27.5 – 29er – Mullet. Which is the suitable wheel size?
In the previous two parts, I was talking about possible injuries because of components and how I tested three wheel sizes to decide whether or not the Mullet was the way to go for me.
How to turn your bike into a Mullet?
I made the mistake of starting to read blogs by keen weekend warriors, who calculated everything on paper and were adamant about certain fork travels (and certain things in general). These blogs left me more confused than enlighten. As an ex-elite DH racer, who after retirement looked after the Australian National DH team for 2 years, I thought I should resort to some of the trusty Aussie pro racers. I will not start name dropping here, but contacted three of them who I knew had experience with Mullets. Two of them came back with – “you are just over thinking it, put the smaller wheel in it, start riding it and do the changes as you ride it.” These boys are regularly in the top 10 at world cups & it just shows we need to be a bit more flexible sometimes. Of course, they have the fine skills to adjust to anything using their extraordinary abilities, to the point where they would be quicker than most of us even on a Kmart ‘bike’. So, maybe we do need to be particular with our set up, but not as much as some of the bloggers.
Anyway, I have tried to put together a digestible journey of my transition from 29er into a Mullet. Here we go:
It is cheaper to turn a 29er into a Mullet. In my opinion, what you need to consider are the head tube angle of the frame, offset of the fork and the length of the cranks. I ordered a 2020 Giant Reign Advanced 1 29er, small size. I knew I would not use the rear rim, so instead of a whole wheel, I just purchased a 27.5” rim and spokes through my local shop and Cycle Station Albury built it up with the original hub. When you are downsizing with the rear wheel the geometry will change and the bike ends up with more rake angle at the front. More rake means more trail, and if you have an enduro bike, that will create an even more sluggish steering feel. My Giant Reign came with a 65 degree head tube angle, which makes it stable and raked out enough already, before adding the ‘mullet factor’. Therefore, I checked the offset of the fork, to see if that had any potential. It is a Fox suspension unit with a 51 mm offset fork, which means the rake is the steepest possible for that brand and make the bike nimbler & closer to the feel & manoeuvrability of a 27.5” steed. It is worth noting here that we now have the option in general terms, of ‘slackening’ our bike any time we want (for steeper terrain), should it have 51 mm forks as standard; by changing to front suspension with 42 or 44 mm offset. Not an issue in my case because I am looking in the other direction with this mullet. If you are unsure about the offset of your existing Fox fork, there is a 4 letters ID on the left lower leg, close to the seal. Visit the Fox website, punch the numbers in and it will let you know what your offset is. The other major brand is Rock Shox & they have the offset on the fork at the right lower leg side under the seal. Rock Shox 29” forks have the choice of 42, 44 or 51 mm. I am not familiar with the rest of the fork brands, so if you have anything else other than Fox or Rock Shox, please do your own research.
Although my new bike arrived with a good set up for ‘mulleting’- aka the steepest fork offset with a good, stable head tube angle; I was concerned about the bottom bracket drop that results from fitting the smaller rear wheel. I rode a Rocky Mountain Instinct demo bike for over a month as a Mullet set up and even with the steepest Mino link setting in the frame, the pedals often caught on rocks while I was pedalling. A new phenomenon, that rarely happened before. So, I opted for an angled headset on my new ride. Most of the manufacturers who produce angle headsets bring them out in 0.5, 1 or 1.5 degrees range. I got the 1.5 degree headset, and the cup has been set up to increase or steepen the head angle on my Giant Reign and that therefore brings the bottom bracket higher up. I had twelve 10 plus km rides on it in the last 3 weeks and it looks like the offset headset has eliminated any possible pedal bashing. If you still have a problem with pedal clearance, I would recommend opting for shorter cranks. Mine arrived with the shortest length, 165 mm being the fitting for the small frame; with medium frames generally fitted with 170 mm and large frames with 175 mm length cranks.
On the crank length, obviously there is reason for the different lengths, but studies have proved that going shorter with cranks length does not negatively affected riding performance. For us, MTBers who are constantly in & out of the saddle, as well as changing pace and gears all the time; a shorter crank can even be beneficial.
Turning a 27.5” bike into Mullet
You need a 29”er fork, otherwise you will have clearance issues with the 29”er wheel and the lower leg arch of the 27.5” fork. Again, it is important to look at the head tube angle of your frame to decide which offset you need to order. Hopefully, you read my rumble about turning a 29er into Mullet above, if not please do, more info about geometry there. Obviously, you need a 29” front wheel or a rim and longer spokes to use with your existing front hub. With the new fork and bigger front wheel, the geometry will slacken, and you will end up with bigger trail and more sluggish steering. An angled headset may come in handy here too, however that is just in relation to steering; as there is less of a concern around the pedal clearance, as the bottom bracket ends up higher.
Just for the record, I got a Works Components branded angled headset, being half the price of Cane Creek. Time will tell if the quality is half as good or not. When you purchase an angled headset, you will end up with two settings. In my case, we set to steepen the head angle but if I flip the top head cup around the head angle will slacken. I will try the latter set up on steep trails, like Bright or Thredbo to work it out if it is suitable to my riding style there.
Thank you for Roger Derrick for editing my writing, Beau Proctor & Darcy Wilkinson from Cycle Station and my Hunstrian friend – Matte Cser with the initial bike set up and parts order.