Nailed it.

You cramped on your first century? In other words, you'd never ridden that far before. And because there were a lot of other riders around, I'd bet you were pushing harder than you really should have been - even after that five minute hard effort to start, especially early in the ride. You paid for that "HARD" effort later.

Welcome to the club.

On my first century I cramped so bad and so suddenly you can see where I cramped on the GPS plot - I almost fell over and I started wobbling all over the road. About 80 miles into the ride. The last 20 miles were hard...