110 to 115degr F is what you would expect driving that speed.
but that RF is getting hotter ( when not in the sun that side) indicates , or higher loads on those tire , or camber angle as I described . then one sidewall gets hotter but the other colder wich makes the insided tire temp to stay reasonable but the hotter side can have such high temp that to much sulfur brigdges form in the rubber wich makes the rubber to hard. This is the kind of damage I was inplying in my former posts.
But now the old tires are off , do you still have them and where the damage only on one side?
so still possible the damage is done by to high temp.