gkmccready

Okay, fourth track day, yet another different swaybar configuration on my '06 C6 Z51. Still on the stock F1 SCs.

First two times out with the car I ran the stock swaybars and the car was very twitchy mid-corner.

Third time out I had Pfadt Pfattys on the car. Stiffest front, softest rear. Car felt better, but not great. Cracked a rotor since I couldn't run the DRM brake duct extensions due to a conflict with the swaybar.

This time out stock front bar, base model rear bar. Car feels pretty good. Comfortable. Faster. Much faster. Maybe I'm just getting used to the Corvette, but it felt pretty good finally.

Now for the oddity... corner entry understeer, reduces mid-corner with maintenance throttle, reduces even more on throttle application on corner exit. The reduction mid-corner might be due to scrubbing enough speed from the corner-entry understeer. But why would throttle application on exit clean everything up? I'm not inducing oversteer on exit, based on feeling, and tire temps are _higher_ on the fronts than the rears. Any thoughts?

Had a great time with www.team-racing.org at Thunderhill. I think we got 7 sessions yesterday. 140 miles on track. Went through nearly a tank and a half of gas. Only had one session cut short when a Camaro oiled down the front straight.

elh0102

Unless you are referring to an extremely large radius turn, or your turn-in point is early, by the apex you are going to be taking out some steering, which should allow more throttle. If the only variable that changes is more throttle, then you should expect more understeer. And as you mentioned, it might also be a matter of having lost some speed at that point. And maybe without realizing it, you are lifting just enough to get some rotation started before increasing throttle. I guess that's why conventional thinking favors some understeer, the natural reaction is the right thing to be doing.

jcmbird

do you think you could be braking a little early[maybe slow entry].when you apply brake its kinda hard to have understeer because weight should transfer to front end. shocks original? weighting of car could be off or missing the camber of the turn.

gkmccready

I really notice this behavior through T14-T15, T2, and T6 at Thunderhill. The part I'm mostly looking to understand is why, on exit, more throttle
_reduces_ understeer.

Tintin

You will get understeer that can be reduced by throttle because the car is not balanced on the entry to the corner and the front tires have too much weight on them. This is usually caused by gliding into the turn, i.e. not holding an even pedal to the apex or turning too hard and not accelerating enough as the wheel is wound in for the turn. When you apply the throttle ,you are causing a weight shift rearward that lightens the front end and allows the tires to recover. I would suggest that you are too early on your turn in and are having to turn tighter to avoid the "LawnBoy" effect on the exit. You are in the wrong place at the start of the turn and are trying to hit the apex whilst gliding causing the problem. Is your car an automatic? You mention that you are going a lot faster. It is pretty tough to balance the car at the edge with an auto unless you have a shift kit that defeats the upshifts and allows the trans to stay locked.

All tires have a limit to their coefficient of friction and you can overwhelm that regardless of the car. An F1 car will understeer into a corner if you glide..

Conversely, you may be carrying too much speed into the corner which will give a similar symptom but rarely can be fixed with throttle. The tecnique I use to deal with an overcooked entry is to momentarily straighten the wheel in the corner, brake, then turn in again. Generally the braking slows you enough that you can turn sharper and still stay on the tarmac. Note the word generally.... This trick requires that you are a very precise driver that hits apexes 99% of the time. If the line is wrong you will certainly be doing agricultural work for a bit...

Oh, and I was T1 champ at T'hill in 96, so I know the track pretty well and I know my tips work. On t2 you are holding the car too tight for sure, let it drift a bit. If you cannot reach the apex without understeer you need a different line, I can run almost flat out around that carousel after I reduce my speed for the turn in from T1. If you are in NASA HPDE go find Ralph Alexander for tips on understeer and throttle, he can help you with this apparent paradox of balance. He was my co-driver in a Honda at the 12 and 25 hour races a few times and is the chief instructor for NASA. Oh, and he has won more than 500 races in a 50+ year carreer....

Try the two tecniques in a large parking lot, you do not have to go faster than 30 mph to see the results, just turn very sharply and try to stay at 30...

gkmccready

Car is a manual.

Much like I believe I'm not back in the throttle early enough on corner exit, sounds like I may not be getting back in quite enough after braking during entry. I'm certainly not gliding to the apex.

T2 you're likely right, I only end up tracking out to only about 1/2-2/3 track. I suspect running on street tires makes my situation a little different, though.

Not sure about turning in too early. A few instructors that I tracked down that were out in A group said my line looked great. And the car feels good once I start to roll in to the throttle -- no fears of agricultural work on exit. Just a fight to get down to the apex on entry; maybe it was just me not reading the tires getting greasy as the session went on and adjusting entry speeds appropriately.

The interesting thing there was if I slowed more for entry and didn't fight the understeer to the apex, my exit speed was significantly slower.

The one common thing pretty much everybody has come up with that I've asked about this is the ability to overload the tiny 245s. And that's something I'm planning to fix shortly...

Thanks!

robvuk

The factory prefers a bit of understeer for general consumption. I would think that using the base C6 rear sway with the Z51 up front would compound that problem. Instead, many people run the same size tires on all 4 corners and it gives the ability to rotate tires too.

Tintin

Dopey me, I didn't notice the mod you made to the bars... You stiffen the end of a car you want to slide.. You need to soften the front, the understeer is because of the stiffer bar... the tire size has nothing to do with it unless you are at the absolute limit..

robvuk

If he's understeering, wouldn't that indicate he's at the limit? The bigger tires in front will definitely reduce understeer.

gkmccready

Absolutely agree and understand... BUT with the stock Z51 rear bar the car was twitchy mid-corner which was even slower than the entry understeer. RAFTRACER suggested I try a 35mm ADDCO front bar with the stock Z51 rear bar -- I figured trying the stock Z51/Z06 front bar with a base rear bar would have a similar effect...

Again, it's not the entry understeer I'm trying to understand, it's why getting into the throttle at exit seems to reduce the understeer... shouldn't a car that's already understeering get worse when you add throttle?

Tintin

No it will be better because of the weight shift I spoke of above where you remove the weight from the overstressd front tires. You cannot make changes to the swaybars alone in the hope that you will improve the car. You need to coordinate the componenets like springs, shock rates (damping and rebound) and tire pressures.

It is difficult (like impossible) to give a full analysis on a message board, you need to make changes at a test day and bring tons of stuff with you to try out. You also need to change things in the front end like camber , caster and toe to start with. I don't know if your car has camber plates, you can use a frame jig in a body shop to bend the frame for more negative camber. I have done that with showroom stock race cars but I will take a wild stab in the dark that you don't want to make a commitment like that... I am quite good at car setup and have had many people drive my cars and say how easy they are to go very quickly in, but it comes down to being able to be absolutely consistent in lap times and inputs so the changes when made can be interpreted in a meaningful way to improve the car.

Sometimes wider tires will reduce understeer but not always. If you go to a wider tire your straightline speed will be reduced because of higher rolling resistance so the lap time could be slower. You are better to get the car to a neutral state with either technique or chassis hardware and then worry about the tires. I am sure that there are suspension packages that will help you that have already been put together. As you have a C6 and want to track the thing, I would call a guy like Lou Gigliotti and see what he has. It may cost some money, but you will spend a ton coming up with a solution yourself.

Take the bloody sway bar off and play with the tire pressures. Raise the rear by 2 pounds and see if it induces oversteer a bit... send me a pm with your phone number and I will help you with the theory. This is something I really know very well.

elh0102

Don't mean to pick at semantics, but you keep talking about more throttle at corner exit, with less understeer. As I mentioned in my previous post, at that stage of the turn (most turns anyway), you're going to have some, if not all of your steering input removed, so I would expect a relatively neutral balance at that point, almost regardless of throttle input. And I agree with you, other variables equal, more throttle will exacerbate the condition in a car that is understeering, up to the point you start to break rear traction. Thirty seconds on a skip pad will prove that.

Tintin

Actually it seems he is sliding the front end through the turn due to the giant sway bar and more throttle causes a weight shift to the rear allowing the front tires to bite due to decrease in load. Throttle often reduces understeer in these situations just as it can reduce oversteer by going to WOT when the rear is sliding. The car is unbalanced by the new variable - the increase in front stiffness... this is racecraft that it takes a lot of time to learn and as I stated above there are a lot of variables that are easier to discuss live than on a message board. If I still resided in the Bay Area I could go to the track and see what is what. As I am now in Arizona, a phone conversation will get you rolling and taking my friend Ralph for a ride will solve a lot of the mystery...

I am sure the instructors that you have are more than competent so your line is probably good. I always ask instructors how many races that they have won before I take their advice as accurate...

gkmccready

So, the front bar is the same as stock. Nothing stiffer than stock. The rear bar is softer than stock. It's the base bar.

The decrease in load allowing front bite is the thing I'm interested in. It surprises me.

You're probably right and an increase in rear pressure might help with the stock bars. The other thing that might help is folks suggesting spacing the swaybar brackets... so maybe I'll try the rear bar stock next time out.

The next time out, though, I'll be on different front tires at a minimum as I corded the stock ones Friday...