There are several choices here:
Longacre Racing pyrometers

Avoid the laser pyrometers. You need a probe type to get under the tire surface.

Greg A

 

Or, the chassis flex (twist) is out of control, like on old 911s. Not uncommon to see early 911s with the inside front off the ground by a few inches on the exit of a tight corner at IMSA races in the 70s. Power-on understeer being their specialty (albeit fast).

I'm enjoying your posts quite a bit, Joe. Keep up the good work.

 

The old volkswagen GTIs/Golfs used to lift their inside rear tire
like a poodle at a hydrant!

 

Thanks Teflon for the lead on pyrometers.
Craig

 

You're welcome. Please let us know what you end up selecting.

Greg A

 

I was thinking of getting a lazer pyromerter (because they are cool). What's wrong with them?

Mike

 

I believe that they only measure the surface temp. What you want is the temp. of the rubber just under the surface so cooling has not affected it as much. You want to type with the small pointed probe that you can stick just under the surface of the tire.

 

Not sure where to start here but I’ll try to jump in and not write a book that bores everyone silly.

Since the current subject is tire temps I’ll share what I’ve learned over the years.

Bias ply tires made this pyrometers very functional because we didn’t run much camber, however, since radials require a static of -2 to -4.5 degrees it makes it difficult to keep the heat in the tire all the way across after you come off a turn and enter the pits. This is because when you come off a turn and the tire stands back up and the outside edge comes off the ground which makes the tire cool very quickly on the outside edge. There are way too many variables to pin point the exact difference you will see each time but, for sure, the outside temp should ALWAYS be cooler than the middle and inside temps. If you ever have temps that look like: 186.185.186, you’re giving up a ton of time and will ultimately burn up the outside edge of the tire.

Here’s an example of a car at Willow using onboard lasers temps real time at its peak temps in turn 9.
Left front outside 221 middle 218 inside 216 with -4.2 degrease on a Yokohama race slick at 29 lbs of pressure then in on that lap to the hot pits and at rest the temps were as follows:
Left front outside 175 middle 205 inside 209.
We increased to -4.5 and got better tire wear and faster times. I don’t have the temps from that run but I believe we ended up with a temp difference in the pits of 45 degrees Fahrenheit from inside to outside. What we really were seeing in the pits is that we couldn’t use any softer of a compound because the overall temp would be too high and the tires would fry.

IMHO, pyrometers on radials don’t really tell you much other than if you’ve selected the proper compound for the track that day. With that in mind I feel either type of hand held pyrometer works fine. A stabber is argumentatively better but the lasers aren’t far hind and much easier to use plus you can use them for so many other things. Ground temp, rotor temp, caliper temp, cooler temps, driver’s compartment temp ….. It’s relatively easy to know when your camber is correct because your tire wear will tell you. The problem being if you drive around town with a track set up, you will inevitably wear out the inside of your tires and going back an forth to the track on the same tires you won't get accurate visuals. Learning to read tires is much more valuable than reading tire temp variations from side to side with a car not in motion because at that point, it’s already too late. On the other hand, pressures are very critical. When you find the right temp you want to keep the car within .5 of that pressure at operating temps

Enough for now, I can hear some snoring … I hope this thread lives for a while. There’s lots of good discussion going on here.

P.S. You can always barrow one of each prometer and test them side by side. I think you won't find much difference and the spread from side to side will be about the same percent

 

No snoring from me... Made me want to stay up later...
Have you tried helium? I was hoping it'd help stabilize
pressures, by not heating/expanding as much. I agree with
you (already agreed with you) that a skid pad with waiting
pyrometer helpers is the only way to hope for decent
readings... If you do get them hot-n-fresh, less than 10 seconds
from the exit from the skid pad, I still think that even with radials
you can tell if you're 6psi too high or low by the typical center
way hotter than either outside or way cooler. It *is* interesting
about the effects of a radical (for streeted cars) 4.5 deg. camber,
which would essentially lift the outside edge clean off the
pavement n the straight, and definitely cool that part of the
tire down real quick. It's too bad you don't have the on-board
temps after the increase to 4.5. I assume it got cooler on the
outside, hotter in the middle and probably on the inside too.
Do you have much data on the amount of change in lateral
grip for streetable (DOT type) tires from cold to hot? I've seen
long-time autocrossers gain 4 seconds over thre runs, and it's
not because they had a lot to learn about the course...
Joe

 

And this is why I wouldn't touch my suspension without consulting Cary first.

Hey Cary, did you get my email? I need to get in touch with you re: setting up my friend's GT3 alignment.

 

Excellent post Cary - Thanks!

 

Joe,

No, I’ve never tried helium only nitrogen. I find it’s still difficult to purge all the old air completely out so at best we end up with a bit of a mix, still allowing some expansion but not nearly as bad as 100% air. I totally agree with you on the pressures when you see a spike in the center with the tempers. You always want to find out what the manufacturer recommends for operating pressure and rim size too and stay with those parameters.

Tyson , you a have a PM

Zippy, thanks!

 

Ok, I'll see where I can get my tank filled with nitrogen to try.
As to purging air, If you fill as best you can with nitrogen,
and then purge it and refill, assuming each purge expells
80% of the tire contents, you will quickly get to as pure
nitrogen as your initial source.
So if with air, your desired runtime pressure is XX psi, you
probably filled cold tires with 2/3rds that. (I'm asking).
Now with nitrogen, is it 9/10ths of XX, or what?
thanks again,
Joe

 

Joe, Cary is correct ... gee what a shock. You don't want to run Helium. Those molecules are too small and you could get leakage. The reason you run nitrogen and not air (air is already 78% nitrogen) is because of water vapor. Water vapor expands and gives larger pressure increases from cold to hot and therefore more change in pressure which is more difficult to control.

So, your goal isn't to get pure nitrogen as much as it is to get dry nitrogen (which any tank is). If you fill and bleed your tires 2-3 times, this will get most of the moisture out. Why use nitrogen? It's readily available, cheep, and safe (won’t burn).

Again Cary is right about real-time laser measurements as being the best. Trying to do pyrometer work is really chasing your tail in my opinion on the track (doable on the skid pad because you can do it quickly) because of the cooling issues and the last turn(s) you finished will skew your data. It is way more difficult to get meaningful data than you would think. Let me give one example. If you are running big camber -3degrees or more, and if your pit is at the end of a big straight (common), when you are accelerating and then braking hard in a straight line you are way heating the insides of your tires, if you took your reading immediately you would think that you were way off when in fact, you may not be.