I know that load rating is the issue with the non-GT version.
I'm no tire expert, but IIRC the
Michelin tire guy (Eric Miller) said that in the case of the PR4 that the GT version has the exact same load rating as that of the non GT version. He said that the GT version is just stiffer. He also said that the perfect tire for the Concours14 currently is the PR4GT not the PR5. He kept referring to frame stiffness, I didn't ask but I was thinking he meant suspension stiffness? He indicated that the sport bikes have the stiffest frames so they have the most compliant tires, touring bikes have less compliant tires and that dirt bikes have the least compliant tires. Again I was thinking that he really meant suspension not frame stiffness, but then that could be just me not wishing to think that my C14 frame isn't stiff? I also don't think of dirt tires as stiff but then they are usually at lower pressures so perhaps he was referring to the tires natural sidewall stiffness at zero pressure. He seemed to think that most would find that the PR5 on a touring bike would double up on the cushioning between the suspension and the compliance of the tire it would feel...squirmy?...I think he said squirmy..might have been squirrely or mushy. (all those tech terms sound the same to me
)
Regardless as to whether I heard correctly or misunderstood what he was trying to convey...The PR4: PR4GT; and the PR5 50/series rears all have the same weight speed rating 73W (270KPH @ 365 kg or 167.77 mph @ 804.6 lbs) and the 55/series rears all are all 75W (167.77 mph @ 853.18 lbs). Again I'm no tire
* expert, but I'd be surprised if the PR5GT came out with a different load rating than the others respective to aspect ratio. (in other words 73W 50/series and 75w 55/series)
*to be totally too honest, I'm not really an expert in anything yet (and considering my age it's not likely to happen, ever.), but I'm getting pretty good at looking up useless crap on the internet.