There has to be some difference between a Road 5 and a Road 5 GT (or a PR4 and a PR4GT) or else why make two different lines of tires and why recommend one for a particular motorcycle over the other?
Of course there is a difference. But there is also a difference between what Michelin does between R5 and R5GT and what Bridgestone does between T31 and T31 GT. By golly if a fat pig FJR must have "GT" then why is there no standard for what this is?
The load and speed ratings are the same 58W and 73W. So there is no safety issue.
You make a GT variant
of a tire so as to reuse all the marketing for the named product. Otherwise you have to explain why one needs a GT5 instead of a Road 5. Consumer expects different tread patterns so you have to go do that too. Or you make a GT variant of an R5, reuse the tread, reuse the marketing.
Why recommend one for a particular motorcycle over the other? Because if you offer Dodge and Plymouth you won't sell twice as many cars but you will sell more than if just Dodge or Plymouth. You will sell more cars if you offer more colors. Rudimentary marketing teaches to never let consumer think two products only differ in flavor or color unless it is only flavor or color.
You make a stiffer tire because some people like a stiffer tire not because "heavy sport tourer requires
". But you don't say "you may like this better than the other", you authoritatively weakly state, "This is the tire we recommend
for heavy sport tourers."
The difference between an R5 and a PR4 is much greater than the difference between an R5 and R5GT or PR4 and PR4GT. So why is this difference tolerated? Michelin authoritatively (weakly) states only the R5GT is the tire recommended
for the FJR. But the PR4GT used to be that tire.
It really doesn't matter, what the name is. They could call it a Michelin Striped Ape, and if Michelin said for your 670 pound (1050 pounds 2 up with luggage) 145 hp sport-tourer ridden under normal conditions for this machine we recommend the Michelin Striped Ape, that's what I would be running right now. It just happens Michelin calls it a GT.
You missed the point. Michelin calls something a GT. Others call something different a GT but both claim GT is what you need. How can this be unless both are correct and both are wrong?
Don't forget, Brawndo Has Electrolytes. It's Got What Plants Crave.