If the world was digital then any rider less then X weight (and being under the manufacturer's limit) would not wear or load the bike more then a rider of Z weight. But the world does not follow this dream. The world is made of shades of grays. The world is analog. A 100lb rider won't load a bike anywhere near as much as a 250lb one.

Consider the auto that carries only one person compared to the one that is always packed with four and all there baggage. Sure the unibody might not wear out much faster but we all know that the brakes and shocks will wear faster with the heavier load. So why isn't a bike the same, it is the same. The bikes frame might not flex beyond design limits but the parts will have a shorter life. Brake pads will be stopping greater mass, chains and cog teeth will see higher peak and average loads, the clamping systems will have to withstand larger rotating or sliding forces and the spokes will go through a wider range of tension changes.

It should be pretty easy to understand that greater forces means more fatigue and wear. You see it in the shoes of heavy people, in their beds and hear it stressing the floor above you when they walk. Again why is it expected to be different for a bike?

Added to all this is the way a bike can be used, shifted, loaded for the same weight. As my last post tried to say how you load a bike (for whatever weight you are) also contributes to wear and problems. Back to the auto example. We all know that jack rabbit starts, race course like braking and not slowing down for speed bumps shortens a car's life. Why, again, do we think it's any different for a bike??

You do have a point in that inadequate maintenance is a factor. But if that maintenance is also replacing parts (not just "tuning" them) how many will still feel that "its" called maintenance? The auto example again, is it maintenance to replace the tires as they wear? To the car as a whole yes. But to the tires, no. We replaced them, not just checked their air pressure or balance.

So what one calls maintenance another calls repairing. As i said this discussion is full of shades of gray. But what it not at question is that how much we weigh and how we treat the bike during our riding does effect it's function.

In post #13 Bill says "Most broken spokes are the result of a poor quality wheel build.
Improper spoke tension on the initial build.
Machine built/trued wheels need a human touch"

I would say that poorly built wheels let the spoke suffer from fatigue sooner. I do agree that most machine built wheels are not as well tensioned as QUALITY human built wheels. But hand building alone is not god's gift to reliability. Andy.