Wheels tires for street?

[EldRick]

When changing wheel width from a wider wheel to a narrower one, which way does the offset change?

Specifically, I'd like to go from the stock 10x19" wheels on the rear of my 1M, down to a 9.5x18", still using the stock 265-width tires.

I want to avoid stretching the tire on the rim, so the rim should wind up 6mm closer to center than stock.

Do I go greater offset than the stock ET23, or less?

[Eyeman]

I'm a tad confused by your question but here goes an answer. The offset of the wheel relates to how the wheel stick in or out. The width, etc are different numbers. So if you want your new wheels to center where the prior ones did you want the same offset. It'll be a narrower wheel but still centered the same as before so it will give you more room to run fuller width tires for that rim. If you buy an et17, it would sit the same distance as your current wheel from the outer fender but more likely to rub with full width tires. If you are worried about rubbing the outer fender, buy a higher +et such as 23, etc.

[EldRick]

That answers my question perfectly - same center = same offset. Thanks!

[EldRick]

After concluding that my original PS2s are now worn (1/8" left)and somewhat hardened (8K miles and five years), I did a good bit of research. My original thought in this thread was just to get a bit more sidewall bulge, to better protect the rims from curbs.
However, my goal has changed a bit - here in the Pacific Northwest, and in Oregon in particular, both country roads and city streets are in miserable condition, and have very rough surfaces with low-quality repairs, i.e. lots of road noise and small bumps.
So I've ordered a set of 18x9/18x10" wheels (EC-7s from Apex) and stock width PSSs (245/265x40). This theoretically gives the stock ride height within a mm, but 1/2" more sidewall Height.
I expect better grip in local road conditions, a bit softer ride, and less tire noise. I'm also expecting that new rubber will be a good bit grippier than the originals at this point with better ability to stay on the road (lower unsprung mass by a couple of lbs/corner and better ability to stay in contact with irregular pavement).

[EldRick]

Got the 18s installed today. The tires are still a little slippery with only about 50 miles to wipe off the mold wax, but the car is quite a bit quieter on rough road surfaces, moderates the jolts from patches, has less tendency to try to follow ruts on the highway, and I'm no longer terrified by potholes. Oh yeah, and the grip on our usual bumpy surfaces seems to be just as well controlled, even with fresh tread.

Net is that the car feels much more civilized, like a BMW, and less like a Mini Cooper S.

BTW, I measured the height from garage floor to bottom of rim: with stock 19" and PS2s, it was 55mm front, and 67mm rear. With 18" and PSSs, it's now 67mm F and 78mm R. IMHO, 19" wheels simply do not put enough air between rim and road for real roads, at least not roads and streets in the PNW.