Help fix my handling issue??

I just posted this to the corvette forum but then kicked myself when I realized that my favorite car guys on my favorite forum would probably be the best place to ask:

Finally took my new (to me) car to the track and was hoping to get some input on a little issue. It is a 2006 Z06 with 88,000 miles on it. It has really big T1 racing sway bars front and rear (rear is NOT adjustable) and Aldan American coil overs. Wheels are 18 x 11 front and 18 x 13 rear with new Nitto nt01 315’s front and 335s rear. It has an aggressive street alignment. The car is really stiff and a bit bouncy. More so than it should be for sure but not undrivable by any means. 

In a nutshell, when I would turn in, the rear of the car felt like a live axle car with a broken panhard rod, but just at the entrance of a turn. In other words, it felt as if you were to grab the back of the car you could move it back-and-forth three or so inches while the tires stayed planted to the ground. Perhaps this is a somewhat normal phenomenon in cars on track but it just felt very unnerving in this car. I would have to initiate the turn, wait for the rear to settle in, and then judiciously apply throttle. Perhaps this is just the way that a high powered car like this acts but I can’t help but think that this can be improved. 


Unfortunately, this was a poor choice for a shakedown session - it is a very fast and unforgiving track and the event was a competition with 15-minute sessions spaced out every two hours, for 4 sessions total. So no time to test, pull off, adjust, get back out, and test again. 

The issue or issues I have I feel might be related to the coil overs. I have a brand new set of Motons that I came across that I plan on installing to see how that affects the handling. I’m also considering swapping the rear bar for the stock 06 sway. Stock, old bushings also sound like they wouldn’t help but I don’t know that they would be the cause ether. 

I thought that the symptoms I described might be something that someone else has already dealt with and solved. Or maybe they point to something else that I’m not thinking of. Any thoughts? 

I have a short video of it on the straight on my Instagram page: @jfryjfry. Doesn’t really show much other than it is a section that my buddy said it was bouncing more than any other car.

a gratuitous photo:

Try playing with the rear tire pressure.  It's possible that with stiff suspension you're feeling the tires flexing.  What happens if you start to get into the throttle before it's done settling?  Does it just settle in faster or something else?

Sounds to me like you are very under damped.  If its bouncy- that means that every transient will also have a bounce back instead of settling in.

I have a work van that does this. It was caused by my rear tires having a lot a squirm in the tread block. It weaseled about until the treads wore in. Probably not your issue, but worth a mention. You say it has new NT01’s, how new?

I'm thinking it's shocks. If you're planning on putting the Motons in, I'd do that and then start troubleshooting if the problem remains.

Before changing sways - how does it feel in steady state cornering? If it's fairly well balanced, leave the sways alone.

Sounds like the bounce is taking the wheels off the ground due to the stiff setup.

Check the alignment first, add a tiny bit of rear toe and see what spring rates you are running when you have the car in the air. Mine ACR is wicked fast on smooth tracks with the 1100/1400 lb spring setup I have but on the street and on any track with even the slightest bumps it is all over the place like you describe.

Also confirm that you are not on full hard or full soft on rebound adjustment on your Adains. Full soft and you will get the same feeling, full hard and you bounce around a lot.

First I'd make sure that there isn't actually something loose and moving around.  I don't think there is but you really want to be sure.  If nothings moving then I too think you've got a shock problem.

Really appreciate all the input.  I embarrassingly do not know the spring rates.  But I don’t think the dampers can keep up with them regardless. 

I adjusted tire pressure and was around 32 hot front and 28hot rear.  Does that sound ballpark???

and good call on double checking for loose things.  

The tires are brand new   I put about 150 miles on the street on them to heat-cycle them  

I think I am going to put the motons on and then reevaluate.   There’s just no way a $1000 system, as nice as they might be, can compete with a $8000 setup.  (Which I didn’t pay anything anywhere remotely close to that for!)

Who knows?  Maybe it will just make the problem 8x as bad!  

You probably don't need a rear sway bar either, or maybe a just a softer bar.

Tire pressures sound low. 

I'd pump up the rears to at least 32 hot, to be honest I'd probably go even higher than that.

And I second the currently underdamped opinions.

Anecdotal support.........I have a pair of Aldon shocks that came off the rear of a friend's 1964 Falcon Ranchero. He had them rebuilt twice by Aldan and wasn't happy with the ride quality at all. He just gave them to me after he swapped to an air ride type of suspension. I removed the springs and I can pump these things back and forth like I'm playing an accordion. They're grossly under damped for the springs . I'll suggest new shocks from another manufacturer for your Vette.

Definitely try higher tire pressure and see if that makes it feel better or worse.  

+1 for higher pressures. I recommend working with cold pressures as much as possible. Try maybe 35 cold all-around (since a C6 is well-balanced) as a starting point and expect to use more. On my Corolla (which has 60/40 weight distribution) I run something between 38F/25R and 42F/27R (all cold pressures) depending on how smooth and clean the track is.

You should also mark the sidewall/tread corners on all the tires to see how much tread (or sidewall) you're using and ideally also log temperatures across the treads when you come in.

As for tire temps, get a pyrometer and compare wear. 

GB, if you run higher rear pressures it will cut down the understeer.

Air pressures in tires have a "spring" rate and affect handling in the same manner.

 The changes are less noticeable but can be used to fine tune.

In all of my FWD cars I found that near equal pressures work the best.  Maybe a little higher in the rear for autoX.

Before addressing transitional response, I'd make sure the fundamental balance is right. Steady state sweepers or a skid pad, adjust the sways/alignment/pressures to get the balance you want. THEN you work on transitions. But there's no point in doing that with parts you're planning to change out regardless, so get your fundamental spec installed and then start to work on fine tuning it.

Tire pressure is tricky because there's a sweet spot. Get above or below that and you start to lose grip. It's really easy to change, though, so some quick experimentation will help you determine which way you need to go.

A couple things come to mind.  Full tread tires do tend to have a noticeable "squirm" to them, even in my Miata.  I have to remind myself of it every time I replace the tires.  The compound is as soft as it's ever going to be, the tread blocks are as deep as they are ever going to be and the tire has as much grip as it's ever going to have . . . all at the same time.  If your car is extremely stiff in it's set up, you are more likely to notice tire squirm from the driver's seat. 

Second, did the "hop" get better as the session wore on?  What were your tire pressures coming off the track?  If the "hopping" gets better as the session wears on, it could be a sign that your pressure is too low to start out with.  Tire pressures are always a balancing act between ultimate grip and responsiveness. 

Where are you all getting your tire pressure info from. Most of the corvette guys running on DOT legal tires start around 25psi cold and try to keep them about 29-30 when warm.

I start with the tire manufacturer, ask them where the compound likes to be. It's all about the hot pressure, the cold pressure is about as important as the temperature of your coolant after your car's been sitting overnight.

NT01s don't have a whole lot of squirm.  They should be in the high 30 psi range hot.

I think it has too much spring for those Alden low-riders.  When I hear it has HD anti-roll bars I begin to think previous owner was more of a shopper than a tuner, and just went "stiffer=better." 

I wouldn't even bother messing with it, if I was about to install a fantastic set of dampers like Motons.  I would ask the NASA guys what they like for spring rates and put those on.  If I had access to a stock set of sways, I would put those on until I had the damper adjustments in the ball park to see what I was dealing with. It's certainly about traction in the brake zone but more importantly adjusting dampers for which end (front/understeer or rear/oversteer) will be the working limit on my turn-in speed and which end will be the working limit on my power application from the apex.  Once that's done, I can see whether additional anti-roll bar diameter will help, just lie there, or make things work (like lift the inside wheel, yikes). 

You have picked a good tire.  For fast lapping in a powerful car, I would be working to get my stable temps consistent on all four corners, in the sweet spot for traction.  With a car as heavy as yours on those tires I would be evaluating 36 psi hot as my starting point.

It's a wonderful track platform and you should be kicking butt in no time.  Wish I was in your shoes!

Keith Tanner said:

It's all about the hot pressure, the cold pressure is about as important as the temperature of your coolant after your car's been sitting overnight.

Hot pressures are the important pressures, yes, but they're very hard to set consistently and they'll even vary per-tire depending on the track layout and which tires the sun was shining on or were shaded most recently...working with hot temps makes sense for teams with a crew who can run over to read tire pressures and tread temperatures as soon as you come in, and ideally also a tire guy who can spend time interpreting those readings. For a one-man-band grassroots racer, choosing cold temps for the hot temps they produce is a much more reliable and realistic approach IMO. You can even make hot adjustments, wait for the tires to cool down, and then measure your new, reliable cold temperatures.

Like Keith, I haven't found cold pressures to be all that useful..   How hard is it to hop out of the car and measure PSI?  I mean, it's not like measuring the temp where it's starting to drop before you get to end of pit road.  For us rookies, it'll hold hot pressure for 5-10 minutes, and even then it'll only drop by 1 or so.  Cold pressures don't take into account that this course favors the left turns vs right turns, ambient conditions, etc..

I've never ran the NTs myself, but the chatter I've read on the champcar forums indicate that those guys try to target 30-32 PSI hot like Weary said.  We generally run smaller tires than the vette, though!