Originally Posted by
KerryIrons
There are lots of examples of chain checkers being wrong, but rulers never lie.
Any instrument can lie. Or, more properly, can be read incorrectly. A ruler measurement of a chain is fraught with issues. The end tab on a tape measures move which throws off the measurement if you are using that end. Measuring between, say, 1” and 13” would give more accurate results but precision can still be quite bad because of the way that individuals measure things. The start and stop point are different from person to person or even from measurement to measurement. If a rule is used, it should be measured several times and the average taken. And, as has been pointed out above, reading the rule can be an issue.
There’s also the problem of
how the chain is measured with a rule. If the chain slack or tight? If it is slack, that’s going to throw off the measurement. Tight will give you a better measurement, something that chain checkers do automatically. The advantages of a chain checker are that it tightens the chain and it doesn’t depend on reading anything.
Some people suggest using a 12” rule and then estimating that last 1/16”. Estimating anything is by definition not accurate. Additionally 1/16” is only 0.5% wear. Most chain checkers will give 0.75% as the no go measurement for 10 speed and lower chains and 0.5% wear for 11 to 12 speed chains. 0.75% on a chain would be 3/32”, not 1/16”. That’s even harder to measure and especially to “estimate”
Originally Posted by
KerryIrons
I was not suggesting that roller and pin wear cancel each other out. I'm simply stating that chains don't exclusively wear on one or the other, which would be the argument that a ruler is not a good way to measure chain wear. If the chain is wearing, the rollers are wearing AND the pins are wearing and the ruler will show the latter, which is a good marker for roller wear as well. For years Campagnolo used simple elongation as the measurement for wear. While roller wear might be slightly more precise than just length, most chain checkers offer no real advantage over a ruler and several mislead the user.
Chains
do wear exclusively on one side. The leading edge of the chain is always going to be under pressure as the chain goes over the top of the chainring. As the chain goes under the cog on the back, the same edge is going to be under pressure. The pin doesn’t spin in the chain so the same side of the pin is under pressure and is going to wear.
Over the decades lots of people have reported their chain checker showing 75% wear on a brand new chain. That sounds wrong to me.
It is wrong and can be attributed to user error. Again,
any instrument can lie.