Originally Posted by
FBinNY
Aluminum has a definite fatigue life. One of the factors is the amount of deflection. Your weight alone would shorten the fatigue life of cranks if you used the full weight such as in hill climbing. But combine that with pedal extenders which push the pedal outward and the twisting torque is increased. Combine both and this is what can happen.
We probably don't see as much of this as we might because of the simple fact that there aren't that many high mileage heavy riders. Also, regular riders (regardless of weight) tend to buy better equipment and are less likely to use pedal extenders.
As you point out, there are a number of aggravating factors besides your weight, so while the actual event was probably a surprise (I broke a number of cranks and pedals over the years, and know it's always a surprise), the fact that it happened shouldn't be.
When you replace this, consider a better level crank, preferably one made for off road use, but even then there's no guaranty of infinite life.
Thanks! I appreciate the insight and advice (and your presence here on this site, always helping)!
A bike shop on the trip replaced it with one from their spare parts bin. It's also a fairly low end crank, but it is wider and has a curvature to it, so I'm hoping structurally it'll be stronger. Since the failure (luckily!) was non-drive side, a full upgrade to more expensive cranks wasn't what I was looking for at that moment, but I'll be taking your advice to heart and be seeking something designed for off-road abuse as a replacement crankset. It'll probably be fairly low priority with the other expenses I have stacked up ahead of it, but hopefully I'll come across a deal somewhere and can get one and get it mounted before the next failure!