A ponderment on tyre pressures

[Funky]

Now to some this may seem a silly question (i can see the quotes on that bit alone) but most of us drop tyre pressures for track days due to this extra heat generated causing more inflation. I am wondering though, when we check tyre temperature, we always do it cold at normally 36 psi, but surely even road riding must generate heat, and because of this is there an ideal running pressure for tyres?

[SlingVTR1000]

usually 42 in the rear and 36 in the front, yes from cold, this does allow for a change, but this is small as you cannot keep heat in a road tyre unless you are caning it all the time, I have a no stop 12 mile ride to work which I cover in about 9 minutes this is 140mph straights and fast 70/80 sweepers into deep braking tight as you like corners and i reckon my tyres at the end are no more than hand hot (50c maybe) racing tyres round a track you are looking at 100c, we dont get anywhere near that temp to warrant lowering pressures, the only advantage is in greasy freezin roads where you can get extra grip through a flabbier tyre which will generate more heat.

[Rsv4Col]

I run 36 rear 34 front on the road but speaking to someone who has used Racetec's on track before he says rear should be 28 hot for the track

[Funky]

So in theory you tyre temperatures reach their ideal running 'hot' pressure ideally from the way you ride. Someone who is faster would need to lower their 'cold' pressure as the tyre gets hotter and the air expands more. Someone who is slower would need their 'cold' pressure higher as the air does not expand as much.

So why don't we pay that much attention to 'hot' tyre pressures? I know it would be a pain in the ass to keep fiddling though, but once you know how much you have to adjust for a given track it should be alot better.

[jon_piscitelli]

Ideally you're looking 36 front and rear hot on normal road tyres.

Power 1, Racetech Interacts, D211 latest track day stuff that is road legal high 20's HOT, sometimes even mid 20's on certain types (Dunlop)

I'd say use what feels correct to you and keep an eye on your tyre, on my road bike (R1 5vy) I use 36fr & r during the winter as the tyre rarely gets up to heat due to cold & wet roads.

In the summer, all depends on how I plan on riding

[deej]

road tyres are designed to run at pressures that allow for them to be warmed whilst riding, the carcas of the tyre is made of different compounds so needs different pressures and heat. A diablo will never run as hot as a racetec so you need higher pressures to keep the tyres shape. Some of the new dunlop ntec stuff that my mate races with does run as low as 21psi HOT depending on the track and weather conditions but thats on a very very sticky tyre on a gsxr1000 that doesnt hold back. Road riding is so different to track riding that theres really no comparison

[Funky]

I know I always run my tyres low thirties on a track day. Would be interesting to see what psi they ate when hot.

[deej]

theres a guy local to me whos a bit of arse and does a little bit of instructing for focused and ive seen him in the garages with a thermometer checking the heat of the rims, if the rims are cold it will affect the heat of the tyre in his eyes. wheres age our resident phase one tyre expert when you need him

[Funky]

I can see how cold rims would create a small micro-climate with cold and warm air, but once you get moving it wouldn't matter anyway.

So does anyone know if tyres have an optimum running pressure, not just a pressure you put to when cold?

[Scotty]

In the pre-N-Tech days we inflated all tyres (slick, inter or wet) to 30psi, give or take the odd psi here and there (I think rear wets may have been 28, but it's been 5 years since I did the Phase One tyres so it's all a bit hazy)
You can't make a comparison between optimum running temperatures and pressures for road and track tyres, the only things that they have in common is being black and round - different carcase constructions and vastly different "rubber" compounds for totally different applications. Track tyres have to get seriously hot, road tyres don't, but they have to grip over a far wider temperature range and heat up quickly, and last far longer...

[gigrower]

I'm going to start with 'I'm no expert but....'

As I understand (and also talking to a mate of mine who races single seater motorbike engined cars), the really important thing is not the pressure of the tyre, but the temperature of the tyre in use. If you leave the tyre pressures high - say road pressures, then they don't get as hot on track and you may not reach the optimum working temperature. The lower you set the pressures to start with, the hotter the tyre will get during track action to the point where it could even get too hot if the initial pressures are too low. The best way to work this out is with a thermometer as soon as you get off and take readings centre, and each edge. For car race tyres, there is good info for what the optimum operating temperature is for each type of tyre from the manufacturer. I've been trying to find this out for some of the bike tyres tho and have been failing so if anyone does know say for Bridgestone BT-003's I'd be really grateful. As I say, I'm no expert so am happily prepared to be shot down over this, but it makes more sense to me than some of the slighly vague suggestions I've had as to how much to lower pressures by for track and it must surely vary from manufacturer to manufacturer.
Cheers All

[Funky]

Tis a good answer, if anyone can find out the optimum temperatures, they're a winner

[Diggler]

Ive spoken to some of the best teams in the BSB paddock and they all say different, in all the years Ive been ridding on track Ive not yet met the one person who is all knowing about the black art of rubber. Best thing to do is find a base settnig and work from there. Alot set there tyres on track days at about 30psi front and back cold. If your good enough to feel that the tyre is doing something it shouldnt be then make small changes, otherwise just ride the bloody thing

[gigrower]

If your good enough to feel that the tyre is doing something it shouldnt be then make small changes, otherwise just ride the [Censored] thing

Definately agree with you on that and I'm one of the first to say just ride what you've got underneath you and enjoy it. On the road, i never bother to do anything much at all to my bikes, but part of the interest in track riding for me is mucking about with the bikes themselves, doing a bit of amateur mechanics and trying to understand a bit better what's going on. I guess it's just every pig to his own bucket!