Tyre pressures (by using temps?)

[djones]

Hi,

I'm wanting to try and learn a bit about how tyre pressures affect the balance of a car using my own road car (on some local mountain roads).

I was also wanting to see how temperatures across the tyre surface reflect what feels good or bad.

Can anybody give me any insight (or links to a good website as I cant find one) into what to look for in terms of temps?

I've seen some people say the middle should be the average of the outer readings??

Indeed is temperature really that relevent when your just adjusting pressures or do you really need to be adjusting camber etc?

I hear people say the tyre pressures are so important for overall hangling/grip but I'm struggling to see it been more than just a small amount.

Thanks for any info etc

[Jersey Tom]

If you're talking about a production car, with DOT tires, on open roads... stick with vehicle recommended inflation.

With regard to changing pressures on a race track... air pressure does a few things.

One, it changes your actual realized wheel rate and can change the general handling balance of your car (much like springs and roll bars). Just like stiffening rear springs will free the car up, so will adding rear air pressure.

Two, it changes your load sensitivity. Myth: Adding pressure stiffens the sidewall and gives you more steering response. Gives you less in some conditions, more in others. In any event, adding pressure all around should make the car more susceptible to balance changes from longitudinal load transfer. This can be good or bad.

Three, it changes your tire deflection and footprint. This is tuning for peak grip. Myth: Taking air out gives a bigger footprint and thus more grip! There's a certain amount of air your tires and vehicle want. Obviously running 5 psi all around a car, the handling and grip would be terrible. This is however where simultaneous camber and pressure tuning is needed. The old "rule of thumb" is to use a pyrometer when you come in from a hot lap, and tune the two to get the inside and centerline temperatures (or left and center on an oval car) to be roughly even, with the outside (or right) 15-20F cooler. This will get you in the ballpark, but not to the front of the pack. There are better ways of doing it which I won't get into

Run too low air pressure in any application (road or track) and you will blow out tires.

[djones]

Thanks for the reply!

Do you know what the 'optimum' temperature for a high performance summer tyre would be? (e.g a Michelin Pilot Sport).

I can only find a bit of info for a Toyo 888 which is a track day/road tyre and the optimum is apparently 85 to 95 dec C. To be fiar that seems very high but what do I know!

[RacingManiac]

unless you are planning to go on track, I wouldn't expect to see your tire anywhere near the "optimum" temperature on street. Simply because it basically equates to very extreme driving manuver on public road....

[djones]

I ultimalty mean for the purpose of a track day (e.g the 'ring where I went last year).

I was hoping that the temps and pressure differences could be seen on the road, just at a much lower level which you could then sort of multiply up for track or more importantly understand when you came to the track.

[Jersey Tom]

The whole "optimum" temp thing is kind of a load of crap, or at least shooting for it by itself. Tires will tend to run at whatever temp they want, primarily a function of speed and load. Slow driver and overly aggressive drivers will also make some changes... the former bringing temps down, the latter bringing temps up but shredding the compound.

Big swings in air pressure will also do it.. either over or under inflating. But then you're really changing how well your footprint is planted, your wheel rates, and all that other jazz.

Long story short, don't worry about temp unless you have specific data for it. Focus on getting the footprint and handling set, and the temp will come by itself. If the tires are running too cold or too hot, that's on the tire company.

[Ciro Pabón]

I use a simple Digatron needle pyrometer. Jersey Tom recommended to use a IR pyrometer some weeks ago, in the Tyre pressure short thread. You can get an IR pyrometer for 50-60 dollars.

http://www.cometkartsales.com/store/gauges/infrared.htm
IR pyrometer


Looking for JTom recommendation I found electric pyrometers (don't ask me how they work) that have a larger range (up to 1000 ºC) so you can use them to check brake temperature.

Electronic tyre temp gauge by Rotax


This is the image I posted at the same thread, no comments needed, I think:



Here you have some very basic tips on tyre temp:

http://www.russellkarting.com/settings.htm

The basic idea is that you look for the same temperature difference among front and rear tyres. You can increase or decrease pressure slightly if the temperature differences are too high (or if you are still working on the basic setup, or if you have rain). You adjust pressure until you get, more or less, the tyre temperature that your manufacturer recomends.

From that on, you try to adjust the tyres you want to heat. In the previous image, you want to set downward the left front tyre (in a kart, at least). This will increase load in the rear right, and the temperature of the diagonally opposed tyre (left front) will increase.

If you have a professional driver you know the guy is crazy anyway, so he will get temperature pretty quick. A regular driver, like most people, will not push the car enough, because they're prudent. I imagine that's what Tom wanted to say in the previous answer, so, for amateurs you try to use a little more camber or adjust pressure to provide a higher temp.

Take in account that the tyres cool on the pit entrance and while you measure, so a few degrees below recommended temperature (2-3 ºC) are OK, what is more important is consistency among front/rear differences.

Race tyres exude a sticky liquid, that's why you want to heat them quickly. "Sport" and regular tyres do not exude anything, because they are not made to be sticky but durable. I don't know in which category your brand falls.

You can find software for checking tyre temps. Jet Tech Pro has a video explaining the software they sell (140 pound or so for a license).

[youtube]http://www.youtube.com/watch?v=fReUkhdDShw[/youtube]

If pressure is low or the tyre is too small for the car (with the low profile tyres this is common) the carcass will deform and give you a hot outside shoulder. You can add camber, but that's not the correct answer. Who among you has tried a 50 series, instead of a 60 and discovered the difference in shoulder wear? It's not the compound, it's the profile.

You can use chalk on the shoulders and discover what's happening (old trick). That short radii, lonely curve, far from the pits, can be increasing your temp and you do not see it in the temp readings by the time the car reaches the pits. Analyzing the wear pattern of the chalked shoulders you could reach some conclusions.

[Jersey Tom]

IR temperature sensors are great for really dialing in a setup, but only if you can get dynamic temperature! Ie through telemetry. I don't like using them with a stationary car. For that, I'd recommend a needle pyrometer.

In a pro race series you'll have to use the combination of the two to balance grip and durability.

[Scuderia_Russ]

We use a Snap on IR gun. It runs off a 9volt battery and does the job well, quite a good bit of kit.