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Measuring chain stretch?(4 posts)

Measuring chain stretch?Mink
Aug 26, 2003 11:26 AM
I've always measured the outside of my chains and replaced them when 10 links measure 10 inches plus one eighth. But it just occurred to me - what if the rollers inside the links are wearing faster than the outer links? Wouldn't that contribute to greater wear on the cogs? I don't want to fork out for an expensive Park tool which measures inside the links, if my trusty tape will do the job. Any thoughts?
Expensive ?.......................I think not.MR_GRUMPY
Aug 26, 2003 11:33 AM
How much is a new cassette ? The "Chain Checker" is the price of a new chain.
re: doing it wrong anyway...Rusty Coggs
Aug 26, 2003 4:41 PM
A foot of new chain measures 12" c-c of pins. replace at 121/16" with tension on chain.Waiting till the often recommended 12 1/8" usually trashes the chain.
chains don't stretch...C-40
Aug 27, 2003 4:59 AM
The Park chainmeasuring tool is simply a length measuring tool. The fact that it presses against the inside of the rollers at both ends does not mean it is measuring wear on the rollers. In fact, the park tool only measures over 5 inches, so it's accuracy isn't that great.

Chain don't actually stretch, as in elongation of the side plates. Chain become longer due to wear between the pins and the bushing formed into the inner sideplates (not the rollers). Take a well used chain apart sometime and it will be obvious that one side of the pin is worn. The pin does not even contact the roller.

Chains are worn when they elongate 1/16 inch over 12 inches. In this length there are 24 pins and bushings. Divide 1/16 by 24 and you get .0026 inch of wear on each pin/bushing. That's what makes the chain longer.

I use a machinist scale and lay one end on the edge of a pin. At the other end of the scale, a pin will be completely coverd by the scale, if the chain is new or not worn. As the chain wears, the pin begins to peak out from under the scale. 1/2 the pin diameter is slightly more than 1/16 inch wear. My chains don't show a fraction of this amount of wear, even after 3-4,000 miles, but I change them annually anyway, becasue side wear on a chain also deteriorates shifting.