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Max spare tire size


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It would be close. I have the stock Michelin 275/70-18 tires and I’ve had my spare out to do some wiring.  As I was restowing it, I remember I was able to shift it around about an inch, meaning there seemed to be room for about an inch more of tire diameter. I don’t remember what was limiting the movement. 

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Yes, the tire calculators say there is about 3/4 inch difference in diameter between the standard 18 and optional 20 inch tires. Your new tire size is maybe another 3/4 bigger. 
 

If you unlock your spare and crank it down just to the point where you can shift it around, you’ll be able to move it and judge how much additional room there is. 

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  • 4 weeks later...

a little off the OP, but I did this calculation last night of my 18 spare vs 20 tires and the 3/4 difference.   That sure seems like a lot of difference for the rear differential.  Stunning they would do this on purpose.

 

I think a full size spare will fit.  Going to try it when I rotate next week.

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17 hours ago, Hagar68 said:

a little off the OP, but I did this calculation last night of my 18 spare vs 20 tires and the 3/4 difference.   That sure seems like a lot of difference for the rear differential.  Stunning they would do this on purpose.

 

I think a full size spare will fit.  Going to try it when I rotate next week.

I think previous discussions concluded that the speedometer calculations were compensated for the 18s versus 20 inch optional wheels/tires difference depending in which option you have. My speedometer (really odometer) seemed dead on based on one of those surveyed 5 mile check stretches we have in WA. I have the standards 18s on the SLT. 
 

As you say, the differential is the same for both options, so the wheel/tire option does make a slight difference in miles per engine rotation. 

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20 years ago I considered replacing my spare with a matching tire and wheel for rotation. Discount tire recommended against that. I realized at that time I haven’t had a flat ever. I even worked off road. I always bought better tires for the application, the best I can find. I have had slow leaks never a blow out. At the risk of jinxing myself, I never had a flat. I do carry fix a flat on trips. 

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47 minutes ago, KARNUT said:

20 years ago I considered replacing my spare with a matching tire and wheel for rotation. Discount tire recommended against that. I realized at that time I haven’t had a flat ever. I even worked off road. I always bought better tires for the application, the best I can find. I have had slow leaks never a blow out. At the risk of jinxing myself, I never had a flat. I do carry fix a flat on trips. 

I agree for normal road driving. My experience is similar. The last blowout I had (and the last time I had to use a spare) was literally about 1986. The OP’s tire size is close enough I wouldn’t worry about it for a short diversion to get service. 

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  • 3 months later...
  • 1 month later...

I know this thread is a few months old, but someone may benefit from the answer in the future.
 

I finally remembered to look at the spare clearance when I crawled under to disconnect my camper camera.  I have the SLT SRW stock michelin 275/70-18 spare, and it has about an inch clearance to the exhaust heat shield, and just under an inch clearance on the opposite side from where it would touch a frame cross member that angles down. So the 3/4 inch larger diameter full size spare for the optional 20 inch wheels and tires should fit with enough clearance that the tire can still be 1/2” away from the heat shield. 

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