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Posted: Oct 19, 2008 7:43:20 pm
Pete



Tyres take a lot of punishment during a track day so here are a few thoughts to help getting it right.

Balancing the wheels and tyres is often over looked before a track day excursion make sure the balancing is spot on.  Go to company that has the best equipment and can balance the wheel for the least added weight. Excessive vibration will not only cause damage but also put you off your driving line and spoiling your track times. 

Also new tyres are not the best choice to start a track day session. Large tread depths will cause the tyres to heat more than normal and this will contribute to loss of traction. The challenge is to ensure that you have enough tread to be legal on the road on your trip home.

Ideally a spare set of wheels and tyres would allow you to have a set of part worn track tyres while at the track, saving your main set for the journey to and from the circuit. This requires additional resources to get four wheels and tyres to and from the track.  So, if your not lucky enough to have a trailer setup, then having a second set of dedicated wheels and tyres wont be possible.

An additional consideration for having a second set of wheels and tyres is to avoid the damage a track day can inflict on your best set of wheels.  Hard braking on the track causes considerable amounts of hot brake dust to impact on the inside of the wheel rims.  The heat can erode chrome or anodize finish and ultimately lead allow erosion.
So we’ve established part worn tyres are best.  Therefore they need checking before attending a track day session.  A visual inspection of the tyres should be carried out to ensure they are in a good serviceable condition. Make sure there are no cracking of the tyre tread or splits in the tyre sidewalls. The last thing you want is a tyre failure at the high speeds you will experience on a track. The damage of an excursion into a barrier is a lot more expensive than making sure you have decent tyres.

You get what you pay for.  Bridgestone SO1 or SO2’s are a great road and track compromise tyre. Michelin Pilot Sport Cup are more bias to the track and are a particularly light weight tyre compared to a standard road tyre.
Valves also need to be considered. For the older 911’s with higher tyre walls its important to have shorter valves fitted.  Larger tyre walls mean more lateral movement under cornering loads.  Longer valves will move and may seep air and reduce tyre pressures. If shorter valves are not fitted then metal supports can be fitted, but I believe these are a compromise. 

Once at the track you need to continuously monitor tyre pressures. High speed cornering and braking will create a lot of heat and consequently tyre pressure will rise.  As soon as you come in from a session on track meassure your tyres pressures straight away and adjust them accordingly.  Getting the right tyre pressure can be achieved by monitoring the scuffing across the tyre face.  If the pressure is ideal then the scuffing will be even and across the entire surface.  Scuffing in the centre of the tyre will indicate the pressure is too high.  If you are fortunate enough to have a tyre temperature laser checker, then after a track session you should measure the temperature across the surface.  If the pressures are correct then the temperate should be even across the surface.  If there is no heat in a portion of the tyre then that may be an indication of incorrect tyre pressures.  It should be noted however that suspension geometry and corner weights and balance can and will have an effect on tyre pressures.

Most tracks in the UK are clock wise and therefore right handed.  As a result the front near side tyre will get the hottest.  This will mean that the tyre pressure for this wheel will raise by the largest amount so keep a close eye on it.
Before going home after a long track day session remember that you will need to adjust the tyre pressures back to their road use pressure.  Make sure you don’t go home with pressure that are too high.

Posted: Oct 20, 2008 8:15:20 am
carlbon



Definitely you should check tyre pressures before leaving the circuit
Usually they will be too low for driving on the road, as you cant get the temps up to the same level on the street

Posted: Oct 21, 2008 11:29:42 am
Pete



I think theres alot to be said for getting the short motorcycle type valves too.  Withe the higher profile tryes and track day cornering loading you need a stiff valve seat.


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