Suspension Analysis Done.

[Musclerodz]

For those that don't like to hear "mine is better than yours", here is some hard numbers for ya. These numbers are not absolute as I have not started fabricating yet. Hopefully I won't have to change anything too much.

Based on 1" dive 2* roll:

bump steer .00"
roll center height 1.79"
roll center migration .01"
camber gain -.50*
caster gain .22*

Analysis was done by Marcus at SC&C using C5 knuckles, Cobra R&P, custom lower a-arms, and proprietary parts from SC&C for the rest (upper a-arms, steering arms, upper ball joint). I also have to build a one off sub for this car as well due to the raised floor and to be able to pick up the points as defined by the analysis. This thing should hopefully go around the track as if it were on rails. I am still learning this stuff so what I can't answer I will get Marcus to help answer.

Mike

[sinned]

Cool Mike, those numbers look pretty good. I'd really like to see the actual graph as obtaing absolute zero bump steer throughout the range of travel is impossible. Marcus is pretty bright and I'm sure he just shot you the best of the results though the rest of the range probably is on par for a one off design. It would be nice to see the RC migration animation as well; see what it actually does through a corner.

[Mean 69]

Looks like a pretty good start. The migration numbers, and bump steer look really nice. The camber gain, although not "the" most important aspect, looks a bit modest at .5 degrees/inch, you might try to shorten the upper arms a smidge, or better, lengthen the lowers and see if you can bump this up just a little. It's not bad, especially if the rest of the stuff is good.

These numbers are a start, but there is a whole lot more to it. What about scrub radius, FVSA, and side-scrub numbers? Track width? I ask because I see that the rack chosen is a standard production rack, in order to get the steering numbers (i.e. bump steer) looking as good as they do, the control arm pivots MUST have been located according to the rack/ackerman/inner tie rod location requirements. Do you have the inner tie rod mounting width handy for the Cobra rack? Seems to be a very popular piece used on many of the vette equipped front units.

Looks like you are on the right track, for track days, you'll likely have to dial in a good amount of negative static camber, but probably not more than -2 degrees or so, give or take. More than this might cause squirrely front tramp under really heavy brakes, probably not too much an issue though. Have fun with it!

Mark

[Musclerodz]

These are dynamic numbers

FVSA 155.2"
caster 6.3*
scrub radius .14
track width 59.5" (I have bumped it out from stock and will be flaring the
the fenders like the Bank's Camaro)

I will be running stock C5 rear wheel specs on C5 knuckles . I will be running adjustable upper arms which will help make track setup easier.

Yes LCA's will be custom made to pick up same pivot as R&P. Standard Cobra or GT rack mount locations are 24" apart. Cobra rack is slightly too wide and I will have to play with arm lengths to get it correct. I was more interested in a GOOD production rack I could easily get if I needed to that would not cost a fortune or have to special order. Most people use the Fox Body GT racks, but after a lot of research on CC.com, I found I could use an '03 Cobra with excellent feedback but would need to install the shorter GT arms.

Marcus has a bunch more stuff on the suspension including the graphs that I have not got yet as what he sent I am still trying to absorb. He did say that the numbers I have are to the point that any change to make something better, made something else worse.

Mike

[sinned]

I will be running stock C5 rear wheel specs on C5 knuckles . I will be running adjustable upper arms which will help make track setup easier.
Mike
Keep in mind when running these adjustable upper arms that any adjustments you make to alignment actually change the UCA length and therefore affect every one of the analysis results previously posted. :D

[Musclerodz]

Keep in mind when running these adjustable upper arms that any adjustments you make to alignment actually change the UCA length and therefore affect every one of the analysis results previously posted. :D
Yep already ran that through my head. Once set up per analysis, any changes will be spefically counted to return back to as designed. Once we come up with a track setting then it will be a matter of counting the turns, shims, or slugs for race day.

Mike

[Mean 69]

That's some pretty darned good stuff, not too shabby at all. I just (finally) looked at the pic's on your site, the car looks terrific, and a very interesting project. Do you have an idea of when the car will be ready? Seems like a lot of cars will be done early next year, could be a really interesting Power Tour/One Lap/Open Track Challenge year if we can all get together.

Mark

[Musclerodz]

Site needs updated. Car is home and ready to go on the big table to start mocking up the front and rear suspension. I doubt I will make the Power Tour as much as I would like to. I am shooting for Columbus next year, but no later than SEMA. As soon as I finish the '69 Blazer I am redoing it will be for sale to finance the power train for this bad boy. I want an LS7, but may have to settle for a stroked LS2. Once the project is a little farther along and I have a dedicated web site that looks professional, I may look at some sponsorship to get this thing done and get it on the circuit (show and track). This car is being built to tear up the street as well as the track and I hope to raise a few eyebrows when I do it.

Mike

[Marcus SC&C]

Thanks for the kind words and constructive notes guys. The idea here was to build a good suspension that would fit in his envelope while using production C5 steering knuckles,hub/bearing assys./brakes etc. with a good OE R&P and SC&C G-5 steering arms. The adj. upper arms alter the geometry less than shims for a comparable amount of adjustment. Also at the track when you dial in a great deal of - camber the shorter arms increase the rate of camber gain as well. As designed it`s a very versatile system. In "race mode" the camber gain can be in the .75*/in. range from ride height (and rising). The bump steer # is misleading (as usual). It does have a *tiny* bit toward the ends of it`s travel maxing out at -.015" over 4" on paper. Not half bad for using a lot of production and existing parts. ;) Combined with the rear suspension we`re working on I think Mike`s gonna have a hell of a ride on his hands. :unibrow: Marcus SC&C

[astroracer]

Very nice... If I read right in Marcus' last post you are seeing -.015 bump "out" at 4" of Jounce? "Bump out" is better then "bump in" any day and .015 is negligable.
I have -.008 bump on my Bad Ast Project @ 3" of Jounce with a stock Vette rack and "B" body style knuckles. Of course I have to move the outer steering point a bit but this was expected.
Good job, was Preformance Trends Suspension Analyser Software used? Just curious...
Mark

[superpro787]

can you explain why bump out is better then bump in

[astroracer]

can you explain why bump out is better then bump in
This is a quote from the Longacre site...
E. How Much Bump Steer?

Ideally you should run as little bump steer as possible. Most of the tracks we see today are old and bumpy. Bump steer on these rough surfaces causes the car to be unpredictable.

Some bump out can make the car more stable on corner entry. Bump in is almost always undesirable.

Some people use small amounts of bump out to create entry stability and an Ackerman type effect in the center of the turn where as the bump setting causes the LF to turn a bit farther than the RF as the RF compresses and the LF extends.

My recommendation is to run .005 to .015 thousands of bump out but never allow the tires to bump in.

If you want Ackerman in the center of the turn then add Ackerman while maintaining proper bump. If you use bump to obtain some Ackerman effect the car will be unsettled as it goes over each bump, which will break the contact patch from the racing surface.

If the design of your car does not allow for such precise bump adjustments then more bump out is better than any bump in. However, strive to get the best bump numbers even it if means replacing parts. Excessive bump over .050 can slow your car down.

As you can see both Mike and I's suspensions are falling right into the recommended range... This takes a lot of work to get it right and the benefits are worth it. :D
Mark

The Longacre site is full of good info...
http://www.longacreracing.com/articles/art.asp?ARTID=13