Hello,

I have recently bought a bike from an LBS. This was the first business transaction that I had with the shop. Anyway, it offers a free 50-point safety check, so I took my old bike in for an inspection. After a checkup, the mechanic recommended to replace the chain immediately. He said it so worn that I would risk further damage to chain rings and sprockets.

However, I have a "non-brand name" chain checker, and it indicates there is plenty of life left. I have attached two pictures below. One has 0.75 check and the other has 1.00. Please, let me know if the chain is worn as said by the mechanic.

Thanks for helping,

There are several factors. Modern drivetrains are less tolerant than older 6/7-speed stuff. There's a good chance the shop is recommending replacement based on the newer intervals, which are as low as 0.5%.
Park Tools recommendation is replace 0.5% replace immediately for 11/12 speed and 0.75% replace immediately for 9/10-speed.
Chain Wear Indicator | Park Tool

Secondly, make sure the chain is taunt when checking, by pressing on the crank (it looks like you did this).
Third, there's some level of manufacturing tolerance to all chain checkers, and tests should be taken as approximate not absolute. Measuring with a 12" steel ruler will tend to give a more reliable (although significantly slower estimate).

Hi hcgaloi,

When a chain needs to be replaced because it has stretched, you should change the cassette also. Why? Because the teeth of the cogs will have been worn lopsided by the stretched chain and mounting a new chain to a cassette with irregularly worn teeth will cause a new set of problems like decreased shifting performance and easier chain slips. This is why many experienced bike mechanics will tell you that cassettes should be considered as "consumables" the same as the chain.

One way to delay replacing the cassette is to replace the chain a little early. Since chains are usually cheaper than a comparable-quality cassette, you save money in the long run. This may be what your LBS is thinking. So the mechanic's advice might be correct.

Kind regards, RoadLight

like the man said, throw the chain checker away, get a steel ruler...

someone telling you to replace a chain 'immediately' is jerking you around and trying to force a sale based on 'fear.'

it's a CHAIN...if it's worn out and you ride it another 50, 100, 150, 200 miles, nothing is going to explode or cause grave damage to the drivetrain.

I've never had to change a cassette out because a chain was excessively worn. yeah, it CAN happen, but there's no hard and fast rule about it...

if you install a new chain and it shifts ok, you're good to go.

shifts like crap, well...that's a good sign that other parts are probably hosed.

I replace the chain on my commuter once a year (3K miles or so) while checking it (with a ruler) a couple times during the season after cleaning. At the end of the season it's usually well worn. I'll change the cassette every 2-4 years depending on how many miles I've ridden just because. I've never had chain skip on the cassette. I also replace the inner cable yearly because I shift a lot and my STI's are hard on cables. Mid range SRAM chain is about $20 and a 105 cassette $30, Ultegra $40-50, so not all that much cheaper.

If you replace a chain within specs, you'll get 2-3 chains per cassette. Plus, you'll know if the cassette needs changing because it will jump and/or shift poorly when a new chain is put on. The bike won't be unrideable, just annoying. Take it for a spin, see if it's running OK or not, and go from there.

Replacing a cassette routinely with a chain is just a waste.

As for the OP: you have three options: (1) Just replace the chain as advised (2) ask the tech why he's advising it and ask him to show you how he measured it (2a): if he uses a ruler to measure a taught chain and gets 1/16" elongation as described, go ahead and change it, otherwise (3): get yourself an accurate ruler and simply measure the chain yourself. If it is 1/16" enlongated, replace it. If not, don't.

I measure chains by taking them off and hanging from a nail and measuring 12 links, rivet to rivet. Actually, I have an old chain that is 1/16" long, so I just hang them from the same nail and see where the rivets line up. If they're equal, replace. If the chain is shorter than the old chain, I run it for a while longer. But I use quick links so this is easy.

I get 3+ chains per cassette.

There are two basic philosophies to chain replacement. The dominant one these days is to replace the chain someplace in the 1/2 - 1% linear stretch range to prevent accelerated wear on sprockets. There's plenty of debate about how to measure, but a decent general consensus about the "safe" replacement range.

The other, older school, philosophy is to forget about trying to replace before killing the cassette, and to run both chain and cassette for about as long as you can. Of course, this may take the chainrings with it, but they're much more tolerant of wear than the smaller cassette sprockets. Running this way, you can probably go to about 2-3% stretch before things go sour.

Either way, you want to know the facts before you decide. My preferred method is the old school 12 measurement with a ruler against a taut chain.

That no-name checker isn't measuring very much chain at a time. Since the amount of wear per link is really tiny, it's easy to see the tool being wrong either way depending on manufacturing tolerances.

One more vote for using a good ruler with a taut chain if you want data you can use to second-guess your LBS wrenches.

Do your own check and decide:

When to replace the chain on a bicycle? - Cycle Gremlin