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Discussion Starter #1
I've been driving a lot of roadrace-type trackdays. My TT is BPU with Eibach Pro-Kit springs and Bilstein struts. I'm using street tires. Does anyone have any experience on where to start with the front/rear tire pressures in the Supra TT?
 
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Start at about 35 psi, with shoe polish to measure tire rollover and hopefully a pyrometer to measure temps.

If you only use shoe polish, adjust until your last run rubs down to the right area (have someone show you).

If you use tire temps, adjust until the center temp is close to either edge.
 

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Well for what it is worth, I am still expirementing with tire pressures but here is what I use so far. I run 37psi in the front and 35psi in the rear. I am running street tires, 245s front, 265s rear in the Kuhmo Ecsta tire. The sidewalls are pretty stiff so you don't need to run high pressures IMHO to prevent shoulder roll over. I am using the shoe polish method to check just where the tire is getting scrubbed in the turn. You are looking for the most tire contact you can get so want the tire to show scrub all the way out to but not on the shoulder. I am going to the pyrometer method soon. Check your pressures between runs!! You can get significant pressure creep. Before I learned to do that I noticed one time (track temps were climbing) that the back end was definitely having a grip/oversteer problem especially under throttle applications. Pulled into the paddock and the rears were 4psi higher than I wanted! Dropped the pressure down and took a little over a second off of my lap time. Good luck. Each tire is different.
 

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vande17941 said:
I've been driving a lot of roadrace-type trackdays. My TT is BPU with Eibach Pro-Kit springs and Bilstein struts. I'm using street tires. Does anyone have any experience on where to start with the front/rear tire pressures in the Supra TT?
Last time I was out on stock wheels - (w/ 235 fronts, 265 rears) - I started at 38 f&r and ended up bleeding a little bit (about 1-1.5 psi after the first session. So probably 37 is just about right...

I've heard a good rule of thumb is 4psi between hot and cold - but I think that depends heavily on the brand of tire. Nothing subsitutes for shoe polish! :)


-Darryl
 
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Discussion Starter #5
Follow Up on Track Testing

Just to follow up... Using Kumho Street Supra Ecsta Tires 245/40-18 & 275/35-18 at Willow springs, the proper tire pressures that resulted in the best handling were 36psi front (cold) and 36psi rear (cold). This is on a Bilstein equipped Supra TT with an Eibach Pro Kit. However, earlier testing also revealed that 36/36 was best with the stock suspension, too.
 

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When I autocrossed my MkIII, I started at 40psi front, 38psi rear, With Dunlop SP8000's. The rears hooked up well, but the fronts weren't quite getting enough grip. I put them up to 43-44 psi, and I got a lot better traction up front. Personally I would start higher and work down.
 
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Tire Pressures

Remember:

1. They are two different cars (MKIV & MKIII), so their tire pressures can not be related to each other at all.

2. Autocrossers tend to prefer their cars to oversteer a bit more than roadracers because it may result in slightly faster times around really tight courses.

3. Individual suspension setup differences on vehicles require very different pressures for a given situation.

4. Whether a track is "fast" or "slow" usually requires a bit of a different setup. Most racers prefer the front to be a little "looser" on fast tracks.

5. Autocrossers set their pressures "cold". Racers set their pressures "hot".

6. Different tires require different pressures. Most DOT-R tires, for example, require higher pressures in order to get the maximum adhesion from the tire due to its construction and compound.
 

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I agree with some of the points of Vande. While Solo 2 (auto-x) drivers may intially set pressures cold, I check my again especially after the first run for pressure creep. I then adjust my tires while they are hot. Most events I run you run in a short enough sequence to have some temp in the tire. Yeah on track events I dial in a little more understeer with the tire pressures because that is what I want initially on turn-in so when I hit the apex and start to roll on the throttle, I can balance the car with the throttle and induce some oversteer on exit. I believe the initial inquiry was about street tires so I assume he was not talking about r-compounds such as victoracers and hoosiers. It is interestin to note just how close the tire pressure recommendations run fromo post to pos though. So it might be a good place to start.
Barry H. 94ttsupra 245s in the front 265s in the rear Kuhmo Ecsta Supras:cool:
 

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Keep in mind that you aren't always tuning for maximum traction or fastest lap time (I know we all want to go as fast as possible). You also need to keep the temps and pressure down. When I was running Ecsta Supra 712's I typically used 36-38 psi. cold. I could have gotten better traction with less pressure, but the pressure rise (heat) was getting to high causing the tire to lose it's grip and chunk slightly. I really needed a little more air in the tire to keep the temps down but I wasn't willing to give up more grip. You generate a lot of heat running street tires the roadcourse so be careful. I too run street tires on the roadcourse but watch those pressures.

Hope this helps, Steve
 
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Discussion Starter #10
Tire Pressures

That's true about running higher pressures to keep temps lower. When running the Supra Ecstas we actually found 36 psi on both ends to give the highest traction and lowest temperatures. This was found using a skidpad, g-meter, and pyrometer.

However, if the tread is not shaved down to at least 5/32 or 6/32 maximum depth the tires will overheat at ANY pressure. I know for two reasons. Firstly, my pyrometer tells me so. Secondly, after four track days, my Supra Ecstas are always toast when they haven't been shaved.

Running street tires at full tread depth results in two problems. The tires go through extreme heat cycles which causes the rubber compound to harden, increasing lap times after every day's heat cycles. Even though the tires look "new", they are destroyed. Then, after more use, the heat causes the tires to chunk, resulting in tread delamination... dangerous.

If you want to run street tires, have them shaved to at least 6/32 maximum depth. The vehicle will be more responsive because there is much less tread squirm. And, the tires will actually last twice as long.
 

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I know what you're saying about the shaved tires,they really do last alot longer,and nothing is smoother at higher speeds,no vibration either.
 
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