My '06 came with 20" wheels & tires. The tires were shot. So I replaced them with what I thought to be stock 18". Did I screw up, or is that indeed the stock size?

 

My 06 XLT Chrome Edition came with 18" Chrome wheels.

 

The 06 came with either 18" or 20". Mine came stock with 20" wheels.

 

my 07 has 17's (stock)

 

You don't say what model it is. Depending on model it could have come with 17, 18 or 20.

 

There is a handy little door sticker inside your drivers side door that tells ya

 

There really isn't a way to "screw up" when switching wheels. It's all personal preference. If you're worried about the speedo being off you could always get a tuner and change the tire size to accomodate the correct size tire on the truck or take it to the dealer. I would test it with a GPS before going through all of that trouble first though because you've most likely got the stock size on as it is..

 

If the 18" wheels have the tire size of 275/65 on them then its comparable to the 275/55r20's you took off of the truck.....verify by looking at the spare tire size....the 06 with 20's came with a 18" spare....

 

Yep, that is correct. Mine has the 18" spare.

 

is there such a solution as a MINI, save space spare for a F150 XL ?? Mine stock spare got stolen so I need to replace it.

 

MINI's parent company, BMW, doesn't even put spares in most of their cars and uses run-flat tires. Are you looking for a "donut" spare? Not sure what you're asking. MINIs have ridiculously small spare tires IIRC.

 

Go to a junkyard and get a wheel & tire... They might even have your spare!