Mountain Bike Mullet Conversion Guide

“Mullet” refers to when a mountain bike has mixed wheel sizes, with the front wheel being larger than the rear wheel. This is also commonly referred to as “mixed wheels” or “MX” for short. The name “mullet” originates from the mullet haircut which featured “business in the front, party in the back”. The most common mullet mountain bike configuration utilizes a 29” front wheel (the business) and a 27.5” rear wheel (the party). However, these wheel sizes aren’t the only mullet configurations as some people also run a 27.5” front wheel and 26” rear wheel to prioritize jumping, along with some other mixed wheel size setups that tinkerers experiment with in their spare time.

In modern times (this article is written in 2023) many bike manufacturers are offering a portion of their bike model lineups with mixed wheel sizes with a 29” front wheel and 27.5” rear wheel. So if you’re looking at a new bike, chances are that your favorite bike brand makes an MX version of a few of their bike models that already come with mixed wheel sizes. Also, many bike brands are designing their frames to be easily convertible between a 29” and 27.5” rear wheel, so you can run either configuration depending on your preference. This is made possible by having either an adjustable rear dropout to relocate the wheel position, or by using an adjustable suspension linkage chip in the frame to accommodate any negative changes in geometry that happen when changing rear wheel sizes - or both! The ability to change the geometry to accommodate for different rear wheel sizes is necessary, as changing the rear wheel size will change the bike’s geometry since the smaller rear wheel shifts the entire backend of the bike downward. This change in geometry subsequently changes the bike’s riding characteristics, most likely in a negative way, so correcting the geometry is necessary for retaining favorable riding characteristics.

The Transition Patrol has always been known as a full 27.5" bike until MY2022 when Transition announced their new Patrol would only be available with mixed wheel sizes.

The idea of mixed wheel sizes is simple - the larger front wheel will have an easier time rolling through holes and over obstacles since that is the leading wheel of the bike (increased speed), and the smaller rear wheel is easier to maneuver through corners and over jumps (increased maneuverability).

The front end of the bike will feel as if it gets “hung up” less when rolling through rough terrain with a larger diameter wheel. This is because the larger front wheel reduces the feeling of the front wheel getting “stuck” between roots, rocks and holes simply due to being a bigger size. Increasing the rollover efficiency of the front end of the bike directly helps the rider retain speed rather than feeling as if rough terrain is just slowing them down. This also creates a more stable ride since the bike feels as if it glides over chunk a little more effortlessly. Since most of a bike’s maneuverability characteristics come from the rear end, it can be beneficial for many riders to simply increase the front end’s rollover, as the larger front wheel doesn’t tend to make much of a noticeable difference in the bike’s overall maneuverability.

A smaller rear wheel tends to feel as if the rear end of the bike can be thrown into corners more effortlessly, and the decreased mass from the rear of the bike tends to increase the “flickable” feeling that many riders love. Also, the smaller rear wheel diameter helps the rider avoid smacking their derriere on the rear tire during steep descents while leaning far back for stability, and that increased booty clearance definitely helps with confidence on steep, rowdy terrain. Since the rear wheel frequently tends to float above the ground while the front wheel generally stays glued to the terrain, the decreased rollover abilities of the rear wheel often go unnoticed by many riders.

Different strokes for different folks. On the left is me and my mulleted Devinci Spartan, and on the right is Tor and his full 29" Transition Spire.

But what if you don’t have a bike with adjustable geometry designed to accommodate for varying rear wheel sizes? If that is the case, then you will have to convert your bike to mullet.

Heads up… Throughout the rest of this article, I’m going to use the word “mullet” as a verb to refer to changing wheel sizes to make the front wheel larger than the rear. Also, I am only going to talk about 29” front and 27.5” rear mullet setups - as that is the most common setup - but you can just change the wheel sizes in your imagination if you’re tinkering with a more uncommon setup.

There are 2 extremely common situations for mullet conversions which we will cover below:

The most common conversion for mullet setups are when riders have a bike with 27.5” wheels in the front and rear, but desire a larger 29” front wheel in hopes of increasing their bike’s ability to maintain speed more effortlessly through rough terrain. Through the years of 2015 to 2019, there were a ton of bike models with 27.5” wheels in the front and rear. In recent years, riding styles have changed and many riders desire a bike that rolls fast, and prioritize speed over outright flick-ability as in previous years. When mullet-ing a bike in this fashion, it’s commonly seen as a way to modernize your slightly older bike since so many new bikes come with MX wheel sizes, making it a fun experiment. Most riders with a full 27.5” bike don’t necessarily hate their bike or anything, but they just like the idea of increasing the bike’s speed without (hopefully) losing any of the playful feeling with the 27.5” rear wheel, while also avoiding the need of buying an entirely new bike.

This is my beloved Devinci Spartan which came from the factory with two 27.5" wheels. I loved how it rode, but I stuck a 29" wheel on the front to see if I could pick up some speed and stability.

Certain riders on bikes with 29” wheels front and rear will reminisce of past years where they had smaller wheels and a more playful ride overall. While less common, you can mullet a full 29” bike by simply installing a smaller 27.5” rear wheel. Again, this helps riders avoid buying an entirely new bike since they likely just spent a ton of money on their new full 29” bike. However, they might be slightly wishing they opted for an MX bike in the first place, so the idea of a mullet conversion begins. This tends to happen when a rider initially seeks outright speed with a 29” bike, but later feels as if they are having less fun or frequently buzzing their butt on the rear wheel during steep descents.

This custom-built Specialized Stumpjumper EVO Alloy is configured with mullet wheels, but these bikes are primarily ran with 29" wheels front and rear.

To convert a 27.5” bike to mullet, there are 2 components that need to change. First, you obviously need a 29” front wheel and tire. You can simply purchase a new 29” wheel, or you could lace a 29” rim to your current front hub. Labor and spokes for a wheel build are expensive, and I would really recommend buying a whole new front wheel unless you have a hub that’s really special to you. Second, you will either need to buy a new fork to fit the new 29” front wheel, or you can purchase new fork lower legs that fit the 29” wheel which is an option for most fork models. Replacing the lower legs rather than the entire fork will save you some money up front, but will require some labor to swap out the lower leg assembly. You might be better off selling the entire 27.5” fork and purchasing a new 29” fork rather than attempting to sell your 27.5” fork lowers which are pretty undesirable. Personally, I would recommend just purchasing a new 29” fork and wheel, and keeping the old 27.5” fork and wheel. When you choose to sell this bike, you can reinstall the original fork and wheel and then transfer the new fork over to the new bike and have a spare front wheel (because your new bike will most likely have a 29” front wheel) - or just sell the 29” fork and wheel since 29” parts are easy to sell.

Swapping to a new 29" fork is also a great time to upgrade your fork! Trying something new can be a huge boost in performance and confidence. I have spent extensive time on both the Fox 38 and RockShox ZEB, and I love both for different reasons.

To convert a 29” bike to mullet, there is only 1 component that you need to install, and that is a 27.5” rear wheel and tire. In this case, I would definitely recommend buying a new 27.5” wheel and that you just keep your 29” rear wheel setup as a spare for three reasons. First, rear wheels take a beating and having a spare will come in handy if the 27.5” wheel explodes during a bike park road trip. Second, you might prefer the full 29” setup over the mullet configuration during different seasons or while riding different types of terrain. Third, you just might feel as if you aren’t as thrilled with the geometry and riding characteristic changes that the smaller rear wheel created, so you can easily just toss the 29” rear wheel back on to ride the bike as it was originally designed.

The above information is just the bare basic rundown of the parts you need to convert your bike to mullet. HOWEVER, these changes will alter your bike’s geometry and handling characteristics - potentially in a significantly negative manner if you don’t choose your mullet setup wisely. To avoid making your bike ride downright wonky with these changes, we urge you to pay close attention to the parts you purchase and the setup you choose to better understand the impacts of mullet conversions on bike geometry and handling. Now, let’s talk geometry changes, fork travel and more to convert your bike to mullet while maintaining its modern geometry and handling.

Rear wheels take a beating! Having a spare rear wheel almost always comes in handy.

If you install a 29” front wheel and fork with the same travel as when it was 27.5”, you are going to raise your bike’s bottom bracket height by about 12mm (~1/2 inch), slacken your head tube angle by about 1.5 degrees, noticeably raise your cockpit height and increase your wheelbase by a couple of millimeters. The slacker head tube might be an advantage on an older bike with a steeper head tube when it comes to descending. However, the raised bottom bracket will almost always be a disadvantage as it raises your center of gravity, reducing the advantages of modern “low” geometry. In modern times, bottom bracket heights range from about 332mm to 340mm. This keeps your center of gravity low so you feel like you’re riding “in” the bike, and this is a big part of why modern bikes feel so stable and corner so well. Some riders may not be experienced enough to tell differences in handling characteristics from a change like this, but this is realistically a big enough change that I would highly recommend avoiding this configuration.

Instead, I would recommend using a 29” fork that has 20mm less travel than the 27.5” fork that the bike was designed around. This will only raise your bottom bracket height by about 4mm and slacken your head tube angle by about .5 degrees. In the grand scheme of things, these are very small geometry changes that are likely to go unnoticed by even the most experienced of riders. The differences in how the bike steers and carries speed with the new larger wheel are definitely noticeable to all riders, and these changes alone will cast a shadow over any of these small geometry changes. With this configuration, you may be concerned about the fact that you are reducing your fork travel by negative 20mm. However, the larger front wheel’s increased rollover simply rolls over bumps more effortlessly than the 27.5” wheel, meaning you are less reliant on fork travel to absorb impact from as many bumps. If you’ve gone this route and feel is if your slightly older bike’s head tube angle still isn’t as slack as you like, I would recommend using an angle headset to slacken the head tube angle rather than increasing the fork travel. An angle headset will only change the head tube angle, and will not raise the bottom bracket height.

In this section, I’m mainly referring to mullet-ing a 29” bike that does not have any adjustment geometry components built into the frame (like flip-chips or adjustable dropouts) that are designed to retain the same geometry between 29” and 27.5” rear wheels. This conversion is both a little more tricky and less tricky at the same since you can’t exactly optimize the setup as much. Since you aren’t touching the front end of the bike and rather altering the rear end of the bike, you can’t really do much to alter the frame’s geometry without starting a chain reaction of negative geometry side effects. Swapping out the 29” rear wheel for a 27.5” wheel will drop the rear end of the bike and lower the bottom bracket height by about 12mm millimeters and slacken the head tube angle by -1 degrees. The bike will surely rip corners very well upon descents with the ultra-low bottom bracket height, but you’ll likely see a big increase in pedal strikes while climbing chunky terrain. Also, bikes are pretty dang slack these days, and while slacking out your already super-slack bike might feel pretty sweet when pointed straight downhill, it will likely be an unfavorable effect on the bike in almost any other situation (climbing, cornering, etc). You can offset this by installing an angle headset backwards to steepen the head tube angle, but that just feels so naturally wrong to do.

Before swapping in a little rear wheel in place of your big wheel, I would highly recommend that you do some research to see if there are any suspension linkage components, either made by the frame manufacturer or by an aftermarket company, that may be able to correct the bike’s geometry with a mullet conversion. For example, Williams Racing Products and Cascade Components are two popular companies who make aftermarket suspension links that primarily change the suspension curves, but they also do make some links to correct the geometry of certain bikes when swapping to a 27.5” rear wheel. Also, some bike manufacturers make spare suspension components to compensate for different wheel sizes. Bikes like the Specialized Stumpjumper EVO have 2 different shock links for both rear wheel sizes which is available to purchase right from Specialized.

Realistically, I would only recommend mulleting a 29” bike in two specific situations depending on the bike’s age. First, if you have a slightly older 29” bike where the bottom bracket height is around 350 millimeters and the head tune angle is around 65 degrees. In this scenario, lowering the BB and slacking the front end is actually beneficial to modernize that bike’s geometry and handling. Second, if you have a modern 29” bike and you spend a ton of time riding chairlifts or shuttling, then owning both a 29” and 27.5” rear wheel might be great to swap back and forth depending on where you are riding. For shuttle or park days with virtually no pedaling to climb, you may feel as if the benefits of the increased butt clearance and maneuverability outweigh any of the potentially negative side effects of the slackened head tube and lower bottom bracket while smashing straight down chunky descents. On different periods where you’re planning on spending time in the saddle and climbing to ride less gnarly trails, throw the 29” rear wheel back on to avoid pedal strikes and enjoy the increasing rollover abilities of the bigger rear wheel.

My enduro bike is a 2019 Devinci Spartan in the full 27.5” variant. I seriously love the way this bike’s suspension platform feels, and I just always feel at home on it. However, I did convert this bike to mullet with a 29” front wheel in 2020 to learn what all of the hype was about. Since mullet conversions were a new thing at the time, I started experimenting. This bike was designed around a 180mm fork in 27.5” form, and when I swapped to a 29” front wheel, I used a 170mm fork to see how the geometry and riding characteristics changed. On the trail, I immediately noticed the front end feeling more planted and stable since it rolled through rocks and roots with more effort. The bike felt like it picked up speed and stability in straight-line descents. However, I started to notice that I felt a bit “off” when turning corners - especially at lower speeds. I felt as if my cockpit was noticeably higher than I would have liked it, and my center of gravity as a whole was raised enough to the point where I was having trouble weighting my front tire to find traction in flat corners. I personally like to set up my bikes to find a balance between great cornering and great descending, but I currently felt like it only descended great. I didn’t want a one trick pony, so I reduced the fork travel to 160mm. Honestly, I didn’t think I would tell much of a difference in reducing the fork travel by just 10mm, but I definitely could. I felt as if that slight reduction in front end height and lowered bottom bracket was able to noticeably lower my center of gravity, and I was able to more favorably weight my front tire on flat corners. I actually ended up running this setup moving forward and never bothered making any other changes since the bike felt very balanced, and I was overall perfectly happy with this setup. The bottom bracket height is at 347mm and the head tube angle was around 63°. On paper, the bottom bracket height was higher than I usually like, but on the trail I didn’t really seem to notice that as the bike still cornered pretty well.

I also did not feel as if I lost out on much of the “flick-ability” of the bike. I was a little worried that the bigger wheel would reduce my bike’s playfulness as I really like to pop off of bumps and humps on the trail. From my experience, the 29” front wheel’s increased rollover speed overshadowed any potential downsides of having a larger diameter wheel on the bike, as the 29” front wheel just had me feeling as if I had more speed on tap to pop off of trail jumps. Also, the increased stability made it a bit easier to point and shoot on random trail gaps I could see in the near distance. I also felt almost identical on larger jump lines, and don’t think the larger front wheel hindered my experience when catching bigger air.

I love the increased confidence gain on steep tech with a smaller rear wheel. I feel as if I can launch myself into tricky situations with plenty of maneuverability with the bike's rear end.

Honestly, I have never ridden a 29” bike that was converted to run a 27.5” rear wheel without being able to properly adjust the geometry. However, I can confidently say that I am experienced enough to know exactly how it would feel.

If you have an older 29” bike (around 2014-2016) and you slap a 27.5” rear wheel in the bike, I would actually think that the bike would ride incredibly well, and this would be a solid upgrade to modernize your bike. Bikes from that era had decently high bottom brackets and steep head tube angles, so the bike will descend and corner noticeably better. The only drawback would be that the seat tube angle would be more slack, and you may feel as if you are hanging off of the back of the bike while climbing more than you would like. However, if you have a pretty modern 29” bike, then slapping a 27.5” rear wheel into the frame may lead to less than ideal results. Let’s use the Transition Spire for an example. This bike has a geometry adjustable flip chip, with a head tube angle of 63° and bottom bracket height of 350 in the HIGH position. With a 27.5” rear wheel, you would have around a 62° head tube angle and 338mm bottom bracket height. While the bottom bracket height ends up at a pretty “normal” spec which will be great for cornering without being so low that your pedals are constantly smacking the ground while climbing, the head tune angle of 62° is just incredibly slack. With this example, the bike will feel amazing on straight-line descents where you aren’t steering much, and you’re just leaning back and letting the bike smash through rough terrain. However, you might feel as if the front end is just too slack for cornering with some “wheel flop” since the front wheel is so far out in front of you. A 62° head tube angle would feel pretty floppy while climbing around corners, so you will likely feel as if the bike is much less versatile now. In the end, you will really have to look closely at the geometry of your bike as it was designed with a 29” front and rear wheel, and critically think of how the bike will ride after you toss in a 27.5” rear wheel.

In any of the above scenarios, whether or not you should mullet your bike greatly depends your exact bike and your exact goals with it. Much of your setup will come down to personal preference, so I would really recommend experimenting with different configurations.

When mullet-ing a 27.5” bike with a 29” front wheel, you may gain some speed and stability, but will lost out on at least a little bit of playfulness, add a little bit of weight and slacken your seat tube angle which may hinder your climbing experience. After I purchased my second bike, a Specialized Stumpjumper EVO with 29” wheels, I ended up switching my Devinci Spartan’s front wheel back to 27.5” and the full 180mm of travel to experiment with. The bike now feels more skittish and less stable, however, it’s super fun. I feel as if the steering is a bit more tight with the smaller front wheel, and I can maneuver through tight obstacles with a little less effort. The increased fork travel is also kind of fun, as it’s just big and squishy up front now. However, if I didn’t have a second bike with full 29” wheels, I would keep the Spartan as a converted mullet setup.

On the other side of the spectrum, if you have a bike with 29” wheels front and rear, and feel as if you’re buzzing your butt on the rear wheel more than you’d like, then going to a 27.5” rear wheel may be a great experiment. Take a peek at geometry charts to consider how this change will affect the bike’s overall personality, and think about whether or not the bike will still fulfill your riding preferences. If your frame has adjustability geometry to accommodate for the smaller rear wheel, I would definitely recommend switching to a smaller rear wheel. I’m only 5’7”, so I don’t have much clearance between a 29” rear wheel on steep terrain where my body is shifted almost fully over the back wheel. I constantly buzz my butt on steep trails with my Stumpjumper EVO in full 29” form, so I almost always grab my 27.5” bike for rides where I know the trails will be very steep.

As you can see, I don't have much room between my cheeks and the rear wheel on this steep rock roll, even with the 27.5" rear wheel on my Spartan.

To sum things up, experimenting with mountain bikes is very fun but isn’t free. The changes in your bike’s riding characteristics and the associated costs to mullet your bike may or may not be worth it to you, so please consider the recommendations that I have pointed out in this guide. Most importantly, have fun with it!

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