The best way would be to have yourself measured by a pro bike shop. If you don't have access to one, then follow these steps, but remember that these are only basic guidelines and are not dead accurate:
- Don your cycling shoes and sit on your bike as you would when cycling.
- Rotate the pedals so that they are in a 12 o' clock - 6 o' clock position.
- Put your heel on the 6 o' clock pedal. Adjust the seat so that your leg is only just bent.
- Once the seat is adjusted, you'll find that when you clip your shoes in, your leg is slightly bent.
Thats about the closest you'll come without proper measuring. Still I would suggest you have yourself measured by a pro bike shop. Incorrect seat height can have you end up with knee-ache.
Cramps are your body's way of telling you that you're pushing the envelope too far. People might tell you to up your magnesium supplementation or use more salt, but the fact is that if your muscles are not used to the exercise intensity, they will cramp, no matter how much anti-cramping supplements you use. The solution: GET ON YOUR BIKE AND RIDE IT.