...us Welsh can give the Scots a run for their money regarding thriftiness you know.
I had a Scottish grandmother, and my beloved late mother-in-law was Scottish. I'll be watching you, young Neil. Heh-heh!
I'm always quite surprised to hear of chains being renewed after relatively low milages. I look after my bike but don't pamper it to extreme and I would be dissapointed if my chain lasted less than 6,000 miles.
I think it is relative, and the cyclist might have something to do with, and the quality of transmission consumptibles that he buys. When I ran open derailleur transmission and took whatever chain the LBS thought right to fit, usually SRAM PC1 and its predecessors, I never saw more than a 1000 miles on a chain. I just assumed that people who talked of thousands on RBT, a place full of trolls, were lying. Then I decided to get serious about cycling but assumed that Gazelle would fit the best, and my successive hub gearbox bikes from Gazelle and Trek came with Nexus transmission groups. I know now that they're cheap rubbish, but back then I was disappointed to get about the same 1000 miles on a complete transmission of chainring, chain, sprocket, maybe 1100 if I was lucky. I was infuriated at the inefficiency and the waste of my time (which was two grand an hour the last time it was available by the hour, decades ago). So I looked into it, and the Rohloff chain is one of the things that interested me in the Rohloff gearbox, which led me to the Thorn forum because Andy Blance, unlike so many bike "designers", isn't a bullshitter. (He's definitely an honorary Scotsman!)
And here I met Stu (moderator before Dan) and others, guys who clearly weren't trolls and weren't liars, talking about getting 10K miles on a chain like it was a commonplace. It was becoming clear that I am exceptionally heavy on my transmission, perhaps because I'm not a cadence pedalist but a masher. I'm a pretty solid guy, a retired rugby and polo player, and I just know I'm never going to make those big round mileages, in the first instance because I started cycling too late to learn a hummingbird cadence. (By contrast, the roadies point me out to each other. "That guy on the green bike has eight thousand on his tyres, and he says they'll make ten.")
So when by buying quality transmission components, including the chain, and enclosing the chain correctly (did I mention that the 1000m Nexus rubbish was run inside a big Dutch plastic chaincase and white-waxed and spotless, not grinding mud in the open), I achieved 4506km, near enough 3000m, I thought I was doing pretty good. I know, by your standards, I'm a wrecker, but by my previous standard, 3000m on a chain is nearly as good as a hummingbird cadence.
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I suspect therefore that it isn't my mileage on a chain you want to watch so much as the relationship to my previous mileage, and then to apply the multiplier to your own circumstances and history. I also expect that guys who already get huge mileages are doing so much more right that I am not, and may not even know about, that they won't get the full multiplier. It stands to reason that cyclists who are already getting really exceptional mileages out of transmission components cannot expect more than marginal improvements, whatever else they do.
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Thing is, real quality components don't cost all that much more than rubbish. If I were a high-mile commuter like Stu or some others we hear from occasionally, I would have paid for the entire transmission chain (chainring, sprocket, chain, Chainglider) in the first year, because I started from so far back. I'm not in this for the cost-saving -- my kick is a maintenance-free bike -- but all the same that's a statistic that's bound to impress any quarter-Scot.