Sometimes when I feel the cramp coming, I back off a bit. Try to engage other muscles to prevent a full on attack of the cramp. However, when the cramp kicks right in a seizes my calf... I have to stop and stretch it out. It'll feel like a nasty knot right in the calf.

I can last longer riding in high cadence, which is why I tend to try to train in that range. My legs get fatigued easier when I do lower cadence and same power. I'll do some training sessions lowering my cadence and see if I can train myself to endure the lactate acid.