So a few days ago I was working on a customers MTB, the bike was a full-sus Cannondale with a SRAM Eagle drive-train. The bike was actually in for a seized bottom bracket (my third SRAM PF30 in as many weeks), but when reassembling the drivetrain, one of my checks was chain wear. In fairness, the chain riding up on the largest sprocket was a give-away, but I did wonder just how worn it was.
After checking wear, I thought it’d be great to highlight a number of links in the chain (at 50cm intervals) and actually demonstrate just how much a chain ‘stretches’ with wear. This stretching is caused by the wearing of the pins and bushes resulting in ‘sloppy’ joints. Of course, once the chain lengthens, the rollers now engage differently with the chainring and sprocket teeth, resulting in wear of those components too.
It may seem a pain to keep on top of chain cleanliness, but a badly worn chain (£30-£60 in this case), may lead to far more costly repairs to both the rear cassette (£60 – £260!!) and/or the chainrings (£20 – £50) …… chain cleaner, £10-20, elbow grease; free.
By the time the chain was at it’s full length (just over 150cms), the wear had had effectively lengthens the chain almost by a full link; this had a massive impact on the shifting and wear of the other components.