Tire sizing.

DaveB

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My 2010 GMC 1/2 ton had 18" wheels and the spare was a 16" rim and tire from the factory. I don't remember the numbers, but the circumference and diameters were the same. Cheapest way to fix would be to go buy a used 275-75-18 to put on the spare rim. Close enough.
 

MK4TDI

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My 2010 GMC 1/2 ton had 18" wheels and the spare was a 16" rim and tire from the factory. I don't remember the numbers, but the circumference and diameters were the same. Cheapest way to fix would be to go buy a used 275-75-18 to put on the spare rim. Close enough.
I don't think they make that tire size to be honest, and I know 275 80 17 are way to expensive.
 

JMCX

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We're talking about a spare here. In the off chance he has to use it the spider gears aren't going to care about a 3% difference. I'm pretty sure he drives a newish Ford which should have a selectable locker. Matching the circumference with a limited slip does matter though.
 

lilduke

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We're talking about a spare here. In the off chance he has to use it the spider gears aren't going to care about a 3% difference. I'm pretty sure he drives a newish Ford which should have a selectable locker. Matching the circumference with a limited slip does matter though.


Having replaced them before id disagree.

I found out the hard way it doesnt take much to wreck them.

But do you


1711563445778.png
 
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MP Kid

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We're talking about a spare here. In the off chance he has to use it the spider gears aren't going to care about a 3% difference. I'm pretty sure he drives a newish Ford which should have a selectable locker. Matching the circumference with a limited slip does matter though.
Bought a SD...
Drive a Ford...
I'm not sure how reliable your information is anymore....:ROFLMAO:
 

MK4TDI

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275 60 20 and the 275 70 18 are very similar with the 18" tire having 13mm more circumference...
 

ferniesnow

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Thanks for all the information (good and not so good). The tire sizes in the original post are correct; spare is 275/65R18 and the wheels/tires on the truck are 275/65/R20.
I am going to go on the side of caution and get a 20” wheel with a 275/65R20 tire for the spare.
 

fj40

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Having replaced them before id disagree.

I found out the hard way it doesnt take much to wreck them.

But do you


View attachment 281446
Was it an open diff and how long did you run it for.
Curious as my spare is 32" run 34" in the summer and 30" in the winter never had a flat just figure if I took it easy should be ok.
 

lilduke

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Was it an open diff and how long did you run it for.
Curious as my spare is 32" run 34" in the summer and 30" in the winter never had a flat just figure if I took it easy should be ok.


I wrecked an open diff spining in the mud on a 98 chev 1500.

You might be ok, i just know they dont like spining. They are meant for taking corners.


Id run it it if i had to, but i know for a fact that a spare tire is cheaper than a diff.

So do what ever you figure. Haha
 

JMCX

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I just looked at my 22 F350. 275-65/20s on the ground. 275-70/18 spare. 20-40 extra revolutions over a mile isn't going to hurt anything. Half the vehicles around you have a space-saver spare. Spinning one wheel excessively in the mud/snow or giant peg-leg burnouts wreck spider gears.
1000017240.jpg
 

ferniesnow

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I just looked at my 22 F350. 275-65/20s on the ground. 275-70/18 spare. 20-40 extra revolutions over a mile isn't going to hurt anything. Half the vehicles around you have a space-saver spare. Spinning one wheel excessively in the mud/snow or giant peg-leg burnouts wreck spider gears.
View attachment 281465
Interesting.
If Ford is putting that on the truck, then it must be okay and not an issue.
I do have enough room for a 275/65R20 on the spare tire holder so a 275/70R18 will also fit in the spare tire holder.
 

X-it

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The sight of those little donut spare tires rolling down the road always brings a smile to my face. And then there are those side-by-sides (sxs) and quads with their tires stretched out for reasons only known to them. You can actually see the difference in size. Instead of measuring these stretched tires, some folks just rely on a pressure gauge. It’s a curious choice, considering the strain it might put on the differentials, but it seems no one really pays much attention to that. And quads and sxs are not limited slip at least on the rear.
 
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