How to determine what causes uneven tire thread temperature ?

How to determine if uneven tire thread temperature is caused by alignment (excess toe/camber) or incorrect initial pressure setting?

It seems that the only other input available to make a decision would be driver feedback (assuming no data log available). If that is the case what should I be looking for when asking the driver?

This is a tricky one, and I'm writing as a reasonably informed lay-person, and NOT an expert, so may be quite wrong - consider it discussion points.

Traditionally, especially with the older cross-ply tyres, one would try and maintain an even temperature across the whole width of the tread, with the assumption that that would give the best grip and tread wear. This meant taking the temperatures at three points - inner, outer and centre of the tread, if it was higher to one edge or the other, camber would be adjusted to suit, if higher or lower in the middle, pressure would be varied to suit.

However, things have moved on, as has our basic* understanding. Camber variations (angle of the tread to the track/road) is continually changing as the suspension moves, the car gains/loses camber in cornering, even the road camber (for some rallies, on highly cambered roads, the cars even need quite a lot of positive camber) will affect the loads, and hence temperatures, on the tread thoughout the race and what is quickest may not have the best temperature, or even wear rate, when analysed in the pit. heck, just the braking loads as the vehicle pits will have some affect. Sometimes the F1 coverage will show footage of the tyre temperatures around a lap, using infra-red imagery, and it can be quite enlightening.

Further, when monitoring the tread surface temperatures, it doesn't take into account the heat-soak affect on the carcass or tyre pressure variations - black science, remember - and there are companies that can sell IR scanners that actually fit to the inside of the wheels and measure the internal temperature across the scanner.

So, for the amateur, I would guess the best you can do is try to maximise the race pace while keeping the tread temperature as close as practical to the tyres intended operating range, which the tyre supplier should have in the tyre spec's, and that should give the best grip and tyre wear.

*Tyre behaviour is still a 'black' science and even the tyre engineers who specialise in this are apparently still trying to figure some of it out.

What I gather from your answer is that even thread temperature distribution is not as important as I assumed initially and that I should focus on being at the manufacturers operating temperature and lap times.

It depends ;-) NOTE, these are my thoughts, get as much info' as you can get, preferably directly related to your particular vehicle and series.

Most tyres have a temperature range the tyre compounds are designed to work within for the 'best' grip and wear, and the temperature range will normally be different for different compounds, so you will usually be best advised to set the car geometry, tyre pressures and compound selection to do that. However, because things like acc'n, cornering and braking all load the tyres differently, hence the tread temperatures will be different.

So, it may come down to the best lap times while controlling tyre temperature, wear and condition. By that I mean you may be OK with, say, more negative camber in short races if that gives the best overall lap and race time, even if it caused more inner edge wear, but a longer race may mean you' re better to run a little less neg' to even out the tyre wear so the tyre changes correspond to fuel stops. A small amount of time may be lost per lap, but more is saved by reducing, or avoiding, tyre changes.

You may be well advised to talk to your tyre representative, if your race meetings are big enough to have one, or contact their tech' depertment - most manufacturers will have some very smart people who can better advise you on the best setup for your specific vehicle, tracks, and conditions.

The most important measure is always the stopwatch. As Gord mentioned, it isn't just the fastest lap but the average lap time across whatever time duration you require...be it a 6 lap sprint, a 2 hour endurance, a 24 hour endurance or even an entire season.

Like most self funded competitors I am more interest in the latter. In fact I would use this to make a set of relatively hard slicks last a couple of seasons.

Hence I would always run even temperatures (within reason) across the tread so I was avoiding over working a particular area which would subsequently kill lap times when they over hardened. I conjunction with tyre rotation I could get a set of slicks to last 2-3 seasons and still get class wins and fastest laps right until they were replaced.

If I had a bigger budget then I would possibly concentrate more on the stopwatch than the pyrometer.

As for the original question, generally speaking -

High center temp = Pressure too high

Outside edge high = Excess toe in

Inside edge high = Excess toe out

Outside edge low, Inside edge high = Excess negative camber

Outside edge high, Inside edge low = Insufficient negative camber

The above will get you in the ball park, the rest will be down to driver preference.

However, the stop watch is king and if a driver is unhappy with a particular setup and goes slower, even if optimal, then go the other way.

Great replies from both Gord and Denis here. The bullet points for what to look for at the end of Denis' last post are spot on and a great starting point for using a pyrometer for understanding tyre pressure and wheel alignment settings.

Also, as he says, the stopwatch is the gold standard! You can definitely end up with a situation where the temperature spreads aren't exactly what you expect but the performance/lap time is better!