I see talk about 20" tires. the ram I am looking at comes with LT285/60R20E OWL tires. are these as good for towing as 18" both are E rated, but I do see a shorter sidewall
I have 20" tires on my Super Duty and really like them and they also make the truck look really good.
On a Ram truck I think the 20" tires look too big since the truck package is smaller so the tire look out of proportion.
Having said that the OD for a 20" and 18" tire I believe are ~ the same. The 20" tires have less side wall which makes the truck handle better and the rims are heavier due to more mass.