By now I am sure you have heard about mixed wheel, or mullet bikes. The set-up of having different sized wheels on a bike was banned by the UCI, due to time-trial cyclists gaining to big of an aerodynamic advantage from having smaller wheels on the front of the bike. However in 2019, this rule was changed, meaning the option of racing a mixed wheel bike for Downhill was back on the table, and wherever there is innovation on the race track, it is sure to make it’s way to mainstream manufacturing soon after. But is the “Business in the front, Party in the back” theory really any good? With racers like Loic Bruni, Martin Maes and Rae Morrison all opting for the mullet bike, surely it has to be worth a try.
I have been on a full 29inch wheels front and back since getting my Trek Slash at the start of 2018, and I loved it. The big wheels ability to truck over the roughest of trails, went perfectly with my habit of just ploughing down the main line as fast as I could. However as the geometry of trail bikes has changed so much over the last few years, with enduro bikes becoming longer and slacker, and high pivot bike accentuating this even more, I was starting to feel like I was missing some of the playfulness of my old bikes.
So why change? Some people claim that tire buzz is one of the main reasons they swap to a mullet set up, but I am on a medium sized Dreadnought, and although I am only 5’6″ (167cm) tall, I have not had many issues with buzzing my butt on the 29″ back tire.
The details behind running a mullet set up is not quite as straight forward as simply putting a smaller wheel in the back. In order for the frame geometry to still work Forbbiden have produced the ‘Ziggy Link‘. By replacing the lower link from the two-part Rate Control linkage, the Ziggy Link recalibrates the geometry to accept a smaller 27.5in wheel. The Ziggy Link is about 5mm shorter than the original lower link, but alters the geometry of my medium Dreadnought from a 462 reach to 457, the wheelbase is shortened from 1244 to 1240, and the bottom bracket height raises from 340 to 347. I am running a 170mm Zeb fork and a 154mm Push elevensix coil shock. With all these changes to the bikes geometry, you have to also consider that you are likely to need to change your bar height, or stem length, when you mullet your bike to compensate for the slacker by 0.4 degree head angle. I tried raising my bar height by 5mm, but in the end put it back to my original position anyway.
The ride feel – I was blown away two corners in to my test track. After six months of riding the Dreadnought as a full 29er I hadn’t noticed how much effort I had been putting in to man-handling the bike around. Sure it was fast and stable, but to get the most out of the full 29er set up, you had to put a lot in to it. This meant always attacking and riding at full pace, in order to make it feel comfortable. The mullet changed this, it made the bike a bit more nimble and responsive, meaning I didn’t have to put as much effort in to maneuvering it. I have been running double-down DH casing tires, and the noticeable weight reduction in the back certainly played a part in making the bike easier to handle. The biggest difference can be felt in the cornering, the smaller back wheel means you can cut a slightly smaller turning circle, and you don’t need to set up quite as early, or as high, to get the bike around tight and awkward turns.
Why does the mullet feel so good though? The smaller wheel in the back, and the adapted Ziggy link does make the bike a little bit smaller, which in turn makes it easier to handle. Whilst keeping the big wheel in the front means you don’t lose any of the grip and stability from a larger bike. The smaller back wheel in theory is also faster to get up to speed, as it requires less energy to rotate a smaller circumference. The lower rear axle height also significantly effects how it feels, by increasing the bikes stability. This is something that has been used in motocross bikes for years, regularly having rear axle 0.75 of an inch lower.
Although a full 29er might be a tiny bit faster in a straight line, trails are never straight. The ability for the mullet set-up to be more forgiving when you end up on a wrong line, and easier to correct these mistakes, means the mullet is faster to get back up to speed. It’s the equivalent of tossing up between speed and acceleration in racing computer game. Don’t forget for those of us who like riding in all weather conditions all year around, the bigger tire clearance in the rear triangle means the wheels are less likely to get clogged up with mud, and keep rolling during those winter rides.
For me; I am sold, I love the way the mullet feels so intuitive, but it is just another part of the bike industry where what works for one person doesn’t work for everyone. If you’re a strong rider over 6ft tall, then you probably won’t feel the same advantages to the mullet that I do. When I account for the increased stability, and manoeuvre ability it’s a win-win for me.
Photos by Jamie Fox @jfox.media