Hi,
I installed 20mm (pro wheel, 40 mm pro axle) spacers to my -07 3 MPS (=European Mazdaspeed3) to make the all-stock look somewhat different.
So stock suspension, wheels and tires, fenders are not rolled. Looks got a lot better but slight rubbing occurs especially from back in bigger bumps. I assume 15mm spacers might be ok, should have a try.
Sorry no pics but math follows...
I started wondering whether this could be calculated and figured out a simple formula to calculate change in tire position. It may be too simple though...
I suggest rim width to be irrelevant in this calculation as tire sits in the middle. I know this contradicts to some web pages where you can give rim width but they calculate rim edges position, not tire's...
So, the place of tire outer edge (which normally rubs first) from wheel fastening point (sorry for terms...) is:
outer edge=tire width/2 - ET + spacer
Example 1: stock tire&rim, no spacer:
outer edge=215/2 - 52,5 + 0 = 55 mm (baseline)
Example 2: stock tire&rim, 20 mm spacer:
outer edge=215/2 - 52,5 + 20 = 75 mm (20 mm outer compared to baseline, of course)
Example 3: stock tire, ET40 rim, no spacer
outer edge=215/2 - 40 + 0 = 67,5 mm (12,5 mm outer compared to baseline = difference in ET)
Example 4: 225 wide tire, stock rim, no spacer:
outer edge=225/2 - 52,5 + 0 = 60 mm (5 mm outer compared to baseline due to 10 mm wider tire)
This estimate might be valid (in considering rubbing) if we assume that outer diameter of tire remains about same as stock. I had a look to some experiences in this forum (tire width, rim ET, stock suspension, fenders not rolled, rubs, does not rub...) and it might be somewhere close. I mean max. 15 mm outer than stock might still be ok.
What do you think, is the calculation this simple (probably not)?