Video: Why Are We Using 12-Speed Drivetrains? - The Explainer

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There’s one topic that’s almost guaranteed to earn a collective groan from mountain bikers everywhere: That the newest drivetrain that has yet one more gear. But despite comment sections filled with varying degrees of suspicion and discontent any time another cog is added to the stack, here we are in 2020 with 12-speed cassettes that I don’t think many of us were asking for...

So, what’s the deal with these 12-speed drivetrains? What did they give us, and what did they cost us?


SRAM, Shimano, and 12 Cogs

To talk 12-speed, we'll first need to take one step backward to May of 2012 when SRAM released their 11-speed XX1 single-ring drivetrain. Clever mountain bikers around the globe had been building their own single-ring drivetrains for years, of course, but this was the first off-the-shelf, purpose-built system designed around just one chainring. Truth be told, SRAM's current Eagle 12-speed drivetrain is only possible due to solutions that were first proven by that XX1 11-speed setup. This includes the completely new rear derailleur that was designed around a single chainring, the narrow-wide chainring tooth shape that helps to keep the chain on, and the XD freehub that allowed for the 10-42 tooth cassette and its 420-percent range.




SRAM’s 11-speed drivetrain was around for four years when 12-speed XX1 was released in 2016 under the Eagle name. The new Eagle drivetrain offered a wild-for-the-time 50-tooth large cog and a 500-percent range. If 11-speed didn’t quite kill the front derailleur, SRAM’s 12-speed was the headshot that finished them off.

And you know the folks at Shimano weren’t just sitting on their hands during all this, right? Of course not, they were working on stuff the whole time; it just took ‘em a bit longer. In May of 2018, Shimano released their first 12-speed mountain bike group, XTR M9100. Why two years after SRAM? Well, they might disagree with my assessment, but to me it looks Shimano spent a lot of time and money working on their two- and three-ring front derailleur drivetrains while SRAM was beavering away on their single-ring systems. Shimano always had the best front shifting in the game, but I think we know how much that matters these days...




That new XTR 12-speed drivetrain included an all-new ‘Micro Spline’ freehub to allow for the 10-51 tooth cassette that offers a 510-percent range, a single-ring-specific derailleur, as well as a chain and all the other expected bits.

These days both SRAM and Shimano have added less expensive 12-speed drivetrains to their catalogs, but there are other ways to run 12 cogs, as well as a countless number of smaller companies offering range-expanding add-on cogs, derailleur modifications, and other things. But for this, we’re just gonna stick to the two big players: SRAM and Shimano.


What's the Difference Between 11-Speed and 12-Speed?

Besides one cog and one click, 11 and 12-speed drivetrains differ by gearing range and tiny but very important measurements. Let’s look at their respective ranges first, which is how wide of a spread you’re getting with a single chainring. Also, we’re only comparing stock drivetrains here, not add-on bits that would further confuse my grade 8-level math skills.




SRAM’s 11-speed 10-42 cassette offered a huge-sounding 420-percent range in 2012, but that’s now dwarfed by the 500-percent range that their 10-50 tooth 12-speed cassette supplies. As their competitor, Shimano’s 12-speed drivetrain can be used with their 10-51 tooth cassette, one more tooth than SRAM, for a 510-percent range. Without a front derailleur and small granny ring, your range has to come from your cassette, of course, which is why cogs keep getting bigger on one end and smaller on the other.

That’s why we started with a 42-tooth large cog on that original 11-speed single-ring XX1 group, but its 420-percent range wasn’t quite wide enough for many riders. These days we have 50-something-tooth cogs that supply a range that topping 500-percent.

It’s the same on the opposite end of the stack, too, with the 10-tooth cog helping to make up for you not having a big chainring to shift into.




So many numbers, but there’s still a lot more to come: I know you guys are just dying to talk about chain width and cog spacing, right? Yeah, me too.

First, let’s go way back to 8-speed chains for some perspective - they were a full 7mm wide at the rivet, which is 2mm skinnier than a single-speed chain. A 9-speed chain is 6.5-7mm wide, while a 10-speed chain is 6mm wide. Chains meant to work with 11-speed drivetrains are 5.5mm wide, and 12-speed chains are the narrowest at 5.3mm at the rivet.

You probably know why chains have gotten skinnier as the number of cogs increased: SRAM and Shimano are squeezing more cogs into the same amount of space between the spokes and the frame, so the cogs have to be narrower and closer together. It doesn’t sound like there’s much difference between a 9-speed and 12-speed chain - it’s just a bit over a millimeter - but the two aren’t compatible at all. If you want to know more about chains, this Explainer episode has got you covered.




Modern drivetrains are precise systems designed to work as complete ecosystems. If you used a 9 or 10-speed chain on a 12-speed drivetrain, you’d likely find that it works poorly; each click of the shifter moves the derailleur a very precise amount, and both the width and shape of that 12-speed chain is designed to interact with the 12-speed cogs and the very precise amount of space between them. 11, 10, 9, and 8-speed chains are too wide and will interfere with the neighbouring cogs, keeping it from shifting properly. I know this guy (okay, it might have been me) who installed an 11-speed chain on a 12-speed drivetrain, and yeah, it worked okay-ish as there’s just 0.2mm difference in chain width, but it was also noisier than usual and was never bang-on.

But can you go the other way? What happens when you use a 12-speed chain on an 11-speed drivetrain? Not much, to be honest, with it working just fine but feeling like it’s only 95% as good as it could be because the chain is a tiny bit narrower and doesn't interact with cogs as intended.




They definitely don’t like it when you do this, but you can also mix and match Shimano’s 12-speed components with those from SRAM. Their 12-speed shifters pull slightly different amounts of cable with each click - 3.65mm for SRAM and 3.5mm for Shimano - which means that pairing a shifter from one company with a derailleur from another isn’t quite ideal. But I do know this guy (yes, me again) who did exactly that and everything worked just fine. You can also play with chains, cassettes, cranks, and chainrings until you lose your mind.

Disclaimer time: all of the above works-ish, but you’ll always get the best results when you keep the ecosystems together as intended. Don't go blaming me (or the manufacturers) for your bad shifting or worn out parts.


What Did 12-Speed Give Us?

So, why do they keep adding cogs, especially as everyone seems to get so mad when they do? And how come we’re up to twelve of them? The answer is pretty straightforward, and it has nothing to do with “planned obsolescence” or a secret derailleur cabal that runs the world. That’d be way more interesting. Below are the main reasons we have 12 cogs instead of 6 or 8 or 10.

We already covered the first one: If you want the range, which most riders do, and don’t have a front derailleur and multiple chainrings, the cassette needs to have a really big cog to have an easy gear and a really small cog to have a hard gear. That’s why many 12-speed cassettes start at 10-teeth and go up to more than 50-teeth.




I know what you’re saying to the screen right now: “But Levy, why can’t we have a 6, 8, or 10-speed cassette with 10 and 50-tooth cogs? That way we’d still have a wide range, but drivetrains would be far less finicky because the cassette spacing isn’t as tight?”

And you wouldn’t be wrong.

Unfortunately, our legs are attached to our brains, and our brains want our legs to spin at a certain cadence, or RPM, that feels right to us. Like a car with a manual transmission, you need to shift to the right gear otherwise your legs will be spinning too fast - your cadence will be too high - or you’ll end up bogging down - your cadence is too slow. You all know that already, but you might not know that a lot of riders are really picky about their cadence, and a difference of one or two teeth can actually feel pretty drastic, especially if you’re the type of rider who covers a lot of ground and thinks about such things.




I get to use different 12-speed drivetrains while riding different test bikes, but I put a wide-range 8-speed eMTB cassette on the Grim Donut. It shifts well, but the jumps between cogs feel HUGE to my legs. Back to cars for a second: Old transmissions often had just three or four speeds, whereas some modern cars can have ten-speed transmissions that improve efficiency and performance because the car can be in a more ideal gear for the speed that it's traveling at. Same thing with bikes!

Granted, that won’t matter to a lot of riders who don’t care about things like cadence or having to walk up the hill.

Also, SRAM and Shimano definitely care about who offers the most cogs and the most range. The upside is that we have two companies competing against each other to make better drivetrains that offer more capability than ever before. But I wonder what we’d be using today if they had spent the last twenty years perfecting an 8-speed drivetrain instead of always wanting to add another cog?

Regardless, 12-speed has given us the ability to have both a very wide range and relatively small, natural feeling jumps between each gear. And with the help of that original XX1 11-speed group, the modern 12-speed drivetrain has also killed the front derailleur for good. Hopefully. If you’re watching this in 2040 and front derailleurs have made a comeback, I don’t know what to say.

We’re also told that not having to consider front derailleurs means that clever engineers can make frames stronger and stiffer, and we can have more tire clearance. And not having a front derailleur can also mean improved suspension performance, especially under pedaling loads, because the forces the drivetrain puts into it are more consistent.




What Did 12-Speed Cost Us?

Okay, so 12-speed is obviously the one and only reason for you having a good ride, but it must have some drawbacks, right?

For one, squeezing 12 cogs into the same space that used to fit 11, 10, and 9 cogs means that everything needs to be more precise. If you bent your 9-speed derailleur or hanger just a little bit, you might never even notice. But do the same thing to your 12-speed drivetrain and you’re bound to get some tick, tick, tick noises at best, or shitty shifting at worst.

SRAM and Shimano are building far better derailleurs than they used to, no matter what anyone says. They’re using better materials, better methods, and tighter tolerances. On top of that, derailleur hangers aren’t made of warm cheddar cheese anymore, so they’re way less likely to bend. All that means better shifting... Most of the time; there’s no getting around the fact that 12 cogs have to be closer together than 8, 9, 10, or 11, making it more susceptible to going out of adjustment.

Another thing I’ve heard many times is how a narrower chain must be weaker than a wider chain. Is there any truth to that? Is a 9-speed chain ''stronger'' than a 12-speed chain?

All testing points towards modern 12 and 11-speed chains having more tensile strength than older, wider chains that featured less advanced materials and construction. On top of that, things like flush pins (how they sit on the outer plate) and better tolerances also help, and 12-speed chains all have to pass that Euro ISO standard that means they’re more than strong enough, no matter how many squats you did during the quarantine.




Okay fine, but high-end 12-speed drivetrains surely cost way more than 11-speed high-end drivetrains did, right? I mean, it sure feels like things have gotten crazy expensive.

Well, in 2011 an XTR two-chainring drivetrain group would cost you $1,495 USD, which is about $1,700 today. In 2020, Shimano’s 12-speed XTR drivetrain sells for a bit under $1,500. So the latest XTR drivetrain is actually less expensive than the one that came before it.

What’s SRAM been up to? Their XX1 11-speed started at $1,449 USD in 2016, which is $1,650 today. In 2020, the XX1 12-speed costs $1,500. Just like XTR, 12-speed XX1 is actually less expensive than 11-speed XX1.

Not only that, but you can also find many of the fanciest groups’ main selling features, like the wide range and shift quality, on SRAM and Shimano’s less expensive drivetrains. You just saw Shimano launch their new Deore group that costs around $300 - that’s for an entire 12-speed drivetrain! SRAM’s NX 12-speed kit goes for $375 USD, and their newest GX 12-speed drivetrain is $545 dollars.


12-Speed Drivetrains: Good or Bad?

Scroll through the comment section under any drivetrain article and you're bound to see riders eulogizing the so-called 'good ol' days' of fewer cogs and fewer problems, but the facts tell a very different story.

Modern 12-speed drivetrains supply both a very wide range and efficient, natural feeling jumps from gear to gear, something that fewer cogs aren't able to do. And thanks to improved materials and tolerances, they're also much more reliable overall, even if they can be a little finicky compared to those 8 and 9-speed systems. 12-speed drivetrains pretty much killed the front derailleur as well, especially after 11-speed showed that maybe we didn't need them after all. That also made drivetrains and frames lighter to boot. And finally, while you can spend a few grand on an XTR or wireless AXS system, you can also get a 12-speed drivetrain for as little as $300 USD, meaning that almost every rider has access to better shifting and more range than ever before.


Where would you like to see drivetrains go in the future: Should SRAM and Shimano keep adding cogs, or should their focus be on something else?

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Previous Explainer episodes:
Episode 1 - What's the Deal with Linkage Forks?
Episode 2 - Carbon Fiber Leaf Springs
Episode 3 - What's the Deal with Chains?
Episode 4 - What's the Deal with Cross-Country Racing?
Episode 5 - The Basics of Modern Mountain Bike Geometry