My 4/4 is a 1986 it states in the book 18 psi for road 24 psi for track . I leave it at 21 psi and find the ride and road holding good . Been that way for years once tried 24 psi on the road it was horrid .
In the very early years of owning Woodstock (a 72 4/4 2 seater) I tried the factory pressures for about 30 miles. Absolutely horrid and I eventually settled on 22 front, 23 read. This worked well for the original tyres (165/82) and all of the wider low profile tyres I fitted during the course of my ownership.
For competition on tarmac, about 30 seemed to be good and for trials, 12 was used! (I was told lower is better, but that was the minimum the regulations allowed).
