Re: Alfa 159 with 20' wheels
acceleration is directly proportional to the rolling circumference of the tyre (not the wheel). a bigger circumference means you are effectively making your final gear ratio longer so your acceleration suffers. the real world difference depends on many things, especially the torque the engine produces. unless you have a turbo diesel you need to consider the effect his will have, i've seen the difference it makes on many cars, some suffer very badly and even lose top speed as well as acceleration (15-20mph loss according to GPS if you stick 17s on a 1.2corsa)
the overall weight of the wheel & tyre will affect acceleration as well, more weight means reduced efficiency. generally the alloy weights more than rubber, so bigger wheels with lower profile tyres will weight more overall.
a wider tyre will have increased rolling friction, this will waste petrol and reduce the speed at which aquaplaning occurs. the vehicle weight is an important factor, a heavier car can have wider tyres.
this is why i always stick to the smallest wheels i can live with, in the case of my 156 that is 16" with 205/50/16 tyres. i would prefer 205/45/16 but it would sit too low, i already have problems with speed bumps. i would rather drink my own wee than stick 18s on. if i had 17s it would have to be on 205/40/17 tyres, but they are too firm so it upsets your handling, especially over rough sufaces when cornering at speed.
looks are bottom of my list, acceleration and handling are top. but as it turns out i prefer a smaller wheel for looks as well, the maxpower look doesnt really do much for me. wheels should be the right size for the car. huge wheels make the car look too high even with lowering springs.
Last edited by jug; 06-11-07 at 13:45.