Wednesday, January 09, 2013

Chain and Cog Wear

Bicycles are wonderful, efficient machines but like any mechanical device with moving parts, those parts are subject to wear. In some cases, like when you pull on the brake levers and notice that it is taking longer to stop than it used to, you get a clear signal that something needs attention. Even the least mechanically empathetic rider tends to notice when they can't stop, so worn brake pads are things that call attention to themselves as they wear. The brake pads aren't the only part of the braking system that wears and elsewhere I've called attention to the problem of brake rim wear.

The bicycle chain is often ignored unless it's squeaking or refusing to shift into the proper gear but in the case of your bike chain, ignorance is not bliss. A worn chain may shift fine and not squeak but as the individual links wear, the chain becomes slightly longer. While this is commonly called "chain stretch" the additional length is not the result of any metal stretching, it's the consequence of accumulated wear of the bushings in each chain link.

Chain wear isn't measured in miles or months. Three thousand miles ridden over the course of sunny summer by a rider who spins in low gears and who cleans her drivetrain weekly is a very different situation than a thousand miles ground out by a commuter on the gritty, rain-soaked Seattle hills. The tool for measuring chain wear isn't an odometer or a calendar, it's the common ruler.

On a brand new chain there is 1/2 inch between each pin so twenty half-links should measure 10 inches (254 mm). If those 20 half-links sum up to 10 1/16 inches or more, it's time to replace your chain. While you can measure this with a ruler, a tool like the Park CC-2 Chain Checker makes checking even easier.

Modern derailleur drive trains have narrower chains and cogs (something I ranted about a few years ago), and the newer stuff really does wear faster than and cost more than the old stuff. So checking your chain is important.

If you let your chain go too long, what happens is that the old chain wears your rear cogs and maybe your front sprockets to match up with with its worn profile. Dirt on the chain works to wear the metal cogs. The pressure is most concentrated on the small cogs, so the smaller cogs and the ones you most use see the most wear. The insidious thing is that you don't notice it until your chain has worn to the point where finally your shifting gets sloppy or the chain breaks. And if you wait until then to replace your chain, you'll find the new chain won't mate with the old cogs (or at least all of your old cogs). The symptom you'll feel is a skipping or popping under load as the new chain tries to settle into peaks and valleys of the worn cogs.

Chains are cheaper than cassettes or chain rings and if you do your own maintenance, a chain checker is a good investment. And the mechanic down at your local bike shop who tells you that you should replace your chain even though your bike seems to be behaving fine probably isn't trying to rip you off. He's probably trying to save you money in the long run.

Keep 'em rolling,

Kent "Mountain Turtle" Peterson
Issaquah WA USA


Anonymous said...

I was just now looking for such a tool. Many thanks for your post, Kent; I've used your link to buy one.

Always appreciate your comments on lights, tools, etc. It would be interesting to hear about some of your favorite tools that you've collected over the years.

Thanks again.


Pat L said...

Kent, check your math. If 20 links starts at 10 inches and wears to 12 1/16", you've got a really, really bad problem. :)

Velosopher said...

Agreed on all counts! My chain checker has two warning measurements... One for "getting close" and one for "buy a new chain now!" For the first chain I used it on, I waited until "new chain now!" And found the new one just wouldn't shift correctly no matter what I did. Seasoned wrench magically solved the problem with shiny new cassette. Moral: don't wait!

Kent Peterson said...

Hey Pat L,

My math was OK but my typing was lousy! I fixed it now, thanks for the catch.

fhfr436 said...

I prefer the newer go/no go chain checkers from Park Tool:
The CC3.2 has 0.5% and 0.75% gauges. In my experience, if the 0.75% passes, it's time to replace the chain.
The predecessor to this model (CC3.1?) had 0.75% & 1.0% gauges, but the 1% was too late and your new chain would jump on the worn cogs.
Your 1/16" in 10" is a 0.63% wear, so that's right in the same range, and even a bit conservative.

Conrad said...

I have the older Park chain checker with 0.75 and 1.0% markers. I agree, if you wait until the 1.0 mark slides in the chain, your new chain will skip. Even if you replace the chain at the 0.75 mark, every third or fourth chain will start skipping and you still need a new cassette. And your chainrings will also eventually wear out or not mesh will with a new chain even if you have been replacing the chain when you are supposed to. It takes a while though.

Bob from Arcata said...

Just found your blog and quickly added it to my bookmarks. Will you recommend a way to clean the grunge off a triple crank? My method always includes poor results, shredded shop rags, and bleeding from puncture wounds. I have removed it to scrub it, but usually just settle for a so-so job. Thanks-Bob

Kent Peterson said...

Hi Bob,

First off, welcome. Have fun digging through the archives of this blog, there's a ton of stuff in there.

To answer your question, you want something thin and pokey to dig the grunge out of cranks and cogs. Park makes a tool that has a brush on one end and a curved plastic claw on the other end with teeth on it. That works pretty well on the cassette and OK, but not great, on the cranks. I've got a tool I made out of a sharpened spoke that is handy for getting crud out of tight places and I've made my own plastic claws out of scrap coroplast and plastic packaging. You kind of visualize what you need and hack a tool into the right shape.

I hope this helps.

Bob from Arcata said...

Thanks Kent. Going to try one of those park brushes, and increase my resolve. Now, to the archive. A long ride first, the rain stopped!

Anonymous said...

Pop open your Missing Link, dip the chain in melted paraffin wax for a moment and Ka-boom, shiny, new chain. Do this every 200 miles and skip the lube. Better yet, keep a spare clean one ready to go.