tyre pressures

[laser2]

I have read several threads and found that lots of people have trouble with tyre pressures. Lots of helpful people start to explain what pressures they run in their cars. This might range from a formula ford that runs an avon on a 13 inch rim and runs maybe 15psi or 19 psi to street sedan running standard 70 or maybe 80 series tyres and runs maybe 50psi.
Along the way we see a whole variety of weights and sizes and horsepowers of cars running a whole bunch of different construction, eg radial tyre vs crossply, low profile stiff construction radial tyres compared to standard "good ride" 65, 70 or above tyres. These are all mounted on various size rims (diameter and width wise).

The interesting part is that lots of people say that you should use your pyrometer to measure the tyre temperature across the tread to determine the correct pressure ie I imagine, you go round the track, change pressures until you get an even reading?

However, if you use this method to determine tyre pressures, what about, just for instance, the effect of camber on the tyre?.
If you corner and don't have enough negative camber to compensate for the roll (and other mechanical flex), I would say that this would show up on the pyro as having too much heat on the outside shoulder? would you agree? I imagine that the temperature reading in this case would indicate the tyre runs on the outside shoulder and that increasing the pressure would reduce the tyres ability to touch the outer shoulder? would you agree with that deduction?
Ok so you increase the tyre pressure so that the tyre sidewalls don't tuck as much on cornering. Does this mean you would keep increasing the pressure till the tyre temp was even? How far would you go before you said that the pressure was not the problem or in fact the answer at all and you began to look at other areas of fault?

Does this simple scenario highlight the problem of using this method for determining tyre pressure? Camber, roll couple, roll rate, polar moment tyre size and compound etc etc etc could have an effect on the cars cornering ability which all have an effect on the resulting tyre temperatures across the tread, ( even driving style can also) so should not all these things be taken into account before you use a pyro to determine the correct pressure? If you change anything on your car height, car weight, camber, spring rate, wheel width, or race tracks (different tracks have different grip levels) Would not any of these change the temp across the tyre??
My conclusion is that there are so many factors that could effect tyre temperatures that using this method to determine pressures is flawed.

[peteconnors]

In my experience the way to go is to take three readings across the contact surface of the tyre. The inner and outer should be the same, which will indicate that the camber is set up correctly, and if the middle reading is the same as the inner and outer readings, then the tyre is correctly inflated. As you said above, there are many factors involved in how the tyre reacts, but the camber and pressure is always the first step for the setup, simply because the tyre is (or should be) the only contact with the track. Once the tyres are setup, then you start work on the next item, after all, why would you try to set up the suspension if the tyres aren't working properly. But every time you make an adjustment to a component, the tyres will more than likely need slight adjustment. I wouldn't go as far as to say that the pyro method is flawed, but it must be remembered that it is just one step in setting up a car. Hope this makes sense; I've not quite woken up yet!

[shiny side up!]

I think that pete more or less gave a pretty good answer. Rarely have I ever had tire temps equal on the outside vs. inside, but within 10F or so has always worked well. We've had quite similar discussions about tire temps (and how to / not to measure them) before in other threads, too, so you may want to check those out...

[Armco Bender]

Some of the Speedway cars where we go every Saturday night are using a system to adjust the tyre pressures while they are racing.Do any other forms of racing use an adjustable tyre pressure system?

[peteconnors]

Should I admit to learning how to set a car up from a computer game...?

[Onlooker]

Do you mean bleed off valves,if so V8's in Oz used to use them but like all things got banned

[shiny side up!]

Yeah, I assume Armco is talking about bleed-of valves, which most series around here ban as well...

[Mattracer]

Originally posted by Onlooker
Do you mean bleed off valves,if so V8's in Oz used to use them but like all things got banned

IIRC, John Bowe may have had an "issue" with bleed-off valves at the Gold Coast one year which possibly contributed to him crashing the car.

If I am wrong, please coorect me.

[laser2]

I wonder if any of you have considered the effect of carcass distortion and its effect on tyre temps across the tread? Especially a grooved tyre ie a tyre with a tread pattern!

[C R Box]

I HAVE OFTEN NOTICED AND BEEN MADE AWARE OF THE EFFECT OF CARCASS DEFORMATION, BUT I'VE COME TO REALISE,IT'S CAUSES ARE LESS TO DO WITH TREAD PATTERNS AND MORE TO DO WITH A PIE AND CHIPS BREAKFAST AFTER PRACTICE.