Hey guys i have been reading alot of the wheel post here and it seems most everyone here likes 20s. my question is do they throw the speedo off any and does the ride quality change? i have a 04 545i with sportpgk and i change the tire to goodyear f1s all seasons. all post welcome!thks

 

Speedo won't be affected if the correct sized 20" tires, with the lower profile sidewalls, are installed. It should keep the rolling diameter consistent.

As for the ride, it usually gets more harsh as you go up in wheel size with the corresponding drop in sidewall height.

 

with 20s though, most have gone (also what we recommend) with the sidewall sizes that are recommended for 19s to have a thicker sidewall, but it will be very necessary and imperative to roll/cut fenders.

 

+1...as long as you get the correct (lower) sidewall TIRE you will still have the same overall diameter as stock wheels if you run 20's. Check out this calculator: http://www.miata.net/garage/tirecalc.html

Input the size of your stock tires on the left side and it will give you overall diameter...then punch in the size(s) you are interested in on the right side, you want 20" tires that are as close as possible in diameter to your stock tires.

 

ride quality will change big time!!!GL

 

get the right size tyres and you be OK
The ride will be ruffer with 19" 20" but I have Nitrogen (N2) in side the tyres so the ride is much better.