Spare on smaller rim

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Dec 15, 2014
Atlanta, GA
My brain hurts after thinking and searching on this one. Having owned many full time 4x4 vehicles, I know my spare needs to be the same or very similar size to the others in the event it is needed.

What I can't seem to wrap my brain around is the rim size. My truck came with 18" rims and the spare is a stock 16". All tire size and diameters being equal, would the rim difference cause damage in an emergency situation? How about tire width?

Thanks for answers to dumb questions :)

All that matters is the height (or circumference) of the tire. 35 on a 15" rim will be fine with a 35 on a 17" rim.

You can't directly match width and aspect ratio though. For example (just made up sizes) 285 70 15 would be 2 inches shorter than a 285 70 17
got it, thanks. If I can get the diameter within an inch would it be ok for an emergency scenario? Just need something to limp to the nearest station. I would think that low speeds and less than 20-25 miles would be ok. Thoughts? Thanks!

It will be fine as long as no differentials are locked.
rim size does not matter its the circumference of the tire should be the same other wise one side of the axel is spinning at different speed. if your "locked diff" you will cause major probs !! if not locked i dont see it being an issue.
As others have said, the tire diameter(and more accurately, the dynamic rolling radius)is most important. The current production Tundra is only equipped with 18" spare wheel, but the regular ground wheels can be 18" or 20". For passenger cars, the spare is a 16" temp-use wheel/tire, but the ground wheel size varies up to 18." The tire size is adjusted to match up correctly. Keeping the rim size within 2" is a decent rule-of-thumb for being able to find appropriate sized tires.

In regards to tire width and even the wheel inset, this isn't really so important as long as it fits on the vehicle without interference. The difference in tire width might make for a difference in feeling of right and left turns. If the inset is mismatched, you might notice some odd tracking and feel like the alignment is off, but it is only temporary until you get it replaced, so no big deal.
You possibly can cause issues with the viscous coupling in the center diff. These are AWD not selectable 4wd.
Do a search on here about tire size differences and you will find threads about some running them and some not. I am of the run the exact same outside diameter of the tire (circumference) on all 4 corners (not +/- 1") based upon my own personal (bad) experiences in an UNLOCKED differential.

I buy tires in sets of 5 and work the spare into the rotation so I always have a spare that is in the same diameter, size, and tread wear as the ones on the truck. Plus I get 25% MORE total mileage out of my set of tires!

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