The mixed Mullet configuration killed the 27.5 ”wheel diameter and is becoming one of the new trends in the off-road world. Once advertised as the perfect intermediate wheel size, the 27.5 ”could not stand up to the inexorable passage of time. In cross country, only frames in the smallest sizes are sold with 27.5-inch wheels, because the established standard is 29er.
This also applies to trail bikes and most enduro MTBs. In fact, the idea of using a larger front wheel has always been liked by some enthusiasts and operators in the sector, so much so that Specialized had already tried it by crossing a 29 with a 26. In practice, on a frame with standard geometry from 27.5 ”, using a large front wheel meant messing up the bottom bracket height, the opening of the head and saddle angles, and overall driveability. So how did the designers go about repurposing 650B frames like Mullet?
The only great facilitator was and is the Flip Chip which acts on the geometry. Offering two settings High and Low, which act by opening or closing the steering and raising or lowering the bottom bracket, the chip makes bikes with asymmetrical wheel diameter consistent.
They might be technically feasible, but why would you want one? What works on a mountain bike for gravity and for enduro - areas where Flip Chips and other devices to vary the geometry have been used with satisfaction for years -, finds concrete application on every single aspect of use on slopes. negative.
In recent years downhill athletes have conclusively proven that a larger front wheel is useful for generating more traction on difficult and steep terrain (including four-time world champion Loic Bruni).
Having a smaller rear wheel instead helps to keep the bike's center of gravity low as well as giving a sturdier rear wheel. In fact, the smaller wheels resist better to impacts on the rear, but not only. By mounting a tire with a slightly larger section than the front, the bike accelerates faster than a pure 29er out of hairpin bends and tight corners, while maintaining good lateral stiffness. Finally, the work of the designers in calibrating the dimensions of the frame, in particular the length of the undercarriage, is easier, without forgetting the optimization of the kinematics of the rear suspension.
It is no coincidence that many leading brands in the cycling industry offer their flagship models for trail, enduro and downhill with dual wheel configuration, pure 29er or Mullet, acting precisely on the Flip Chip to optimize geometry. Among the most representative of the scene, in particular for the impact it had in recent years in the development and affirmation of the "low, long and open" geometry, we find Transition. It now offers a Mullet version of its renowned Enduro Patrol MX with 160mm of travel front and rear.
Canyon, world leader in the mail order sector, has recently relaunched the full suspended Spectral, which is placed between enduro and trail riding, even available in three configurations: 27.5 ”, 29er and Mullet. The work done on the freeride / park riding Torque is even more refined, with two front triangles made specifically for 29 "/ Mullet and 27.5".
Another small but iconic brand, the North American Evil, offers the mixed diameter on the updated version of the long travel Insurgent: a good 168 mm at the rear with even the Superboost 157 × 12 mm spacing, derived from gravity, for the rear. Still on the subject of mountain biking icons, Santa Cruz offers its historic Bronson “all-around” MX version with 150 mm of travel on both wheels.
This is a special case, because it was born as 27.5 "and then converted to Mullet, bending to the influence of the trend and dynamics of the market. One of the significant enablers of this shift to mixed wheel setup has been the development of long travel 29er single plate forks, such as the latest Rock Shox Zeb and Fox 38.
The designers have finally unlocked the full potential of travel in excess of 160mm. on the front suspension, to get the best out of enduro bikes, regardless of whether they are 29er or Mullet.
What about the world of eMTBs? Here the mixed diameter seems to be depopulated, with the pure 29ers in the background. A 27.5 "rear axle (with a slightly wider tire if not Plus) gives more traction as well as the possibility of designing more compact wagons, a fundamental requirement considering the natural size of the engine and battery. Is this the beginning of the end for the pure 27.5-inch setup?
Bikers with a reduced height - roughly under one meter and 70 centimeters - might still prefer the platform with smaller wheels, but if they start looking elsewhere, then we could start and prepare the final farewell to the dear and old 27 and a half.
