Help me understand...

[wellis77]

If you haven't seen my build thread to know what I need help understanding, you can check it out HERE (https://www.pro-touring.com/showthread.php?63825-quot-Rookie-Touring-quot-69-Dart). To save you the trouble of going through, I'll paraphrase:

I'm building a '69 Dart using 2003 Viper suspension. Problem is, the UCA's are too wide to fit my 5.7 Hemi between them. The only option was to shorten the UCA's. I picked up some from AFCO that are about 1.5" shorter than the stock Viper. That however, changes my geometry and I need to figure out where to locate things and determine if I can use the stock Viper LCA's (preferred option) or if I need to build some shorter ones to optimize the geometry.

I downloaded a trial version of Suspension Analyzer from Performance Trends, plugged in my data as it sits now with the UCA's in almost the same Y & Z locations as stock Viper, but larger X. Attached are some images I pulled of the input data and output. The only input data I did NOT change was rollbar, spring rate, camber and toe. Now I need help understanding whether this data is any good or not and what I can do to optimize it. I don't have my chassis engineering book with me to help me understand the info but I'm hoping some of the suspension guys here can help.

Thanks and HAPPY NEW YEAR!!!
Will

https://static1.pt-content.com/images/pt/2011/01/frontview-1.jpg

https://static1.pt-content.com/images/pt/2011/01/report-1.jpg

https://static1.pt-content.com/images/pt/2011/01/data1-1.jpg

https://static1.pt-content.com/images/pt/2011/01/data2-1.jpg

[exwestracer]

The short UCA length is giving you a fair amount of camber gain...which isn't all bad, but it depends on what tire/wheel combo you are using. The more sidewall height you have, the more camber gain you will need. Hard to say what is "right" or "optimal" until you match the geometry to the tire.

[wellis77]

Thanks Ray. The wheel/tire I'm using is an 18x10 wheel, with a 275/35-18 tire.

[JRouche]

You know whats weird is you didnt get as much camber gain (not always a good thing, more is not always better) as I thought you would by shaving 1.5" off the UCAs. I would have expected to see more of a dive, a fast dive in camber than the program shows. 1.5" off the top should have shown a massive camber gain, specially at the 2 inches of dive.

Which means one of maybe more things. One is the stock suspension didnt have ANY camber gain due to the car and it didnt need it and tire wear was more important. Or two, the software isnt giving proper numbers. Ok, or three is that the arms are so long that 1.5" is not that big of a deal. They would have to be pretty long. And no doubt, they prolly are.

Im thinking number three, massive arms and one and a half inches is petty.

So with all that. Just going off of the computer output I dont see an issue. Id like to set it up on my caster/camber gauge to see the real numbers. Kinda hard for me to see removing 1.5" out of the top doesnt create more of a change.

But.. With that full degree of toe makes me think the program is seeing the changes. The toe numbers are a lil high, and they should be with the short upper arm. And that would be due to the 1.5" of upper arm. Thats ALOT of toe change. But not something you couldn't correct for. Thats kinda simple. If the camber and caster numbers are correct then I think its doable. Just gotta mellow the toe out some. JR

[Motorcitydak]

I know that you are getting a custom steering rack. Try messing with the numbers and use a wider rack, that should decrease your toe changes during the suspension cycle.

That graph only gives readings for 2 inches up and down. Am I correct in assuming that you will be running more than 4 inches of total travel? I assume at least 6-8 for the front which would make for a better ride.

Also, Im very new to the design of a front suspension but I thought that the lower arm mounts and the arms themselves are supposed to be level with each other and that the uppers are the ones that get angled to create suspension geometry voodoo.

[Bjkadron]

If you have the time I would imput the stock specifications, then print them out and compare to see exactly where you are coming from and see what the changes did.

[wellis77]

Thanks for the input guys.

@Steve, I can definitely play with track width but can't go outboard any further without running into rubbing issues at full compression. The Viper air springs I "hope" to run (limiting factor may now be the shorter UCA's but we'll see) allow just under 4 inches of shock travel so that's where that number came from. My understanding is the same as yours about the LCA being level and dive being adjusted in the canting of the UCA. The Viper stuff is just plain odd to me in that regard. The UCA's are almost level while the LCA's are mostly canted.

@BJ, unfortunately I'm out of time for this trip and am losing my demo of suspension analyzer (I'm on a Mac and was borrowing a PC for it). Over the next six weeks I'm going to get back into the Herb Adams book and study up on this some more to make sure I understand as much as I can, what certain changes will do to things like camber gain and toe. When I get back I will be playing with a few various changes to see what they do and I like your idea of comparing the stock Viper stuff in order to see what it starts with and where it goes.

@JR, Thanks a bunch for your feedback. That's what I was hoping to hear. I still want to do some more study and analysis of what I have before I solidify the settings but it's good to hear I'm going in the right direction.

Thanks again guys.

[Bjkadron]

Thanks for the input guys.

@Steve, I can definitely play with track width but can't go outboard any further without running into rubbing issues at full compression. The Viper air springs I "hope" to run (limiting factor may now be the shorter UCA's but we'll see) allow just under 4 inches of shock travel so that's where that number came from. My understanding is the same as yours about the LCA being level and dive being adjusted in the canting of the UCA. The Viper stuff is just plain odd to me in that regard. The UCA's are almost level while the LCA's are mostly canted.

Well If you think about it it is doing the same thing either way. It is more the difference in angle than the tilting. We are just used to seeing it on the UCA.


@BJ, unfortunately I'm out of time for this trip and am losing my demo of suspension analyzer (I'm on a Mac and was borrowing a PC for it). Over the next six weeks I'm going to get back into the Herb Adams book and study up on this some more to make sure I understand as much as I can, what certain changes will do to things like camber gain and toe. When I get back I will be playing with a few various changes to see what they do and I like your idea of comparing the stock Viper stuff in order to see what it starts with and where it goes.

I see, does the demo expire? or it is a limited program and you just have it on the borrowed PC? As for comparing it to the stock viper, I thought it was a good idea because you are using mostly viper components, and the viper geometry must not be too shabby since it currently holds lap records around the ring and Laguna Seca. Just remember that your track is MUCH narrower and you will have more weight transfer and roll so a little extra camber gain is probably a good thing.


@JR, Thanks a bunch for your feedback. That's what I was hoping to hear. I still want to do some more study and analysis of what I have before I solidify the settings but it's good to hear I'm going in the right direction.

Thanks again guys.

[wellis77]

Thanks Ben. The demo expires after 10 days, and it's on a borrowed PC; double whammy! My in-laws have a PC as well and I may try it on their's when I get back, just to do some more playing with it.

[exwestracer]

Well If you think about it it is doing the same thing either way. It is more the difference in angle than the tilting. We are just used to seeing it on the UCA.





Just one thing to add to that, Ben. If you use the LCA for camber gain, it will be pushing against the bottom of the wheel (and contact patch of the tire), rather than pulling the top in. That's why we normally try to keep the LCA level, to minimize side thrust from the suspension.

[wellis77]

Ray, when you say "try to keep the LCA level", are you referring to the side to side (front view) or front to rear (side view)? Would it be a smart move to level the LCA's in the X & Y planes then relocate the UCA mounts?

[exwestracer]

Ray, when you say "try to keep the LCA level", are you referring to the side to side (front view) or front to rear (side view)? Would it be a smart move to level the LCA's in the X & Y planes then relocate the UCA mounts?

If the LCA is at much of an angle in front view, it will have an effect on camber, as noted. If it is angled in side view (pivot bolts), it will force a caster change with suspension travel, as the lower ball joint is moving up and down at an angle. Some racers use this as a tuning tool, but for all around use you're probably better off keeping it flat in both planes.

The UCA mounts are typically angled in side view to give braking anti-dive (usually the rear pivot is lower than the front). Be careful with this angle, as anti-dive is designed from the factory for the original car weight, F/R weight distribution, and stock tire design. Too much anti-dive will make the front end too stiff and chatter the tires under heavy braking. Having said that, if you're pulling everything off a Viper; the stock anti-dive angle (UCA pivots relative to ground) should serve you fairly well.

BTW, back to your original plot of the camber gain with the shorter UCA... With that low profile tire, you probably don't need as much progressive camber gain as your simulation is giving you. Note how it only gains .685deg in the first inch of travel (good), but gains almost a full degree more in the second inch. If the car is stiffly sprung (NOT always the best for grip) and corners very flat, you should be ok. If you let the front end move around (softer) to go easy on the tire sidewall, you may end up with the outside of the tread pulling up. If as you say there is only 4 of available travel, don't give it a second thought, it will have to be stiff as hell anyway to keep from bottoming something.

[Bjkadron]

Just one thing to add to that, Ben. If you use the LCA for camber gain, it will be pushing against the bottom of the wheel (and contact patch of the tire), rather than pulling the top in. That's why we normally try to keep the LCA level, to minimize side thrust from the suspension.

I was talking about side view for anti-dive. But I may be slightly confused.

[exwestracer]

I was talking about side view for anti-dive. But I may be slightly confused.

No, you were right. I misread that in his post. Normally you would see the anti-dive in the UCA, but I'd think the LCA would have to be canted the opposite way (down in front) to get the same result...?

[Bjkadron]

No, you were right. I misread that in his post. Normally you would see the anti-dive in the UCA, but I'd think the LCA would have to be canted the opposite way (down in front) to get the same result...?

It is, the front is down. If you can see the tiny numbers on his inputs. I don't see any reason it wouldn't work as you are basically tilting the Z-axis (of the regular setup: UCA Tilted) forward the same amount as the anti-dive angle. The suspension moves exactly the same. If that wasn't clear let me know.

[wellis77]

Ben is right. The front is definitely down on both the UCA and the LCA. They are both down just a little bit; the front UCA is down 1/4" while the front LCA is down 1/8". I thought it was strange the anti-dive was setup this way, between both control arms rather than just setting the LCA level, front to rear and side to side, then lowering the rear of the UCA. This seems to make a pretty long side swing-arm length (to me anyway). Both arms canted the way they are also creates a higher side instant center which, if I understand correctly, creates the huge percentage of anti-dive, 47.3%. Herb Adams book mentions some street cars have as much as 30%, while this seems to have quite a bit more. The result of that would be the car stays level under hard braking, correct? If that's the case, to me that would be a good thing.

Ray, you mentioned the camber gain from 1" to 2" is a bit high, but since I'll only have a max compression of 2" I shouldn't be too concerned. Is that amount of camber gain going to make the car feel unstable, and if so, how can I reduce the amount of camber gain?

I may just have to spend the $250 and buy the software so I can play with some settings...

[Bjkadron]

Ben is right. The front is definitely down on both the UCA and the LCA. They are both down just a little bit; the front UCA is down 1/4" while the front LCA is down 1/8". I thought it was strange the anti-dive was setup this way, between both control arms rather than just setting the LCA level, front to rear and side to side, then lowering the rear of the UCA. This seems to make a pretty long side swing-arm length (to me anyway). Both arms canted the way they are also creates a higher side instant center which, if I understand correctly, creates the huge percentage of anti-dive, 47.3%. Herb Adams book mentions some street cars have as much as 30%, while this seems to have quite a bit more. The result of that would be the car stays level under hard braking, correct? If that's the case, to me that would be a good thing.

Ray, you mentioned the camber gain from 1" to 2" is a bit high, but since I'll only have a max compression of 2" I shouldn't be too concerned. Is that amount of camber gain going to make the car feel unstable, and if so, how can I reduce the amount of camber gain?

I may just have to spend the $250 and buy the software so I can play with some settings...

Ok wait.. If they are both down, and the upper is down more that would cancel out the LCA tilt, and give a negative value for the antidive. Where did you get the numbers? did you measure them directly from the frame?

Antidive helps account for softer spring rate that would normally cause brake dive. But it does cause caster change under braking which can be disconcerting.

If you want to we might be able to go in together on the program and when you are done with your suspension I could use it for continued development on mine.

[wellis77]

My measurements I pulled from the suspension components on the chassis table after pulling the Viper frame section out. The numbers I mentioned in my last post are output numbers that came from suspension analyzer. I'll try to attach the jpegs for you to get a better look at, maybe you can download them and get a better look.

That may not be a bad idea to go in together on the program since I only need it for this one build. I wonder if it can be loaded to one computer or more than one? Hmm. Have you tried the demo of it? You may want to first to see if it's something that will be all good for you.

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43420

[Motorcitydak]

Can you run that program on a Mac? Ill be needing it too when I have to set my stuff up

[wellis77]

You can if you run windows via a virtual PC (i.e. Parallels). I run Parallels and have windows on my Mac but the time period expired so I'm out of luck on that one. The more I think about it, the more I'm leaning towards buying it just because I can play with it on my time over the next 6 weeks and dial in my setup. The dilemma is by the front only version, or the rear as well so I can dial in the rear geometry for my car too; $150 difference though.

Another option is from Auto-Ware, though I don't really know much about it. You can find it HERE (http://www.auto-ware.com/software/asgp/asgp.htm). Seems okay and they seem to have pretty good support to.

[exwestracer]

Ben is right. The front is definitely down on both the UCA and the LCA. They are both down just a little bit; the front UCA is down 1/4" while the front LCA is down 1/8". I thought it was strange the anti-dive was setup this way, between both control arms rather than just setting the LCA level, front to rear and side to side, then lowering the rear of the UCA. This seems to make a pretty long side swing-arm length (to me anyway). Both arms canted the way they are also creates a higher side instant center which, if I understand correctly, creates the huge percentage of anti-dive, 47.3%. Herb Adams book mentions some street cars have as much as 30%, while this seems to have quite a bit more. The result of that would be the car stays level under hard braking, correct? If that's the case, to me that would be a good thing.

Ray, you mentioned the camber gain from 1" to 2" is a bit high, but since I'll only have a max compression of 2" I shouldn't be too concerned. Is that amount of camber gain going to make the car feel unstable, and if so, how can I reduce the amount of camber gain?

I may just have to spend the $250 and buy the software so I can play with some settings...

About the only way to slow the progression is to lengthen the UCA (which you said you can't do). Raising the UCA mount will slow the gain from start to finish, but you may not have enough gain at first.

If both arms are canted down toward the front (side view), and the upper is tilted more than the lower, then your IC for anti-dive is outside the wheelbase (ahead of the car), no? The anti-dive may work that way because the vehicle weight doesn't have the same leverage over the front suspension with the fulcrum that far ahead of the C/G. Interesting idea, and one I'm not familiar with. With the UCA at a higher angle, you should be losing (slight) caster on bump (and under braking), as Ben pointed out. Your simulation results don't show that, so something isn't making sense there...

[silver69camaro]

Will, I've been playing with the Viper front in WinGEO and I gotta admit it doesn't look too bad with a short UCA. The only thing that I see is a fairly bad RC migration during cornering and bump/rebound. The RC vertical change is double of what it should be (should move in a 1:1 ratio), and the lateral movement is actually going in the wrong direction and at about 4 times the rate of what I'd like to see. If you limit your overall travel you can mitigate these effects, but that takes the fun out of driving the car.

Can you shorten the LCA proportionally? If you want, send me the XYZ specs you are using so we're speaking on the same page.

[wellis77]

Hey Matt, thanks for dropping in. On account of I have jet lag, I've been laying thinking "since I shortened the UCA 1.5", why not build a set of custom LCA's that are identical, but 1.5" shorter". So yes, I can shorten the LCA.

I'll PM you the XYZ specs shortly. Thanks.

[MrQuick]

I think you did the same thing I did when I ran the numbers through PT. Where are you gettting the control arm pivot height measurments from? As in position. You are on the right track with the shorter arms. Keep your ratios the same.

The measurments did not jive and it wasn't till I mapped it out on paper at full scale did I understand what was going on. The imporant thing here is IC, RC location and migration.

My PT version died and will not run onmy new computer.
Vince

[wellis77]

I may have to map it on paper as well, but the pivot locations are measured from the ground. I hope I understood your question right. If so, I thought that's what the PT Y measurement comes from, the ground. X is from vehicle centerline, Z is from the spindle/axle centerline. Let me know if I misunderstood your question.

[MrQuick]

Hey Will, but at what location was your Y measured from? From the ground to what point at pivot on the control arms. It will be clear once you think about it. An inch can make a huge difference. That is where the analyser gave me problems.


Vince

[wellis77]

I went to the pivot center for all locations, be it X, Y or Z. This is particularly difficult for the ball joints. Where should the measurement be made to at the pivots?

[wellis77]

So after chatting with Vince (Mr.Quick) for a bit I realized one problem with the measurements I took which led me to finding a second problem with my UCA pivot inputs. First I wasn't measuring the height at the center of the pivot. I measured height at the front of the front bushing and the rear of the rear bushing (for both upper and lower control arms). What this means is the LCA vertical measurements are off 3/32" to 1/8" (too low for the front and too high for the rear) and the UCA vertical measurements are off 1/16" (too low in the front and too high in the rear). The more dramatic is the fore/aft of the UCA is WAY off. Now that I'm back in Switzerland I only have the incorrect UCA measurements, but it looks as though the front UCA should be in the range of -2.5" to -3.5" and the rear UCA should be in the range of 6.5" to 5.5". What I put into the software was -5.1 front and 4.6 rear. I have a feeling these two changes will have a dramatic impact on the results, especially the fore/aft of the UCA. I will still probably have to shorten the LCA by @ 16.7% (proportional to the UCA change) but these alone will likely have a big impact.

I have to figure out what I want to do for software so I can get these updates plugged in. Since I shortened my UCA I don't think I can fit the standard Viper air springs between them so I may have to go with something with a shorter stroke. In talking with Britt from Ride Tech, in order to not notice a difference in ride quality I need to keep my suspension travel at 5 inches. Based on my motion ratio, if I need to go to a shorter stroke shock, I'll have to move the control arm shock mount in about 3/4".

I sure am glad there are a lot of smart people here to help me get this all worked out. Thanks everybody, you have now idea how much I appreciate the help.

[wellis77]

If both arms are canted down toward the front (side view), and the upper is tilted more than the lower, then your IC for anti-dive is outside the wheelbase (ahead of the car), no? The anti-dive may work that way because the vehicle weight doesn't have the same leverage over the front suspension with the fulcrum that far ahead of the C/G. Interesting idea, and one I'm not familiar with. With the UCA at a higher angle, you should be losing (slight) caster on bump (and under braking), as Ben pointed out. Your simulation results don't show that, so something isn't making sense there...

I mapped this out Ray with the UCA pivots at -2 9/16" and 5 7/16 (rough estimate) and the IC for anti-dive is behind the car at 20' 1 7/8" with the height 2' 5 15/16" above ground.

[Bjkadron]

I was thinking those numbers looked really strange.

[exwestracer]

I mapped this out Ray with the UCA picots at -2 9/16" and 5 7/16 (rough estimate) and the IC for anti-dive is behind the car at 20' 1 7/8" with the height 2' 5 15/16" above ground.

Ok, I was just going off the tilt values you had given in post #16. If they are both tilted down (forward), and the top more than the bottom, they HAVE to converge at the front.
The values on your original chart:
https://static1.pt-content.com/images/pt/2011/01/data1-1.jpg
back up what you stated above. The LCA seems to be tilted more, so your IC would be to the rear.

[wellis77]

Yeah, the LCA is tilted just a bit more than the UCA. What would the impact be if I were to rotate the control arms down so the LCA is level? The IC length would remain the same but the the height would be 7 1/4". Would that have an effect on handling at all?

[MrQuick]

What I would do is find your IC relation to center of gravity and try to stay around that intersect. We are still taking front suspension correct? Find your CG, IC's and don't forget your roll centers.
If anything I would recommend doing a rough plot out and adjust from there.
Remember the Vipers had no ABS or track control so relations I would assume determined anti dive and anti squat locations.

[wellis77]

Yeah definitely still talking front suspension. CG is going to be tough since I can't way the car at all, best I can do is take a rough guess. I heard a super general rule once that said you can use the cam shaft as an estimate? If that is a decent starting point, I'm close already but I do need to take a closer look at roll centers. I need to read up on them a bit more as well to make sure I fully understand them, there effects on handling, and how they change.

[j-rho]

If you limit your overall travel you can mitigate these effects, but that takes the fun out of driving the car. How so?

[exwestracer]

Yeah, the LCA is tilted just a bit more than the UCA. What would the impact be if I were to rotate the control arms down so the LCA is level? The IC length would remain the same but the the height would be 7 1/4". Would that have an effect on handling at all?

Your side view IC mainly has an effect under braking and caster change in bump and droop. With the limited travel you have available, rotating them shouldn't have a huge effect on overall handling. Leveling the LCA will make the suspension more compliant over bumps (better ride quality).

Keep in mind that those stock control arm angles may likely have had as much to do with packaging as optimal geometry...

[Bjkadron]

Keep in mind that those stock control arm angles may likely have had as much to do with packaging as optimal geometry...

Actually, as serious as Dodge was when they re-did the viper, I highly doubt that they would have compromised geometry for packaging. since their goals included setting record laps all around the world with the car.

[MrQuick]

and they did, many times over but i agree, there is alot of room for everything else. Looks like they optimized the suspension then designed everything around it....after plopping the V10 dead front center that is.


Vince

[paul67]

What about the McPherson strut option,I have posted a bit more on the project update page by mistake,doh!!!

[Bjkadron]

and they did, many times over but i agree, there is alot of room for everything else. Looks like they optimized the suspension then designed everything around it....after plopping the V10 dead front center that is.


Vince

dead middle center is more like it.. the whole thing and all the accessorys are behind the front wheel centerline.

[wellis77]

Thanks for all the feedback and info so far guys. I'm looking forward to getting this figured out but it sounds like keeping the angles of the control arms in their stock positions may be the way to go, just shortening the LCA proportionally to the shortened UCA. We'll see when I get it on paper, in my head it sounds great!

Vince and Benjamin, I'll PM you guys in the next couple days. Need to figure out logistics with me being in Switzerland.

Thanks again guys, this has been very helpful so far and I'm always open to learning more so feel free to keep the discussion going. More to come...

[wellis77]

I managed to get another demo version of suspension analyzer and I've been playing with a lot of different combinations. I "think" I might have something that is a good compromise; granted I haven't exactly studied this stuff, but I did stay at a Holiday Inn Express like 5 years ago... I scanned the reports and attached them to this post. Take a look and let me know what you think. If I'm WAY off and this setup sucks, let me know. Thanks guys!

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[ArtosDracon]

Can we get the long measurement screen too? You can just to a print-screen and post it with or without the picture.

The only thing that jumps out at me is that you're set to Ackerman Error, which is the distance from "ideal" ackerman, not the actual Ackerman angle itself.

[wellis77]

Yes I can get that added, it will be a few hours though. Can S.A. be changed to show the ackerman angle itself rather than the error? I didn't look for that, didn't cross my mind, but when I animate the suspension I can watch the ackerman angles or use the dynamic feature and set the dive, roll, and steer and the main screen will give me the ackerman angle as an output. I'll get the rest posted in a few hours. Is there anything else you can think I should post? Thanks Robert.

Will

[wellis77]

Here is some data for you Robert. Here is the print-out of all the measurements as well as everything in a static position.
https://static1.pt-content.com/images/noimg.gif

And here is a screen shot of the same data but with 1" dive, 1* roll, and 2.5 steer (is that supposed to be degrees, inches, feet???).
https://static1.pt-content.com/images/noimg.gif
https://static1.pt-content.com/images/noimg.gif

Thanks for looking at it.