Tires

[yelwoci]

Most racing tyres based on road tyres use similar pressures to those used on the road.
My 185x80x13 D84J Dunlops run about 34psi cold, giving 40psi hot.
Because these tyres have a lot of material on the tread surface the carcass must be reasonably rigid, otherwise the structure overheats.

Slicks on the other hand have a different construction and need to run hot. they have very little material on the tread surface.
They also have mechnically stronger side walls.
Most slicks run between 17-22 psi.

Odd ball stuff such as mud racing etc, may use balloon tyres with as little as 2psi.

IanC

[IAM]

I understand that the tire pressures on race cars are no where near the pressures for road cars.

Can anyone tell me what the pressures are for different forms of racing and what the reason for them being so low is?

Thanks.

Ian

[Franklin]

The opposite extreme is Bonneville land speed tires where inflation pressures are in the 100 psi range.

[IAM]

Where I'm really trying to get is the pressures used on Indy cars, F1 cars and (Don't hit me ) NASCAR. I had heard they start with about 13 or 14 PSI, which as you say, IanC, with the tyres you use, the pressure would increase.

Is there an optimal pressure for racing i.e. 28 to 32 PSI and they calculate how the pressure will change with the extra heat and hence the much lower "cold" pressure?

Ian

[Warwick]

we always used a pyro to set our pressures and tried to get the temp reasonably even across the whole tread area,nitrogen is also used in some types of racing as it doesnt expand as the temp rises so the pressures stay the same.

[Brad Grant]

Tyre pressures....what a can of worms that opens!

Tyre pressure is all about carcass shape. What this means is the pressure that results in the maximum footprint size measured at operating temperature. So what is the correct pressure that should be used? Easy..the pressure recommended by the company that makes the tyres (the company concerned if it is worth it's salt will know!).
The manufacturer of the tyre builds the carcass to have a particular shape or profile when fitted to a "recommended " rim. What that pressure is depends on tyre construction. Tyre construction varies depending on application.The two different constructions of tyres used in racing are bias ply and radial but there is heaps of different constructions for each type, again depending on application. For example both types of tyre can be made with very stiff side walls or very soft ones, different numbers of nylon overlays etc. However the tyre must be the correct size and construction for the car and it's intended use otherwise tyre pressure recommendations mean nothing and you can come up with your own scientific method of what is correct.

[THR]

Things that affect pressures.
make
size
width
ambient temp, esp at start of run
castor, camber, and tow
Weight of the car, which is the big main factor.

to set pressures, the only thing u can do is see where the tire gets hot, and where the flow or rubber is being taken, this also applies for camber setting. and both are linked to some degree.
for instance on my kit car, weighing 650kgs, tires at rear (where the engine is) are runnign about 22 psi, front 20
the camber is too high at the rear (feeling where they get hot) so this need to be changed to 1deg, and pressures redone.

easier to come down on pressure, rather than go up. so, set to 30ish, and reduce by 2psi each run, and u will notice a difference, and a peak will appear at the optimum temp.

[Dino IV]

Hi Warwick,

which racing series did you had in mind when you mentioned nitrogen filled tires?

[Crash Test]

Dont take this as fact, but i once heard that GP bike teams had tested inert gases in their tyres, which i guess would include nitrogen.

[Peter Mallett]

I know the ORECA team uses nitrogen in its Viper tyres.

[enzo]

Nitrogen is used because it is "dry" air - very little water content. The really sharp teams will also use an in line dessicant filter to remove the last of that moisture. The use of nitrogen is applicable to ALL car class ( or bikes), and is an absolute must for maintaining consistancy.

Pressure rise will vary widely if moist air is used & as a consequence, the grip of the tire.

[Dino IV]

Are inert gasses inside tires also used in F1 or isn't that allowed?

[kev]

The Batmobile (from the movie) runs 8 psi.

[Brad Grant]

some examples of tyre pressures that I know from actually supplying and fitting them. Race tyres are my job. I work with international race teams right through to club motorsport competitors.

Yokohama V8 supercar radial slick run 32psi hot
yokohama racing radial run 42psi hot.
Yokhama group N radial slick run 44psi hot.
Yokohama crossply side car slick run 17psi hot.
yokohama f3 radial slick run 21psi hot
Yokohama AO33 rally tyre run 36 hot
avon formula ford ACB10 crossply run 19psi hot
avon group N radial slick run 44psi hot

All these pressures have been arrived at through testing and development by tyre engineers. The important thing is fitting the correct size of tyre to suit the weight and horsepower of the vehicle and that the tyre must be fitted to a recommended rim size. The important thing with pressures is tyre carcass shape. What this means is with the tyre inflated on the rim and the tyre is at operating pressure the footprint is at it's maximum size. Everyone knows that if you overinflate a tyre that the tyre bolges outward like a ball in the middle and runs on the middle of the tyre. The higher you increase the pressure the more it runs on the middle of the tyre. Conversely if underinflated the tyre footprint bolges inward at the centre and the tyre runs more on the outside edges of the tyre. This princple apllies to tyres but you still get some anomolies like the the mud type tyre.The idea there is to get "floatation" over the mud with the biggest possible surface area and allow the tyre pattern to work. The tyre carcass actually conforms to the ground shape as well when the pressure is very low but a tyre like this will offer very little carcass stiffness for cornering. You may even roll the tyre off the rim. There are also some valid reasons to alter tyre pressures in unusual conditions to get some benefit eg deep water on the race track. Increasing tyre pressure artifisially high gives a more rounded carcass shape and less footprint area therefore less chance of aquaplanning.

I could go on and on about tyre constructions eg bead fillers, flex points, edge capping, plies, thread thicknesses etc..but it would take me days to tell you what each does and how each affects tyre pressure. If anyone really wants to know more just ask.

[Dino IV]

Okay, I got some information through a friend with a friend at McLaren.

They run their F1-cars with nitrogen filled tires.
So I assume all the teams use it.

Forgot to ask about pressures though. About 25-30 Psi maybe? Rain tyres are run at higher pressures to insure the grooves keep their open thread. Maybe Brad Grant or someone else can shed some light on this one.

Cheers!

Dino IV.