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Originally Posted by LarThaL
1. The wheel widths have a significant impact on the width of the actual contact patch. A stretched tire will allow for maximum contact patch, however too stretched will upset the tires ability to properly handle lateral loads.
2. Too narrow a wheel obviously causing bowing resulting in a reduced contact patch.
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Agreed. However the 220M wheel widths still are within the tire manufacturer's recommended rim widths for 255/275. Further, the slight 12/7mm increase in tire width does not alter the shape of the contact patch that much.
Quote:
Originally Posted by LarThaL
3. Tire weight is more important with the front tires than the rear. The fronts are involved in steering and take the bigger initial hit over bumps, etc. Hence you will feel the extra rotaional mass more with the fronts than the rear. That's not to say the rear weight is not a factor at all, just not as much as the fronts.
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I need to point out that greater tire weight has two distinct detrimental impacts on performance. First, increasing unsprung weight reduces the suspension responsiveness since there is more mass to move up and down to react to road imperfections; which has a negative impact on handling. Second, rotational inertia increases the energy required to accelerate or decelerate the rotation of the wheel; which has a negative impact on acceleration and braking.
I cannot really comment on the fact that unsprung weight has less impact in the rear, I am not enough of an expert in suspension design. However, increasing rotational inertia front or rear has the same detrimental impact on acceleration and braking.
Quote:
Originally Posted by LarThaL
4. 245/265 is really optimal on the 8.5/9.5 set-up that the M3 comes with. Honestly I am surprised they didn't move to a 255/275 set-up with the ZCP package. The extra 0.5" wheel width makes the 359 wheels perfectly suited to take 255/275. At stock offset, there is also no rubbing with 255 on the ZCP wheel.
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8.5/9.5 wheel widths fall pretty much in the middle of Michelin rim width recommendation for the 245/265. Although I actually prefer the 255/275 setup on my 220Ms for the additional grip it provides. It is a question of personal choice I guess. I cannot directly compare the two setups though, because when I moved to the 255/275 setup I also switched from PS2 to PSS. However I now feel the car is better balanced with more front end bite; it has better turn-in and slightly less understeer.
I agree that BMW could have gone with a 255/275 combo for the ZCP wheels. They may have decided to stay with the 245/265 for comercial/logistics reasons
