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Discussion Starter · #1 ·
FYI just wanted to give some data on what I ran this past Monday:
- Victoracer V700's full-tread heat-cycled
- started at 40psi cold
- tires got greasy and worthless at ~44psi hot
- 40psi hot appeared to be the correct temperature for several hot laps (at least through the corners -- I tend to take it easy in the boring straight stretches)

This was on 255/40/17 fronts and 275/40/17 rears on stock rims. Running Carbotech XP10s.
-Chris
 

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Good info, Chris. Thanks.

My experience with Victoracers is about the same, but last few track events I ran a couple psi less hot, depending on the track setup I'm more like 34 to 38 hot.
 

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Discussion Starter · #3 ·
Thanks for the data, Nick -- could you help me to understand why you chose less pressure? I want to make sure I'm not overdoing it on the tires. I beat 'em up pretty good in ~4 sessions of 30 minutes.
 

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how are you deciding on the right temp? based on feel and overheating the tires? tire roll over? or with a pyrometer?
 

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I usually run 40 psi cold with no problems on the V700's. Of course, our ambient temps (cold) are usually higher than Chris and Nick's!
 

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Discussion Starter · #6 · (Edited)
turbomx5 said:
how are you deciding on the right temp? based on feel and overheating the tires? tire roll over? or with a pyrometer?
Based on feel and overheating the tires. As you know it's easy to feel when the tires get greasy if you pay attention -- then just back it down until they don't get that way...

What are your thoughts on the proper way to measure/decide?
 

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Although the question was not posed to me, I'd like to chime in. I am a believer in the pyrometer. Immediately after the car comes in, take three readings of each tire - inside middle and outside thread.

Tire pressure is adjusted so that the middle temperatures match the average of the inside and outside; camber set such that the inside and outside match. I learned this back in the late 70's and early 80's, and don't remember what kind of tolerances were used, but the general principle was to test, test and test, and try to match within each tire the temperatures as well as you could. Tha towul give you even wear throught the tire, and extend it's life.

I learned this on a 1973 Porsche RSR, so the overall temperature bias was waaaaay to the rear; I think that in a Sup it will still be towards the rear if less so (rear hotter than front); There will also be a bias towards the outside tires.

Of course, I am too lousy a driver to even attempt this in my own car...

Cheers
Rich B.
 

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yep. exactly what I would have said. Only change is that if you aren't making camber changes at the track, just use the pyrometer to make temp change across the the tire linear. I also look at the sidewall of the tire and make sure the tread is rolling over as far as I want it to.
 

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Discussion Starter · #9 ·
Thanks, Rich. I appreciate the education. :)

I'm not hardcore enough to go that far yet, but perhaps I'll invest in the pyrometer.
 

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I don't have a pyrometer even though I understand how valuable that info is to really know how the tires are behaving. But I have been on the track when another Supra bud who was a more serious racer than me had a pyrometer, so I got some feedback from him; but mostly I just went by how it feels, if it gets "greasy", and marking the tires to look for how far they roll over. Not the best but that's all I had to work with. We have some pyrometers in work that I think would work well on a tire surface, I'll try it.
 

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Nick -
THat is what I do, too, but because I am slooow!
One of the nice things about using the pyrometer is that if the car is feeling greasy, and you have localized overhearing, you can extend your tire's performance by adjusting alignment; if the tires are overheating uniformly, then you are simply overdriving the car and you ought to back off s a little; if that is the case, you can look at which tires are overheating to figure what you are doing too aggressively.

Cheers
Rich
 

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or in the case with the supra, you simply don't have enough tire under the car to handle the heat its 3100+ lbs create...
 

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Well, talking as someone who crewed endurance cars, you have to drive to your limitations; if overheating the tires is one of them, driving for a 1/2 hour session is not the same as for a qualifying lap.

I would say that if the tires got greasy and one ended up going slower, then one averdrove the car for the conditions (e.g tire size and/or session length).

Cheers
Rich
 

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Chris, you said that the tires behaved at their best when they were at 40psi hot. What was the temperature when cold that brought them to 40 hot?
Mike
 

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Discussion Starter · #16 ·
TempesTT said:
Chris, you said that the tires behaved at their best when they were at 40psi hot. What was the temperature when cold that brought them to 40 hot?
Mike
Mike -- that depends on which tires take more of a beating. I started with 40 cold and then drove the car, adjusting the pressures after 2 sessions to get them all to an even 40psi hot.

Basically, the approach is to start with an even cold temp, then adjust to an even hot temperature after each session...
 

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Chris, I would imagine that each track would expose each tire to different loads, and hence heat each one up differently, right?
If you measured the cold pressures after you found the sweet spot I'd be interested to see the numbers.
Thanks!
Mike
 

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Discussion Starter · #18 ·
Yes -- but there's more to it even than that, because there are other atmospheric variables that come into play as well.

In short I don't think there is an easy "cold" number I could provide you. :(

That's why it's best to start with 40 cold and drop the pressures to get to 40 hot. HTH
 

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I used to agonize over temps but the more people I talked to the less value I placed on them. I guess the most convincing argument is that the measured temps really mostly reflect the last couple of corners, or straight that you came off of before taking the measurements. At Mosport for instance the pits are shortly after the long back straight which is then followed by a sweeping right, and then a low speed left as you slow to exit the track. Whatever you measure in the pits is not going to be representative of the temps while hot lapping as the 3/4 mile straight and one fast right will have changed it significantly.

I really now only carefully monitor tire pressure, keeping the Kumhos to 40 psi where they wear very evenly and don't roll over too much. I used to run around 42 and may try 38 to see how I like it...of course every setup will be different.

Bruce
 

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Agonize? Wow. I suppose I just haven't made it to that phase yet. If I'm out on the track w/the roof off, I have some space to myself to make some mistakes, and I'm driving consistently with apexes, downshifts and braking points, I'm happy as a clam. I've never sweated alignment specs or TP's or the like.
To each his own though. I'm sure after a few more track sessions I'll understand the obsession! :)
 
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