right, just picked up some 18's for my uk turbo (1998),

they have got 225 40 18 's on the back,

and 225 35 18's on the front ???

i take it its not a good idea to use them with different sizes?

and what size should i have on a classic lowered 30mm to avoid rubbing?

 

No its not a good idea to have different diameter tyres on.

215/35/18 is about the limit. I still get some rubbing on mine with weight in the back.

 

As above,215/35/18 is the limit really and even then they might rub with people/weight in the back.

 

maybe i should stick with my 17" speedlines?

will they fit over prodrive alcon brakes?

 

P1's with 18's came with 225/35 but most people use 215/35 as it's a more common size.
Depends on the make of the tyre weather u can get away with 225/35 or not. Toyo's tend to be quite narrow, the Avon ZZ3's i have now are a lot wider than my old Toyo T1-S and both were 215/35.

 

215 /35/18 mate . 40s will rub like **** with people in the back . trust me i know

 

ive had 225 35 s fitted tonight, shall see tomorrow if i have issues...