Tyre Pressures. (Especially track days).
Discussion
Tyres are a black art. They all look the same, they are round and black, but in fact they are all very different in terms of constuction and materials.
The single most important thing to get right is the pressure you inflate them to. This will ensure you get the most from them regardless of type fitted.
It is important that you always check the pressures with the tyre up to opperating temperature. Essentially left unchecked the pressure will increase as the tyre heats up. That means the pressure in your rear 911 tyres could easily increase to over 50psi if you put the car round a track.
What this would do is bow the tyre outwards on the contact patch with the road surface and only the centre of the tyre would be in contact with the road.
Under inflated the tyre will roll over on it`s edges when cornering, those same rear 911 tyres would allow the car to roll over and the car would want to oversteer and be generally loose.
Lots of things affect the temperature of the tyre. Ambient air temp, track surface temp and how hard you are cornering being the main ones.
They only way to really tell what the best tyre pressures for your car, (and also if the suspension is set up), is to use a pyrometer. This is a little probe which you push into the tyre tread and it measures the temperature of the rubber. You take an outside reading, a centre reading, and an inside reading.
In very simple terms you are looking to get an even spread accross the tyre. The two outer readings are mainly controlled by the suspension settings, particulaly the camber angle of the wheel. For a road car there will be little you can do to change this. If the outside temp is hotter than the inside you need to increase the camber, ie. move the top of the wheel into the car. That is why race cars have such massive camber angles, to protect the outside of the tyre when cornering hard. What you can try to do is ensure the centre temperature is in the middle of the two outer temps. This will, in theory, give you the best pressure setting for that particular tyre / suspension combination. It is only theoretical though. In practice other factors may case you to change pressures. If the tyre is rolling over on it`s self when cornering you may want to increase the pressure for instance.
Each trackday you attend will probably give diferent readings. The recent day at Silverstone for instance was cold, the track surface was variable and there was a lot of slow traffic. Potentially under those circumstances your tyres may not heat up as much as a blistering summer`s day with no one else on circuit and you`re running at ten tenths.
If you really want to get the best from your car and it`s a car that spends most of it`s life doing track days then seek professional help in terms of setting the angles up and so on. If you`re just running a road car on an occasion day then initially aim to keep the pressures the same as for road use once the tyres are hot, (this will mean letting air out as the tyre heats up).
Finally try to check things like pressure as soon as possible after you come off the circuit. There is little point in going off for a poo, a mars bar and a can of coke then coming back to the car 5 minutes later when it`s cooled down.
Hope that gives a little help, it`s not the definative answer and different tyres on different cars will give different readings so don`t assume just because Babba`s Bridgestones on his 996 run at a particular pressure the Bridgestones on your 3.2 Carrera will be the same.
As usual keep smiling and see you all in the carribean over the winter !!
Henry
The single most important thing to get right is the pressure you inflate them to. This will ensure you get the most from them regardless of type fitted.
It is important that you always check the pressures with the tyre up to opperating temperature. Essentially left unchecked the pressure will increase as the tyre heats up. That means the pressure in your rear 911 tyres could easily increase to over 50psi if you put the car round a track.
What this would do is bow the tyre outwards on the contact patch with the road surface and only the centre of the tyre would be in contact with the road.
Under inflated the tyre will roll over on it`s edges when cornering, those same rear 911 tyres would allow the car to roll over and the car would want to oversteer and be generally loose.
Lots of things affect the temperature of the tyre. Ambient air temp, track surface temp and how hard you are cornering being the main ones.
They only way to really tell what the best tyre pressures for your car, (and also if the suspension is set up), is to use a pyrometer. This is a little probe which you push into the tyre tread and it measures the temperature of the rubber. You take an outside reading, a centre reading, and an inside reading.
In very simple terms you are looking to get an even spread accross the tyre. The two outer readings are mainly controlled by the suspension settings, particulaly the camber angle of the wheel. For a road car there will be little you can do to change this. If the outside temp is hotter than the inside you need to increase the camber, ie. move the top of the wheel into the car. That is why race cars have such massive camber angles, to protect the outside of the tyre when cornering hard. What you can try to do is ensure the centre temperature is in the middle of the two outer temps. This will, in theory, give you the best pressure setting for that particular tyre / suspension combination. It is only theoretical though. In practice other factors may case you to change pressures. If the tyre is rolling over on it`s self when cornering you may want to increase the pressure for instance.
Each trackday you attend will probably give diferent readings. The recent day at Silverstone for instance was cold, the track surface was variable and there was a lot of slow traffic. Potentially under those circumstances your tyres may not heat up as much as a blistering summer`s day with no one else on circuit and you`re running at ten tenths.
If you really want to get the best from your car and it`s a car that spends most of it`s life doing track days then seek professional help in terms of setting the angles up and so on. If you`re just running a road car on an occasion day then initially aim to keep the pressures the same as for road use once the tyres are hot, (this will mean letting air out as the tyre heats up).
Finally try to check things like pressure as soon as possible after you come off the circuit. There is little point in going off for a poo, a mars bar and a can of coke then coming back to the car 5 minutes later when it`s cooled down.
Hope that gives a little help, it`s not the definative answer and different tyres on different cars will give different readings so don`t assume just because Babba`s Bridgestones on his 996 run at a particular pressure the Bridgestones on your 3.2 Carrera will be the same.
As usual keep smiling and see you all in the carribean over the winter !!
Henry
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