All other things being equal, wider tires get more bite in a lateral direction. The contact patch shape has more aligned molecules interlocking with the pavement in that direction. For better forward grip the narrower tire has more aligned molecules in that direction. If that isn't intuitive, try comparing the effort to push an eraser width-wise and length-wise along a desk top.

The wider drive tire on dragsters is needed to handle the massive torque and aerodynamic loading from wings (when equipped) at an ultra low air pressure . The high load and low pressure increases the SIZE of the patch putting more molecules into play. Since plus size street tires require more psi instead of less, the same benefit cannot be derived from wider tires on a road going MINI.

 

Fantastic reply hsautocrosser! wow!
So all things being said it doesn't make much of difference at all. the larger diameter will reduce the acceleration.
So do you think changing the bushings can make a difference as someone suggested previously?

 

You're welcome.

Firmer bushings can improve handling by reducing play in the suspension. Might help with acceleration as well although I have no experience with doing it for that purpose. I suspect your only significant change will come from stickier tires (that wear out faster.)

 

the answer is simple

look at a "race car" for Indi in the 50's

then look at one today

did the tire get taller

or wider

 

My 245 Star Specs get real slippery when the temps fall below 60*