SHOP MULLET GRAVEL BIKES NOW
If you've been following mountain bike trends over the last few years, you'll likely have heard the word 'mullet' being used, mostly to describe a smaller 27.5" rear wheel paired with a larger 29" front wheel. Less often, but becoming increasingly commonplace, the word mullet can also used to describe a specific drivetrain setup, with road bike shifters up front, but a mountain bike derailleur and cassette out back.
SRAM have been setting the stage for mullet drivetrains for some time, whether intentional or not, with the advent of wireless electronic shifting. While electronic shifting has been around for more than a decade now, and 2025 marks a decade of SRAM's wireless eTap (now AXS) groupsets, the pieces have really fallen into place the last couple of years for mullet bikes. But what does it really mean, and why is it a good thing?
Early 1x Setups
Those that have been around the mountain bike scene for a long time will remember the transition to 1x drivetrains - while mountain bike front derailleurs had their time, and grant riders the utility of a very low gear for climbing steep hills, their days were numbered. Many of us had been experimenting with single front chainrings with chain guides on pedally bikes long before 'enduro' was a bike category, or a race format. The truth is, front derailleurs added complexity, were a common point of failure, and reduced ground clearance.
This was the future, we just didn't know it yet
Add to that the inconvenience of a dropped chain on a rough descent - a limited gear range was preferable to frequent dropped chains for most people. It took SRAM's clutch rear derailleurs and pioneering narrow-wide tooth profiles to really put the nail in the front derailleur's coffin for mountain bikes, and bring us a useably-wide range 1x cassette, but we got there.
1x drivetrains are the standard setup on mountain bikes now - such as this SRAM GX Eagle mechanical drivetrain
Front derailleurs still reigned supreme on drop-bar bikes for a long time, though, despite gravel bikes facing many of the same problems as mountain bikes, the limiting factor here being the rear derailleur and cassette. Typically drop bar shifters use a different cable pull ratio (that is, the amount of cable pull the derailleur needs per shift click to change one gear), so gravel bikes running road shifters were limited to road bike gearing. 1x drivetrains were possible however, with groupsets like SRAM Force 1. They were common on cyclocross bikes, and made their way onto some early gravel bikes, but lacked the range and tight ratios to be widely adopted among gravel bikes.
The Advent of Electronic
The advent of electronic shifting changes this, however. Shimano's Di2 system allowed users to pair a mountain rear derailleur with road shifters, although required the system to be 'tricked' to make it work, and Shimano's 11-46t cassettes didn't provide an appreciably wide range to replace a double crankset. The introduction of SRAM's AXS mountain bike groupset and their XPLR gravel groupset changed things, however.
SRAM's XPLR groupset brought 1x functionality to drop bars, with 1x specific cranksets, derailleurs, cassettes, and programming. The gear range on the 12 speed XPLR groupsets was still relatively narrow however, designed for racing on flatter terrain like you might find at Unbound in Kansas, not the steep mountains of BC or elsewhere.
Why Go 1X on a Gravel Bike?
While the reasons for going 1x on a mountain bike are pretty obvious, and many of the same reasons apply to gravel bikes. Removing the front derailleur gives more room for knobby tire clearance. Removing the chainrings gives more ground clearance. The narrow-wide chainring profile makes for better chain retention over rough ground, so fewer dropped chains. Fewer derailleurs means less complexity overall, and usually less weight.
This Aspero-5 sports a wide range Force/XO Eagle mullet drivetrain
Obviously ditching the front derailleur has some drawbacks, such as reduced range. You're not going to get quite the same bottom or top end, and those that ride smoother gravel or want to ride more on-road might miss the top end, whereas bikepackers might miss the bottom end. Fewer chainrings and a wider cassette also means fewer ratios and wider gaps between them. Again, those that are more road/fast gravel focussed might miss the tighter ratios, but SRAM's new RED XPLR 1x13 groupset aims to solve that problem.
Mullet is Here
Whether or not SRAM AXS was designed to be cross-compatible across mountain and road, we're not sure, but it worked, and it worked easily. A SRAM road shifter simply pairs and works with a mountain rear derailleur, meaning you can achieve a mountain bike range, with drop bar shifters, unlocking wide range, and 1x clearance and chain security. Note that SRAM do officially support this combination - you can check their compatibility chart here.
Despite mixing flat top chainrings with an Eagle chain, the SRAM mullet drivetrain works, and is something we're seeing coming as standard spec on some bikes, such as the Specialized Diverge and Diverge STR, Cervélo Áspero, Giant Revolt X and others. Now that SRAM have launched their Eagle Transmission drivetrains, that gives even more options for those gravel bikes with UDH-compatible dropouts to run a super robust wide-range mountain drivetrain on their gravel bikes.
Mix and Match
The other beauty of a mullet electronic drivetrain is options. The ability to mix and match derailleurs means that you could in theory swap between a wide-range mountain derailleur and cassette for big exploration days, and a tighter ratio XPLR derailleur and cassette, for example the new RED XPLR 13 speed, for flatter gravel and racing. While that's not something that most people are going to do often, it's nice to have the option without having to replace shifters and brakes too.
So there you have it, a short history and explanation of mullet drivetrains. Mullet drivetrains aren't for everybody - for some the even wider range of a 2x setup makes more sense, and for others it's all about the tight ratios of the XPLR groups. For those of us that want the security of a narrow/wide chainring and the range of a mountain drivetrain, mullet is the way to go.
SHOP MULLET GRAVEL BIKES NOW
Bonus: Mechanical Counterparts
Here's the bonus section where everybody wins. That wide-range technology has trickled down to mechanical drivetrains now too. While they don't have the flexibility of adding a front derailleur as easily, Shimano's GRX 1x12 mechanical combines the drop-bar pull ratio with a long cage RX822 derailleur that's compatible with their mountain chain and 10-51t cassette.
SRAM also recently rolled out their Apex XPLR 12-speed group which is available in either an electronic or mechanical flavour, the latter of which is available in an Apex Eagle configuration, compatible with the drop-bar pull ratio and a 50t or 52t cassette. Rejoice, for mere mortals can now benefit from wide-range MTB drivetrains on drop bar bikes.
Want to mullet your gravel bike but not sure where to start? Contact us and have our customer service team help you spec out your dream bike.
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