I’m looking for technical help or recommendations on: __running different sized wheels
I have the stock 16" rims with 205 45 R 16 tyres and recently acquired some very lovely 15" rims with 195 50 R 15 tyres on them. I think this results in a 2.6% difference in circumference.
My plan was to use the stock rims for track day tyres and swap them round to the 15" for the road. However, with the current tyres am I risking putting the alignment out due to the size difference? Presumably the mileage / speedo will be affected too.
What if I bought some 195/55 R15 tyres for my gorgeous 15" rims - could I then swap them round without worrying about misalignment and speedo issues?
Just go with the two different set of wheels you have, you do not need to change the tyre size at all. Your 16 tyres will cost more than any equivalent 15" and there will be far less choice.
That’s great news Nick, thank you - but forgive me for double checking - are you sure the alignment would not be affected by the different heights/wheel sizes. As well as giving the engine an overhaul I am close to getting the suspension upgraded along with polybushes - which will include a wheel alignment. It would seem silly to have all this done only to fit wheels which put the alignment out?
The direction in which your wheels are pointing and the camber and caster are not set by the wheel. Changing width and offset will affect contact patch and scrub radius, and will potentially alter the feel of the car, but not the alignment. If you reduce the positive offset of the wheel, so it sticks further out, you will get more leverage from the contact patch and this can or will increase the potential to tug through the steering which is not inherently bad.