Prolene

I have A032Rs and I understand performance tires need to warm before being able to supply maximum grip. Is it the case a tire's performance might be said to become "greasy" during the course of lap sessions? "Overheating?"

I know that in one particular session, the back of my car began to lose grip in way it seemed not to before, though I could have been trying to go faster; though it seemed there was much less grip capability. The rear pressures were about 32 cold, fronts 36. Front tires were fine in grip, it seemed, so I was getting a lot of oversteer towards the end of that session.

davepk

Prolene,

I think your pressures are a bit high for A032R's...
When running BW on Sat on my A032R's I was getting an 8psi pressure rise cold to hot and I was running 28psi (f & r) cold for 35 - 36psi hot... I usually notice the tires starting to get squirmy around 38 - 40 psi and anything over 40 can be scary.

I have never noticed any of the R Compound tires that i've run to become "Greasy". I have only seen the stock SO2's do that when pushed too hard. Though the SO2's recovered from that once they cool, they never seem to recover fully... You'll also notice a discoloration of the tread i believe is associated with it.

fluxen

Yes, any tires, race or not, can get greasy when they get too hot. That session must have either been longer than the others, you had less traffic holding you back, you were going faster, or you were sliding the rear around more (trail braking or earlier throttle application?). Of course it's also possible something was on the track, but that shouldn't stay with you around the whole course. Just my $.02

Prolene

Thanks for the replies. I think that with the higher pressures and length of session and pushing it 'playing' with the NSX, less aggressive alignment, all contributed to the tire heat and oversteer.

s2k2fast4me

Overheating is not uncommon at all in race rubber, even at short duration events like an autox. Alot of factors can contribute to overheating like tread depth, compound, alignment, surface temps, driving style, etc., etc.

At autox events, we often heat up Hoosiers (autox compound) and Kumhos to the point where they become greasy, especially the Kumhos. Two drivers and summer temps often are the reasons. We bring along a water sprayer with cool water to spray down the tires between runs after we think they are too hot.

Obviously cooling with water is not really an option at a track event while you are running. You can minimize the heat buildup by driving smoother with less slip angles, but if you've got new tires with lots of tread you may overheat just due to the amount of tread flex. I'd be hesitant to start with lower pressures as I would think that would contribute to faster heat buildup. I have zero experience with A032's, so wouldn't know what to say about what the upper limit on pressures wrt optimal response is.

-Andy

Mike Schuster

I know nothing about A032Rs, but for factory S02's greasyness is very often due to overheating. It is critically important to measure tire pressures at the end of your session to see what hot, operating pressures you had. Last time at Sears Point with brand new tires 38psi front and rear (measured at session end) got a tad too greasy (to much oversteer in turn 6). Reducing front and rear to 36psi completely solved the problem on my stock car with a very modified custom alignment.

Prolene

I should have measured the temps after that slippery session. Perhaps the lower initial rear pressures caused more heating as well, which could be measured as well, if the pressures checked out not too high. Certainly the fronts acted fine, and they started with a higher pressure. I know UL told me he liked 39psi all around hot, on his A032Rs. So better examination on my part of temps/pressures would help in evaluation.

Mike Schuster

Measuring tire temps is not too useful, IMO, it is just hard to get good data because of the high rate of cooling, and even if you measure quickly you are then only measuring what was going on (maybe) in the last corner rather than the whole track.

You have got to realize that temps change in fractions of a second. This is one reason why the car cannot corner immediately at its max g loading at turn in. (There are other reasons too of course). The tires have cooled off running down the prior straight and it takes a bit of time for them to come back up to operating temp as you turn in. Then as soon as you exit the corner they cool off again. This is frustrating, but you just have to learn to live with it and drive the car accordingly.

Tire pressure on the other hand changes slower and integrate what is going on over the whole track better. If the pressures rise too high due to heating then you go outside the tire's best operating traction band. This is why it is often the case that reducing pressures works for someone who is running their car at or near the limit a lot.

If that doesn't work, and if your car is reasonably balanced neutrally (so that overheating is not due to an unbalanced suspension) then you are just overdriving a tire rubber compound that was not designed to take the heat you are generating. This typically happens to me when I run rain tires on the open wheel car and the track is drying out. They just get too hot no matter what the tire pressure is and burn up, and just you have to pit and change them. A good dry R compound shouldn't do this, but who knows?

Mike Schuster

One more thing I forgot to say about temps. Do check for visual signs of melting of rubber, what it looks like is obvious once you see it. A little bit of melting is OK in my opinion at least for S02's - I get this regularly and it doesn't seem to affect the car's balance and performance in a negative way.

statueman

Here's sort of my understanding of tire pressure and temps from karting as we were always adjusting the pressure to keep up with track/tire temps during the day. I'll probably find out auto-x is completely different!
More pressure, hot sooner, traction sooner, traction goes away sooner.
Less pressure, hot slower, traction slower, traction stays longer.
If my tires were getting "greasy", I'd probably try taking out a lb or two.
How's that from someone who knows little! Feel free to correct me. Eespecially you Mike, sounds to me like you know of what you speak.