There ought to be one of those standard flow charts for preventing, resolving cramps. At the end of flow chart everyone will be recommended to hydrate (more), increase electrolyte intake {Nuun, Heed, Endurolytes, .............**, take Tums (after onset), stretch, use rollers after each ride, don't ride so darn hard, etc.

My experience has been that over-exertion which can occur on the tandem on steep pitches is the precipitating factor. The cramping may not occur immediately, but I've damaged the muscles and at some point later in a ride a minor surge will give me those hot flashes in my quads which foretell doom.

I rode a 100K yesterday with 5000' of climbing. My single is not particularly low-geared, but I pedaled seated slowly on some pitches of 16% without the extreme effort involved in captaining the tandem - no cramps resulted. I did hydrate, had Nuun in my water bottles and took a few Endurolytes. I'm also web searching for the pagan god of cramps.