Originally Posted by 12JKR
Smaller rim might be better off road because there may be more of a contact patch when aired down. Larger rim will be better on road because there is less sidewall (less roll). Never compared first hand though.
I don't think the contact patch increase would even be worth the effort, but the price difference between 33" tires for 17's, and 33" tires for 15's is more than enough to cover the cost of rims in most cases (less rubber, higher price tag. genius). 15's are cheaper long term, especially if you run M/T's or similar that don't wear all that well on pavement.
also, if you run 15's, you get a nice bonus of being able to order your tires in plain 'ol english. 33X12.5 is a lot easier than 792\ 14 - 46% X .9 squared to the third power.