Having different size wheels makes no difference to the diff matey.
The diff allows the wheels on the same axle to spin at different speeds... for example like when taking a left hand bend the passenger wheel will be travelling at slightly different speed to the outer wheel because the outer wheel has more distance to travel.
So fitting a smaller wheel to one size of the axle makes no different to the diff.... it will do exactly as it was designed to do.
Hope that makes sense?
