Tire test in magazine AND determining tire pressure

I just got the latest issue and was happily surprised to see a track test of all the current HOT street tires.

I noticed in one of the charts that it had tire pressures listed. There was no indication if they were hot pressures or cold pressures. They seemed rather low to me (like 28psi).

It got me to thinking: What is the best way to determine the best tire pressure for road racing on street type tires (Chump / Lemons)? I would prefer to NOT buy a ton of tires and wear them out through trial and error.

I am leaving this open ended (not a lot of detail) in order to get the most discussion....

Rob R.

Nothing new here, chalk or shoe polish combined with pyrometer testing...the BEST way is an F1-style thermal camera setup that will blow through several Challenge budgets on a single wheel

Pyrometer-wise, am I recalling correctly that if you think you're in the ballpark on camber, pressure should be adjusted in an attempt to get tread-center temp roughly in line with the average of inner and outer?

I figure camber or toe way out of whack may make for anomalously high or low temps which could drag the average away from what it should be...

Can you explain teh chalk or shoe polish and pyrometer testing?

It seems to me that changine camber would have an effect on both of those methods without changing pressures.

How do you know when to change camber and when to change pressures?

In reply to wvumtnbkr:

In my simplistic view (not having had time to gather much experience yet, so mostly based on reading): With a pyrometer, if the inner is much hotter than the outer, you've got too much negative camber (or possible toe out). If that's in the ballpark, then you compare the temperature in the middle of the tread with the average of the inner and outer temps.

The average should compensate to some extent for camber/roll/etc making inner higher than outer or vice versa, but still give somewhat meaningful info about whether insufficient pressure is leaving the tread resting too much on the shoulders/sidewalls for support, or too much pressure is causing the tire to work the center too hard.

EDIT FOR EXAMPLES: Let's say your pressure's good, but you've got too much negative camber: You might read 200 inner, 180 middle, 160 outer. The inner is hotter than the outer, indicating too much negative camber. But when you average 200 and 160, you get 180, the match with the middle temp indicating correct pressure. Not that it'll ever be that tidy or clear. If it were 200, 180, 140, you might conclude that you had a little too much pressure, since the inner/outer average of 170 is lower than the middle temp of 180, and inner/outer difference would still indicate excessive neg camber. Again, example is simplistic.

As with all things, I'm sure there are nuances I haven't learned yet and having certain items too far out of whack may give non-intuitive readings. For instance, strictly theorizing here, if your pressures were way low, you might end up heating the outer sidewall and picking the inner tread face completely off the ground, resulting in the middle of the tread reading higher than the average of inner and outer tread areas even though that indicates the opposite of the situation.

I find that pyrometers lie. For one, isolating the pressure variable only works if you are using a skid pad, not a full track lap or autocross run where the temps will be focused on what the last hard turn was. It is also extremely hard to be consistent from lap-to-lap and run-to-run. There is also a lot of technique involved in how/where you insert the probe, how long you let the reading settle, and how quickly you move from point-to-point and tire-to-tire. Surface-reading IR pyros are useless as the temp you want to read is in by the cords.

I use a timer and a skid pad. Repeatable and variable-isolated.

How to do skidpad testing

Thanks for the response.

Maybe I am missing something, but the link seems to take me to a bunch of facebook pics.

Rob R.

you just have to keep searching …

https://www.facebook.com/notes/hollis-racing/how-to-do-skid-pad-testing/417124891704816

Andy Hollis wrote: Surface-reading IR pyros are useless as the temp you want to read is in by the cords.

Unless you can put them over your tires and log their outputs as you drive. That's the next best thing to an F1-style setup.

GameboyRMH wrote:

Andy Hollis wrote: Surface-reading IR pyros are useless as the temp you want to read is in by the cords.

Unless you can put them over your tires and log their outputs as you drive. That's the next best thing to an F1-style setup.

Real time telemetry data of tire temps is incredibly revealing. Especially for track use (not so much for autocross as things happen too fast). I've looked at data traces for the former and it is shocking how high peak temps in a corner can be and how quickly they come off the spikes just as the steering wheel is beginning to unwind.

What do you do if the tire temps are too high accross the tire?

Thanks,

Rob R.