Perhaps someone has slayed this dragon and can assist me. My 350Z is just about perfectly tuned in terms of a streetable race suspension. Everything works well and I don't want to mess it up by making any major changes. The only issue right now is that the car pushes from the middle to the exit of carousels and sweepers (middle of 3rd gear to middle of 4th) and it's limiting the speed I can build to enter a straight.

The car is being built for time attack. I run a square setup on 275/40/17 NT-01's, Koni yellows and RS*R Ti1000 springs, Cusco sways adjusted to the softer setting on the front, 3 degrees neg front and 1 degree neg rear. Toe is within factory specs. I have 3.91 gears and a Nismo GT 1.5 diff, I think set on about 66% lock. I'm making 250 whp, N/A.

I am wondering if some aero would help. Any suggestions?

 

the only way aero would help in that condition is putting a decent salad bar (actually something that really works.. not a poser wing) and stiffening the rear springs...
no matter what you do... if it's pushing on the exit of "slow" corners it's probably very neutral in high speed or even with a light oversteer... you need stiffer springs in the rear to allow the rear to rotate better at lower speeds, but the wing will allow you to gain back grip in high speed corners and don't kill yourself because the rear end jumps around at 130mph.

 

Quick question, how does the car behave if you enter slightly faster into the corner. Does it tend to push away from the apex, or oversteer a bit until it settles mid-corner as you apply throttle.

 

If I come in too hot in a sweeper, there will be a little initial oversteer, as you mentioned. I have had some luck controlling this by managing the release of the brake pedal, but it will step out a bit.

I don't understand how the salad bar wing would reduce understeer, but I bet it would help with the oversteer at high speed corner entry.

 

ok,

Here's my theory...so take it with a grain of salt. Sounds like the car is fairly balanced. What it sounds like is an issue we all do sometimes. You come into a fast corner like a sweeper or long carousel slower than expected. Once you realize that you could be going faster and apply a more aggressive throttle to build the speed up where if feels the car should be after the apex once you know the car is set and stable. By doing so though you lift the front after the chassis is already set. This starts the understeer late in the corner and it just pushes the rest of the way until track out unless you unwind the steering a bit.

As I said, this is something we are all guilty of sometimes, even the pros. Part of it comes from learning the corner you are attacking. Chuck Hawks and Peter Krause have data showing this happens to every driver if the car is fairly neutral, and if you look at their client list you will see we have this in common with some impressive others. Two things you can try next time when you are out is

1) Apply the throttle sooner, but lighter
2) Very slowly increase you entry speed on the high speed corners until the car feels balance through out the whole turn.

If either of these work then the car is probably ok. If the car pushes despite the throttle application, then you can address that with other solutions.

 

Maybe your diff is locking too much...pushing the front

 

Sounds like a reasonable explanation, Marty. You are very tactful
I will have to play with the concept next time out. I agree that the diff probably plays some role also, and may someday pull it apart to reduce the active surfaces just a bit.

 

Have you you played with tire pressures up front at all? Is it a "Safe" understeer or a terrible plowing/scrubbing feeling.

 

*quote*
putting a decent salad bar [...] and stiffening the rear springs.

 

Try a little later apex on the corner.

 

I agree with the altering the driver before altering the car but one other item could help in additonal high speed cornering is additional caster. Not sure what the rules of the class you run in would say about the parts needed to change it. Also note its a tradeoff with low speed cornering. Additional, pressure changes in tires can help as well (as stated by Sharif) especially if you currently run a higher pressure in the front.

Note: When I'm referring to high speeds I'm talking about 80+

 

It's just the kind of mild understeer you get in a steady state turn (big 180 carousel) that you feel when the car is at the limit of its traction circle and you have to feather the throttle to maintain speed. I'm not sure how to late-apex such a turn. I usually try to hold a tight line and unwind it at the corner exit. Is that a good technique, or is there some sort of double-apex that is faster?

Oh, and again, will a splitter or other front aero help? I can mess with tire pressure. I was running around 36 psi hot.

 

Splitter up front will help. But based on what you are describing, you car seems pretty darn balanced with a hair more understeer than you would like on higher speed corner exists. As such, I would be looking to make minor changes, such as lowering tire pressure up front, or softening bars. I wouldnt make wholesale changes to your setup. I think you are close!

 

+1

Just what I was going to suggest!

Even a foot later apex can have a HUGE effect on corner exit, and it doesn't hurt corner entry too much either.

 

If you have adjustable shocks you could slow down the transfer of weight to the rear under acceleration and it could help.

 

In a 100mph corner, most amateur drivers in a momentum car prefer a little bit of steady state understeer (a 3,200 lb. 350Z making 250 rwhp IS a momentum car). Being able to get on the gas early in the corner is generally more important then how much you're on the gas at corner exit. If, with your current setup, you can get on the gas a second sooner then if the car was more neutral then that should carry over to a higher corner exit speed.

As mentioned above, it sounds like some subtle adjustments are what's needed. Also, yes a splitter will help.

 

agreed... and depends on what you want at the end of the day.. because I think you lose more time with a single "oversteer control" than a single "understeer management" event per lap. (when the car is damn close to be perfectly neutral)

 

Good point , Do you happen to have any on track video? Not particularly of the one corner just your driving style in general.

 

Agreed, a little understeer is a lot better than oversteer. I had that problem last season, and it was very frustrating. I tuned it out with rebound adjustment, diff fluid, and tires. No video, I need to get a camera mount. Perhaps we can revisit the topic in April with some "evidence". I'll work on apexes also.

 

Sounds like, if you're balanced properly, you should be able to get on the gas a little faster to give you a better exit - maybe letting the car float out the rumble strip. We'd need to see pictures/video of the turns you're having problems with.

Q: Are you having this problem all of the time? Or, just at a specific track and corner?