17" spare for 18" tires

Should be OK. Most compact spires are smaller then the tire on the vehicle. I sure wouldn't run it any longer then I had to though.

Don

on edit: not sure it would be a good idea if your towing however. I think I would order five rims and five tires. The other thing is will the 18" spare fit into the space that the 17" came from. I bet it won't.

Hadn't thought of that I'll have to look

Yes, our truck has a 17" spare and 20" OEM on the ground. Book says to not use 4x4 if spare is on the ground, but otherwise it is OK to run the spare in any position.

I wouldn't do that. Even in 2 WD, there's still a differential between the wheels on each axle, and the difference in rolling diameter will have that differential working like mad. It is going to get hot. And while you could probably get away with it for 5 or 10 miles at city-street speeds, take it much farther, or up on the freeway, and you'll be risking serious damage.

I know. I had a differential explode in flames on me once. So, been there, done that, ended up costing over $1500 to fix. And that was 15 years ago.

Texan, is your truck a dodge 4wd?

Nope, a Chevrolet 4x4 with the NHT package and GM will pay any warranty if it is damaged by using the different size spare, as they approve it.

Maybe I should check my owners manual, never thought of that!!

You posted the same question twice. Why???

http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/27499561.cfm

kohana wrote:
Maybe I should check my owners manual, never thought of that!!

If Dodge offers optional sizes, then it will be in the book. GM offered 17", 18" and 20" wheels on our model.

How big is the actual outside diameter of the two different sizes? If it's no more than the difference between the stock tire and the stock spare then I would run it for a short distance.
Running a big difference will damage the rear end no matter what the manual says. The spider gears will be spinning like mad all the time and they are not designed to do that.