Dumb question probably

[Phil3333]

Is there any reason that your spare needs to be the same size as your running tires, in other words why couldn't you just use a 37" spare if you were running 40" tires

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[DailyMoparGuy]

You need to have the same diameter tire or else you’ll bind up the axle/differential.

 

[kooltoys]

im not a machanic, so I'm sure it way more technical.. Jeeps a straight axle vehicle, its not good for 1 side of the axles to turn at a different rate then the opposite side of the axle

 

[Phil3333]

Why, donut spares don't bind up the diff

 

[DailyMoparGuy]

Why, donut spares don't bind up the diff

Donut tires are typically the same diameter. Different widths for sure though. Also if it was an emergency and all you have is a smaller tire, be sure to put it on the non-driving axle.

 

[Phil3333]

Oh I always felt like they were smaller,oh well I figured it was a dumb idea

 

[DailyMoparGuy]

Oh I always felt like they were smaller,oh well I figured it was a dumb idea

No such thing as a dumb question!

 

[texanjeeper]

I've never seen a donut tire that was the same diameter as the regular tire. They're all much smaller than your regular tire, at least the ones I've seen are.

 

[DailyMoparGuy]

I've never seen a donut tire that was the same diameter as the regular tire. They're all much smaller than your regular tire, at least the ones I've seen are.

I should’ve said it that way too “at least the ones I’ve seen...”

I guess some manufacturers could go smaller donut spare and instruct the owner to only use on non-drive axle.

 

[CerOf]

If you’re close In size(height) wise, you’re fine. This isn’t an all wheel drive vehicle. The axles aren’t locked side to side.

If I lose one of my 35s, I’ll roll with the stock 33. Fully inflated 33, and can air down the other side of the axle’s tire to high 20s to get prettyclose to same diameter, and head to the tire store fir permanent fix.

 

[Kevin_D]

If used as an emergency spare, it won’t hurt anything. Most, “Space-saver spares,” are smaller.
Although as pointed out, don’t try it on an AWD vehicle.

Kevin

 

[BlamBlamTheMonkey]

I've never seen a donut tire that was the same diameter as the regular tire. They're all much smaller than your regular tire, at least the ones I've seen are.

IIRC, when there is a donut that is a smaller diameter it should only be on 2WD vehicles, and the owner's manual will point out that if you get a flat on the drive axle, you move a regular sized wheel from the non-drive and put the donut on the now-empty spot

 

[Planerdude]

Is there any reason that your spare needs to be the same size as your running tires, in other words why couldn't you just use a 37" spare if you were running 40" tires

Pretty sure as long as your axle is not locked, it should be ok, the diff is designed for both tires to turn at different rates, as in cornering, the outside wheel is traveling at a greater rate than the inside wheelbut im no engineer

 

[Phil3333]

That was exactly my logic

 

[ShadowsPapa]

I've never seen a donut tire that was the same diameter as the regular tire. They're all much smaller than your regular tire, at least the ones I've seen are.

They call them compact spares for a reason. I've got a couple of them here - much smaller than the tires on the car.

The only time there's any problem is with locked axles or limited slip axles. In that case, put the spare where there's no limited slip function (depends on the type of limited slip setup of course)

Planerdude may not be an engineer - but he's sure got the gist of it.

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