Having opened a can or worms I felt more research is needed so I started looking at "recommended" pressures for a range of cars.
Findings:
1. Almost every modern car has different pressure recommendations for normal and loaded driving and these are further modified for normal and high speed driving. On my BMW the pressures for loaded high speed are higher than normal and fully loaded.
2. The difference between front and rear pressures seems to be linked to weight distribution, with a bigger difference for cars with a rear weight bias.
3. Manufacturers increasingly fit wider tyres to the rear wheels on powerful rear drive cars.
4. Aldermog's original 2009 rear Avons lasted less than 20,000 miles. The fronts look good for 40,000 but will be replaced next year when they are 6.
5. Properly inflated tyres should be 3 to 4psi harder when hot than cold. If more than 4psi they are overheating which is accepted as meaning under inflation or over loading and if less than 3 psi they are over inflated or under loaded, or both.
So Milligoons thermal imaging test can be replaced by a tyre pressure gauge. But I like his logic!
Where does this lead?
I believe that in the absence of evidence to justify the MMC recommendation of 22psi all round for the S2 Roadster a front rear bias makes sense. Aldermog has 4 leaf springs that need all the help they can get.
I do wonder if MMC under inflates tyres so they warm up a lot as the supplied tyres are working way under their recommended load. As mentioned previously the Avons fitted are Code 91 when based on the car weight they should be 81 at the rear and 75 at the front. Such tyres don't exist in the sizes needed.
I think handling would be improved if the front wheels carried 195 section tyres, not 205 section. Difficult to do without new front wheels.
I need more information: tyre pressure settings seem to be something of a "black art" and whilst I'm not sure that MMC are right I'm not sure they are wrong!!
