Tire behavior on track.

I am running 235f/295r PS2s on the track with 37f/42r psi hot pressure. Throughout a session the car will consistently transition from oversteer to understeer in med-slow turns after about 3 laps and I am wondering what causes this. Early on, the car will have a lot of front end grip and i'll be playing with the car to keep the rear end in place, but after 3 or 4 laps the car will push. I will have to lift more, delay power longer and keep adjusting my inputs. Is this normal or is there any way to have a more consistent car? I am also wondering, is this is a street tire heat issue that would be resolved with an R-comp? I am having trouble understanding why as the tires heat up (equally) I lose more front end grip than rear.

Quotes source post: 6481016

A few questions: 1) What cold pressures are you starting at? Sounds like you might be starting too high all the way around, with too big a gap between F/R. Most run PS2 below 40 hot, shooting for around 36/38. IMO, 5 psi difference is really too much for these tires. Lowering the rear pressure will help the understeer. 2) How much push are you getting? Is it tire squealing, "oh crap I'm not going to make the turn" push? Or is it "I'm driving pretty fast and the car won't turn quickly enough" push? Somewhere in between? Also, how does the car behave in other types of turns (besides slow-med speed)? 3) What temperatures are you running? Temps are an OK guage, but you really need to know if you are running the right temps for your tires. A few comments: All of my Michelin tires (including Cups) took a few laps to heat up. I never liked them for that reason. In a 20 minute session, taking 3 laps to get all the way to temp is 1/4 (or more) of the sesssion. I would disregard their behavior when cold (the first few laps) with respect to changing the setup. The car's behavior when all the way up to temp is really what matters (brakes, tires, engine, and driver). I assume you are running 235/40 and 295/30. In my experience, this combination tends to promote a little understeer. When I run 295 or 305 in the back, I run 245 up front. I run 235s with 275 and maybe 285, but I don't run 285s much because of the small diameter. If the car is setup properly, and the tires are behaving like they should, understeer is usually caused by diving the corner (i.e., braking too deep and turning with the car improperly loaded). -td

Do you use nitrogen?

what's your alignment settings? The car naturally understeers and I typically have to do an abrupt lift and/or trailbraking in order for the rear to rotate. I run 36/38 hot. Maybe you're overworking the tires.

1) never measure cold PSI, only hot 2) How much push are you getting? Is it tire squealing, "oh crap I'm not going to make the turn" push? Or is it "I'm driving pretty fast and the car won't turn quickly enough" push? Somewhere in between? Also, how does the car behave in other types of turns (besides slow-med speed)? ----I guess the latter. I don't really trail brake unless the front end isn't biting and i will do minimal trail braking to get the front end to bite. Generally I take a sweeping arch, slowly turn in and slow the car down by rolling resistance, continuing to add steering input as the speed drops. The early laps I feel I can drive harder into the corner and i'm fighting oversteer, later I have to slow the car down more and the rear stays planted. here's a lap around VIR north from this past weekend. not terribly helpful since you can't see my feet http://www.youtube.com/watch?v=NOdvQgheaJ0 3) What temperatures are you running? Temps are an OK guage, but you really need to know if you are running the right temps for your tires. ---I don't know. Guess that would help a lot No Nitrogen Alignment is: Front: -2.5 camber, 0 toe, 8degs caster Rear: -2 camber, 0.3degs toe

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- wow, that's quite a trick! signed- wiseass

I think you are way too high on the hot pressures, I had RA-1s up to 42 psi once all the way around by accident, they were super sloppy and gave out on after about 3 laps. PS2s are street tires so keep the pressures at the optimal. Try setting them back down to 34 psi hot all the way around and work from there.

Ya I will play around with tire pressures more, reduce the split between front/rear and take a tyre pyrometer next event. I still find it odd (I don't fully understand) how the car consistently changes balance as the tires heat up I presume equally. I also noticed one of my rear sway bar brackets (mount to the shock body) was lose which didn't help...

It's funny becuase with my setup my car gradually goes the other direction over the duration of a session. How's wear on the tires? I ask because my initial thought is you've got too much negative camber in the front for street tires. !!! Hard to imagine but I'd be willing to bet you're not using the front contact patch effectively and causing it to overhead and traction to go off. Put track tires on there and your camber is good and I bet grip is consistant throughout. I actually found at -3.0 last season I was running too much camber for the Toyo's I had on the car. Temps were more consistant at around -2.7 My intention was to move to Hoosiers and go back to -3.0 at the front this season but I'm not going to be going to the track at all this year Wouldn't hurt to either add some front tire or take away a little rear. 40mm stagger is my preference.

Quotes source post: 6482635

He uses pure Helium, makes the car lighter.