I think my translation may be different then yours. The narrower the tire is the less the overall resistence. This is mostly because of wind drag. A softer tire be it compound and or air preasure will deflect less there for lowering "rolling resistence". In the aplication we are discussing, the trailer itself should already block most wind. Now, I am no scientist (ditch digger by trade) but it seems to me for a trailer I would want a nice fat tire to roll smooth and eat up the bumps. I have not pulled one yet but will be this summer and I guess I will put my theory to pavement then I will know for sure. Although i am certain that we are discussing very negligable amounts of resistence maybe its better left for lab discussions