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Old 10-01-2009, 02:25 PM   #1
Back Road Runner
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Default Getting tires up to temp - low tire pressures?

Hopefully this is a simple question. I run RE01Rs on my Forester (245/45/R17), and in most cases I will barely get heat into the tires at an event. It generally takes a significantly long or very aggressive course to get temps up.

I've had a habit of running pretty high tire pressures, 40psi. I know the RE01R is relatively insensitive to pressures compared to some of my previous tires, and I have dabbled with them at pretty low pressures back when I was getting a feel for them for daily use. I tend to set as high as I can get away with without the tire riding up on the center.

My question is a matter of flex and flex causing heat build up. I assume that I can step to a lower tire pressure and get more rapid heat up of the tire during an event. As long as camber adjustment follows along with the added flex, I assume there are also no ill side effects to this either. Am I correct in the idea that I should probably be running quite a bit lower pressures to aid heat up of the tire?

I'll make a side note that I've had no issue at 40psi. The tires don't warm enough to really have any issue. I may have 1 tire out of 4 that might be slightly warmer then it would be just cruising down the highway.

Any insight on the pressure relation to temp ramp up?
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Old 10-01-2009, 02:45 PM   #2
PitwrkzZ1
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I run 245/45/17 RE01Rs on my 02 WRX. I used to go up to 40, but the shoe polish tells me that the optimal pressure for me is 36 front and 32 rear, hot. At these pressures the fronts are pretty evenly hot (I run -3.5 front camber) after two or three runs. Even running a relatively low pressure in the rear, they still barely get hot.
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Old 10-01-2009, 04:48 PM   #3
Boxologist
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u'll get more heat w/ higher pressures. thats what i find at much lower tyre pressures on the re01r's(running 25+ psi at 10am negates the need to throw a spin on course if starting the day at 22psi).

YMMV as the Fossie weighs in twice what i'm at.
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Old 10-01-2009, 09:41 PM   #4
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Hmm, I was under the impression that tire flex was a major part of heat up in tires.
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Old 10-02-2009, 08:33 AM   #5
neilschelly
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Yes, lower tire pressures will warm up more. And please don't run 22-25psi on street tires - that's way too low and probably dangerous. If you get any significant tire rollover (easy at such a low pressure) or the tire loses its bead, your wheel will hit the ground. Best case scenario is you'll only damage a rim, but a totalled car isn't out of the question.
-N
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Old 10-02-2009, 01:12 PM   #6
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Something is seriously amiss if you can't get that tire on a Forester to over heat. Do you compete in really cold weather maybe?
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Old 10-02-2009, 02:05 PM   #7
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It can be 90F out and it won't matter. It can be tire dependent. The RE01R is a pretty durable tire, and the 245 size does put a decent amount of rubber under the car. For example, back when I got my summer rims, they came with Toyo Proxies 4 in a 225 wide size. Same car, although different suspension back then, much softer, I ran two events and pretty much took the last half of the tread right down to the wear bars. They'd chunk rather then get gooey. The RE01R is kind of this way too, but they are much tougher and show more scuff then chunk if anything at all. I've never had the RE01R get sticky or slippery or anything. I may get smoke off one tire while braking (ABS disabled), but that's about it.

Sure if the course is a minute and a half long, I'll get heat into them.

Most courses here are around 45 seconds give or take. Weather does vary a bit living in Minnesota, so the race season can easily range in temps from 60F to 100F.

The Forester is 90% Impreza, and the weight is still around 3200 lbs with just about the same bias. On 245 wide tires, I do find it hard to get the tire sticky. On a relative sense of wear, this is my 3rd summer running the same tire. I do around 3-4 auto-x events a summer plus a test and tune day or two. My times are mid pack, but I'm at least 500 lbs. too heavy and half the power I need to be to be competitive. I do run the car hard although more smoothly then aggressively.

At most, I'll have one tire with a good bit of heat in it, one of the fronts depending on if there's more lefts or rights. The one front will actually have a bit of heat. The other front will be warm. The rears will have barely any heat in them. I've been at events too where the "hot" front was no warmer then it would be just driving around. It's been a very, very rare time that I've had a tire or even a part of the tire actually hot and sticky.

Last edited by Back Road Runner; 10-02-2009 at 02:10 PM.
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Old 10-02-2009, 03:45 PM   #8
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Yeah, I took the 07 Pro Solo Finale win on RE01R's on my civic in ST. I'm pretty damn familiar with the tires characteristics. I could heat them up just fine on my car, and I had more tire vs. weight then you've got (205 tire, 2100lbs) and less power then you have. There is nothing wrong with the tires or your tire pressure. Get a pyrometer and give us some real numbers here.

Oh yeah, and I'm in New England, and even on cool days on a 30 second course I could get plenty of heat in the tires. Warm days required a water sprayer to keep them cool enough.
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Old 10-03-2009, 11:27 PM   #9
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A pyrometer will probably be on the list for next year.
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Old 10-04-2009, 04:45 PM   #10
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Quote:
Originally Posted by neilschelly View Post
Yes, lower tire pressures will warm up more. And please don't run 22-25psi on street tires - that's way too low and probably dangerous. If you get any significant tire rollover (easy at such a low pressure) or the tire loses its bead, your wheel will hit the ground. Best case scenario is you'll only damage a rim, but a totalled car isn't out of the question.
-N
nahhh. next u'll be telling me not to start off w/ 15-16psi in my hoosiers next year.

edit: whiy don't we have a stick poking smiley?

edit2: this will work
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