Why RE-71R's torn up after one event?

[Icecreamtruk]

@ZDan cool that you are into nerdy bits as well then! When I was talking about pressures, I always meant hot pressures, cold pressures are mostly irrelevant as just as you say, the rise on pressure while out there on the track depends greatly on ambient temperature as well. Some days I need to go out at 22psi, some days I need to go out at 26-28psi to get in the same 30-32psi range, which is also why I usually need several sessions.

For tire temps, I dont take them hot in pits without a cooldown lap, because it will tell you exactly what you are implying, surface temperature. My cooldown laps are fast enough to keep some heat on tires, but slow enough that I dont have to touch the brakes (mostly, sometimes traffic gets in the way), Im only trying to cool the brakes (and a bit the engine too, so I keep rpms low).

So my observations after taking temps after this kind of cooldown are that temps rise or stay about the same a bit after pitting, and then start to go down, but relatively slowly. 2-3 minutes after pitting, its still within 5-10F of their temp after I pitted (I do try to go deep with that needle point, but obviously its still only a couple of mms of penetration).

So anyways, I dont know exactly why I got the temperatures I do, but as an example, two events ago I was at a track where I was overheating the tires (temps were in the 220-240F range after pitting), for the next session I dropped the pressure by 4 psi (32 to 28, it was on nankang AR1s, their website even recommend very low pressures) and after doing a similar session my temps were in the 170-180F range. Could I have been avoiding overheating the tire after knowing in advance that they were overheated? Probably. I went faster, so I wasnt driving slower, maybe tidier? The temperature on my datalogger says 1C higher temp on that session, so if anything tires should have been hotter. Later that day, in the afternoon, the temps dropped quite a bit, and so did my pressures, I noticed the tire started rolling over so I pitted and measured temp and pressure, it was in the 25-26PSI range and temps only up to 140F. I pumped the pressure back to 30PSI hot for the next session and after it when I measured temps I was at 170-190F.

I dont fully understand those measurements. I mean, I can see the pattern, but I dont understand why it does what it does. If you or anyone wants to illuminate me on that, I would greatly appretiate it.

As a side note, I do a lot of sim racing to keep in shape during the winter. On sims (Assetto Corsa and Iracing), higher pressures = higher temperatures on the tires. They are, of course, cold pressures as you cannot really set hot pressures, but higher cold pressures end up being higher hot pressures, not relly rocket science there. So there has to be something there that can be somewhat easily explained.

[strat61caster]

fwiw chatted with an old friend today who crews/tire tech for some sports car racing (they'll fly him out to Sebring, Daytona, etc) and it's not uncommon for those cars to be sent out at like 22 psi and the drivers are supposed to keep off the curbs for a few laps until they get heat in them. Said they'll go as low as 18 psi, targeting 26-28 psi hot. Didn't poke too much as to what tires or such, real racecars have different problems than street cars at grassroots stuff, but thought it was interesting.

[churchx]

There are different things in "real racecars", that might not be applicable to ours .. yet interesting to read about.
For example, IIRC at F1 brake heat is also partially reused to keep tire temps hot enough to grip well by design. Or how things like tire warmers change picture, where it was interesting to read, that after banning them in european touring car championship, it resulted many drivers adjusting brake bias in first laps exactly to get more heat into brakes/tires, to get them upto working temp treshold quicker, and then changing brake bias back.

[ZDan]

Originally Posted by strat61caster

fwiw chatted with an old friend today who crews/tire tech for some sports car racing (they'll fly him out to Sebring, Daytona, etc) and it's not uncommon for those cars to be sent out at like 22 psi and the drivers are supposed to keep off the curbs for a few laps until they get heat in them. Said they'll go as low as 18 psi, targeting 26-28 psi hot. Didn't poke too much as to what tires or such, real racecars have different problems than street cars at grassroots stuff, but thought it was interesting.

What cars, what tires matters, of course. FWIW Hoosier recommends running higher pressure at Daytona, 40-42psi+ hot for A7 and R7 DOT radials:
https://www.hoosiertire.com/news/art...ecommendations.

Same bulletin recommends as low as 30psi hot for dedicated non-DOT racing slicks, so what tires matters *A LOT*!

What pro race teams run for pressures on well set-up lightweight purpose-built race cars on big wide racing slicks has pretty much nothing to do with us...

In relation to this thread, if you aren't a professional who knows exactly what the ramifications are, I wouldn't go out on track with 18psi! I don't go out with less than 26psi COLD. Sometimes 24psi COLD in the tire 1st morning session for the tire that sees the most pressure rise.

[TunaNoCrust]

Originally Posted by ZDan

In relation to this thread, if you aren't a professional who knows exactly what the ramifications are, I wouldn't go out on track with 18psi! I don't go out with less than 26psi COLD. Sometimes 24psi COLD in the tire 1st morning session for the tire that sees the most pressure rise.

Hi Dan!

I have had very good luck sticking with the manufacturers recommendations, especially their minimum pressures. Those pressures are implying the car is properly setup, when I didn't have enough camber I had to run a couple psi higher to alleviate some of the roll over....that Poor Michelin Man didn't last too long on the shoulder.

[Icecreamtruk]

Also, two things nobody has mention but I guess most people already know. The heavier the car, the more pressure you need in the tires. The wider the tire the less pressure is required (or the other way around, narrower tires require more pressure).

[strat61caster]

Thread has been apples to oranges to pears for about twenty posts now, figured I'd throw a banana at the cornucopia.

[ZDan]

Howdee, Chuck!

Originally Posted by TunaNoCrust

I have had very good luck sticking with the manufacturers recommendations, especially their minimum pressures. Those pressures are implying the car is properly setup, when I didn't have enough camber I had to run a couple psi higher to alleviate some of the roll over....that Poor Michelin Man didn't last too long on the shoulder.

I reckon not...
TBH I haven't looked into "recommended minimum pressures", do tire manufacturers publish such? I would guess their recommendations would be a bit higher than we'd want to run as cold?

Today's test: Commuted to work at 75-80mph at ~10:00, 75F, tires went from 29/30 to 34/36 over 17 minutes. So figure that +5psi pressure change is due hysteresis in the tire from normal driving, the additional +5psi I get at the track is from additional heat into the tires from friction at the contact patches, and heat into the wheels from the brakes. And I guess the thermal mass of the air in the tire is enough that it takes ~17 minutes for hot pressures to fully develop, though presumably tires themselves and brakes and wheels get up to temp a lot quicker.

Just thinking out loud now...

[TunaNoCrust]

Originally Posted by ZDan

Howdee, Chuck!

I reckon not...
TBH I haven't looked into "recommended minimum pressures", do tire manufacturers publish such? I would guess their recommendations would be a bit higher than we'd want to run as cold?

Today's test: Commuted to work at 75-80mph at ~10:00, 75F, tires went from 29/30 to 34/36 over 17 minutes. So figure that +5psi pressure change is due hysteresis in the tire from normal driving, the additional +5psi I get at the track is from additional heat into the tires from friction at the contact patches, and heat into the wheels from the brakes. And I guess the thermal mass of the air in the tire is enough that it takes ~17 minutes for hot pressures to fully develop, though presumably tires themselves and brakes and wheels get up to temp a lot quicker.

Just thinking out loud now...

For example, on the Federals they were unknown to me so the manufacturer recommended minimum was a good place to start. Plus our cars are on the light end of the industry for 17-18" wheels.

You are commuting on RE71Rs?

[ZDan]

Originally Posted by TunaNoCrust

For example, on the Federals they were unknown to me so the manufacturer recommended minimum was a good place to start. Plus our cars are on the light end of the industry for 17-18" wheels.

You mean minimum recommended by Federal, or by Toyota? What is their recommended minimum?

You are commuting on RE71Rs?

On the BRZ. Yok A052s on the Cayman.

[TunaNoCrust]

Originally Posted by ZDan

You mean minimum recommended by Federal, or by Toyota? What is their recommended minimum?


On the BRZ. Yok A052s on the Cayman.

This is the tire manufacturer's recommendations....most have information somewhere as to suggested hot temps, cold/hot pressures, and camber amounts as well.

https://philstireservice.com/shop/federal-fz-201s/


Which vehicle was the commuter test on?

[ZDan]

Originally Posted by TunaNoCrust

This is the tire manufacturer's recommendations....most have information somewhere as to suggested hot temps, cold/hot pressures, and camber amounts as well.
https://philstireservice.com/shop/federal-fz-201s/

That's pretty nice to have, don't usually see that kind of detail, usually just max pressure which is kinda useless...

Which vehicle was the commuter test on?

Porsche. Just watched the pressures on the dashboard until they reached max.