Confused, I rode my 17 SD CC KR with 8' bed and 18" Michelin vs a ride in same 17 truck and 20" rubber, I felt a difference (improved) handling in 20" rubber vs 18". Appreciate all input and advice... JB

 

they should both be a 34" tire +/- or at least within .8" of each other. That being said the 20" wheel would have a stiffer sidewall resulting in a more responsive feel to the driver. If the 18" wheels are not properly inflated you may have experiencing a little "give" in the sidewall making it feel a little mushy and top heavy.

I was told sometimes dealerships under inflate the tires a little to give a softer ride when people test drive.

that is my guess, let me emphasize the key word in that statement "guess"

cheers