Are single chainring mountain bikes usual?

Question

I just bought my son a typical+ mountain bike in a typical Frech sports shop (a BTWIN 530 at Décathlon) and realized that it has only a single sprocket at the front, and 9 sprockets at the back:

I have never seen that before (not that I looked very much, but I am used to the 3 + ~7 combinations) and was wondering whether this is

• usual
• expected
• unusual but why not
• you have been scammed

I can, worst case, return the bike but Decathlon, while being a Mr and Mrs Everyone shop, is usually fine (I casually rode their bikes for years).

LATE EDIT: thank you for all the answers so far - in light of the excellent details I got there I should have probably noted that this is a bike for casual, usually on-road biking.

LAST EDIT: thank you for all the answers - this is really a great SE site. It was near to impossible to choose THE answer, sorry for the others where I could just +1 (the update on road usage was great, thank you)

Answer 1

A 1x drivetrain (single chainring) is pretty much the standard now in mountain biking - you will notice the rear cassette is much wider than the classic 3x7 setup you are used to. The wide rear cassette gives a wide range of gears (although not always as wide as the old 3x7). Most also have also moved to more speeds(sprockets) in the rear (i.e., 11-12 speed), if the 1x9 has a large range (which it appears that it does), it will have larger steps between gears than a 3x7 drivetrain you are used to.

Other changes in modern mountain bike drive trains are:

• rear derailleurs are usually clutched to better retain the chain and control chain slap
• a front single chain rings using narrow/wide tooth configuration to again better retain the chain

Better chain retention and a single rear derailleur means that riders have to think less about gears. In the modern setup you do not have to think about chain management, as the chains generally remain in the selected gear. Contrast this against a 3x7, where you often had to remember to shift Big-big (big ring, big cassette) before downhills to improve chain retention. This leaves the rider to focus more on navigating the terrain.

In terms of the pictured bike, the drawbacks relative to a 3x7 are likely a reduced range between the hardest and easiest gear and larger jumps between gears.

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Update - on road usage

The OP updated the question to note that the bike is intended for casual on road use. The 1x setup is really tune for trail usage were speeds are slower. Relative to the reference drive train (a 3x7), out of the box it will be less functional for on road use due to it being under-geared for the road (i.e., on the road you may find there is not a "hard" enough gear). This can be alleviated by swapping out the front chain ring for a larger chain ring (as well as road friendly tires). The gearing is more "tunable" than reference drive train, where there were little option in the market to change the 3x chainrings to different sizes.

Answer 2

My understanding is that performance-oriented mountain biking has evolved to take on tougher and more technical terrain. If you design a bike specifically for a 1x drivetrain, then all else equal, it should free up some clearance to enable wider tires. This is because you don't have to account for how the front derailleur would otherwise hit the rear tire. The advantage of bigger tires is meaningful in this segment of the market, and perhaps for some gravel bikes also. As other answers have detailed, 1x has become de rigueur on mountain bikes.

A secondary benefit is that riders no longer have to worry about how to time a front shift while they are bouncing around on rough terrain. When the bike is bouncing, there's a higher chance that a front shift will cause the chain to jump off the chainring. It's best practice to ease your pedaling up slightly, as this seems to decrease the chance of dropping a chain.

In road settings, I don't perceive 1x as having any meaningful advantages. We are bouncing around less, which lessens the chance of dropping a chain that way. Modern road bike tires have increased considerably in size, but current generation performance road bikes can take 32mm tires at most. The front derailleur doesn't even start to affect tire clearance until at least 40mm, and possibly more, which is in the size range that gravel bikes use. On the road, 1x leaves greater gaps between cassette cogs. In group riding, when you're matching the speed of the group, this means you will probably be further away from your optimal cadence than the people on 2x drivetrains. In any case, 1x is not a scam, but the cost-benefit tradeoff is clearly the poorest on road bikes. No professional road teams have adopted 1x drivetrains wholesale aside from Aqua Blue, which folded due to financial reasons but did seem to have some issues with either their 1x drivetrains or something else in their setups (e.g. the bike's interaction with the drivetrain).

There are some specific drop bar niches where 1x could make sense, however. In criteriums, flat time trials, and flat triathlons, 1x incurs slightly lower aerodynamic drag. This is because one chainring and the front derailer are removed. This is offset by slightly higher overall drivetrain friction, and significantly worse friction in the lowest gears. In cyclocross, you are also bouncing around a fair bit, and you have to worry about avoiding all the other racers around you. Removing the cognitive load of when to do a front shift would be a possible gain, and it certainly would be no loss. When racing cyclocross with a 2x drivetrain, I quite rarely shift to the big ring - and interestingly, riding in the small ring and the small cogs is quite bad for drivetrain friction, so I suspect that the real-world drivetrain friction on a 1x setup in cyclocross is lower than the real-world friction on a 2x.

Answer 3

The configuration is not unusual at all. It has even become quite common, the smaller front ring and the quite wide ranging cassette for decently spread gearing. It also brings a gain of weight, simplifies maintenance and removes complication from shifting.

If your riding terrain is not too hilly the steps between the 9 gears should not be too steep, since normally 1x configurations have more expensive 11-speed or 12-speed group sets. But those could also excessively stress a junior rider.

Answer 4

this bike has an 11-42t Microshift cassette with

11-13-15-18-21-24-28-34-42 cogs

typically previous 9-speed drivetrains used an 11-34t cassette

11-13-15-17-20-23-26-30-34T.

which was updated to 11-36t

11-13-15-17-20-23-26-30-36T

However these were typically accompanied with a triple or double chainset.

Recent Shimano 9 speed MTB chainsets are 40/30/22 triple or 36/22 double

This resulted in a range of (40/22) * (36/11) = 5.95 for the triple 11-36, and 5.36 for the double.

This 1x has a range of only 3.82x.

So your bike loses on maximum top speed (if you can pedal fast enough), or on easiest gear, or both.

The chainring at the front is a 32t, so the maximum top speed is effectively 20% lower.

At 100rpm your bike will do 38kph in top gear. https://www.bikecalc.com/speed_at_cadence

As far as the bottom goes, you have a 32/42 easy gear, which is about 24% harder than the 22/36t on a triple or double setup. In addition, if you consider the easiest three gears on the 1x9:

• 32/28 = 1.15
• 32/34 = 0.94
• 32/42 = 0.76

with a triple or double setup:

• 22/20 = 1.1 (or 30/26 = 1.15)
• 22/23 = 0.96 (or 30/30 = 1)
• 22/26 = 0.85 (or 30/36 = 0.83)
• 22/30 = 0.73
• 22/36 = 0.61

So you can see in effect that the bottom three gears on the 1x9 correspond to gears 2, 4, 5 on the 3x9 or 2x9.

The other negative features of the 1x drivetrain to note are:

• larger chainrings with larger cogs are more efficient in friction terms (e.g., 44/22 is more efficient than 22/11), though this is likely not significant at this level of bike
• there is a larger cadence gap between the 15t and 18t cogs than the 15t vs 17t on the 3 or 2x setups
• the cassette will wear out more quickly, since whereas you might have pedalled 40/20 before and a larger cog wears out more slowly, now you will be pedalling a smaller cog on average, which will wear out more quickly
• the cassette, being larger, is more expensive to replace
• there is no front derailleur to help keep the chain from falling off the front chainring

The positives of this setup are:

• for children who do not understand multiple gear ranges, 1x is easier to understand
• it may reduce manufacturing and labour costs for the manufacturer
• 1x setups are 'on-trend', and may be easier to sell, even though at this price point the setup is less than optimal (more expensive 1x systems will use even larger and more expensive cassettes that have a wider range)
• for much more expensive bikes with dropper posts and fork remotes, the extra clutter of a front shifter may be a negative; on such a bike as this one, this isn't a big concern
• there may be a very small weight saving (a heavier cassette, but no front derailleur, shifter or cable) - this should not be a concern on such a cheap bike.

This is not a bad bike per se, but this is what manufacturers are selling now. You might struggle to find a bike with a traditional 3x setup, and if you do find one it might have very low-grade components on it, as manufacturers are trying to put 1x on all MTBs. So if you don't like the 1x, make sure you have a well-priced alternative with suitable components.

I personally ride MTBs often on-road over a long 1% downhill gradient of several km, and I would find a 32t chainring quite limiting as I prefer to grind more than spin, especially at 100+rpm. But if you are riding exclusively off-road and without high speeds then you should not find this a problem. Also for children and others cycling at leisure speeds then this would not be a limiting factor.

Answer 5

There are already excellent answers here, so I just want to provide a simple tl;dr kind of answer.

Nowadays this setup is usual, we can even say it is even expected. It is possible thanks to modern read derailleurs and wide-range rear cassettes.

• Easy to maintain: You don't have to worry about a front derailleur and there is one shifter less to worry about which as a bonus gives you a simpler handlebar setup
• Robust: less moving parts means less things that can break and cause trouble
• Resilient: with the right front sprocket, you have less risk of loose chains when hitting hard terrain, a pothole or while doing jumps

Answer 6

This is quite ok.

Personally I've moved from 2x10 to 1x12 (sram nx) and this made my xc bike noticeably faster. The one thing that no one mentioned before is that you really might not need such low gears that you've had with 2x or 3x. This (at leas for me) is because you have the ability to switch gears smoother and in one direction while you're approaching an uphill. So you don't loose so much kinetic energy while changing the gear since you can pedal all along.

Sorry if this is not clear, I've tried my best