Upgrading to 18" truck tires

If you have a limited slip rear end, it is an issue. And without locking/unlocking front hubs, I would not want to drive very far! Chris

I kept my 17" spare. As said, it isn't good to run mismatched diameters with an LS differential. It will wear out the clutches, and possibly overheat the gear oil.

I figure worst case is having a flat on the rear, and having to move wheels around so that the spare ends up on the front. A hassle, but not a deal breaker to me.

I drove about 500 miles home on that 17" spare, and no issue. It was on the front.

Why can't you just get a new tire on your spare to match the diameter of the 18-inchers. The 17" wheel is not the problem, it is ultimately the sizing difference of tire's diameter. As long as they all stand the same height it would not be a problem regardless of where the "spare" was placed.

clotus wrote:
Why can't you just get a new tire on your spare to match the diameter of the 18-inchers. The 17" wheel is not the problem, it is ultimately the sizing difference of tire's diameter. As long as they all stand the same height it would not be a problem regardless of where the "spare" was placed.

Way too logical..:B

BTW - (OP) you can compare tire sizes (diameter) in inches on various Internet sites.

Pick up a used 17" tire in the diameter you need to match the diameter of your new 18s"..;)

.

Coach-man wrote:
Actually, "truck" tires are 19.5", not 18". Rickson tires will sell you the wheels, and a variety of 19.5 truck tires, as well as programing your computer to compansate for the larger tires. They claim 8 plus years on a set of tires!

I did the switch from 18" to 19'5" for my F350 SRW. Rickson Truck Wheel in Hunt Valley Maryland supplied me with 5 wheels and I installed the Michelin 245 70R XZE 19.5" tires - LR H. The diameter was so close to my 18" that it hardly effected my speedometer at all.
The ride is not bad and it really gives you a tire and wheel combination that will last. My tires and wheels are two years old and they look brand new.

bigdon68
Maryland

clotus wrote:
Why can't you just get a new tire on your spare to match the diameter of the 18-inchers. The 17" wheel is not the problem, it is ultimately the sizing difference of tire's diameter. As long as they all stand the same height it would not be a problem regardless of where the "spare" was placed.

I think the point is to use an existing spare, and avoid purchasing a new tire that may never see any use. Same reason he wouldn't buy a 5th 18" wheel and just let it hang under the truck.

But if you wanted to do that, a 285/70-17" would be in the diameter ballpark.

Bayley wrote:
UPDATE: Well I found some new take off 275/70/18E's from a 2015 Ram 2500 for a heck of a price on Craig's list.
I'm going to make the change but I now have another question:
A spare doesn't come in the deal so is it alright to use my current 17" spare? I called a tire dealer and they said it wouldn't be an issue if I didn't run it in 4 wheel drive.
anyone have any experience with this?
Thanks again for the help!!

Any truck with limited slip axles require the same diameter tires on the same axle. Two different diameter tires will damage the limited slip. If you were going to use a smaller spare, you'd have to move one of the front tires to the rear and mount the spare on the front. And you couldn't use the front wheel drive.