trail_rat – Member
dont know who they are – but its certainly not true in any shape on an MTB – maybe on a road bike.
“They” are Park Tools, who make a lot of money out of it by selling chain checkers that tell you to chuck perfectly good chains. About third new chain in it will skip on the partly worn cassette so you bin a perfectly good cassette also.
The principle is to keep chain and cassette meshing together, and if they are the same level of wear they’ll go on for ages. If you stick a new chain on then you risk it skipping. Hence the “advice”. Simply don’t put a new chain on until the whole lot is shot, which is way longer in my experience (having been experimenting with this) than chucking three chains and a partly worn cassette.
There’s the risk that the chain snaps, but modern MTB chains are tough, especially KMC chains, and with power/missing links they are easily fixed and will run on and on. So the need to replace with a new chain early is rare.
Though then you might wear down the chainring, but they are longer lasting and if you replace it, a NW ring is unlikely to have issues skipping with an old chain. Can be more of a problem with a double/triple set though.