Where do you get the design life from? That's not something that manufacturer's publish. Even if it is correct for other materials, it is not with regard to steel. Steel frames are designed to not exceed the fatigue limit. Off-the-shelf frames are likely designed for 85th or 90th percentile usage, which will be a combination of rider weight, usage, road conditions, luggage, etc. all combined into a stress model in the frame.Bonzo Banana wrote: ↑3 Jun 2021, 8:44pm I think bikes mostly will cope at first but you prematurely shorten the life of the frame by increasing the level of fatigue. The frames are designed to last about 7-10 years of use within their weight limits but excessive loads could cause instant failure but much more likely to reduce that lifespan perhaps to only a couple of years.
A strong or heavy rider might exceed the strength or fatigue limit of a lightweight bike, but few riders, even very heavy ones, will exceed the fatigue limit of an expedition bike, using it mainly for every day cycling.
Steel that stays within fatigue limits has a theoretically infinite life, limited by things like rust, damage, etc.
Note that I am not saying that a steel frame will last forever. But if looked after, it will last years & years & years. Many people ride bikes that are 70 or years old. The oldest bike in our house is 60 years old, and the oldest regularly ridden one is almost 30 years old.
(also minor point on usage: riders do not technically increase the fatigue, but the stresses, which can lead to fatigue.)
Do you have some evidence for this?Bonzo Banana wrote: ↑3 Jun 2021, 8:44pm Some brands have had a huge number of recalls for failing frames like Decathlon.
I'm not sure what you mean by overbuilt. They design frames for the market they want to target. Additional strength & durability has a reason, otherwise it's just extra cost.Bonzo Banana wrote: ↑3 Jun 2021, 8:44pm Some brands do go the other route and have more overbuilt frames.
I don't think that the manufacturer's weight limits actually do much to inform buyers. Some manufacturers are more cautious than others, and we don't have any way to know to what extent usage profile and caution have contributed to their weight limits. I agree with TC. It is largely backside covering, peppered with getting-out-of-warranty-claims.Bonzo Banana wrote: ↑3 Jun 2021, 8:44pm Manufacturers and importers have to clearly state the weight limits on bikes so the buyer can make an informed choice but obviously some people choose a higher level of risk. It's not just about weight though, a very strong rider can prematurely fatigue the bottom bracket area and those who ride mountain bikes can be very light but do many aggressive jumps and landings and do damage. The weight of the rider isn't the only factor in how a frame or forks can fail in use.