I generally don't mind the heat on a bike, and actually prefer hot days on the golf course. But last week I took the SS out for my normal workout ride (28+mi with as many hills as I can find in the Chi burbs). I had to cut it off and head home (<15 mi) because I felt like death was imminent. I barely made it onto the back patio and collapsed in the shade for 10 min before I could get up. It was mid day, 103 actual, and 110++ heat index. Tried again the next day (only 94) and felt strong the whole way. Charged the hills and even tacked on 5+ as an easy spin down.

Seems like somewhere between 94 and 103 is a hard barrier for me. Doesn't seem to be linear. Cross that barrier and the body wants to shut down. Weird.