The previous owner put 15" alloys (MB wheels 5X, 15x6.5. 20 lb) on my new to me '03 Protege5. What reason going smaller in wheel size and Reading specs says it had 16" wheels from the factory. How does this alter my driving performance? It's got Firestone 185/60R 15 84T all seasons on it now. I would like to give it a little more zoom zoom and optimize its potential. Any wheel/tire suggestions? Thank you

 

There may been several reasons. Perhaps he got a good deal on wheels and tires. Doesn't really matter now though.

The standard size is 195/50R16. If you look at tire size comparators, the 185/60r15 is same diameter so there's no real impact to performance or speedometer calibration. You just get a bit more sidewall. This *may* allow a bit more sidewall flex under hard cornering but I honestly doubt you could tell.

 

Pros of Smaller diameter wheels
Smaller size wheels = less rotational mass = better acceleration.
More profile (tyre thickness) = Helps your suspension Dampen road bumps
Lighter Steering

Cons
More sidewall flex when cornering hard so car feels wobbly in corners
Tyre Manufactures dont commonly make high quality tyres for small rims so good tyres may cost you a lot at this size but ive never looked cause Ive never found any

Summary
Proteges technically should only use 14inch or 17inch wheels. In between those the speedo will read incorrectly so when you think youre doing 100km/hr youll be really doing 97km/hr give or take. I tried different tyre sizes to bring the speedo back in line with 15s or 16s but it never came back until i increased diameter to 17inch. But my reference point was a 2001 1.6 Protege which was the car I was trying to setup correctly. May be different in other models because it depends if they made any changes to how the speed was calculated in those models. I just based it off their standard wheel and used that to calculate which wheel rim size I could go to without affecting the speedo. I used to think it was only the rolling diameter but width and profile also affect the speedo not just the diameter. Dont ask me why, I was using an online calculator.

https://tiresize.com/calculator/