I know it sounds a stupid question and I feel embarrassed about writing it and I couldn’t think of a decent title for the thread.

But Im having my 2004 WRX remapped on Friday and Im having my wheels refurbed/painted tomorrow, the question is that I have 225/40/18 tyres on at the moment with the alloys that are going to be refurbed and wont be back until Monday.

Now I have a set of 18inch wheels with tyre size 215/35/18 that will go on as a replacement until my wheels come back Monday, The question is will the different tyre size affect anything on the rolling road when I have it remapped.

Sorry for the stupid question, but hopefully someone can answer it.

 

The complete diameter of the rim=trye should not change,

bigger rim but smaller profile of tyre.

You will be fine

 

Read closer cookstar - rim not bigger

 

ooops


It will still be fine

 

Alloys are the same style, size and same offset just different tyre size. I thought I would ask before I changed the wheels over and had the car on the rollers, just incase it affected anything.

 

http://www.miata.net/garage/tirecalc.html

 

It won't affect the mapping at all.........

Simon

 

Shouldn't affect the mapping.

The actual road speed will be different, but as the car calculates this from a gearbox output, it will not affect the mapping anyway.

It will add a (further) element of overreading to your speedo though, so you won't be going as fast as indicated, as for a given number of rotations of the wheel, the travelled distance will be less, as the rolling radius will be smaller on the tyre (because you have a narrower tyre, and a lower profile).