Supercharged111

This is on my Camaro, I expect the Z06 would be more straightforward. Up front, a 1/8" crank on the spring perch yielded something like a 75# shift and brought the diagonals within 16#. This change also helped with the left/right ride height disparity, however my l/r weights are skewed a bit. So I decided to try and shim the back, I threw 3/32" worth of shim on the opposing rear and my weight on that wheel didn't change by a single pound. If I stack more back there, it will make the ride height disparity even worse and give the car an odd stance. I figure part of the reason the rear didn't react the way the front did is due to the difference in wheel rate. Wouldn't it be ideal to get the l/r to match? Or am I still that much better off having it be less bad with good diagonals and shjtty l/r balance?

Bill32

Cross weights are the last thing I'm concerned with.

My priorities are:

Front to rear % (rake).
L/F to R/F being as close as possible (for equal turn in)
L/R to R/R (though the front's more important)
L to R (without screwing up the ride height too much)

fatbillybob

Bill,

Are the goals of a purpose built single seater different from a converted tintop car? For example purpose built you can build for almost perfect L/R weigh. In tintops that never happens, Every corvette will have a light RR and heavy LF even if simple things like battery is relocated.

F/R % (rake) I have never heard of. corvette Tintop rake setting is started at factory rake then tweaked and tested measured from reference points after ride height is set. Are you doing something different where if the weight on rear is "X" you know how that translates to a rear rideheight change and therefore the Rake? Also, why is this important on a car with real aero like yours? Is that because the mechanical grip needs to be setup for low speed turns first before you tune the aero?

L/F to R/F being as close as possible (for equal turn in). Is that more for equal braking? I thought making equal left and right turns was when cross weight was 50/50?

Lets say your car is 1500lbs and my vette is 3000lbs. Lets say the difference between LF and RF weight is 15lbs. Which is 1% of your chassis weight. Too me it is 1/2% of my chassis weight. Do you know if there is a percentage of chassis weight the average driver will feel or see in laptimes?

Bill32

The goals are the same for any car on the track, achieving them is obviously different, Purpose built cars are much easier to set up and usually have more adjustments (like we have 6 different things we can adjust on the shock/coilovers) Yea, any street car has built in challenges. This is why the new Z28 track car has the battery in the center of the spare tire compartment.

And every thing must be done with the driver or simulated driver weight in the car.

Rake and areo are separate (wings are adjustable). Rake on a Corvette can be changed by jacking or lowering both sides of the front or rear (guys like Phoenix would know what works on a Corvette way more than me). Any time you change the corner weights on a Corvette, you're moving the rake a tad. On our cars, I can adjust the rake and the corner weights separately. Rake will be different on different cars, I have a formula Ford that really likes reverse rake (front higher than the rear).

Mechanical grip is more important than the areo and the areo has to be balanced against drag on the straights, varies track to track. And corner exit speeds and more speed on that straight is what brings your lap times down, not necessarily corner speed.
We have to look at laptimes and the top speed/RPM on the longest straight when we adjust the wings, plus driver input, plus the gear ratio for 5th, etc.

L & R front weights are for cornering, yea, they will contribute to equal braking but brakes don't win races.

The cross weight will vary even on our cars, I want the car setup for equal contact patches in left and right corners and max traction on corner exit, that comes by equalizing the left to right.

Our Atlantic is actually 1,136 lbs. dry. the Formula Ford is 906

For me, I could easily live with 15 lbs. on a Corvette, less would be better but...........

I just finished setting up the Atlantic with a 2 lb, difference on the front and a 12 lb. difference on the rear. Trying to get the rear any better would have just screwed up the front because of the cross weight jacking.

Supercharged111

I've got like an 80# l/r split up front and out back. With the collars adjusted evenly, the right side sat higher than the left. I've been wondering if the "frame" is tweaked on this thing. Having not paid much attention to others' numbers, I don't know if my car is way off or par for the course in my class. FWIW I stacked 200# of iron in the driver's seat to simulate me.

Bill32

Yea, iron, antifreeze jugs filled with sand........

The right will usually sit higher on most cars, probably from being driven with only the driver in the car.

The number of turns on the collars isn't that important except when you first put them on the car.
Adjust your weights and don't worry about that dimension or the ride height unless the difference is huge.
We hardly ever have even ride heights after getting the corner weights where they should be.

Also, have you checked the rollout (circumference) on your tires? It's very possible you'll have a surprise there and that can affect your ride height.

And, did you disconnect one link on each sway bar before you put the car on the scales?

Supercharged111

Fvck! I totally forgot to disco the sways. Guess what I'm doing tomorrow. Would new tires eliminate said rollout issue? I've got some fresh RRs to throw on next weekend.

Bill32

Sorry to wizz in your cornflakes..........but we've all done it at least once.

No, new tires won't help. What you're trying to do is get an average for a set of tires knowing that the next set will be different. Sometimes you get a new set of tires that have the same rollout but usually there's a difference. The last set of slicks I measured had almost a 3/4 in. difference at the same psi. Equalizing them raised the car and changed the scale readings.

This is NOT a big deal and you don't have to do it. But it's just another thing to check.

fatbillybob

I have never worked with a real aero car. When tuning a car with real aero like yours do you setup for mechanical grip by testing what setup works best taking the wings out of the equation by setting the wings to a wing angle to zero their effect and test mechanical at speed? Or do you know the wings really come into play at speed "X" and test mechanical up to that speed then test with aero and come up with a compromise setting for the race?

Bill32

Well, the only new cars I've worked on are the Formula SCCA's, I was building new ones that Van Diemen shipped to SCCA Enterprises Customer Service Reps. Those were set up to Van Diemen's suggestions.

Setting up the Formula Atlantics or Formula Fords is done to specs that other guys ran as a starting point (including wing angles) and then doing test days.
Understand that I work mostly with SCCA (amateur) drivers, some are very fast, some aren't. And only some can provide good feedback.
Though I prefer to drive the cars myself.
Test days are expensive, you burn up more tires, work the engine more, etc. than you do on a race day.

The only way you can do it is to start with a known setup and drive the car. Get all the alignment and corner weights done , get laptimes, tire temps and driver feedback. Then make changes.

The areo will have an effect at almost all track speeds. About all you can do is take some wing out if the driver says the car is 800 rpm low at the end of the main straight, go back out and see if that affects the handling in the corners, etc. You may dial in more front wing if the driver says the car is pushing in a lot of corners but it could be the sway bars, shocks or the driver himself.
And you can easily blow half of a test day just playing with shock adjustments.

When a driver comes to me with a new (to him) racecar, I always tell them that it's going to take 2 years (2 full seasons plus a couple test days) just to learn how to set it up. And every car is different. The difference between out Reynard Atlantic and our Swift Atlantic is huge.

None of it is easy, it takes time and money. Doesn't matter if it's an open wheel or a stock C5. Make changes (right or wrong) and see what happens. Guys like LG, Rippie, etc. have done this for years and years, that's why they're good at it.