What effect Would a donut spare have on a differential?

[Bluevitz-rs]

Originally Posted by mrpj

I agree -
But if you are some distance from the nearest place where the flat tyre can be repaired or replaced, or home for access to another jack (if owned)or some means of supporting the car and only have the vehicle jack, there really is no other option. How many of us carry around a trolley jack, axle stands etc.?
Hence, I would suspect the 50mph limit to allow for the smaller width tyre.
I have been in that situation and, if driven sensibly, it does not pose a problem.
e.g. take corners much slower, think ahead, remain a longer distance from vehicles in front etc.

You need to think outside the box a bit.

Jack up the rear and replace the rear tire with the spare. Then jack up the front and put that good tire on the front. Not too difficult