# Hot Weather Tire Pressure

I was at the track yesterday and the temperature was very high. Quite a few racers went down and the track owner said it was due to the hotness of the track.

I asked a few riders as well as the track owner how they should adjust their tires for the heat and they all gave the same answer…put less air in. But I’ve always believed (been taught) the opposite. I’ve been taught that in cold weather you put less air in the tire…which causes more friction (between the road and the tire due to the flatter tire)…which causes the tire to heat faster/more which gives good grip. And in hot weather if you put less air in, then the combination of more friction due to the flatter tire will cause the tire to heat too much…making it slippy.

So…just trying to figure out who’s right…all the racers…or me.

The key is to stay in the optimum PSI>

A hot tire heats up about 4 to 5psi on an auto tire on a hot day.

Just bear that in mind.

if 30 is the optimum cold temp, just do that when the tires are cold. It will be fine when its hot.

A few psi wont burst it

[quote=“Mordeth”]I was at the track yesterday and the temperature was very high. Quite a few racers went down and the track owner said it was due to the hotness of the track.

I asked a few riders as well as the track owner how they should adjust their tires for the heat and they all gave the same answer…put less air in. But I’ve always believed (been taught) the opposite. I’ve been taught that in cold weather you put less air in the tire…which causes more friction (between the road and the tire due to the flatter tire)…which causes the tire to heat faster/more which gives good grip. And in hot weather if you put less air in, then the combination of more friction due to the flatter tire will cause the tire to heat too much…making it slippy.

So…just trying to figure out who’s right…all the racers…or me.[/quote]

I think you are right, but for slightly the wrong reason.

I think a lower pressure heats the tyre due to greater internal friction, since the tyre is flexing more. I think that’s why an underinflated tyre fails, due to internal overheating. I dont think the greater contact patch is so much of a factor.

You can’t spell tyre either, but I suppose its the way you were brought up.

[quote=“Ducked”]

You can’t spell tyre either, but I suppose its the way you were brought up.[/quote]

tire
2 /taɪər/ Show Spelled [tahyuhr] Show IPA ,noun, verb,tired, tir·ing.
–noun
1.
a ring or band of rubber, either solid or hollow and inflated, or of metal, placed over the rim of a wheel to provide traction, resistance to wear, or other desirable properties.

Keep in mind that with either a hot or cold day racers generally use less air than the tire or bike manual says. But I’m saying that you would use less on a cold day than on a hot. So on a very hot day you’d use more air than normal…but still probably less than the manual/tire says.

Based on my school boy physics (backed up by the interweb) hot air expands and cool air contracts, therefore putting less air in when it’s hot would make sense from a physics point of view.

[quote=“Mordeth”][quote=“Ducked”]

You can’t spell tyre either, but I suppose its the way you were brought up.[/quote]

tire
2 /taɪər/ Show Spelled [tahyuhr] Show IPA ,noun, verb,tired, tir·ing.
–noun
1.
a ring or band of rubber, either solid or hollow and inflated, or of metal, placed over the rim of a wheel to provide traction, resistance to wear, or other desirable properties.[/quote]

Neither can they, probably for the same reason. (OK tiresome, I know).

I know nothing of racing, but if the internal friction thing applies on the street I can’t see why racing would be less so. Why was the heat unsticking people? Tyres so hot they were slippery (does that happen?), the track slippery with transferred tyre compound? Tyres so underinflated they compromised handling?

This would make sense entirely from a temperature POV. But a second variable would be what changes occur to the traction of the tire at high temperatures. And probably a question that needs to be asked of experienced racers (motorcycle or car).

This would make sense entirely from a temperature POV. But a second variable would be what changes occur to the traction of the tire at high temperatures. And probably a question that needs to be asked of experienced racers (motorcycle or car).[/quote]

It makes sense, but its wrong.

(I think)

Yeah, heat stroke will do that.

Depending on how cold cold is, I would say that putting too little air in tyres when on ice for example tends to have a negative effect as there is less directed pressure on the surface of the road and so tends to cause eary slippage. Remember high school science when you melted ice by concentrating pressure using a thin thread. The ice would melt under it and again freeze on top causing it to stick to the thread? This is why many ice-racers use thin, spiked tyres instead of the snow racers who tend to use very large, wide tyres to distrubute the vehicle’s weight and so prevent sinking into the snow. At the same time as using larger tyres for the snow, the same tyres are often given heavy treads to plough through into and through the snow. These larger tyres would be given a lower PSI given the larger volume of air within them a opposed to the narrow ice-tyres which require a higher pressure to provide enough directional pressure.

None of this has anything much to do with heat improving performance however, but more to do with friction, which is not quite the same thing.

It is difficult indeed to produce heat in tyres when it is cold, and providing heat in these circumstances is not as important as improving friction. Heat is used to improve friction, this is true, but it isn’t the be all and end all in tyre performance. Aquaplaning is yet another instance where the lack of heat is not the issue at all, but the design of the tyre’s tread and sipes.

If we are talking dry track on a hot day, then I would suggest that reducing the normal volume of air in the tyre to adjust the pressure down to normal optimum levels would have the effect of maintaining the profile of the tyre and allow it to flex and maintain its normal footprint on the track. Allowing the pressure to increase will surely cause the tyre to perform outside of its intended values.

the amount you would put in would depend on the length of the race, as well. The lowest I ever raced with was about 15 psi, for a 5 lap sprint race on a 10 degree day. the tyres just got up to decent temperature after the third lap or so. on a longer race, i would have used 18-20 psi., with the tyres getting up to good temp at lap 5 or so, and lasting longer…

(ducati single, about 100 kg and 35 HP)

I would say there is more variables here. Less air in the tire would mean less mass and therfore it would increase it’s temperature faster. More air would increase the mass needed to heat up.

Then you also have the fotprint of the tire changing while the air change it’s volume based on temperature.

the mass difference is negligible. At low temps, the low pressure leads to massive amounts of sidewall and tread flex that heat the tyyre faster.

At high temps, run no more than a couple of psi less than normal (when measured COLD), or the pressure inside the tyre rises too much when the tyre heats up (something only really noticeable when the car is driven hard). For most people, who wouldn’t know what end of a tyre pressure gauge was what, or how to add air in normal conditions, i don’t think there is any concern at all. Far worse things are likely to happen to a car in the hands of an owner like that than overpressure tyres.

710 cap, anyone?

[quote=“urodacus”]the mass difference is negligible. At low temps, the low pressure leads to massive amounts of sidewall and tread flex that heat the tyyre faster.

At high temps, run no more than a couple of psi less than normal (when measured COLD), or the pressure inside the tyre rises too much when the tyre heats up (something only really noticeable when the car is driven hard). For most people, who wouldn’t know what end of a tyre pressure gauge was what, or how to add air in normal conditions, I don’t think there is any concern at all. Far worse things are likely to happen to a car in the hands of an owner like that than overpressure tyres.

710 cap, anyone?[/quote]

So at low temps you can run a tire fairly low. But in hot weather you say to only lower it a few psi.

So I think it would go something like this as a rough example. Tire says run it at 32psi.

Racer finds he gets best performance on a warm day running it at -8psi. And on a cold day -12psi. and for a hot day he should put a bit more perhaps -4psi.

Is that roughly how the curve would work?

I know two guys went to germany with there bikes to test the free speedlimits.
One increased he’s preshure and the other did not.
The one did not burned up he’s tire and needed a replacement.
The one using the higher prshure is a driving instructor and told me that higher speed required more air.
When in doubt do what works for you.

hugely variable here. low profile tyres should be run much higher pressure than the low limits i mentioned. But my old duck single ran tyres that were round in cross section…, but they were fairly hard too, this being the 1980s and all…

read more good stuff at www.tirerack.com

[quote=“Mordeth”]

So at low temps you can run a tire fairly low. But in hot weather you say to only lower it a few psi.

So I think it would go something like this as a rough example. Tire says run it at 32psi.

Racer finds he gets best performance on a warm day running it at -8psi. And on a cold day -12psi. and for a hot day he should put a bit more perhaps -4psi.

Is that roughly how the curve would work?[/quote]

With my street bikes, I have always run about 32psi. With my race NSR, I have experimented a bit, and now I usually always run 26psi cold, and it doesn’t matter if it’s a hot or cold day. I have raised my PSI up for practicing just to see what happens, and I find that my tires start slipping right away. During the last race, its was hotter than hell, my tires were really worn, but I feel that if I would have used about 24 or 25psi, that might have saved me from crashing, or at least crashing so early in the race. For the Longtan race track, it seems like almost every racer is using the 26psi setup. I would really love to know more about the advantages and disadvantages of changing tire pressure for racing. I don’t think many of the Taiwanese care too much about this, but I think it’s extremely important. Should have run different PSI setting in the rear then the front? With my riding style, and the way my NSR is setup, I tend to put a lot of stress on the front tire. I wonder if using different tire pressure settings would help balance the bike out more.

Almost basic enough for me.

http://www.sportrider.com/tech/tires/146_0206_motorcycle_tire_pressure/index.html

[quote=“Ducked”]Almost basic enough for me.

In that article it says a few times about less air cooking a tire. I really think that the riders should have put a few extra psi’s into their tires on Sunday to lessen the effect of tires overheating. But it seems some of them did the opposite…which should have exacerbated the problem.