Whats the answer, who knows?

[Meldrew2]

I have 2 C320 cdis one with 17" wheels and the with 18" wheels. The 17" car accelerates quicker than the 18" car and is faster overall. I can only put it down to wheels.

It would be an interesting experiment to swap wheels to see if the same difference remains or if the difference is due to some other factor, such as engine wear or a dead body in the boot of one car.