Originally Posted by
cyccommute
You seem to be assuming that there is a defined lifetime for a bicycle frame. What would you estimate is that “lifetime”? I have tracked mileage on my bicycles since 1989. I have yet to see a mileage that defines what a “lifetime” for all bicycles might be. Some individual bikes have had short lifetimes and others have yet to find the failure point.
One problem is that we calculate reliability on populations, but we experience failures on units. As @
gauvins noted, every frame will fail eventually if it remains in service. As you note, some fail more quickly than others. I suppose that it would be possible to determine the lifetime for a single bicycle frame if we had knowledge and capability do quantum calculations on a bike frame. Of course, developing that knowledge for a frame would cost a large multiple of the frame price; so in practice, as we do with SUVs and hard drives, we estimate MTBF, run them, and cuss a lot if they fail "early."
You keep making mountains out of mole hills. Quality control in our age is far superior to what it was 40 years ago. Frame breakage from frames that have escaped quality control is still a very rare event. Frame breakage in general is a very rare event.
Quality control costs money. Bike brands negotiate QC along with prices. If every bicycle frame were built with six sigma process and quality control, you'd expect three or four failures per million frames. Isn't it interesting that the major bike brands seem to have developed policies for frame warranty? Why do you think they went to that trouble? Why do you think so many brands warranty their frames for 3-5 years, instead of the old lifetime warranty?
Breaking a frame is a rare event. Your 1% failure rate would mean that between 150,000 and 200,000 bicycles break per year (15 to 20 million bikes are sold each year). There would be far more reports of broken frames on the Bike Forums than there are. My 0.0001% failure rate is only 20 bikes fail per year. Mine estimate is probably too low but I would be very surprised if frame breakage per year topped 1000 across the world per year.
That 1% number was a "ferinstance" to illustrate how and why you might want to plan for the event of a frame failure. Let me guess at your observed failure rate:
Years riding: 60
Rides per year: 200
Total rides: 12,000
Observed failures: 4
Average failure rate: 1 in 3,000 rides
Since I'm just guessing at those numbers, feel free to update with better numbers.
For comparison, my best estimate is about 1 in 2,500 rides for my personal bikes (I only reported the frame the broke on tour).
I wonder how many bicycles have been ridden more than even 1,000 times?