Rolling radius of 2 same diameter wheels with same tyres fitted to each axle will always be the same?
He doesn't want stretch so will be having wider tyres on the rear, as the side wall of the tyre is a percentage of the width of it, the rolling radius will be marginally different front - rear.
For example the difference in rolling radius between 215/40/18 and 205/40/18 is 0.7mph at 60mph
