Front geometry quiz.

[pav8427]

Can anyone tell if this set-up will or will not perform reasonably.
So far I have only been checking from ride height to 4" of compression.

FVSA;
RIDE HEIGHT= 100"
-1.00=72.62"
-2.00=56.83"
-3.00=46.32"
-4.00=38.72"

RCH;
RIDE HEIGHT=3.23"
-1.00=2.64"
-2.00=2.13"
-3.00=1.74"
-4.00=1.48"

CAMBER CURVE;
RIDE HEIGHT=90*
-1.00=90.68*
-2.00=91.58*
-3.00=92.70*
-4.00=94.06*

I do realize that I can get a more aggressive camber gain, but I think that the FVSA length will get to be to short to quick.
Also, this is set up with 0 camber at rest and with 1* dialed in my upper arm length will be shortened by about 5/16". that should add some.


Thanks, Doug

[sinned]

What about the lateral RC migration?

[pav8427]

I still have to address that part of the equation. Until I get my CAD guy to set it up or get a copy of Performance Trends, I am looking for input on the basics. Atleast to fine tune these points before I give the PT demo a shot.
Around here, a 10 day demo may end up being 4 hrs if I'm lucky.
I know the RC height change vs. the amount of suspension compression should be reasonably close, but if they differ, would it be better to have the RC height change less or more than compression?
Also, when does a person worry about how short is to short for FVSA length during compression? And at what point that happens?
I.E. is the change from 100"@ ride height to 56.83"@ 2" compression to drastic.
Anyone happen to know a quick and easy way to set this up in Solidworks to get good results?

Doug

[Marcus SC&C]

We could use more info but as it applies to a "normal" PT car my first impressions are that the FVSA is VERY short and does change too rapidly,the RC is slightly too high (I`m betting you`ll have quite a bit of lateral migration also) and the camber gain is fine but don`t obsess on it. If you have to loose a little to get the FVSA longer and the RC down a bit don`t sweat it. C5 Corvettes have geometry that`s not directly applicable to most muscle cars but since they`re a gold standard I`ll mention that their FVSA is over 300",RC about 2.5" and camber gain only about -.25* at 1" dive. Lateral RC migration is well under 2". It`s a very benign suspension design that helps average drivers look exceptional. A typical muscle car will need more camber gain than that (it`s narrower,taller,higher CG,more front weight bias etc. etc. than a C5) and you`ll have to sacrifice some FVSA but try to shoot for a happy medium. Mark SC&C

[pav8427]

OK. With that in mind, heres the other end of the range that I have layed out. The ride height is probably going to be a little lower via. smaller diameter tires.

FVSA:
RIDE HEIGHT= 130"
-1.00"= 86.84
-2.00"= 65.11
-3.00"= 51.65
-4.00"= 42.34

RCH;
RIDE HEIGHT= 2.487"
-1.00"= 1.88"
-2.00"= 1.34"
-3.00"= .914"
-4.00= .629"

CAMBER GAIN;
RIDE HEIGHT= 90*
-1.00"= 90.55*
-2.00"= 91.32*
-3.00"= 92.31*
-4.00"= 93.54*

Again, you can see I am using just the basics for comparison.
In your opinion, do you think the FVSA could be longer yet?
What direction would you suggest to slow down the change in
FVSA length if this is still to fast?
I am stuck with lower arm length of 15.00", but I could re-do my uppers(about 8.25"w/1* camber dialed in)(8.5"w/90*) if need be.
Also,what other info would help you advise better?

Thanks, Doug

[High Plains Mopars]

I'm not new to suspension geometry, but having just done grassroots evaluations, I am unfamiliar with your terms and measurement methods. What source are you using to get your calcs from? Not trying to start a fight, but you've got some terms I've not seen before and I'd liek to know more.

Where I cut my teeth, roll center height and camber gain curve were two of the most important factors to initial design. Roll center typically was a symetrical position 4" above ground and camber gain varied based on track banking with more gain necessary for flatter tracks.

[pav8427]

If that was directed at me.
I'm not new to it either, just don't know as much as I would like.
The dimensions I have were derived from a general 2D drawing on Solidworks w/o introducing any body roll. Then I would run the suspension through its motions, measuring as I go.
I know that I would be able to get more info if I was the person who actually was running the CAD program, but it happens to be our designer at the shop and he doesn't have much extra time.
What terms are you considering as unknown?

Doug

[sinned]

I'm not new to suspension geometry, but having just done grassroots evaluations, I am unfamiliar with your terms and measurement methods. What source are you using to get your calcs from?

Which terms are unfamilair to someone with suspension design background?

I actually put RC migration towards the top of the list as this is the one aspect that tends to move on most chassis' and changes the way the vehicle handles. Camber gain is also fairly important.

[High Plains Mopars]

All my experience has been with stock stub based oval track cars. Being how computers were only used by NASA (the agency,not the racing organization)at the time, all my layouts were done 2d on paper with a protractor, compass,pencil and lots of erasers. I gleened the info from Mike Martin, Steve Smith,and Carroll Smith. Practical questions were usually directed at local racers willing to talk to a stupid, but eager, kid taking up too much of their time.

How about these ;
FVSA; ride height =130" What is FVSA and how would a ride height be 130"?

Camber gain, ride height =90* The * equals what?

[sinned]

How about these ;
FVSA is Front View Swing Arm; it refers to the imaginary line that intersects at "x" if you were to run a line through the upper and lower control arms hitting both the pivot points of each arm and extended out to where they would meet.

ride height =130" I think he meant his FVSA length was 130" at normal ride height.

What is FVSA Answered above

and how would a ride height be 130"? Answered above

Camber gain, ride height =90* The * equals what? * equals degrees in this case.

Clear?

[High Plains Mopars]

Yes, that makes sense now. Different than I'm used to, but it does make sense.

So the FVSW distance ends at the instant center on one end and from which point on the other end, the ball joint or control arm pivot?

The camber gain seems rather low. If memory serves, we used around 1* of gain for a track with banking over 20* and moved this up to 1.5 to 1.75* per inch for flatter tracks. The flatter the track, the more gain we dialed in.

We also used a front RCH of 4" and a rear RCH of 10-11" With a CGH around 15-17", this gave us a very short moment lever arm and really limited body roll.

[Norm Peterson]

Yes, that makes sense now. Different than I'm used to, but it does make sense.

So the FVSW distance ends at the instant center on one end and from which point on the other end, the ball joint or control arm pivot?

FVSA?

You can consider it to "end" at the longer of the distances from the FVIC (Front View Instant Center) to the following points:
(1) the center of the contact patch, and
(2) the loaded ball joint.

When these lengths differ, the wheel rate differs from the rate you'd compute from spring rate, spring mounting angle, and spring seat position along the control arm.

FVSA length is also an indication of the rate of camber gain. The shorter the FVSA the faster the camber gain.

The camber gain seems rather low. If memory serves, we used around 1* of gain for a track with banking over 20* and moved this up to 1.5 to 1.75* per inch for flatter tracks. The flatter the track, the more gain we dialed in.

Something more like 0.5° per inch is more streetable, particularly with the softer spring rates used by most people on the street relative to what I see in the online circle track supply house catalogs. Street car weight is usually greater, which also increases suspension motion for any given input. Don't forget that camber gain under suspension compression does not distinguish between bumps, cornering roll or braking, and too much can adversely affect tire tread life. The larger lateral thrust that would occur when one wheel hits a bump with lots of camber change is something most people would rather not have to contend with all the time.

We also used a front RCH of 4" and a rear RCH of 10-11" With a CGH around 15-17", this gave us a very short moment lever arm and really limited body roll.

I'd really like to get the CGH in a V8-powered car I could drive on a daily basis that low.


Useful off-topic hint: the [Alt] 248 key combination will generate the "degree" character. You have to use the numbers on the keypad, as using [Alt] with the "typewriter" numbers won't work.


Norm

[Patrick]

" ° " Cool

[Marcus SC&C]

The second set of numbers looks better. 130" FVSA static isn`t bad for street car but what`s more important is what it does dynamically. Again with the amount of camber gain your getting I would suspect it`ll be short. Ditto the RC,you can work with different RC heights but a lot of lateral RC migration will make a car hard to set up and hard to drive fast.
HPM, circle track dynamics are totally different than everything else. A setup that works awesome on a short oval will probably be a train wreck on the street or a road course. Just the nature of making all left turns on banking. Mark SC&C

[pav8427]

I realize that RC migration should be kept to a minimum, but in your opinion how much is acceptable?
Also, if I can get even 10" more out of the FVSA length and have around the same camber gain would that be better?
I would imagine these last #'s would be a decent place to start, then modify them (preferably longer FVSA?) so that the lateral RC is minimal.
I am actually setting up the FVSA length and letting that determine the RCH.

Doug

[sinned]

FVSA should be as long as possible.

RC migration should be zero although that is very difficult obtain (it can be done though). I would shoot for less than 2".