Originally Posted by
DaveSSS
With some chains, like Campy's, measuring only elongation is worthless, since the chain rollers and side clearance wear far faster. Using a 12 inch precision rule is plenty accurate, since 0.5% is a totally arbitrary amount of elongation that someone decided to advertise as the best time to change a chain. While changing at that point will make the cassette perform longer before new-chain skip occurs, there's no proof that 0.4% or 0.6% isn't better. If several chains are used in a rotation, each chain can be used longer, since new-chain skip will never occur and each chain could be used until 1% elongation was reached, IF it's the type of chain that wears primarily by elongation - not all do.
Again, how can a 12 inch precision rule be accurate at measuring 12” plus any amount? It is precise to exactly 12 inches. Anything over 12” is an estimate and, therefore, inaccurate. Over 12 inches and you might as well use axe handles as a measurement.
As for your assertion that some chains don’t wear by elongation, then why does
Campagnolo say to measure the elongation? The suggestion I’ve found says
Here, you need to use a set of calipers to measure the distance between the rollers over 6 outer chain plates. If the length is 132.6 mm it is time to change the chain.
That’s a length measurement. In other words, a measure of elongation. The numbers, by the way don’t seem to work. 12 inches is 304.8mm. 12 inches of chain is 24 links. Divide that by 4 and you get 76.2mm over 6 links. That’s 56.4mm short. Something is not right here.
However, Campagnolo chains aren’t really that widely used. Chain gauges work for 99.9% of chains as a quick measurement. Using one isn’t going to deprive a rider of too many miles on their chain.