Spare tires and size matching

[buck91]

How closely should a full size spare match the OD of the rest of the tires on a 4WD with clutch type LSD on the rear axle? For example the tires I have now are rated at 33” OD and will be replaced with the same 285/70/17 but rated at 32.7”. 635 revs per mile vs 632. If I mount a used tire on the spare this seems completely interchangeable…. But how far can we take it. If I go with 315/70/17 for a rated OD of 34.4” and 605 revs/mile would that same used tire function adequately as a full size spare or would it be too far offa cause issues? The goal is to be able to run the full size without concern if the need arises.

 

[SwampSurvivor]

With a clutch type LSD I'd rotate to keep the tread as close as possible then throw the spare on the front if you need and swap a good front to the rear.

 

[UG_Passat]

How closely should a full size spare match the OD of the rest of the tires on a 4WD with clutch type LSD on the rear axle? For example the tires I have now are rated at 33” OD and will be replaced with the same 285/70/17 but rated at 32.7”. 635 revs per mile vs 632. If I mount a used tire on the spare this seems completely interchangeable…. But how far can we take it. If I go with 315/70/17 for a rated OD of 34.4” and 605 revs/mile would that same used tire function adequately as a full size spare or would it be too far offa cause issues? The goal is to be able to run the full size without concern if the need arises.

Why not purchase a wheel/tire set that is the same size as the other 4 and mount that in the spare tire carrier?

Unless.. you can't, or it hangs down too low.

 

[CapriRacer]

This is a question you should be asking the vehicle manufacturer. I'll bet, though, you get "all 4 have to be the same". So just take the opinions expressed here as that. - opinions!