CSX3170 on 200TW tires chapter three

[Cobra #3170]

I thought I would post an update on our effort to make my car handle with 200 TW tires. We have found that the car is very sensitive to rake angle and works well within a .1 to .2" range, a big surprise to me. We are running 3.2" front ride height frame to ground and a 3.4" rear ride height. I used to run as much as .7" of rake but it doesn't work nearly as well as the low rake set up. Front camber is -4.0 and rear is -2.7 tire wear looks even with these camber angles. Front wheel rate is down around 140 lbs/" which is quite low rear is 235 lbs/" which seems to work well with fronts. Rear bar is .562 solid and front is 1.25 hollow, it seems to balance the car when both are either full hard or full soft. We are now changing front springs in 25# increments and seeing significant differences so the car is sensitive to changes at these settings. Maximum cornering G's are around 1.01 so no cigar there. We are going to try some different rears in a few weeks because of rear wheel spin but are just about locked in on the suspension springs and bars. I lowered the front roll center to around 1" and it seemed to help initial turn in, rear is 1.75". Shock settings really help us to adjust to varying surface conditions, especially rebound. Shocks are Penske 8700 triples. I put Torsen thrust bearings under the spring seats and we can actually change ride height on the grid now by jacking the rear up, turning by hand and counting turns, a great tuning tool. Last time out we picked up 2 seconds by raising the rear ride height .15" to eliminate mid corner understeer.
Here is a video of me overdriving the crap out of it, but it was fun.

[ame]https://www.youtube.com/watch?v=-oVRJKivBls[/ame]

[Morris]

Bruce.....

Very good....now the best part is to work with the shocks to get the car to respond to your driving style....so that you and the car are one.....the shocks are the secret on any performance vehicle......(once the springs & bars are established).....a 180* degree turn will be the best test .... To tell what the chassis wants to do.....

[Cobra #3170]

Originally Posted by Morris

Bruce.....

Very good....now the best part is to work with the shocks to get the car to respond to your driving style....so that you and the car are one.....the shocks are the secret on any performance vehicle......(once the springs & bars are established).....a 180* degree turn will be the best test .... To tell what the chassis wants to do.....

You are correct Morris, shocks will make the difference, I wish I had JRI's they have a greater range of adjustment without re-valving. My understanding is that Penske no longer owns Penske shocks but is a big investor in JRI. I am thinking about getting digressive pistons because all the action is around 1-2" per second in this sport.
The good news is that we can make the car worse with either bump or rebound so they are in range. The car still needs to be evaluated on a slippery (sealed asphalt) surface to make sure that we have the range of adjustment to make it work. We carry a set of soft springs which would work but I would rather use shocks and bars because they can be adjusted in minutes. A complete spring change is about 20 minutes with two of us working.

[ERA Chas]

Fantastic work and science Bruce.
But the thought occurred that none of us can benefit from your setup-no other originals I know of autox here.

Having said that, is it possible that a KMP or late CSX with the original frame and suspension could, in theory, mimic your exact parts and settings?
And results??

[Cobra #3170]

You are correct suspensions are different but wheel rates and essentially camber angles could certainly be used. I suspect most people with those cars would probably use better tires though such as Avon or Hoosier. That would require a much different set of camber, spring and bar rates. Once we are done with the 200 TW project the plan is to do the same thing with Hoosier or Avon and again share the results which would be more useful to most Club Cobra members. That is next years project if money and health hold out.
The huge negative camber is due to lots of roll from the soft springs.

I wish I had this set up for the 2012 Laguna Reunion, much easier to drive than what I came with and would probably work well with vintage Goodyears.

I forgot to mention that I switched from Willwood Poly matrix-E brake pads to Carbotech AX6, much better modulation.

[dallas_]

Good stuff guys, thanks for posting. This is the best kind of thread on CC but seems all to rare these days.

I'll try to remember the comment on the brake pads since I'm running the Poly Matrix E pads now. Hard to imagine 'much better' than those, but it's worth a try!

[Tommy]

There's nothing like solving a system of 15 equations with 16 interacting variables, one of them being the driver. ... I really liked the part of the video where you were able to approach full throttle for a moment. It seemed like you had unlimited power on tap. Or at least more power than you could use on that course. ... Great fun!

[750hp]

Originally Posted by Tommy

. ... I really liked the part of the video where you were able to approach full throttle for a moment. It seemed like you had unlimited power on tap. Or at least more power than you could use on that course. ... Great fun!

I agree!!! I had the video playing from 0:13 to 0:17 seconds over and over and over and over

[Cobra #3170]

Originally Posted by Tommy

There's nothing like solving a system of 15 equations with 16 interacting variables, one of them being the driver. ... I really liked the part of the video where you were able to approach full throttle for a moment. It seemed like you had unlimited power on tap. Or at least more power than you could use on that course. ... Great fun!

Thanks Tommy,
We cannot ever get over 1/2 throttle on these tires and it gets worse, from about 3500 to 5500 it gains 200 horsepower so you have to start backing out of it as it picks up RPM or it will go up in smoke. The Falken tires loose lateral grip really quickly if you spin them at all so you have to be extra careful or good on the throttle, I am neither. It is making 700 HP at 5750 and it gains another 150 or so at 7700 so the problem exists from 3000 or so to red line. I found the best technique is to get into pretty hard and slowly roll it back when you see some daylight. This car would be really fast with a 300 inch SBF but it wouldn't be nearly as much fun.

[Morris]

Bruce

How much pressure are you running in your shocks ??

And have you varied the pressure ??

[Cobra #3170]

Morris,

125 PSI and yes we have tried up and down 25 psi but I prefer doing it with springs after we see a trend from shock pressure change.

[Tom Kirkham]

Fantastic.

[Morris]

Bruce

"Front wheel rate is down around 140 lbs/" which is quite low rear is 235 lbs/" which seems to work well with fronts. "

These wheel rates are to low for a car going on a race track.......but for a autocross car they will work......

You don't want folks using these numbers on the race track at speed expecting a good handling chassis.....just saying...

Morris

[Cobra #3170]

This set up was for 200TW tires and works way better than a higher wheel rate approach
I have run as high as 375# front wheel rate and every where in between in 50# or less increments. The set up would be a good starting point with Vintage Goodyears too. The key here are the bar rates which brings balance to the car. Your wheel rates have to be tied to available grip. If I had more available grip I would have higher wheel rates. I have to say though, that using the minimum wheel rates that will work yield higher grip if you have proper camber control. My plan will be to go through a similar
program next year with race tires to determine the best wheel rates and geometry.
I don't think I recommended this as a race set up since it is for AUTOX use and would have too much over steer for a road race car.