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Spare Tire Size?

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tja1977

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I have a 2020 Ram 3500, HO-Diesel, 4X4, Crew Cab, Short Box with LT285/60R20 tires which are on 20" Rims. My question is, is it normal to have a LT275/70R18 spare tire which is on a 18" Rim? I thought 4X4's had to have the same size Tire/Rim. Thanks in Advance.


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I don't know if that is standard practice for RAM. But...
Only the external diameter really matter. Those two tire sizes have about 0.3in difference. The 20in is bigger new but a worn 20in by 3/16 measured on threads would actually be smaller than the spare.
I would not be worried. If you are, and you need to use it, just always put it in the front or move your front to the rear (if flat is on the rear). Stay in 2WD until repaired. But you still can use 4WD on loose ground and slow speed.
 
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yup the outside diameter is close enough. if you look at in tire revolutions per mile the 285/60-20 is going around 603 times in a mile and the spare is going around 609 times in a mile..not if you take curves and turns into the equation you will see they are really similar. I would not worry about running it on the rear as long as I kept speeds at a normal rate.
 
Agreed on everything you guys said. This is how I had it on my 1500. Ran over a piece of metal halfway through a roadtrip and had to put the spare on the rear. No issues whatsoever after that. Got the tire patched/reinstalled once we got there.
 
Ditto on all the above.

Tip: If you upsize tires, you really should upsize your spare to match.

I went to a 285/65R20 and 285/75R18 spare. It's closer to the 20" (+0.6%) than the factory setup was (-0.9%) but will probably be a little farther off after primary tire wear.
 
What is the largest diameter tire that will fit in the stock location?
 
Most 35's fit without issue.

Most 37's will not fit, some have reported they got one to fit if the tire/wheel is angled a bit and/or aired down.

But that's based on what I read on the internets.
 
Thank You All, for your replies. I just wanted to make sure this was a common practice by RAM, putting a different size spare on a new 4X4 truck. I also wanted to make sure, that if I do have a flat, that I do not tear something else up on the truck, until I can get it properly fixed. Thanks Again!
 
Sawboss3 said:
Mine came with 30" tires on 17" wheels.
Click to expand...

OK, I didn't realize they put 245/70R17 tires on any of these trucks anymore. However, that implies the spare tire location under your truck is different than mine and I don't think that's the case.

That said, my 285/65R20 are spec'd at 34.6" and while it fits, it's up against the heat shield.
 
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