We are back in the bike lab learning all about mullet bikes. What is a mullet bike? It’s 79er, a 97.5″, a pennygnarthing. It’s a mixed wheel size mountain bike. Why? The idea is you get the best of both worlds — the big 29″ wheel to handle the business up front and the small 27.5″ wheel for the party in the back. Does it actually work that way? Read on and find out.
Mullet Bike Setup
Ibis Mojo 4 Platform
I used the Ibis Mojo 4 for this experiment. It’s a great candidate for a mullet conversion. You’ll see why in a second. So you just swap out the front wheel of a 27.5” bike with a 29er hoop. Easy peasy. Done – right? Not quite. First of all, you need a 29” fork in order to run a 29” front wheel. So I swapped out the stock 27.5” Fox 34 140mm with a 29” Fox 34 130mm. Why the drop in travel? 29” forks will always have a longer axle to crown measurement than a 27.5” fork with the same travel. I dropped 10mm to help mitigate this increase in front end height. Even with the drop in travel, the fork was still taller than the stock version. Combine that with the added axle height of the 29” wheel, and things can get out of control quickly. I did everything I could to maintain the geometry of the Mojo 4, but it still changed a bit in mullet mode.
Geometry Change
I was curious to see how much the geometry would change with a mullet conversion. I knew the head tube and seat tube angles would get a bit slacker, but I wanted to know by how much. I went full nerd on how to figure this out. I build a little jig to hold the bike completely level so I could take accurate measurements of the angles. Sure, I could have used a bike geometry model, but where’s the fun in that? Keep in mind, I used bubble levels and a digital protractor to measure all the angles. It’s not a perfect system and there’s some room for error. When it was all said and done, I ended up using an online bike geometry model to corroborate my field measurements. Bit of a brag here, I wasn’t far off at all.
The critical measurements I looked for were the head tube angle, seat tube angle, wheelbase, and bottom bracket height. I didn’t really have an accurate way to measure reach and stack but those will change as well.
STOCK MOJO 4
HTA – 65.4
STA – 74.3 (actual)
Wheelbase – 1268
BB Drop ~ 15mm
MULLET MODE
HTA – 64.1
STA – 73 (actual)
Wheelbase – 1277
BB Drop ~ 11
The head tube and seat tube angles get slacker because the front of the bike gets taller. The wheelbase gets longer because of the difference in fork offset and axle to crown height. Keep in mind, because the fork is on an angle, there’s a horizontal component to the increased axle to crown height. That horizontal length adds to the wheelbase. The bottom bracket drop comes up a bit, again due to the taller front end. All in all the Mojo 4 works pretty well as a mullet. The head tube gets slack, but not silly amounts of slack. The seat tube is pretty steep originally, so you can afford to make it a little slacker without affecting climbing performance too much. It’s a long bike, but a couple of extra millimeters aren’t huge in the wheelbase department. Enough nerding out. Let’s talk about how this thing rides.
Mullet Bike Ride Impressions
I took a lap in the standard 27.5” setup just to set a baseline for this bike on this trail. Speaking of the trail, I picked one that had a lot of rocks, roots, and chunky bits. It also had plenty of flat awkward technical sections as well as steep rollers and a couple of jumps. It’s a great trail for feeling the differences in wheel size. Next, I swapped forks and repeated the same trail. I could feel the difference immediately. It’s not subtle — at all.
27.5” Baseline
I’m not getting into the details too much here. If you want those, go read our review. I just wanted to set a quick baseline for the bike on this trail. In the tight, technical bits, the handling was very quick and easy to steer. It wasn’t too difficult to pick my way through the rocks. I did, however, have a couple of rough rides through some of the rockier and steeper sections. The bike doesn’t want to monster truck too much. It’s happier to dodge and weave. Overall I enjoyed the ride, but I did feel that some of the sections were pushing the limits of the bike a bit.
Mullet Mode
Spoiler alert – from the first rock roller I knew this was going to be good. I liked seeing the big wheel out in front of me. It gives you a degree of confidence seeing a big wagon wheel handling the business end of the bike. Without a doubt, it handled the business better. It went up and over rocks easier, smoothed out transitions at the bottom of rock rolls better, and overall added a level of capability to the bike that 27.5” couldn’t provide.
Uphill Winner – 27.5”
The Mojo 4 is one of my favorite bikes for climbing. It is quick, efficient, and handles technical terrain very well. Mullet mode makes it quite a bit slacker, and that generally never helps climbing performance. The big front wheel feels a bit less manageable in technical terrain as well. Picking my way through and around rocks on the climbs was harder. The win goes to the stock 27.5” setup.
Cornering Winner – Mullet Bike
I’m a big fan of 29ers. For our western US trails, they handle the wide-sweeping turns a little better than a 27.5” for me. They seem to track a smoother arc through the corner without the need for as many micro-adjustments. 27.5” wheels clearly handle tighter corners and berms better though – especially the awkward rocky ones. The shorter wheelbase and smaller radius let you steer the bike instead of just leaning it.
Cornering on a mullet is really the best of both worlds. You get the nice smooth arc of a 29er with the added maneuverability of the 27.5”. The front wheel swings wide while the back wheel kind of dives inside and cuts a tighter path. It feels pretty different from anything I’ve experienced before. I prefer it over a full 29 setup even. Only in flat, tight, and rocky sections did I prefer the agility of the full 27.5” bike. The win goes to the mullet.
Capability Winner – Mullet Bike
I’ll start this with a caveat. If I could run the Mojo 4 in a full 29” setup, that would be the most capable bike for rough and rocky terrain. That bike doesn’t exist, so the battle comes down to 27.5” vs mullet. The mullet is on another level of capability. Even with the 10mm reduction in front travel, I felt far more confident with the slacker geometry and bigger wheel. It made light work of some sections I struggled with on the stock setup. It carried speed easier and held its momentum through wheel-grabbing sections of trail. I was able to push the bike harder when things got rough. I’d take the mullet, hands down.
Jumping Winner – 27.5”
The only time I could feel the imbalance between the two wheel sizes was in the air — especially bunny hopping. It’s a little tough to describe but you almost feel like you’re “stink bugging” on every jump. The front wheel only makes it off the ground a little bit while the back wheel is nice and high. I’m sure with more time spent on a mullet setup, you’d find the proper balance. Even then, I prefer jumping with small wheels. 27.5” takes the win.
who is The Mullet Bike Setup for?
If you love the feel of a 27.5” bike in most situations, but feel a little outgunned in nasty, rocky terrain, a mullet might be the solution. The added capability doesn’t come at much of a cost either. The bike still remains fairly quick and spry, but goes up a level or two in capability when things get rough. The front wheel motors over rough terrain much better than its 27.5 counterpart. Alternatively, if you’re a die hard 29er fan, but want a quick, jibby bike, go mullet. It is more maneuverable and fun than a full 29er without giving up the front end feel you’re used to.
Mullet Bike Conclusion
Am I a mullet convert? Yes and no. I’ll hang onto my 29er for flat out speed and capability. The mullet can’t quite match a full 29er in rough terrain. I will however take a mullet over a 27.5” any day of the week. So the question no longer is 29er vs 27.5” — its 29er vs mullet.
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