What are the different chain link speeds and why are they important or what is the difference?

I have recently broken one of my chain links on one side while cycling. Wishing to fix it I discovered a user describes his similar situation in the stack question here.

I noticed the manufacturer KMC offers 10-speed and 11-speed, does the speed denote the sizing and weight or its chain connector and locking mechanism?

The number of speeds a bike has is a measure of the number of different gears the rider can choose from. Ignoring a couple of historic variations...

When we talk about chain speeds, we count the number of separate sprockets, or gears, that make up the cassette mounted on the rear wheel. A 10 speed chain is used on a bike with 10 sprockets in the cassette and an 11 speed chain is used on one with 11 sprockets in the cassette. Etc.

If you have numbers on the shifter, this will be the same as the highest number on the right hand shifter. Otherwise it’s a case of counting.

The chains themselves get narrower (on the outside dimension) as the number of speeds increases, because the sprockets are squeezed into very nearly the same space, so are placed closer together and the chain needs to fit between them.

The length, the weight, the chain connector and locking mechanism are all separate design choices, but it is considered essential to match the number of speeds on the bike to the speeds of the chain. The user in this question was having problems with a 10 speed chain on a 9 speed bike, falling between the chainrings.

As for the historic exceptions, these would include referencing ‘vintage’ bikes and/or bikes where the number of sprockets at the back is less than 8.

• Thank you for explaining this to me! Commented May 12, 2019 at 16:20
• "[I]t is considered essential to match the number of speeds on the bike to the speeds of the chain" Is it? My understanding is that a chain suited to more speeds than you have gears (e.g., a ten-speed chain on an eight-speed bike) will work just fine, except that it will be more expensive and less robust. Commented May 12, 2019 at 17:07
• @DavidRicherby : An 11- or 10-speed chain might not work properly on an 8-speed cassette. The gap between sprockets being wider and the chain thinner, there might the risk of the chain falling between two sprockets. Although having checked it right now, the sprockets (and the chainrings) effectively 'take' the chain. It doesn't ride on top of teeth as I had suspected. Commented May 12, 2019 at 17:27
• @David fair comment, I’m not backing that up with anything. For the sake of this question, I consider it to be. A chain too wide will cause problems and as you note, a narrower chain will be more expensive. Neither of these are desirable for the OP, be it mechanical or financial. I wanted to try and keep the lid on the can of worms but have failed XD Commented May 12, 2019 at 18:08
• @Swifty Yeah, for the sake of simple explanation, it's easier to say "Use the right chain" than "You shouldn't use a chain designed for fewer gears than you have; it's probably OK to use a chain designed for higher speeds but they cost more and wear faster so best not o." Commented May 12, 2019 at 18:11