At the risk of thread drift, I was talking this morning with the guy who fit my current bike, which is now relegated to the trainer, about sit pain on the trainer after 70 mins or so. I always attributed it to the absence of natural changes in sit position on the trainer vs. what happens on the road.

He pointed out a second factor: on the fluid trainer, the increase in resistance that comes from speed is designed to mimic the wind. On the road, when the wind actually does it, there's an element of lift on your chest that lightens the sit pressure.

Just one more reason why the trainer is a poor substitute for riding, and why I'm praying for Spring and a rapid solution to SRAM's hydro recall.