Establishing correct tyre pressures with diffent size tyres
Discussion
Ive fitted different size wheels and tyres to my Griff and would like to find the correct pressures to run them at.I have taken temperatures accross the tyre profile but with the negative camber im running there is quite a difference from one side to the other and an even temp all accross is impossible.
How do I arrive at the best pressures? As the negative camber will allways run the inside edge hotter should I be looking for the minimum discrepancy possible accross the width? Or should I set the wheels with zero camber to measure temps then re-set camber afterwards?
I'm guessing that finding the least discrepancy with the camber already set is probably correct but I cant find any reference to measuring the temps and taking into account the obvious effect the negative camber will have.
How do I arrive at the best pressures? As the negative camber will allways run the inside edge hotter should I be looking for the minimum discrepancy possible accross the width? Or should I set the wheels with zero camber to measure temps then re-set camber afterwards?
I'm guessing that finding the least discrepancy with the camber already set is probably correct but I cant find any reference to measuring the temps and taking into account the obvious effect the negative camber will have.
I'm no expert but since nobody else has had a go at this...I was reading a great book about the 917 last night and the John Wyer team mechanics adjusted camber to get uniform temperatures across the tyre. Ended up with virtually zero camber settings on the front, forget the rear. Doesn't help re camber/pressure relationship. Apparently they always ran 3 degrees castor (caster?).
All tyres and compounds will have a optimum operating "hot" temperature where the tyre grip, longevity, degradation and wear will be at its optimum. The tyre manufacturer will provide this information along with the optimum "hot" tyre pressure. That is always the goal for that tyre and for most road tyres the tolerance of acceptance allows for summer/winter.
To set a tyre for the road from non standard oem you need two things, a tyre temperature gauge and the ability to know that the grip for the tyre when driving and handling seems optimum.
To set a tyre for a race car you need 3 things, a stop watch, a tyre temperature gauge and the ability to know that the grip for the tyre when racing and handling seems optimum.
The absolute optimum for road use is the temperature across the whole contact patch being the same as the recommended hot operating temperature and running at the recommended hot pressures.
The two compromises are:
operating lower than the recommended tested Pressures but in the correct hot operating temperature range. - seen with light weight vehicles or being overtyred
Operating higher than the recommended tested pressures but in the correct hot operating temperature range. Seen with heavy vehicles or being undertyred.
More complex variables include being overtyred but usage of inner or outer part of tyre only creating correct pressure and temp but only only a certain amount of the tyre...acceptable if the handling and grip is fine, although will create non uniform tyre wear...( consider loosing some tyre)
In all cases the optimum temp for the tyre needs to be known or it may feel great but they last about 100 miles
How you get to the above is the harder bit......trac,, castor, camber, toe all after road testing, different days and seasons... In general people get obsessed with tyre pressures ( which are important) but play 2nd fiddle to the more important factor tyre temperature.....
To set a tyre for the road from non standard oem you need two things, a tyre temperature gauge and the ability to know that the grip for the tyre when driving and handling seems optimum.
To set a tyre for a race car you need 3 things, a stop watch, a tyre temperature gauge and the ability to know that the grip for the tyre when racing and handling seems optimum.
The absolute optimum for road use is the temperature across the whole contact patch being the same as the recommended hot operating temperature and running at the recommended hot pressures.
The two compromises are:
operating lower than the recommended tested Pressures but in the correct hot operating temperature range. - seen with light weight vehicles or being overtyred
Operating higher than the recommended tested pressures but in the correct hot operating temperature range. Seen with heavy vehicles or being undertyred.
More complex variables include being overtyred but usage of inner or outer part of tyre only creating correct pressure and temp but only only a certain amount of the tyre...acceptable if the handling and grip is fine, although will create non uniform tyre wear...( consider loosing some tyre)
In all cases the optimum temp for the tyre needs to be known or it may feel great but they last about 100 miles
How you get to the above is the harder bit......trac,, castor, camber, toe all after road testing, different days and seasons... In general people get obsessed with tyre pressures ( which are important) but play 2nd fiddle to the more important factor tyre temperature.....
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