A weight limit is not a normal specification for a Diamondback bicycle. It is an included spec for trikes. To the thoughtful cyclist, the reason weight is an issue for trikes but not for bikes has to do with their construction.
Why Trikes Have Weight Limits
Uprights and recumbent Deltas have weight limits because they have a rear axle differential, which can collapse under heavy loads, particularly when weight bangs down from an unexpected bump. While Tadpole trikes do not have a rear axle differential, the rider is so close to the ground (often with less than 3 inches of clearance) that rider weight alone can be enough to bend the frame sufficiently to lower ground clearance too low for safe riding. Weight limits for adult trikes can go as high as 500 pounds, or around 246 kilos. Weight limits for Tadpoles average half as much.
Why Bikes Do Not Have Weight Limits
The diamond shape of the bicycle frame makes it nearly impossible to collapse. The weak point in a bike is not in the center, as it is for trikes. The weakest point of a mountain bike, or any bike for that matter, is the axle, particularly the front one. When off-roading, whether on a mountain bike or a BMX, front axles can take a terrific beating even with a rider of moderate weight. When a front wheel comes crashing down on a flat or uphill surface, the front axle is subjected to a force equal to the mass the rider is placing on the front forks times velocity squared. It is for this reason that serious mountain bikers upgrade from stock to titanium axles.
Weight Adjustments for Bicycles
Whether talking about the weight of the load or the weight of impact, cyclists address weight issues in five areas: axle strength, spoke tension, tire inflation and fork suspension. Titanium axles eliminate the axle component from the worry list. As for suspension, you have to ask yourself how much banging you're going to put the bike through. Suspension means a lot if a smooth ride is what you are looking for, but it means nothing for true mountain biking. Suspension forks have no place in off-road biking or even curb jumping. It doesn't take much of an impact to pancake even the best of them. Suspension forks do not belong on a bike that will be used off road. And, finally, spoke tension and tire inflation can both be increased to compensate for heavier riders.
- mountain bike downhill image by Maxim Petrichuk from Fotolia.com