Tire/wheel advice: 305/20 vs 315/21 traction?

[415hanz]

My M6 is on stock wheels w 305/30/20 Michelin PS4s and still have some traction issues w 2nd gear and such but generally pleased. I found some wheels I like but they are 21s… can anyone speak on the difference between 315 tires on 21in wheel compared to 305 width on 20inch in terms of traction and will the ride be significantly worse, already feels rough as is.

Any thing else I should consider when going up in wheel size?

[SCD-1983]

Originally Posted by 415hanz

My M6 is on stock wheels w 305/30/20 Michelin PS4s and still have some traction issues w 2nd gear and such but generally pleased. I found some wheels I like but they are 21s… can anyone speak on the difference between 315 tires on 21in wheel compared to 305 width on 20inch in terms of traction and will the ride be significantly worse, already feels rough as is.

Any thing else I should consider when going up in wheel size?

I am currently running 11x21" wheels in the rear, with 305/25R21. I'm generally satisfied with traction, but ride comfort suffers. And the tire cross section decrease from 30 to 25 will make your rims more vulnerable to potholes.
I believe the 315 width will increase your traction, but the ride comfort is a concern, IMHO.
And I'm in my 5th set of wheels, OEM 20" 343 and 601, then 3x 21".