Stupid Question

[aggi]

I want to buy a spare wheel to replace the space saver in my E46 328ci coupe. Any suggestions for decent outlets appreciated... and now the stupid question...

Is the wheel size the external diameter of the wheel from the edge of the rim to the other edge?

[fixedwheelnut]

Wheel size is the diameter of the wheel rim in inches, ie 15"/ 16"/17" etc the width is noted as J ie 7J/ 7.5J/ 8J etc and usually marked on the wheel somewhere, you then need to make sure the tyre size matches the others on the car, i.e 235 / 40 R 17 tyre =
a tyre for a 17 inch diameter wheel rim
235 mm wide tread
and the profile [height of tyre sidewall] is 40% of the width [235mm]= 94mm
On top of that you have various speed ratings V, W, Z etc and should aim to have same make tyres on the same axle.