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Fast & Dirty
2009 Forester XT 4 speed auto
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4,039 Posts
Discussion Starter #1
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.
 

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Premium Member
2015 Highlander AWD XLE 6AT
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4,255 Posts
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
 

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