[SubieOutlaw]

Title says it all.

I have a never used full size spare. 215/60R16 and used 225/55R17s on the FXT. I a need the spare on my road trip do I need to disable the AWD?

8/32" tread on used 225/55R17.

 

[crewzer]

I would think that you’d want to place the slightly-undersized f/s spare on the rear axle and disable the AWD, especially on an improved road.

Using specs for the Michelin MXV4, a new 215/60R16 tire turns 797 revs/mile (=79.50” circumference). A new 225/55R17 tire turns 778 revs/mile (=81.44” circumference). The 1.94” difference is considerably outside Subaru’s sort-of recommended limit of 0.25”.

The circumference on the used 225/55R17 tire drops to 80.85”, but that’s still 1.35” more than the f/s spare.

However, the tire size (i.e., 216/60R16) is nominal, and the actual physical measurements vary form one brand and model to the next. It might be worth looking up the actual tire specs and/or measuring your tires' individual circumferences to see how close they actually are.

HTH,
Jim / crewzer

 

[4x4max]

You know, I wonder if anybody's AWD system has actually ever gone bad because of uneven tires. Know of any cases?

 

[pleiad7]

You know, I wonder if anybody's AWD system has actually ever gone bad because of uneven tires. Know of any cases?

http://www.subaruforester.org/vbulletin/f72/need-expert-info-advice-38535/#post439860