Offset, Wheel Diameter, and clearance

[Gary Morrison]

In my car's previous incarnation I had TSW Hockenheim 15" wheels (35mm
offset), with 205 x 50 x15 tyres. The car was lowered with Eibach springs
and it rubbed through the splash guard in the front wheel arches on both
sides. Rubbed on hard cornering. Wider tyres (ie on 16" or 17" wheels would
have been a real problem.

Regarding offset, and without getting into the theory, I now have a 15" 45mm
offset wheel and while with the 35mm offset wheels the car felt quite
"light" in the steering at speed in a straight line, now with the 45mm
offset wheels it has some weight to it under the same conditions. Same
tyres.

I believe that if you have added spacers to your 35mm wheels Matthew you
will have reduced the offset further. If you have added 10mm thinking you
will make it "45mm" you will actually have made it 25mm. As the offset (from
wheel centreline) increases the line that the hub mounts to moves towards
the outside of the wheel, and the wheel moves further into the wheel arch.

The reason many Roadsters with aftermarket wheels will have other than 45mm
offset is that 45 is very hard to get. Most aftermarket wheels are in the
range 35-38mm. (I guess thats where the bulk of the market for other cars
is)

Gary