance to the arms, more neg offset will move the wheel in and it will contact the A arms MUCH more easily. Look at rim to tie rod end clearance too.
David

[baz67]

Yes you could, but(there is always a but in suspension) the longer control arms will effect the front geometry. It would lessen side scrub. It would lessen the overall camber gain by an effective lengthening of the control arms arcs. Than can be fixed with new pickups, but(there it is again) then you need to do some design work. While you are at it throw in a new spindle design... On and On and On and On. That is what this Katz guy is trying to talk me into.

Yes it will increase the motion ratio. Just put more spring in it. It would get to a point where you are just designing a new frame.

Who knows if this Tsubai guy is even a guy. For all we know, Tsubai may be some super secret CIA/pro-street artificial inteligence computer sent here to halt the upward progress of the pro-touring movement.

Brian

[Salt Racer]

Yeah, better stay away from Katz guy. He's been known to sweet-talk people into some fancy suspension schemes that cause massive delay of projects. He's a trouble.

I don't know exactly what (who) Tsubai is. I'm thinking he's more of a wanna-be-racer, closet street rodder. He probably enjoys polishing chromed brake rotors and never takes his car out on tracks, even though he says otherwise. I know the type.

OK, I think I bad-mouthed about myself enough.



So, for someone like myself that has OEM C5 rims with allot of offset, it would be advantageous to work towards a longer upper and lower A-arms instead of spacing the rim out with an adaptor. I would need to confirm that I can fit the knuckle inside the rim without interference. But the scrub radius and side scrub would be reduced.

I believe that my adaptor is 1.75" thick, so my other question would be if I moved the knuckle out that amount would this significantly affect the motion ratio of my spring and shocks if they remain in the stock location?

Generally yes. But better check where you're at right now as David suggested. If I'm not mistaken, UCA/UBJ interference is the limiting factor on A-body. You'll need some sort of drop knuckles.

IIRC, A-body swallows 9.5" rims w/ 6" BS up front - I think that's what Jeff Smith had on his '65 Velle for a while. Anyway that's +0.75" offset. OE Z06 front rim has +56mm (+2.205") offset. So everything else being equal, Z06 rims will reduce scrub radius by 1.455". This actually might work out pretty good.

Motion ratio will be affected by fair amount. Let's say your LCA measures 15", and spring/shock are located 8" from inner pivots (my wild-azz guess), and you lengthen the arm by 2". Motion ratio will be 78% of what you currently have, assuming track width remains the same.

I wouldn't worry about springs - all you need to do is increase rate(make sure LCAs can handle the added stress). The downside is increased mass from heavier springs and heavier LCAs.

I'd try to move shocks outboard however. Might be easier to notch the frame rails and mount coil overs.

Shock shaft speed will be much faster if the shocks are left in OE location. Revalving may be necessary. One benefit of leaving shocks in OE location, though, is the difference of shaft speed between high speed mode (hitting bumps) and low speed mode (body roll, pitch) will be greater. So it might be easier to fine-tune valving. This is just my guess, however.

[B Schein]

Yeah, better stay away from Katz guy. He's been known to sweet-talk people into some fancy suspension schemes that cause massive delay of projects. He's a trouble

Yeah gives you plenty of time to work on other people’s projects. :crying: :crying: :crying:

[Salt Racer]

Yeah, yeah, I know. I just sent you e-mail. Next batch of blueprints will be on your way this weekend. We switched the server and now I can finally send file attachments, so you won't have to bug JP anymore (BTW, thanks for all the help JP).

[jeffandre]

Yeah, yeah, I know. I just sent you e-mail. Next batch of blueprints will be on your way this weekend. We switched the server and now I can finally send file attachments, so you won't have to bug JP anymore (BTW, thanks for all the help JP).

Katz has always been a great suspension resource for us on this forum (as has David Pozzi, Norm Peterson, and others) and I applaud his efforts at keeping it real. Now we need to get him setup with TeeToe (Tyler) so that he can devote his time to testing everything on tracks that we could use. All this knowledge is a overloading me, good thing I can print this for future reference...

[Salt Racer]

Why thank you Jeff.

I already have a new job lined up, and I'll be devoting my time designing and testing cool stuff in sunny&warm SoCal.

About the only things I'll miss about Seattle are winter-season microbrews and this awesome potato chips called Tim's Cascade Chips.

I'd have taken job at ATS last year if it weren't for my iffy immigration status (I'm legal, JFYI). My future is still uncertain, but I just have had enough with street rods and show-oriented hot rods. Then I got to know my new boss is starting this killer job soon in SoCal so I decided to take a chance.

We'll take many old pony cars to a new level - par with JP's II Much in terms of performance.

[Mean 69]

Let's see, it is the middle of winter, and today the weather is perfectly clear with a mild breeze, temp's in the mid 60's, and clear blue skies. I think you are making the right choice to come down here. Who is it that you are going to be working with again? Don't forget, Cal. Speedway, Willow Springs, Buttonwillow are all really close, as is Laguna, Vegas, Phoenix, and on-on-on-on.

I think I figured out what Tsubai stands for. Top Secret Underground Bad A$$ Intelligence. It must be a government computer program gone "mad."

I'll offer a small tech opinion here. I changed the front tires on my 69 recently from a 235 on an 8" rim, to a 265 on 9.5" rim. Backspacing on the 9.5" is 5.5", and on the 8" I "believe" it is 4.5". The old fronts are at the shop, I can measure later (yes, I now have a shop!!! yippeeeee!!!!). Anyway, the increase in rubber on the ground, and "assumed" increase in scrub was immediately noticeable, from my power steering pump. It had never been a super strong unit to begin with, I currently run an AGR fast box, but slow speed steering manuevers would really upset the pump (my wife even told me I had to fix it, you could hear it over the too-loud exhaust!!!). I swapped to a real pump, a KRC unit with remote reservoir, and the squealing is completely gone. So, it would seem that scrub radius is very important.

That said, I'd have to take the stance that I'd still opt for increased track over a slight increase in scrub, especially if I had a suitable power steering setup. My guts tells me that the additional grip you'd get from a wider stance would outweigh the downfall of an increased scrub radius. This is only my gut, and from a clean sheet design requirement standpoint, minimizing (or controlling) scrub (radius, as well as dynamic side scrub) is way up there, second only to roll center control, in fact. From a car that is already designed though, I think you want as much track and rubber on the ground as you can get, obviously to a practical limit. That said, it would certainly be interesting to test on the track, as the high speed behavior of the car, especially on the straights, could be really interesting. Still, with a good p/s unit, I think the assist masks alot of the the nasties.

Great thread, gets you thinking for sure!
Mark

[baz67]

Ya Mark your email is what got me thinking that I should think a little smaller tire. I will not have an issure with the PS system. Scrub radius was not the deciding factor on my BS choice. It gave me more options in the future. I still can get back to the factory track width with just a .125 spacer on each side. It will be fun to compare our two cars on feel though.

Brian

[baz67]

edit because I put in wrong thread

Brian

[wally8]

Take it easy there Mark, you're almost making me feel bad for turning down a job out there. Too many people for me anyway :-)

Congratulations on the new job, Katz.


Wally

[Salt Racer]

Let's see, it is the middle of winter, and today the weather is perfectly clear with a mild breeze, temp's in the mid 60's, and clear blue skies. I think you are making the right choice to come down here. Who is it that you are going to be working with again? Don't forget, Cal. Speedway, Willow Springs, Buttonwillow are all really close, as is Laguna, Vegas, Phoenix, and on-on-on-on....

Hmmm, I must have a temporary memory loss. I can't remember his name... :hammer: ;-)

Lots of tracks nearby. Yeah baby!! :headbang:


...That said, it would certainly be interesting to test on the track, as the high speed behavior of the car, especially on the straights, could be really interesting. Still, with a good p/s unit, I think the assist masks alot of the the nasties....

I was gonna say. Testing is in order. I'll bring several extra spacers to Buttonwillow.


Thanks Wally!

[jeffandre]

Wait till the June PHR and find out ( :secret: )

Craig Morrison and Katz Tsubai did a great story with diagrams and lots of pictures and in this case a picture (or diagram) IS worth a thousand words..

A quote that sums it up:

Scrub radius is the measured distance at the road surface between the Steering Axis and the centerline of the tire

Just read the PHR article with Katz's head in it, great info in an easily digestible chunk. Thanks again for helping me move in the right direction, should be able to figure out my scrub radius on my next day off. Will shoot for roll center figure as well.

[Steve1968LS2]

Just read the PHR article with Katz's head in it, great info in an easily digestible chunk. Thanks again for helping me move in the right direction, should be able to figure out my scrub radius on my next day off. Will shoot for roll center figure as well.

I tried to edit out his head but it was just so large and he took the pictures to make this impossible.. ;)

And it was a very good article.. I gonna buy him a can of POR-15 for xmas though..

[David Pozzi]

Let's see, it is the middle of winter, and today the weather is perfectly clear with a mild breeze, temp's in the mid 60's, and clear blue skies. I think you are making the right choice to come down here. Who is it that you are going to be working with again? Don't forget, Cal. Speedway, Willow Springs, Buttonwillow are all really close, as is Laguna, Vegas, Phoenix, and on-on-on-on.

I think I figured out what Tsubai stands for. Top Secret Underground Bad A$$ Intelligence. It must be a government computer program gone "mad."

I'll offer a small tech opinion here. I changed the front tires on my 69 recently from a 235 on an 8" rim, to a 265 on 9.5" rim. Backspacing on the 9.5" is 5.5", and on the 8" I "believe" it is 4.5". The old fronts are at the shop, I can measure later (yes, I now have a shop!!! yippeeeee!!!!). Anyway, the increase in rubber on the ground, and "assumed" increase in scrub was immediately noticeable, from my power steering pump. It had never been a super strong unit to begin with, I currently run an AGR fast box, but slow speed steering manuevers would really upset the pump (my wife even told me I had to fix it, you could hear it over the too-loud exhaust!!!). I swapped to a real pump, a KRC unit with remote reservoir, and the squealing is completely gone. So, it would seem that scrub radius is very important.

That said, I'd have to take the stance that I'd still opt for increased track over a slight increase in scrub, especially if I had a suitable power steering setup. My guts tells me that the additional grip you'd get from a wider stance would outweigh the downfall of an increased scrub radius. This is only my gut, and from a clean sheet design requirement standpoint, minimizing (or controlling) scrub (radius, as well as dynamic side scrub) is way up there, second only to roll center control, in fact. From a car that is already designed though, I think you want as much track and rubber on the ground as you can get, obviously to a practical limit. That said, it would certainly be interesting to test on the track, as the high speed behavior of the car, especially on the straights, could be really interesting. Still, with a good p/s unit, I think the assist masks alot of the the nasties.

Great thread, gets you thinking for sure!
Mark

Mark,
For autocross, I put 10" wide ft tires on my 67 Camaro they had a bunch of positive offset because they were just street mag wheels, I had to boost pressure on my PS pump or I couldn't turn the steering.

I think if you are running on a track, extra width is great, but steering can suffer as was discussed, BUT! it's the driver's job to get the car down the straight. :)

A street driven PT car should have good street manners and steering feedback/scrub would be a higher priority in that case, compared to a primairly track driven car.

[jeffandre]

I spent 30 minutes getting my car in position yesterday and found that my current scrub radius is 1". That's on a 71 Camaro with 19x10's using 7.5" bs. The amount of spacing I may need will increase the scrub radius by that amount, so figure the rotor hat at a minimum puts me at 1 5/16", not including any other adjustments like alignment and ride height that will affect it a bit. I also confirmed that at my current ride height the LCA is angling upward as it goes towards the LBJ by 2-3 degrees, so all in all I am very happy. Now to figure the roll center...

[dennis68]

I also confirmed that at my current ride height the LCA is angling upward as it goes towards the LBJ by 2-3 degrees, so all in all I am very happy. Now to figure the roll center...
Unless I read that wrong that is definitely not what you are looking for, running the LBJ above the LCA pivots leads to interesting RC migration and low RC height.

[jeffandre]

Unless I read that wrong that is definitely not what you are looking for, running the LBJ above the LCA pivots leads to interesting RC migration and low RC height.

Dennis,
You read it right. I could swear I read something a while back that related to the control arm angles, and that the lower one should angle slightly upward with the upper one angling upward even more, which increases camber in bump on my car. I cannot find it now, the search function failed me! It appears that my LBJ center is slightly above the LCA mount centers, so I will look a little more closely tonight. I just ran an angle gauge and approximated the angle from the center of the front bolt to the center of the LBJ, but I did not do the same for the rear as my wife was calling me for dinner. I'll check them both tonight, but either way I am going to be flat or angling upward as you go out towards the LBJ. This is with my frame about 4" off the ground, so the only way I can see changing the angle is to raise the car some more, which I would prefer to avoid, it is higher than I am used to anyway. I will keep looking for the post about the control arm angles, it may have been from David Pozzi (and of course I may have misunderstood it, wouldn't be the first time).

[jeffandre]

Dennis,
I spent an hour searching the old forum suspension posts and found 3 quotes that appear to say what you said, that I need level or upward angled LCA's for optimum handling. I will take a very close look tonight and see what I come up with at the current ride hieght. I am hoping to lower the car some more, which will make the LCA angles worse! Here's the stuff I found so far:

chicane67
Registered User
Posts: 177
(7/26/04 1:12 pm)
Reply
Re: Lowring the front end
The measured designed ride height is from the centerline of the forward lower control arm bolt to the plane of the ground. Now, of course this is dependent on the OD of the tire and wheel package you are going to use, but the measurement from **** is between 9 and 9.5". This can be corrected by making sure that the forward lower control arm bolt and the lower ball joint centerline are parallel. So, that is what you are trying to accomplish........bolt to joint parallel to the ground.

CarlC
Registered User
Posts: 148
(5/30/04 10:09 pm)
Reply
Ride Height
As a basic rule of thumb...

If the center of the sphere in the lower ball joint is higher than the center of the of the front A-arm pivot bolt at normal ride height handling will be adversely affected.

For road manners making the center of the ball joint 1/2" lower is a good idea.

katz
Unregistered User
(1/20/04 8:20 am)
Reply
Minimum side scrub is easier to achieve with near-level LCAs. The center of lower ball joint is slightly above the centerline of LCA tubes so that also makes LCAs look angled down more than the actual LCA angle (center of inner pivot to ball joint center).

[dennis68]

This is with my frame about 4" off the ground, so the only way I can see changing the angle is to raise the car some more, which I would prefer to avoid, it is higher than I am used to anyway.
Drop spindles are your friend :pat:

[Mean 69]

Hmmm... I'd recommend dropping your setup into a demo version of the Perf. Trends Sus Analyzer. It would be really interesting to see how things look under bump/roll. I read somewhere, I think it was Staniforth, that you "have to start somewhere, might as well make the LCA angle parallel to the ground." At first glance it would seem that the RC would move abruptly with what you describe, but heck, who knows? It'll depend a lot upon the UCA inclination, and of course, the length of both arms/spindle height, etc. I can't imagine a situation where downward sloping LCA's could result in a FRCH above ground, but don't let a negative FRCH scare you, unless it is pretty nasty (i.e. over an inch or two?). Map it out and play with it. Can you fit a "drop" BJ on the lower? Not sure that would help, not thinking too clearly so forgive me if it is stupid.

More importantly, HOW DID YOU FIT THAT MUCH WHEEL UNDER THE WELLS?!?!?! I saw your post on the other thread about offset, didn't realize you had a second gen. We'll have to chat soon!

Mark

[wally8]

So if my math is right, you're up a little more than 3/4 of an inch at the LBJ over the inner pivot of the LCA?

This is the exact issue I'm having as well given a typical tire size and my desired ride height.

A tall LBJ will get you back about half that distance but that's about all. I'll second (or third, or whatever) the idea of level a-arms being preferred.

That's the issue with stock spindles. The pin height just doesn't work out. I just got some numbers on a Coleman unit. I'm going to compare it to my stock setup. Unfortunately I didn't make it out to the shop tonite (seems ridiculous since it's only 80 feet from the house but my new baby girl is keeping my attention these days :-) ).

Unfortunately it seems a lot of the typical aftermarket drop spindles have a little too much drop.


Wally


Wally

[jeffandre]

Okay, spent some time adjusting things and decided that a 275/30/19 is too ridiculously short for my car so a 285/35/19 is in the works. That allows me to raise the front another 1/2", resulting in level LCA's. Frame to ground clearance is 5". I have never had that much clearance before, but it will make for a better handling car on the street and track as I need more room for travel anyway!

Rechecked scrub radius, currently right at 1", but the B-body spindle, 3rd Gen hub, and rotor hat are not installed so I am guessing it may move to 1.25-1.375"?

The wheels are 19x10 CCW's with 7.5" bs that John swears won't fit due to control arm clearance issues. He is absolutely correct if I ran any of the regular aftermarket arms, but my Vette Brakes arms are not curved along the sides so the wheel has more room to turn into the control arms. I know that there will be slight tire rubbage on the sway bar, so the goal is to limit the steering to the same amount that my son's 3rd Gen TA and my Toyota truck have, which is fine (my current 3rd Gen fast ratio box will allow me to turn another 10 degrees over the previously mentioned vehicles, which may have to do with a difference in length between my pitman arm and my son's).

I cannot use tall UBJ-s as they would move the UBJ/UCA into contact with my wheel, and I also cannot use drop spindles as they will move the wheel into contact with my VB spring bolt, all being the price for big backspacing. Right now I believe I will be perfect with the 285's on the front.

[Larry]

[Devil's voice]...Build longer A-arms and revised knuckles. You shall have both small scrub radius and widest track possible....[/Devil's voice]

I picked up a Trans Am tube frame, bare. I didn't get the body, so I'm thinking along the lines of a street-driven Modified style ride with at least 335s all around that I can take autocrossing, drag, track, etc. This may be going too far, but the new MT Sportsman's SR 29 x 18 tires have me wondering. Other than maximum legal width for the street, the sky's wide open. I obviously don't have to be concerned about body clearance either.

Okay, if there's no limitation on track width, what would you recommend for my project as far as spindle height, SAI, UCA/LCA lengths, etc?