ORIGINAL: mot250
It is not the size of the wheel that matters, it's the overall diameter of the tire, which I heard is only .6 of an inch difference between the 18's and 20's, therefore neglegible by all counts, expecially as a temporary spare.
The only way wheel size would matter would be if the brake calipers were different sizes but since both wheels are availabel on the R/Ts that is not an issue either.
Thanks for your help. In this day and age and with auto manufacturers cutting back....I hope they throw in a jack with the spare. Nothing would surprise me anymore.