First time on r comps.

The front end is chattering in the corner, get on the gas and it fixes it cant carry any entry speed because of it.

Tires are BFG R1's, pressures to start are 30F 26 R, end of session 34F 33R.

I took the rear spring rubbers out and lowered the rear. The ass end was all over the place, this helped a bunch and dropped 3 seconds off the lap time.

Go up or down on pressure or what?

You enter the corner, the car starts to push and the tires chatter, skip, gas pedal pedal helps it.

All input welcome.

My new best is 2:02 at NOLA.

Less front roll stiffness > Soften the front sway bar, less front spring rate, less compression on the front shocks.

If none of those are easy, you can try less rebound in the rear.

If the tires are used, try swapping ends to see if the fronts are harder then the rears.

Try backing off the front sb end link nuts a couple of turns. Make sure the Dbushings on the front sway bar are lubed and the bar rotates freely. I've seen poly bushings seized up here. That has to effectively add a lot of front spring rate.

And make sure everything else in the steering, Kmember and suspension is tight. Check the front hubs for play, they can chatter when worn.

I don't think that's enough front tire pressure. How do the little triangles look?

With Toyo/Hoosier/Yokohama, starting cold pressures of 21-26psi are typical. YMMV. Too much and they'll feel nice and crisp at turn in, but start sliding after a few laps and turn to grease. When pressures are right, turnin may feel soggy, even after they are up to temp, but the grip will be consistent for the rest of the session. A tire pyrometer is a good tool to have in your box, but like a lot of things there is a learning curve to get thru before it's useful.

Sidewall rollover is less useful a tuning tool for race rubber, they typically have much stiffer sidewalls than a street tire and won't roll much in the useful range of pressures.

VID

http://www.youtube.com/watch?v=YaCRdy4mBVw...eature=youtu.be

Fun stuff at the 12:50 mark.

You can see the whole car vibrate/chatter, gas pedal makes it go away.

I will soften compression of the fronts and up the rebound.

I thought tire pressure was low as well, I start at 36-38-ish. I thought the Z28 shaped right up after going from 32 to 36. What should tread temps be, and how do you know? Our cars are pretty heavy out front, don't they need more air?

I find myself disagreeing with Blaine for the first time... probably at my peril Perhaps our tracks up here in the Great White North use a different asphalt or something, but I also find the starting and finish pressures too low.

With me in it, my car weighs 3400 lbs. and I use Hoosiers and Continentals (also Hoosiers) and a calibrated pressure gauge. I use dry N2.
I've kept records for many years using pyrometers to take multiple readings across every tire, at every race. Depending on OAT and track temps, the fronts need 35 to 37 PSI "cold" and will end up at 42 to 45 hot. This varies of course, with all kinds of variables at play, but my data is as real and as carefully plotted as possible. I never get chatter, and I get very good tire life. Oh, and I guess the pavement isn't all that different as these number are valid for PIR (OR) and Laguna Seca (CA) too!

Listen at 4:44 and 8:56

https://www.youtube.com/watch?v=xKIDff6zT5c...eature=youtu.be

When I open the wheel or get on the gas it goes away

I can't see the video from here at the office, but we fought that in autocross. When you turned the wheel and the tires started to chatter (and the car quits turning) you have to learn to unwind the wheel and get the contact patch flat on the ground. That could be a case of too much camber (caused by too much castor) where the tire gets up on the edges. That always seemed to be the issue in autocross (tighter turns).

How are your caster bushings??? I've had weird front end issues as a result of these being torn up.

Loose upper control arm bolts were the cause of my chatter issue. I think any play in anything that results in undamped motion of the ttire can cause it.

All of my front bushings are fine.

Would the 35/19 bar combo cause this?

Here are the plans for later. Started a new job so I am done for a little while.

Detroit Tru Trac diff for the rear, I already have it....I think the 219,000 mile stocker is done.

Put the 22mm rear bar back on.

Trim the bumpers in the rear.

Tire pics. They were rotated at the end of day 1.

What is the line forming on the right side of the tire? This the LF.





LR

It looks like you're wearing through the sticky compound and getting into the base tread compound. Or that's what I think I'm seeing.

You're on Strano springs, right? Seems like you need a bigger rear bar or stiffer rear springs to balance the handling. I think your problem is you're making the front of the car work too hard, taking too much weight off the inside front tire. I was on Strano springs and Strano bars. Perfectly balanced handling. Also, are you trail braking at all? Maybe you need to keep more weight up front for turn in.

What kind of job are you starting?

I had the 22mm rear bar on it, you could not get on the gas at all unless the car was straight with it. Even with the 19 bar it does not, just not as bad.

More weight on the front makes it worse, gas pedal or opening the wheel makes it go away.

You have a PM on the job.

That was in street tires though, right? I had the same problem with lighting up the inside tire, once I went to track tires, it was unreal how early I could get in the power.

I'd be willing to be a beer that with track tires and the big rear bar, you'll be happy.

Same on both tires, the 19 bar and the shocks set on full loose in the rear helped it.

I think my rear diff is worn out.

My car does this in Autocross on low speed tight corners. I am also curious about this issue. It feels like the front end is hopping in my car.

Usually that's due to castor "picking up" the contact patch and the trick (as unnatural as it feels to do it) is to straighten the wheel some until the car turns as it should.

Opening the wheel and or getting on the gas makes mine go away.

I took my spring rubbers out of the rear, it dropped the rear an inch(at least). Made the rear have MUCH more grip.

My axle snubbers have been trimmed about an inch, I can push the car down in the rear with my hands about 1.5 inches and you can feel them hit.

How much "free travel" should the rear have sitting still should they have? How far should I be able to push the rear down with my hands before they touch?

My 3rd gen has most of a turn removed from the 1LE springs, but I still use the upper spacer/isolator with the rear lowered to about the same as yours is.
I have cut about 1/2 the rubber from the limiters for the axle, but almost never hit them, and certainly can't do it using my considerable weight on my hands. It simple won't bounce that much with my DA Koni's set to give me the best cornering. I suggest heavier damping (and rebound in you have DA shocks) and maybe heavier springs too. JMHO

I put the Detroit TrueTrac in the car, trimmed the axle snubbers and the car feels amazing. I have more grip on cold tires and damp streets than I did at the track. You get on the gas now and it drives out of the corner with grip, planted.

Unreal, wow!


On that test drive the rear was 3/8 lower than the front, I came back and put a length of heater hose on the top of the springs. The ride height now is 26.5 on all corners.


Now I want to get back to the track and see whats up.

If you can do this with shocks installed then the shocks are shot.

With no shocks you can bounce the back of the car pretty good - hitting the bumps stops I think would be easy, but not a good metric for ride or bump stop height.

What about zero rake in the car?

I drove it again today with the rear raised even with the front, still good rear grip just not as good as it was (it seems).

No longer touching the bump stops on the street.

I may have missed it, but did you trim the bump stops when you lowered the vehicle? My rule of thumb was that the bump stops were trimmed to allow additional shock piston travel, but prevent the shocks from bottoming out at full compression of the suspension.

I at first had the black SLP stops on with the spacer and the car was all over them. I put the white Z28 stops on with no spacer, at the track the ass of the car was all over the place so I removed the rear spring rubbers.

This helped a BUNCH with rear grip but never got time to trim the stops at the track.

I just got around to trimming them.

Also installed a new diff in the car.

Big difference overall on the street.

I had a brain fart of sorts, the rack legs were under the car when I was bouncing it and this is what I felt hitting.