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Old 09-19-2019, 08:56 PM   #15
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Stopwatch > pyrometer
They are both important tuning tools. It must be mentioned that track conditions change too, so a stopwatch one day is not the same as a stopwatch the other day.

Also worth noting it's 2019, by stopwatch I assume you mean super high refresh rate GPS datalogger, not an actual stopwatch haha
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Old 09-19-2019, 09:46 PM   #16
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Thanks all! I knew I could count on the Twins brotherhood. Gave me a lot to chew on. Obviously I have entered a brave new world with these tires and must "unlearn what I have learned."

I'll take it from here but these are the answers to your questions:
  • DOT codes indicate manufacture in 2018 for all of them, in the 46th week specifically for the worst tire
  • Last alignment a year ago; will definitely get that done soon
  • Pressures were around 32/33psi hot, though I stopped checking the fronts early in the event, and that's probably part of my problem
  • Went with stock size for these, 17x7 215/45R-17
  • Camber also stock
  • Butt dyno dialed in? Yeah AFAIK and I didn't feel any rollover
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Old 09-19-2019, 10:50 PM   #17
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Front camber is your friend, you need more of it... Camber bolts is the easiest/cheapest way. Not quite enough, but a lot better than stock which is disturbingly close to zero...

Also, zero toe all around for alignment is a good place to be for handling and tire life. Never just get a generic alignment, specify exactly what you want or you'll just get "in the green" which is a quite wide range of toe settings...

The outside edge of the middle rib in the RE71R wears down *fast*, that's just the way it is. When you have half tread left overall, the middle rib will be radically beveled with the outer edge worn almost to the bottom of the tread.

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Old 09-19-2019, 11:31 PM   #18
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Really interesting seeing everyone here running entirely different pressures than what I run, lol. Maybe I'll try a run at these mid-30s pressures and see what happens.
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Old 09-19-2019, 11:53 PM   #19
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DS/CS legal camber bolts are the OE 14mm bolt, Google will point you to the right factory part, stick that in the top hole, push in, tighten, take to high quality alignment shop and hope you can hit -1.3 on both sides, don't bother going back to the alignment shop without at least that. Other camber options bump you to STX, imho burn up these tires before jumping into that pool.

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Really interesting seeing everyone here running entirely different pressures than what I run, lol. Maybe I'll try a run at these mid-30s pressures and see what happens.
They'll feel nice, but you'll go slower, been there, done that. If you ever get chatter from overdriving you'll nearly eliminate it but at the cost of ultimate grip imho.

When I said 29 that's usually my target and I'll bleed a pound out of whatever end needs more grip so really 28 hot is my 'optimum' as above lots of factors, maybe you've got a gauge that reads different to mine,a longer haul between course and grid, etc. 27 psi is close enough to what I run that I doubt you're leaving much on the table. (For OP this is a 245/40/17 on 17x9, I'll be surprised if you can get away with much lower than 30psi but could be wrong you're not pinching like most do)
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Old 09-20-2019, 07:14 AM   #20
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My experience is at road courses, no autoX. To get to the quite low hot pressures strat is talking about, 27-28psi hot, I'd have to go out ~18psi cold. I seriously doubt that would give any more grip, it's likely well into a range where increased rolling resistance = slower, and likely getting into the realm of *dangerously* low...

I don't agree with the notion that less pressure => more grip is an absolute truth. Not for a radial tire at autoX/road course on appropriate radial tires anyway. As opposed to a dragstrip with a very tacky launch pad and drag tires, which is a very different scenario...

When I get to work later today I'll look at lap times over a session from Watkins Glen (in Cayman, not BRZ) last week, with cold pressures 24/26psi and hot up to 36/37psi (outside rear saw 40 one session early in the day) and see how my best lap times compare early to mid-session. Very hard to get reliable data, though, as there's traffic to contend with. Also later in the session, 200tw street tires can be overheating so fall-off in laptimes can be due to that rather than "too much pressure".

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When I said 29 that's usually my target and I'll bleed a pound out of whatever end needs more grip so really 28 hot is my 'optimum' as above lots of factors, maybe you've got a gauge that reads different to mine,a longer haul between course and grid, etc. 27 psi is close enough to what I run that I doubt you're leaving much on the table.
How do you know 28psi is optimal? What is the fall-off in time above and below that pressure? You'd need to be able to test isolating pressure from other effects, which would involve many runs over the same course, adjusting pressure first in one direction and then in the other, multiple times, to account for other factors changing throughout the day.

I seem to be able hit lap times within a few tenths over a fairly broad range of pressures. But it's impossible for me to test lap times vs. pressure in isolation, without a ton of other variables coming into play, which makes drawing hard conclusions impossible. But from what I've experienced I don't think there's a whole lot of difference in lap time potential for me from 30psi to 36psi.

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(For OP this is a 245/40/17 on 17x9, I'll be surprised if you can get away with much lower than 30psi but could be wrong you're not pinching like most do)
FWIW I'm on 245/40-17 RE71R on 17x9 on the BRZ, -3 front -2.5 rear camber. Which should be tolerant of lower pressures. But I never experienced anything suggesting that running less than 34 hot was buying me anything in terms of lap times at the track. Or that inadvertently running more than 36 hot was hurting me all that much.

For OP, with limited camber and 215s on 7" wheels, I doubt that running 28psi hot vs. 34-36psi hot is going to be worth anything. But again, I don't autoX... You're likely totally fine at the 32/33psi hot pressures for autoX.
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Old 09-20-2019, 07:41 AM   #21
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I agree with you, apples to oranges

Doing scientific tests is hard, test and tune days exist with shorter simple courses and skidpads to reduce variables, 28 feels good to me and is reflected in consistent times that I'm happy with. Lower and I find the tire less predictable causing errors, higher and I feel that I'm losing lateral grip, unfortunately I did not have good Accel data to support that only the stopwatch. I've also spoken with people I respect with similar setups and we've arrived at similar results.

Edit: approx -4 and -2.3 camber here iirc, been awhile since I've been on a rack.
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Old 09-20-2019, 08:42 AM   #22
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If overheating is brought up, low pressures = more flex = more heat into tires.
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Old 09-20-2019, 10:36 AM   #23
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I don't agree with the "low as you can go" approach to tire pressures...
And anyway, there's no definite point of transition between "sidewall is not rolling over" to "sidewall is rolling over". Radial tires are very stable over a fairly broad range of pressures. Also this may be a recipe for running too much pressure for under-cambered cars, and too little pressure for cars with track-appropriate 3-4 degrees front camber.

For most of our cars, there's going to be a quite broad range of pressures that will perform well, IMO there's no reason to try to find the lower limit.

You can invest in a pyrometer and try your best to get actual representative hot temps, but then you still have to correlate that back to what is the best temp distribution across the tread for quickest times for your car.

Or you can just run 34-36psi hot pressures and not worry about it any further, for 99% of us that's going to be close e-damn-nough...
Like you say, for 99% of people this is good enough. 99% of people also dont bother learning or trying new things, so there's that. Like I said, I dont do autocross, so this is more of a track approach. But with pyrometer in hand and timing every single lap and a datalogger to look at speeds and lateral forces thru the corners and a decent butt dyno, here's what I found:
  • The 200TW "cheater tires" like the RE71R, A052 and rival S always overheat, there wont be a point where you wont be able to get enough temperature on the tire, on the dry.
  • There is a clear point where you can clearly feel the tire rolling over, its not progressive at all, 1psi higher the car feels awesome thru the turns, 1 psi lower and the car feels like a boat after initial turn-in and is much harder to settle.
  • The lower the pressure, the faster I went, but sometimes I would need a second or third lap to get ideal temps on tires, all depending on pressure and ambient/track temps.

For my last few set of tires, all of this on 17x9 +35 wheels, -4.7F/-3.0R camber and 0F/0.05R toe (toe-in rear) and on teh same day (70F ambient temp, dry and humid):
  • Yokos A052 235/45R17: Fastest times were on 31PSI up front, 30PSI on the back, hot pressures. At 30PSI on the front, the tire rolls over mid corner on certain sections of the track and becomes squetchy drive and a few tenths slower. Higher pressures were also slower, at 34PSI up front the car felt better, but was slower ultimately, almost a full second on a 2min track.
  • Nankang AR1 235/40R17: Fastest times were at 29PSI up front and 28PSI on the rear. Lower than that the tire was very hard to drive, it felt as the tire was about to come loose from the wheels. These tires took 3 laps (including outlap) to heat up properly at this pressure. Higher pressure made them slower, about 1.5 seconds slower at 36PSI (that was as high as I went, no point in going higher on these). They were also about 1 full second slower than the yokos.

Now do with this information what you want, flush it down the toilet for all I care, but I just want to point out that the "as low as you can get it" statement from me came from my own personal data gathering. I have been bitten on the ass many times already by trusting what "experts" or "experienced" people say.
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Old 09-20-2019, 05:01 PM   #24
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Note to OP et al, this is regarding track pressures, not autoX!

Icecreamtruk, what are your cold pressures? I'm getting hot pressures up to 36ish going out with cold pressures of 26ish.

I would have to start with cold pressures of about 20psi to get 30psi hot pressures. And I'm not going out with 20psi...

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Like you say, for 99% of people this is good enough. 99% of people also dont bother learning or trying new things, so there's that.
99% of people are more likely to get themselves into trouble than to actually do any better by trying to "optimize" their pressures based on nebulous concepts like "tire rolling over", especially if they go into it with the idea that "lower pressure is always better/faster"...

I don't mind learning new things, but I have never had anything like the resources required to truly hone in on "optimal" pressures, which would pretty much take an open track mostly to myself and multiple sets of same make/model tires from the same batch on the same make/model wheels. Long/short it ain't happenin...

For 36psi hot, which feels fine to me on my streetish setup cars, I'm already going out with cold pressures as low as I feel comfortable with.

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[*]The 200TW "cheater tires" like the RE71R, A052 and rival S always overheat, there wont be a point where you wont be able to get enough temperature on the tire, on the dry.
Better to err on the *high* side as lower pressures => more heat... So this is kind of an argument against running "as low as you can go".

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[*]There is a clear point where you can clearly feel the tire rolling over, its not progressive at all, 1psi higher the car feels awesome thru the turns, 1 psi lower and the car feels like a boat after initial turn-in and is much harder to settle.
If you are near the ideal pressure, changes in pressure of +/-1 or even 2psi shouldn't *drastically* affect handling behavior. If dropping 1psi yields major fundamental changes in handling behavior, that would seem to indicate pressure is lower than the ideal range and falling into the abysmally-low range.

I.e. I don't think pressure vs. lap time should be a step function, where 1psi below "optimal" is a handling disaster. And if that *were* the case, it would again argue for ensuring your tire pressure is comfortably above the step...

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[*]The lower the pressure, the faster I went, but sometimes I would need a second or third lap to get ideal temps on tires, all depending on pressure and ambient/track temps.[/LIST]
Wait a minute, are you talking about ideal hot pressure after only 1, or 2, or 3 laps at a time?

Also, a proper test for "optimal" pressures? Ideally with pressure the *only* variable, with enough runs at different pressures to remove effects from other variables including heat in the tire, number of laps on the tire, time of day, driver being "cold" vs. "hot", etc. etc. Ideally testing would also be *blind*, i.e. driver doesn't know what pressures he's driving on. Not easy to arrange...

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Now do with this information what you want, flush it down the toilet for all I care, but I just want to point out that the "as low as you can get it" statement from me came from my own personal data gathering. I have been bitten on the ass many times already by trusting what "experts" or "experienced" people say.
Of course this argument says that no one should blindly trust what you say either! In an ideal world they could find out for themselves what their "ideal pressures" are. In the real world, I think they're going to be better off to err on the high side for hot pressures at the track. Which is more like 34-36psi fully developed (after multiple laps) hot pressures. 28-30psi "hot" would have people going out in stockish cars with narrow tires and no camber with only about 20psi in the tires. Not a great idea IMO...
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Old 09-22-2019, 11:47 PM   #25
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@ZDan Overall I agree with you on the argument of erroring on the high side and it all being safe. I dont want to argue or anything, it seems like you want some honest answers to some of the questions you raised after my post, so here they are.

For cold pressure, depending on day or track I go out at 22 to 24psi. I dont drive like I stole it on my first session, Im aware of my tires being underflated, and even if somehow I wasnt, I can feel the tire distorting under braking and turning. I rarely get the pressure I want in one session, it takes 2 or 3 sessions doing small adjustments to get it right. I also dont set equal presures on all corners, more on that in a second.

Lower pressure = more heat. I've heard this a number of times, but I wonder if its actually true, because the pyro says completely the opposite. Higher pressures = more heat, lower pressures end up with less heat on the tire. I imagine it has to do with people thinking the rubber moving more with lower pressures or the bigger contact patch makes it heat up more, but thats not what the pyro says to me.

Im not running 2-3 laps at a time, I run 20 minutes sessions. But at the same time, I run time trials, so only the fastest lap count, the rest I use it as practice if I know I have tires to spare and that Im not destroying them by overheating them. On a street tire, the fastest lap is almost always the first lap out of the pits (first full lap after the outlap). When I say it takes 2-3 laps to get the ideal pressure, what I mean is that 2-3 laps in will be my fastest lap on that tire, meaning usually that pressures were too low and I was having to deal with the tire rolling over, or not heated up enough yet (im in canada, track days can be cold sometimes).

Regarding pressure changes, 1-2 PSI dont change my car into a mustang, but might be enough to gain or drop half a second. Half a second can be the difference between first and sixth place in a time trial, so to me, it is drastic. If you go under the point where the tire starts rolling over, it will handle quite different, taking more time to settle up during turns, and getting easily upset by bumps and curbs (and times suffer much more).

Thats all I got, more or less, if you have more questions, shoot away. I know this all sounds very subjective and non scientific way but the stopwatch doesnt lie, even if a driver isnt Senna, as long as he can drive to his limits every time out, the stopwatch will tell you if the change was good, or bad. Its then up to the driver/team to either record information on what changed and the effect it had, or chuck it all up to external factors and decide it did nothing or little.

Edit: forgot to add, this all works very well for a car that is track ready, at least suspension and alignment wise. Trying to optimise pressures too much when you have too little camber is just going to end up killing the tires. I imagine that somebody looking to extract the absolute maximum of their tires will have taken the time to get an alignment dialed up to maximise tire performance, otherwise, yeah, "36 hot and your good" is as good as anything else.
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Old 09-24-2019, 03:12 PM   #26
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I dont want to argue or anything, it seems like you want some honest answers to some of the questions you raised after my post, so here they are.
Excellent, I don't consider this an argument as much as a discussion I have an open mind and I know I don't have all the answers.

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For cold pressure, depending on day or track I go out at 22 to 24psi. I dont drive like I stole it on my first session, Im aware of my tires being underflated, and even if somehow I wasnt, I can feel the tire distorting under braking and turning. I rarely get the pressure I want in one session, it takes 2 or 3 sessions doing small adjustments to get it right. I also dont set equal presures on all corners, more on that in a second.
FWIW:
I go out with ~27psi first session (sometimes as low as 24 on the corner that gets worked hardest), and I drive it hard from lap 1. Even when I didn't plan to! Bleed pressures down to 36 all around after 1st session, repeat as required throughout the day.

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Lower pressure = more heat. I've heard this a number of times, but I wonder if its actually true, because the pyro says completely the opposite. Higher pressures = more heat, lower pressures end up with less heat on the tire. I imagine it has to do with people thinking the rubber moving more with lower pressures or the bigger contact patch makes it heat up more, but thats not what the pyro says to me.
There is a difference between tread heating and carcass heating. Lower pressures will work the carcass of the tire more and generate heat from hysteresis. Smaller contact patch from high pressures at high slip angles may give more short-term transient localized heat at the tread, some of which heats the carcass but some (most?) of which is quickly convected and radiated away.

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Im not running 2-3 laps at a time, I run 20 minutes sessions. But at the same time, I run time trials, so only the fastest lap count, the rest I use it as practice if I know I have tires to spare and that Im not destroying them by overheating them. On a street tire, the fastest lap is almost always the first lap out of the pits (first full lap after the outlap). When I say it takes 2-3 laps to get the ideal pressure, what I mean is that 2-3 laps in will be my fastest lap on that tire, meaning usually that pressures were too low and I was having to deal with the tire rolling over, or not heated up enough yet (im in canada, track days can be cold sometimes).
Are you able to monitor pressures while on track? I'd always assumed that tires got up to pressure relatively quickly, within a couple or 3 hot laps. But in the Cayman where real-time tire pressures can be displayed on the dash I found that I would only gain ~1.5 ish psi per lap at Watkins Glen a couple of weeks ago. Pretty much crept up the whole session.

I think that what happens is that the tread does get up to temp very quickly, but that pressure, which is related to *carcass* temperature and wheel temperature, increases at a much slower rate. It takes some time for the mass of air in the tire to heat up.

Worth noting that pressures can continue to rise on the cooldown lap and even in the pits for short time as heat from the hubs and brakes continues to go into the wheels and the air in the tire, unlike tread temperature which falls off quickly.

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Regarding pressure changes, 1-2 PSI dont change my car into a mustang, but might be enough to gain or drop half a second.
Half a second is huge. Obviously you don't want to be there in your critical 1st laps. So again, better to err on the high side. If pressures go "too high" after 2-3 laps, for your purposes, so what?

But given that track and weather conditions are changing throughout the day, and repeatability variations, how do you *know* that half second is due to pressure and nothing else?

Quote:
Half a second can be the difference between first and sixth place in a time trial, so to me, it is drastic. If you go under the point where the tire starts rolling over, it will handle quite different, taking more time to settle up during turns, and getting easily upset by bumps and curbs (and times suffer much more).
If 1st lap is the opportunity for your absolute fastest lap, you'd like to be right at optimal pressure for *that* lap, which again implies highish starting pressure given that you aren't likely getting to max pressure for several laps.

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Thats all I got, more or less, if you have more questions, shoot away. I know this all sounds very subjective and non scientific way but the stopwatch doesnt lie, even if a driver isnt Senna, as long as he can drive to his limits every time out, the stopwatch will tell you if the change was good, or bad. Its then up to the driver/team to either record information on what changed and the effect it had, or chuck it all up to external factors and decide it did nothing or little.
For most of us who track regularly, there's just too much going on to be able to say that 1psi changed lap time by a few tenths to a half a second. Not to mention that for most of us, all else exactly the same, there's going to be at least 2-3 tenths variablity due to driver anyway. Obviously it can be a lot more than that depending on driver!

Quote:
Edit: forgot to add, this all works very well for a car that is track ready, at least suspension and alignment wise. Trying to optimise pressures too much when you have too little camber is just going to end up killing the tires.
I kinda think optimizing pressures will somewhat automatically preserve tires a bit. Optimal pressure for a street car not 100% set up for the track will likely be a bit higher vs. dedicated track car.

Quote:
I imagine that somebody looking to extract the absolute maximum of their tires will have taken the time to get an alignment dialed up to maximise tire performance, otherwise, yeah, "36 hot and your good" is as good as anything else.
I daresay it's better than 28-30psi hot! Speaking for my situation, I have -3/-2.5 camber and slightly stiffer springs, but mods are minimal for classification purposes for time trials. I would say that for my car and for a lot of street/track cars, "34-36psi hot" is a good approach.
But based on my observations at the Glen I may revise my approach to cold pressures for the 3-lap time-trial...
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Old 09-24-2019, 04:54 PM   #27
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@ZDan Yeah you are pretty much spot on on most things. I just wanna come back into the temperature and pressure relation topic, since I find it interesting.

Whether or not the extra movement on the carcass is generating heat is of course not a question, it is generating more heat. But what I wonder is, if that heat is actually more than the heat generated from the extra pressure on the tire. I measure temps with a needle pyro so it should not be surface temps that I get but rather the actual core temps (or closer to it at least). On the same day, with track temps not varying much, dropping about 4PSI on the tire made the temps drop by about 15F after a 4 +2 laps (out lap, 4 hotlaps, cooldown lap). Where is the extra temp coming from at higher pressures? I dont think it is from more tire slipping or extra slip angle, I wasnt getting much more of that anyways, I think its the interaction of pressure and temperature.

Disclaimer: its about to get a bit nerdy.
We arent in a lab, but the ideal gas law should still apply to air to some degree, and PV = nRT gives us a simple way to look at it. Tire volume (V) does not change, only the shape of the contact patch does, R is a constant, n changes (goes up) a bit, but a very minuscule amount, so small that its ok to assume it a constant. So if the product PV goes up (pressure increases), so must T (temperature) if the law is to be respected. My readings at the track seem to indicate, altho not linear, that this is what affects temps the most, as higher pressures have always yielded higher temperature, not once has it been the other way around since I started monitoring it.

Before recording this, I was convinced it was the other way around, and was setting my pressures accordingly (lower pressures for more temp and vice-versa) and I could not understand the results I was getting. Every time I made an adjustment, it got worse so at some point I stopped caring and started doing the "34-36psi hot and forget it" method. I then got the pyro to check my alignment settings, not for tyre pressure adjustment, and it was then that I started noting this on the recorded that. Im actually able to get better times after adjusting pressures now, most of the times at least.
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Old 09-24-2019, 08:49 PM   #28
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Quote:
Originally Posted by Icecreamtruk View Post
@ZDan Yeah you are pretty much spot on on most things. I just wanna come back into the temperature and pressure relation topic, since I find it interesting.
Me too!

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Whether or not the extra movement on the carcass is generating heat is of course not a question, it is generating more heat. But what I wonder is, if that heat is actually more than the heat generated from the extra pressure on the tire.
For sure it is. If you're talking about heat generated from the "extra pressure" on a smaller contact patch running higher tire pressures, consider that you may be getting more heat onto the smaller area, but it *is* over a smaller area. Overall, shouldn't be much if any more heat into the structure of the tire.

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I measure temps with a needle pyro so it should not be surface temps that I get but rather the actual core temps (or closer to it at least).
You're still measuring temps near the surface of the tread of the tire, and not near the internal structure of the tire. And what is heating the air inside the tire is the *inside* surface of the rubber, you're definitely a long way from there. I hope so anyway!

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On the same day, with track temps not varying much, dropping about 4PSI on the tire made the temps drop by about 15F after a 4 +2 laps (out lap, 4 hotlaps, cooldown lap). Where is the extra temp coming from at higher pressures? I dont think it is from more tire slipping or extra slip angle, I wasnt getting much more of that anyways, I think its the interaction of pressure and temperature.
Something else going on for sure here. It's been a long time since I used a pyrometer, partly because I didn't find it as useful as I expected it to be. As I recall it's best to come in HOT, not after a cool-down lap, and preferably have someone there to measure temps immediately right in the hot pit. And even then you get more info about the last corner than average tire temps around the whole track.

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Disclaimer: its about to get a bit nerdy.
I'm IN
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We arent in a lab, but the ideal gas law should still apply to air to some degree, and PV = nRT gives us a simple way to look at it. Tire volume (V) does not change, only the shape of the contact patch does,
For different initial pressures? I'd say volume does change a small amount. I mean, a flat tire has less volume than an inflated one! If you mean no volume change as tire heats up on the track, again there will be *some* volume change but in that case small enough to neglect.
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R is a constant, n changes (goes up) a bit, but a very minuscule amount, so small that its ok to assume it a constant.
OK, now you're *definitely* talking about different initial pressures, more molecules pumped into tire to increase pressure, I don't think we can neglect that, I mean, that's how we are increasing P, by increasing n!
Quote:
So if the product PV goes up (pressure increases), so must T (temperature) if the law is to be respected.
It's not clear what you're saying here, but based on your "n changes" comment above, I have to think you're talking about temperature added to the static tire by adding pressure? If so, P is going up with n as you add air. Any tiny amount you raise the temperature of the air already in the tire by increasing its pressure is going to be offset somewhat by the new air going into the tire, which is seeing a pressure DROP!
Even if there was one, it would equalize back to ambient over time. Assuming we both arrived at the track with our desired starting pressures, you at (say) 22psi and myself at 26psi, we are starting out at the exact same tire temps, I don't have higher temps in my tires just because the pressure is higher. that's not how PV = nRT works. (my college roomate's mnemonic for this: Per-Vert equals neRT)

*If* you're talking about pressure gained by being out on track, that is due to the temperature change of the air inside the tire. Pressure goes up because temp goes up, not the other way around! But the important temperature here is the temp of the *interior* of the tire, and the wheel.

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My readings at the track seem to indicate, altho not linear, that this is what affects temps the most, as higher pressures have always yielded higher temperature, not once has it been the other way around since I started monitoring it.
I'm gonna say this is down to where you're measuring temps: at tire tread, well outside the structure of the tire. Those temps might locally be higher. But the interior tire temps are going to be higher with lower pressures.

Going back a few years, but back when Garry McCoy was throwing his 2-stroke MotoGP bike around, sliding the rear all over the place, people were *amazed* that he wasn't quickly overheating the rear tire, as that was a huge problem for most bikes/riders at the time. A theory was that he was *working* the tire less by lighting up the rear and sliding it around, so while outer tread surface temps may have been locally higher, the internal tire temps were lower due to less deformation under loads! Like I say, this was a "theory"...

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Before recording this, I was convinced it was the other way around, and was setting my pressures accordingly (lower pressures for more temp and vice-versa) and I could not understand the results I was getting. Every time I made an adjustment, it got worse so at some point I stopped caring and started doing the "34-36psi hot and forget it" method. I then got the pyro to check my alignment settings, not for tyre pressure adjustment, and it was then that I started noting this on the recorded that. Im actually able to get better times after adjusting pressures now, most of the times at least.
Well clearly you're paying a lot more attention to this than I am, so I'm not going to say you're end results are wrong for your driving style and your car setup! 34-36 hot seems to work for me and I don't have enough open track time available or driver consistency to determine where the optimum is.
For sure if I don't want to go out on less than 26psi in general, 24 psi absolute minimum on the tire that sees most pressure change, I'm going to see hot pressures of 36psi by end of session, so just based on that I don't see myself trying to run less.
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