Spare Tire Size Question

[RamVenture]

My 2012 2500 4x4 SLT has Ram R18 rims. I thought they were original to the truck, but looking at the door sticker it was actually shipped with R17 rims. Current truck tires are GB KO2 275/70 R18 (33.2" diameter). My spare tire (original) is 265/70 R17 (31.6" diameter). I'm thinking I should probably replace the 10yr old tire. My question is, will running different size tires damage any axle components? Most cars don't have full size tire spares so didn't think it would, but just finished replacing rear brake pads and noticed when I turn one wheel the other wheel turned in the opposite direction. I guessing this is a feature of a locking differential (this is my first truck so new to some of this stuff). I figured it would be okay to put the spare on a front tire so long as I'm not running in 4x4 mode. Didn't really want to spend money on spare tire just yet but now wondering if I'm being foolish. If the different tire size won't damage any parts, then i'll keep the steel rim and get a spare tire with higher side wall (275/70 R17). Does anyone know if a 275/70 R18 wheel set will fit under the truck in spare location? Don't want to carry the spare in the truck bed. Thanks guys.

 

[bcbender]

The only thing that really doesn't like different tire sizes are the limited slip rear differentials. It sounds like you may not have that, but either way, I would not run two different size tires on the rear axle as it still will work the side gears constantly with power being transmitted through them. I had the same size tires and rims on my 04 and the OEM 17" spare, I only used it once (long story) and at that time I put it on the front to get me home since no harm there just back driving the front diff a little but all the 4th gens are disconnected so again no problem with the mismatch for emergencies Just have to move the front to the back. I cannot comment on your truck for the spare fitting, but on my 04 with the MAG HYTEC pan, it was a no go. have to put one up there and see if it clears the exhaust and the rear pan.. maybe an OEM pan might be OK.

EDIT ( on long cross country trips, I threw a spare K02 I had in the bed incase I needed it where I could not source a new one, no rim, just the tire)

 

[AEdelheit]

I have an 06 but believe up to the 2014 2500 change they all fit spares similarly, run a 35" spare in the stock location with an aftermarket cover. The trick it to use a ratchet strap to the tow hitch to keep the spare pulled to the back of the frame otherwise it will hit the rear diff cover on compression.

 

[RamVenture]

Thanks for the information. My differential is not limited slip. Sounds like I should get a matching rim and tire. Didn’t notice spare tire close to differential cover but will take a closer look. Looks like I got about 1in space around the spare tire and frame. It will be close.

 

[AH64ID]

Where are you located? I have an extra 275/70R18 OEM spare.

 

[RamVenture]

Where are you located? I have an extra 275/70R18 OEM spare.

Thank you for the offer. I’m located in Casa Grande AZ (in between Phoenix and Tucson). Is this close to you?

 

[AH64ID]

Thank you for the offer. I’m located in Casa Grande AZ (in between Phoenix and Tucson). Is this close to you?

I’m in Boise, ID. It’s a long haul to Casa Grande, I’ve done the drive to Tucson a few times.

 

[RamVenture]

Yes, that would be a long drive. No worries. We were up in your area last June.