The big talking point in pro downhill and enduro racing this year is wheel size. Last fall, the UCI relaxed rules stating that riders in downhill and enduro events had to run the same size wheel front and rear. Racers immediately began experimenting with bikes using a 29” front wheel paired with a 27.5” rear wheel. This combination is commonly referred to as a “mullet” setup.
The mullet has already found success at the highest levels of racing. Three-time UCI downhill world champion Loic Bruni won two World Cup downhill races aboard a mullet Specialized Demo. The rising star of enduro Martin Maes won the opening three rounds of the Enduro World Series with a mullet GT Force. Plenty of curious riders are now thinking about taking their own 27.5”-wheeled bikes and converting them to mullet bikes with a 29” fork and front wheel.
Is this trend here to stay or destined to become part of The Pro's Closet's Museum? Should you ride a mullet bike? To learn more, we investigated the history of mixed-wheel-size bikes and considered the advantages and disadvantages. The short answer: It depends.
Coming Back in Style
Though it may seem novel, this isn’t the first time the bike industry has played with mixed wheel sizes. Many astute Internet commenters immediately pointed out that the Foes Mixer is a mullet bike that's been in production for several years. Some may also remember the Specialized Big Hit from the early 2000s, which paired the 26” front wheel with a 24” rear.
Our bike museum even features a mullet bike dating back to 1985. The Velocitech Mountain Machine pairs a 24” front wheel with a 20” rear to make the ultimate hill-climb machine.
One of the most eye-catching mullet bikes in our museum is a more recent experiment. Travis Brown’s 2007 Trek 69er hangs above the front desk of our shop and it utilizes the mullet concept to make a faster singlespeed race bike, featuring a 29” front wheel paired with a 26” rear wheel.
Mullet Theory Explained
The early 2000s were still early days for 29" wheels, and they had yet to receive the wide acceptance they enjoy today. The first 29” wheels were heavier and more flexible than their 26” counterparts. Big-wheeled 29ers had unrefined geometry that made riders feel perched atop the bike rather than “in” the bike. They were more difficult to handle, especially for shorter riders, since the larger wheels required more force to move around and provided less room to hang off the back. Critics felt that 29er bikes weren’t maneuverable, playful, or fun enough to ever usurp smaller wheels.
But despite criticism, 29" wheels have some obvious advantages. Larger wheels more easily roll over trail obstacles like rocks and roots. They also have a proportionally larger contact patch, which provides increased traction. The mullet bike was created as a way to exploit the benefits of big wheels while minimizing the downsides.
A larger wheel on the front provides that desirable increased roll-over and traction. This is more beneficial on the front of the bike because it increases a rider’s ability to hit obstacles at speed and maintain control. The smaller rear wheel is lighter, stiffer, and easier to accelerate. The smaller wheel also keeps the wheelbase short and makes the back of the bike more maneuverable and playful.
The mullet setup is an attempt to get the best of both worlds, and it seems to be highly effective, as evidenced by recent race results.
The 69er: Mixing Business with Pleasure
Let's take a closer look at the Trek 69er in our museum to see how the concept fared. Brown is a mountain biking legend who represented the U.S. in the 2000 Olympic Games and in numerous UCI world championships. He’s also a two-time singlespeed world champion, so you know he's a little crazy. In 2007, he had been retired from professional racing for three years. Ever the innovator, he kept experimenting with new technology and was drawn to the 29” wheel and the benefits it could provide as a front wheel. So, using his influence at Trek, he had the 69er designed and built. It was meant to be the ultimate singlespeed weapon.
The 69er came about before the popularization of 27.5” wheels, so it uses a 26” wheel on the back. With the 29” front wheel, the 26" rear looks almost comically small in comparison. But it is significantly stiffer and easier to spin up. This can be hugely advantageous on a singlespeed bike, where you often have no choice but to muscle the bike up to speed in a hard gear.
The fork Brown chose is a cult classic, the Maverick DUC 32. This DUC 32 was custom-made for the 69er. It has 100mm of travel and a moto-inspired, dual-crown, inverted design with the stanchions at the bottom. A massive 24mm thru-axle further improves stiffness. The head tube was designed shorter to keep the handlebar stack low. The frame is made from hydroformed aluminum with wide tubes and a thick wishbone seat stay. This made the 69er incredibly stiff and many reviewers referred to the ride quality as “brutal.”
The 29” wheel paired with the stiff Maverick DUC 32 fork and slack (for the time) 69-degree headtube angle allowed the front end to plow through trail features. The 26” rear wheel, in comparison, felt incredibly responsive and playful. Because the rear end was so short and stiff, it had a tendency to dance around when following the big front wheel through rough terrain. It truly was one of the wild examples of a mullet bike — all business in the front, with tons of party in the back.
All of this added up to a bike that was fast and lots of fun, but it did not last in a crowded and evolving mountain bike market. Production ended after only a few years. Like the hairstyle and the mullet bikes that came before it, it became unfashionable as more clean-cut, matching-wheel-size bikes became the norm.
Is a Mullet Bike Right for You?
History likes to repeat itself and mixed-wheel-size bikes have slowly been coming back into style. Today, Mullet bikes have new advantages working in their favor like modern geometry, lighter and stiffer 29” wheels, and the option of a 27.5” rear wheel which is much closer to the 29” wheel in size and performance. Thanks to those high-profile race results, a lot of riders are wondering if they should consider a mullet bike.
Enduro and downhill riders stand to gain the most from a mullet set-up. While 29"-wheeled bikes have had some success in gravity racing, widespread adoption has yet to happen; 27.5"-wheeled bikes remain popular with many riders. As a result, the majority of wheel-size experimentation is occurring in enduro and downhill.
It's unlikely that turning a modern XC race bike into a mullet will improve performance as it will affect the geometry in a way that negatively impacts climbing. The 29er has firmly established itself as the dominant wheel size in the XC world, front and rear.
There are currently very few bikes that come stock from the factory with mixed wheels. For most riders, riding a mullet bike will require swapping out the fork and front wheel. This means mullet bikes are suited for those with some mechanical inclination who want to experiment and aren't as worried about future resale value or changes in a bike's stock geometry.
In general, putting a 29" fork and front wheel on a 27.5"-wheeled bike will raise the front end. This slackens the head angle (which is beneficial for steep trails), increases stack (something that can bother riders who need lower handlebars), and raises the bottom bracket.
Putting a 27.5" wheel in the back of a 29er bike is a possible option, but it's less ideal because it will lower the bottom bracket, increasing the risk of pedal strikes. Plus, the chain stays will still be too long, since they were meant for a 29" wheel. One of the benefits of a mullet bike is shorter chain stays, which usually improves handling. That's why it makes more sense to convert a 27.5"-wheeled bike with shorter chain stays.
Smaller riders or riders with shorter legs are likely to benefit from a mullet bike. Any rider who has struggled to feel comfortable maneuvering a 29er bike on steep or technical trails may find that offsetting a 29" front wheel with a smaller rear wheel will make a bike feel more nimble, smaller, and easier to handle.
Riders with 27.5" bikes who are curious about 29" wheels but don't want to buy a new bike or riders who want to maintain the playfulness of their 27.5" bike but want to improve front end roll-over and traction can also benefit from a mullet set-up.
We'll have to wait and see if the mullet bike concept sticks this time around. But no doubt, bikes like the Velocitech Mountain Machine and the Trek 69er won't be the last famous mullet bikes to end up in our museum collection.
If you're considering converting your current bike into a mullet bike, check out our collection of 29" wheels and forks. If you're looking for a bike to convert and experiment on, check out our 27.5" mountain bike collection.