(04-25-2019, 07:00 PM)Cormanus_imp Wrote: Thanks, Aussieflyer. I'm still confused, I think. I took kennyw's post to mean what you said: wheel = rim + tyre. I took the diameter to be the diameter of the wheel. A 17" rim is immediately going to reduce the diameter by 1" so surely you'd have to put a higher profile tyre on it to achieve the same diameter as an 18" wheel with a standard tyre.
Sorry mate I have a way of making simple things sound complicated ... or so Mrs Flyer often tells me!
You are correct assuming the tyre width is a constant. Below are some examples of Bridgestone's current range which all have a 655mm outside diameter:
T31 - 140/70 x 18
T31 - 160/70 x 17
RS10 - 200/55 x 17