Mountain Bike 1X Gearing
Less is more.
- Ludwig Mies van der Rohe
It's not a very well kept secret that mountain bikes have evolved a lot over the past few decades. Suspension is an obvious big one. Materials and construction are two more that jump right out at you. Geometry is a little more subtle, but no less important. And disc brakes... you just can't appreciate disc brakes enough unless you've ridden something with an old pair of cantis on a cold wet day recently.
The most recent revolutionary change in modern mountain bikes -- and maybe most misunderstood -- is single chainring, or 1X (say "one by") gearing. The whole idea of dumping the front derailleur didn't quite resonate for a lot of people in the beginning. It's a setup that has been around for years, but it was always viewed as giving up some gear range in the interest of a marginal increase in reliability, and it just wasn't for everyone.
Enter: the variable-width chainring, often called narrow-wide, and the clutch derailleur. The tooth shape of Narrow-wide chainrings increases their ability to control and hang onto the chain, making dropped chains a distant memory in most cases. Add to that, a clutch-enhanced rear derailleur and you have a drivetrain so well tamed that even long travel rear suspension can run all day long through the craziest rock gardens and not manage to shake the chain loose.
But what about that lost gearing?
It's in the cassette.
By pushing the cog count to 11 or 12, the overall range can finally be expanded without creating unreasonable jumps in cog size from one gear to the next. Have a look at the chart and we can explain.
On the far left is a fairly typical triple chainring drivetrain combination of 42, 32, and 22-tooth chainrings, paired with an 11-36t cassette. Plotted on the graph are the high speed in high gear (at a reasonable offroad, seated, top-end cadence of 85 RPM) and the low speed in low gear (at an uphill-grinding 60rpm). We kept the chart focused on 29x2.3 wheels to keep things concise and relatable for most riders.
As you look across to the right, you'll notice there's not a lot of variation in the low gear. The simple fact is that a difference of a few teeth on the large cog doesn't produce a very large change in gear ratio. So the idea that you can't climb as effectively on a 1X system is a load of hooey.
Where you see the dramatic change is on the high end. You can clearly see that the 42-11 is a big gear, topping out at something like 28 MPH at 85 RPM. Where, exactly, that's useful on a trail, we're just not sure. Maybe it would come in handy if you like to pedal to the trailhead and can't resist jumping in with any road group ride you might come across. Everyone has their thing.
Back here in the real world, though, it looks like a 30 or 32-t chainring give plenty of usable speed for knobby tires on dirt and the occasional cruise on blacktop from trail to trail. Going with a 28t could work well for riders who don't feel rushed on the blacktop or maybe spend a bit more time at the low end of the gear range and want to keep a tidier chain-line more of the time. Go 34 or 36 if you're a segment striver or on smaller wheels.
Long-story-short, less chainrings is more reliability on the trail, more weight saved, more maintenance avoided. You dig?