Howdy!
I just purchased a 2009 Suburban and noticed that the spare is a 17" rim size, but the wheels that are on the vehicle are 20". If I find a matching 20" rim to use for the spare, will it fit up under where the 17" spare is now? I think it should, because, I think the 20's are a factory upgrade.

 

Easy enough to check. Measure the spare tire seating cavity and check the size of tires on the rig and see if will work. The 20's likely have a different/lower sidewall profile and likely will fit.

 

My Tahoe with factory 20's has a 17 spare. P265/70/17 . Take a look at the tire sticker inside the drivers door and it will tell you the correct spare tire size for conformation. The spare has the correct diameter to match the '20's if you get a flat. No need to mess around with swapping out the spare.

 

Yeah, I guess my question is, "Why?"

 

Probably 17 rim clears all the brake rotors so just a variance in tires sizes to match tire diameter for a one size fits all rim for production costs over a lot of vehicles. A real spare is better than the air pump and can of fix a flat they put in my '15 Malibu from the factory or a compact spare for sure.

 

I guess I should have been more specific. I know that a 17" spare is completely fine. I have one in my 09 Denali.

My question was for the OP - why replace the spare with a 20" wheel? Completely unnecessary and a waste of money. I've been driving for over 35 years. I currently have 7 cars. The last time I actually needed/used a spare was in 1995.

For the money OP would waste on the spare "upgrade," they could put the money towards something actually useful, like a tune.

 

We got our 2005 Yukon Denali in 2010, had fancy upgrade or aftermarket 20" Sacchi wheels/tires on it. The spare was a smaller stock-type wheel/tire.

We found that we had to buy a special thin-wall socket to R&R the wheels, a regular lug socket was too big of diameter. Even AAA a couple of months ago had to use OUR socket when Mrs. Cusser had a flat on the road.

Another bad thing with those fancy wheels is that the spare tire needs different/factory size lugs and a different lug wrench should the spare need to be mounted. So I don't remember if we ever had one of those factory wheels up underneath, but I doubt it - think we would've just put a damaged tire in the rear compartment to go to the tire shop.