I've noticed when running downhill my hamstrings have been feeling tight; I stretch after the run but the tightness remains for a couple of days after.

I've only really noticed the tightness as my running mileage has dropped off.
I'm thinking that the biking might be causing the hamstrings to shorten.
The hamstring never seems to fully extend on the bike although I'm pretty certain my seat height is set ok. I haven't changed anything on the bike.

Hoping some of the cyclists on here can help me out?