John_V 

I always stretch at the beginning of a long charity ride since I don't get a chance to do any warm up rides prior to the start. I have never had any issues during or after the ride when I stretch. I did have issues on one ride when I got there late and just in time to start and wasn't able to do my stretching. I had to wait until I got to the first SAG station to stretch because my thighs were starting to cramp.

On my daily rides at the MUP, there's almost two miles of service road before it gets to the main loop. I normally ride this part of my first lap at a slower pace just to warm up and then finish the rest of my ride at my normal, faster pace. This has worked well for me and until it no longer works, I think I'll continue my normal routine.