Hi dswiders and another big welcome to thr forum if you didn't get it the other day before the server "crash"! Gtigrl and myself did a GTI drive day last month at Sandown with VW and Murcotts driver training. They insisted that we ran a minimum of 38 psi all round in our tyres. They mentioned that manufacturers reccomend lower pressures for a smoother ride only. There is no proof that higher inflated tyres will lose grip quicker. I run 38 all round in the GTI, customers Mk5s I set at 38F, 36R if they are normal type drivers.
With 18s I would set to 38 all round. Cheers, Andrew :) :)