Over and over again, people ask about tire pressures, and invariably one of the responses is "use a pyrometer". Let me be the first to admit that even if I had a pyrometer, I wouldn't know how to use it to save my life.. . .

I don't have a pyrometer, I know that it is essentially a form of thermometer, but how the heck does one use one to determine optimum tire pressure for racing?

I would greatly appreciate an idiot's guide with specific examples. . . .

Thanks!

 

Me too. And, are those infrared ones that you "point and shoot" the right kind to use?

 

Pyrometers are useful because they can tell you if you are running the right pressure, AND give you info about camber.

The idea is that you take 3 temps on your tire right after you get done with the course. You take one temp on the inside edge of the tire, one temp in the middle, and one temp on the outside edge.

If all 3 temps are equal, you are running exactly the right pressure and exactly the right camber for the course conditions. So this is what you want.

On a car like a mini with too little camber, typically the outside edge will be warmer than the inside edge.

With too much camber, you'd be hot on the inside and cold on the outside edge.

With too much pressure, you'd be warmer in the middle and colder on the edges.

I'm no expert in this, either, but those are the basics.

 

checking tire temperature to verify pressure settings is relatively easy ...


take the temp of the tire at three points across the tread.. inside, middle, outside..

they should be relatively equal..

if the center is cooler than the outsides... add air
if the center is hotter than the outsides.. loose air...

the point and shoot pyrometer while acceptable are not as accurate as the probe type. the surface of the tire will cool during your cool down lap (gee why do they call it that??).. the sub surface temps will take longer to drop..

i am using a cheap point and shoot .. works ok for me..

is this any help?

a

 

I guess even though the "point and shoots" aren't as accurate, it's the relative thing we're after here so they work fine?

 

Point and shoot are OK.........frankly I am a bigger believer in monitoring tire pressure and keeping it where you want it. (Given a known and stable suspension set up)

 

Given the negligible cost difference between the point and shoot and the conventional pyro's I'd rather use a conventional needle type that gets inserted into the rubber itself.

Too many variables with the point and shoot versions, I have seen large temp ranges that are not so apparent otherwise.

 

The pro's use the needle type. For the amateur and ocasional user, a pyrometer is overkill. If you are going to be messing with your camber and tire pressure on a constant basis, i would say, a pyromenter is worth it, otherwise, it is best to see who's got one and borrow it.

At my road racing, luckily, Goodyear always has a guy that will check them for you as you come off the track if you want them checked.

 

But without using a pyrometer (needle or otherwise), how would you know that your pressures are optimal? Optimal pressures are set through feedback gained from tire temp readings.

I doubt event the best of professional drivers can "feel" a 5 degree temp difference from seat of the pants driving.

Chalk marks on the sidewall are only helpful in determining sidewall rollover, they will not tell you if you are a few psi high in pressure.

So if I am missing anything, please share your methods with us. Just trying to learn here.

 

I've read the same thing from other places. (a really corney place I saw this same info was from the manual for Papyrus's NASCAR racing game...the game allows you to monitor the temps O M I on each of the four tires).

 

In addition to tire temps, I imagine a pyrometer can be used to check all sorts of temps like ingoing and outgoing intercooler temps etc. Would one type of pyrometer be better for multiple applications? Any recommendations for brand and model?

 

Longacre probe, a basic one, about $100. Has setting for Brake or Tire (brake being a much higher number).

Yes, I've used mine to check intercooler temps when spraying down at National events as well.

Most of the info here I agree with so I won't add much. I will tell you that as you get better with one, you take more temps than just outside, middle, inside. You might stab the tire in 12 spots going across.

Be careful where you check the tire on the outside temp. You could be too close or too far from the sidewall. When you first start checking the tire that day, poke the tire from the very edge of the tread, then move a quarter of an inch and check again. Do this until you find the hottest spot and that's what you'll continue to use as the "outside" spot.
This technique applies to the whole tire, but the outside is where I see the biggest mistakes made. For example: Someone will probe the outside/middle/inside as 129/125/122 (very reasonable on a camber challenged MINI). However, if they had moved their probe 1/4" on the outside, they would've gotten 137...

Don't sweat this as much when you're new to doing it, but just be aware at how erratic temperatures can be on a tire.

Brian

 

I've never used a pyrometer, but you can feel quite a difference in the way a car handles with only a pound or two in pressure difference. I use pressure all the time to dial in what I want the car to do. On racing tires you can see pretty quickly what is going on as well. You can use pressure to dial in or out some oversteer, understeer. It seems to me that you could have optimal pyrometer/pressure settings and not have the car doing what you want. I think all a pyrometer allows you to do is get the initial settings quickly.

 

IF you can adjust camber, the pyrometer does a lot more. But since you can't on most of the MINIs (stock/front), you're correct, it's just good for a quicker initial tire pressure adjustment.

Brian

 

I've had 2 probe type pyrometers and found the following:

Yes, they go into the tread and are not subject to the cooling of the surface.

You can, however, get less than accurate readings if you don't stick the probe in the same amount on each insertion.

Depending on the car, sometimes it's a PITA to get the probe in the tire without turning the wheel (which you remember only after the engine is off and the car has stopped rolling) or without laying on the ground to check the rears...

Both stopped functioning somewhat prematurely, I think due to the probe gong bad, and no one would sell me a replacement probe. So, I had to replace the whole pyrometer.

Now I have an infra-red and I'm very happy with it.

With infra-reds, remember to get it really close to the tire, so your "sample area" is smaller.

The only readings that really matter are the outside tires. If the last corner on the course is a good sweeper, your outside tires will give you completely different info than the insides, which are at an odd angle to the pavement, and if the inside tire is spinning a little, it'll tell you that you have too much tire pressure, too much negative camber, etc. The outside tires in that corner are more accurate in telling you what you want to know. If the last part of the course is a a bunch of offsets, it might be a little harder to decipher the info you are getting.

Don't get too ****. As was mentioned earlier, 10 degrees across the tread is pretty close (especially on cars with little or no camber/caster adjustment). 120/130/140, or a higher spread means you need to do something.

You can also get a fairly good reading with your hand, provided the tire isn't too hot. Your hand can tell 10 degrees of spread in tire temp...

Charlie Davis

 

Wow, This thread is old.

OK, I use a probe pyrometer.

You must check tire temps immediately after your track or autocross run. You cannot wait even a short time as the temps are dropping the second you are done with your run or session. This is a very dynamic situation. Use the lowest possible pressures you can. I use 33 psi in the front and 30 psi in the rear.

For a stock MINI, your temps will help a little to allow you to adjust tire pressure a little probably you can try to get the temps as even as you can but without enough negative camber especially in the front you will be running very hot on the outer edges.

For a modified MINI you can write down your temps and adjust between runs and see how you do, then make a note of what pressures seem to give you the best temps or the best run times or both. This can be tricky, your skill level will likely allow you to drive better as you get used to the track or course so you may start the day driving poorly and using your tires in less than perfect ways. Later you'll drive better and likely tend to wear and heat up your tires more evenly.

Therefore I don't usually check temps until after the second run out of four or at least wait for the tires to warm up a bit.

Very true about checking temps across the tire in more spots than just three and also true about pushing in the probe to the same depth. In addition if your tires are a bit worn you will generate more or less heat as a result of tire wear. And the course itself will determine your turns (more right or more left) and the optimal speeds you'll be going so it can change at an autocross each month so what might work one time isn't going to be always best everytime.

If you have different autocross or track sites the surface, the weather, and your individual tires or wheel size are all factors.

Even your driving style will be a factor in making the best use of your tires. One driver may go slower and generate hardly any heat while another might overdrive corners and heat up the outer front edges excessively.

I usually chalk my tires in four places, check pressures in between runs- usually right before I drive since temps are dropping as the tires cool between runs. You can cool them more with a water spray if you like. As the tires heat up the pressures go up. If it is a cooler day the pressures will be a little more consistent. Short autocross courses don't generate much heat- I often hardly get above 125 to 130 degrees. Front tires are much hotter than rears.

Some tips from tirerack.com
http://www.tirerack.com/tires/tirete....jsp?techid=64
http://www.tirerack.com/tires/tirete....jsp?techid=58

 

Yeah, the info after the first run is rarely of any value...

Also, the BFG guys who used to support Pro Solo events told me that they prefer to find the pressures you like hot, and then inflate the tires to whatever cold pressure generates those pressures hot. In other words, if you find that 33f/30r is where you like the tires hot, and you need to start at 29f/28r to get them up to 33/30, that's better than starting at 33/30 and bleeding. their theory on this is 2-fold. 1) Starting lower will bring the tires up to temp faster than starting at that desired pressure and bleeding them back after the pressure is too high. 2) The hysteresis of the rubber is higher when cold, so the tire is stiffer when cold. As it heats up, the rubber gets softer, so the increased pressure takes the place of the stiffer carcass.

I've been doing this for the last 15 years, and like this approach...

Charlie Davis