I imagine if front and back wheels were same height and 130mm wide when cornering the front and rear tires would be riding on same profile, where as typicality thinner front tire during cornering is on the side while wife rear is more to the flat of the tire. Uneven tires would seem to put unnecessary strain on the frame for style points or I could be wrong
A biker babe sitting on the rear half of the seat would need larger tires on the rear. Larger tires better traction. Narrow tires narrow axle which might require the engine to be positioned off center to allow the drive and driven sprockets or belt pulleys to be in alignment.
The front tire is the control guide, the rear is the drive guide. Having a larger/same size front as the rear makes CONTROL harder. Go design your bike, build it and let us know what hospital ward you are in, some wards screen your mail.
Depends on ACTUAL motorcycle. BMW/2 had 3.50x18 front and rear, Harley FL,FLH FLE all had 5.10x16 to start from factory or option 4x18 like WL, EL. Some of crotch rockets have fat front tire, smaller diameter rims but about same width as back tire. Lighter, thinner smaller width tire is lighter, more responsive to bumps, handles better in some situations.
