Originally Posted by
DaveSSS
You're totally wrong there. A change in pitch only includes wear between the pins and inner plates. That's what makes a chain actually become longer. Using calipers like Campy illustrates is not a measurement of change in pitch, because it adds the wear of both the lD and OD of two rollers to the actual elongation or change in pitch.
Is the chain longer than it was when it was installed? We have a noun that we can use to describe the process of something getting longer...it’s called “elongation”.
Measuring only between the pins is true change in pitch. My math for the 12 inch rule is correct. A 12 inch machinist's rule will be made with extreme accuracy over it's entire length, so it's appropriate for the job. 0.5% over 12 inches is .0625 and half a pin is about .070. Close enough for an arbitrarily assigned value.
Yup. A machinist’s rule can have extreme accuracy over its entire length. It may even be accurate for measuring a new chain without wear. The problem, again, is that you are measuring past its entire length. Once you exceeded the limits of a measurement device, any measurement past that point is an estimate and, by definition, inaccurate.
Additionally, any time you use “about” that is also an inaccurate statement. Is half a pin 0.070”? Or is some other number? We are being told that the machinist rule is superior in measuring chain wear compared to a chain checker but then everyone uses terms like “about”. And if the value is some “arbitrarily assigned value” why do you and others use such precise values?
I still prefer an overall length measurement. On a 50 inch chain, 0.5% is 1/4 inch. My current chains are 55 inch, so 1/4 inch is a little less than 0.5% elongation. To be exact 0.275. You will find brand new chains shorter and longer than nominal, just due to accumulative error. I've found both cases with brand new Sram Force AXS chains. One has 1000 miles on it and it's still a little short.
If you had been clearer in your original statement that you were measuring over the entire chain, you would have avoided confusion. That said, are the chains you are referring to 50 inches and 55 inches to the thousandth place? Since you say that chains are shorter or longer out of the box, claiming an accuracy to the nearest 0.001” is a bit of a stretch.