I completely understand not having the same WHEEL, but it makes sense to have the same SIZE wheel and tire. It's extremely important on 4x4 and anything with posi traction. And I disagree completely about it being a "temporary" spare tire. Maybe on a car, but on a truck it's made to be used. On a car it really is an inferior tire, that's why they call it a donut.

 

THIS!!!!

Again I am not surprised by the replies on this board, most of the readers are new to trucks or never get them dirty.

 

On a 4x4, or a 2wd with a locker of posi, the only thing that really matters is OD (overall Diameter) and load range. ON these trucks, the spare is the same OD, just on a 17 inch wheel. The 18 and 20 inch wheels on the truck are different wheels, but the OD on the tire is the same. That is why they put the 17 inch spare under there. Also, the Load Range or Index, needs to be at or above what is on the truck in case you have a load on the truck when you need the spare. Since a 17 inch steel wheel and tire is cheaper than a 20 inch, you get the 17. Still gets the job done, just doesn't look as pretty.

 

I think my 05 has the same size rim on the spare as the stock rims as my XLT only has the 17 inch rims on it. As I had to use the old spare back in November of last year. When I had a blowout on my way to work. Only had the spare in use for about a day as the next day I put a new set o tires on the truck even though the other 3 still had plenty of tread left on them as they only had about 30k miles on them. But with one blowout didn't want to take a chance on the other 3. But who would want to use the ugly rim the spare has for a long period of time reason why I only used mine for about a day and got a new set of tires on it and the spare back under the bed.