I have a problem I’m trying to solve and can’t see to.

When I ride in doors on the trainer ( same bike set up ) my hamstrings get really tight when I ride. I can do about an hour to an hour and half before I need to stop. I’m riding at a low FTP pace. Just some endurance stuff. When I ride out doors I don’t get that same tightness. It’s better on the trainer if I set straight up with out my hands on the bars.

I’ve checked the set up on the trainer ( different bike ) about 5 times to ensure same set up on road bike but I’m sure from this post I’ll check 3 more times which can’t hurt.

Could it be anything else ? It’s actually more pronounced at endurance pace than say doing intervals but those I tend to do only an hour workout so it could just be a time thing.

Thanks