Originally Posted by
pdlamb
Your probability discussion is still incomplete; you forgot to mention confidence levels, for instance.
Quit being so literal. “One in a million” is a conversational method of saying something is rare. I haven’t done any detailed analysis nor have I ever said I did. It’s a wild ass guess, nothing more.
Your one in a million broad-brush "conversation" still doesn't hold up. For instance, if the Mean (bike) Trips Before Failure (MTBF) was 1,000,000, even if you made one bike trip per day on average, it'd be over 2,700 years an average cyclist would ride before, on average, one bike failed by frame breakage. How long you been riding again?
Again with the being literal. “One in a million” doesn’t mean in any way one person doing a million miles. It means one person experiencing a frame failure out of a million other people using the bike. Nor does it mean that if a million people doing 1 mile is going to experience a frame failure.
Now if you want to get down into the details of reliability and sparing analysis, that might be relevant to touring. It's going to be tougher to fix or replace a bike while on tour than riding around home, where you've got default SAG support available -- friends or family to pick you up and take you and your bike home. So if a touring bike has an MTBF of one in 10,000, and you're going for a 100 day tour, the chances of the bike breaking on tour is 1%; uncomfortable, perhaps, compared to your mythical 1,000,000, but probably not worth carrying a spare frame. It's much less than your chance of getting a flat, for instance, where it's worth carrying something to get you back on the road because the probability is much higher. Now if you're [MENTION=108802]mev[/MENTION] and going on a three year trip around the world, you want to at least think about how you're going to finish the trip, or even get home, if your bike breaks.
Your 1% failure rate is just as mythical as my 0.0001% failure rate, although I think mine is probably closer to the true value. Bicycles can fail but not
all bicycles fail. I have worked on around 15,000 bikes at my local co-op. Most of them are abused beyond what anyone on the Bike Forums would tolerate. I can’t honestly recall any bike in that number that has had a broken frame unless the bike was run into something.
The possibility of a frame breaking on tour is so low that it’s not something to worry about at all. Frame breakage might have been worse many years ago which is where this myth about steel got started but with today’s metallurgy and frame design, it’s not something to even be considered while touring.
If we could get some honest input from one of the major bike brands, you'd have a better idea what the true failure rate. They're more likely to have run the numbers, and figured out that they're going to need X% spares in the warehouse to address frames breaking within the warranty period. I don't have a reference, but I've got it stuck in my head that "X" was about 1% -- at least before Covid cleared the warehouses.
I would say that the number of spare frames in a warehouse is probably much lower than 1%. Trek sells 1.5 million bikes per year around the world. That would be a stock of 15,000 bike frames. Since breakage is a random(ish) event, they wouldn’t use all of them yearly. In 10 years, they would have a significant percentage of 150,000 bikes in warehouses somewhere.
If you break a frame you aren’t likely to get a new frame that is the same as the frame you broke…I got the closest bike they could get for the model year when I broke the frames. They seem to just pull one from the line rather than keep a back inventory. My Stumpjumper Pro was a 1998. It was replaced with a 2003 Stumpjumper Pro, not another 1998. The same happened with my Specialized Rock Combo.