Tyre Pressure

[PaulF]

Following my question here is there a formula to give ideal tyre pressure based on tyre size and rider weight?

I realise that it's fairly subjective and dependant on preferences, road conditions but a starting point would be useful!

Thanks

[rogerzilla]

Whatever the maximum recommended pressure is at the rear, about 20% less at the front.

[PaulF]

Thanks - why lower at the front?

[rogerzilla]

It carries a lot less weight, unless you're riding a penny-farthing.  The typical weight distribution is 40/60 F/R, but reducing the front tyre pressure all the way to two-thirds of the rear one is risking pinch punctures.

[Ian H]

The better* the tyre the higher the pressure.

*Thinner, more compliant carcase meaning that it will ride smoothly over rough surfaces. A really good racing tubular tyre will happily run at 120psi and still feel slightly soft under thumb pressure.

Touring road tyres are a compromise between low rolling resistance and puncture resistance. The more rigid the carcase the slower it will roll over rough surfaces, in which case a lower pressure (as low as say 80psi for 28mm or wider) will be more efficient for that tyre.