I have a C4 with C5 wheels, anyone running 325/30/18 wheels on this setup?
or is anyone out there running 325 tires on a C4 at all,? If so any problems? :cheers:

 

There have been many posts here about different Tire Dimensions. Some of our fellow forum members are running tires as large as 335/18. At least I seem to recall at least one post to that effect. Lots of folks are running 315s all around. I'm sure you'll get other posts giving other sizes successfully used by members. My next move is 315s all around.
:yesnod: :yesnod:

 

I've successfully run 315's all around, as well as semi-successfully run 335's in the back with small (1/4" thick) spacers due to tire-to-trailing arm interference. The problem with the small spacers like that (which I didn't think about until I started snapping wheel studs) is that the wheels on the C4 are hubcentric, and that small spacer is just thin enough that the spacer itself doesn't have a hub for the wheel to center on, but thick enough that the wheel no longer rides on the hub of the car. The result? The studs which weren't designed to carry the full load of the car are now doing so. This is a bad thing. The spacers out there for fitting '88-up wheels on '84-'87s are thick enough that they have their own hubs and help maintain the hubcentricity of the wheels, so there isn't a wheel stud problem there.

I do know that you can run wider that the 315's in front or back, but you will need wheels with an offset that will end up sticking the tire slightly outside of the fender well. If it were me, wanting to keep the tire inside the fender well like I do, I'd hold off on anything wider than 315's for the street until I get a chance to make those trailing arms I've been talking about. Unfortunately, I've been so swamped with work that I haven't had time. I should have time in the beginning to middle part of May, so I'll try it then and let folks know how they come out.