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What is a mullet bike and could it spell the end of the 650b concept?

Mullet bike YT Capra
(Image credit: YT)

There might be a global shortage of new bikes, but one category where demand is low, has generated a new trend.

Once touted as the perfect intermediary wheel size, 27.5-inch hasn’t endured. In XC riding, only the smallest of frame sizes will configure with 27.5-inch wheels – the standard is certainly 29er. This applies to trail bikes and most of the enduro category, too.

So what are frame brands doing with the legacy 27.5-inch or 650b models? They’re turning them into mullets bikes.

What is a mullet bike?

Well, the idea of running a larger front wheel has always appealed to some, but on a frame with standard 27.5-inch geometry, all you end up doing is messing with the bottom bracket height and handling agility. 

So how are bike designers managing to repurpose 27.5-inch frames as mullet bikes? The one big enabler has been the geometry chip. By offering two settings, which slackens head angle but also adjusts the bottom bracket height, geometry flip chips have made the asymmetric wheel size bikes possible. 

They might be technically viable but why would you want one? What works in downhill mountain biking, applies to all other aspects of mountain bike descending. And downhill racers have conclusively proven that a bigger front wheel is useful at generating more traction on tricky and steep terrain. 

Having a smaller trailing wheel helps keep overall bike mass low, and also gives you a more impact-resistant rim at the back. Smaller wheels are tougher and the 27.5-inch rear wheel with a big tire, accelerates quicker than a pure 29er out of tight switchbacks while retaining good strength. 

In the last weeks, the industry has seen no fewer than three new mullet versions, of esteemed legacy trail and enduro bikes.

mixed wheel size

(Image credit: OEM)

A flood of mixed wheel size frames 

The first of these is from Transition. It now offers a mixed-wheel size version of the Patrol, with 160mm of suspension travel at each end.

Rolling a 29er front wheel and sitting at a 63-degree head angle, the Patrol MX isn’t shy of venturing down the steepest of technical descents. To aid stability, Transition has also stretched the reach of its new aluminum Patrol.

Fellow Pacific Northwest brand Evil, is now offering mixed wheel sizes on its updated Insurgent. The company has boosted frame travel from 150- to 168mm and opted for Superboost 157x12mm rear axle spacing.

If you fancy the idea of a 29er front wheel rollover, with a lighter rear wheel, but want it all spinning in a carbon-fiber frame, the Evil Insurgent MX is a deal. And with a 170mm front fork and 168mm rear, you’ll never be underbiked, even at the bike park.

mixed wheel size

(Image credit: OEM)

A classic 27.5-inch frame goes halfway 29

The third new mullet bike release has been from Santa Cruz. 

Bronson is an important name in the Santa Cruz product line-up, being the brand’s first 27.5-inch bike. It has now bowed to the influence of trend and market dynamics, being reconfigured as a mullet.

With the new Bronson, you get 150mm of VPP rear suspension, balanced by 160mm of front travel, and the benefit of that 29er wheel.

Each of these new mullet bikes is a reconfiguration of proven enduro bike platforms. It will interesting to see how customers who have resisted the move to 29ers, might embrace these mullet bikes.

With its aluminum frame, Transition’s Patrol could appeal to larger riders, or those on a budget, who like to go big – and are hard on bikes.

Evil’s Insurgent MX has massive amounts of suspension travel and a light carbon-fiber frame, with excellent Dave Weagle-designed suspension.

For those riders who want a mullet and believe in the concept of short links separating the terrain impact forces on a dual-suspension bike, the Santa Cruz Bronson will appeal. With its VPP suspension system having additional bearings to smooth out your ride.

One of the significant enablers for this move to mullet bikes has been the development of longer-travel singe-crown 29er forks. With RockShox’s Zeb Ultimate and the new Fox 38, designers finally have access to 29er single-crown forks beyond 160mm, which make the enduro mullet concept work.

Is this the beginning of the end for pure 27.5-inch? Compact enduro riders might still prefer the smaller wheel platform, but whether there are enough of them to sustain its future, could become debatable.

Lance Branquinho
Lance Branquinho is a Namibian-born media professional who graduated to mountain biking after injuries curtailed his fascination with trail running. He has a weakness for British steel hardtails, especially those which only run a single gear. Rides: Morewood Kwela Cotic Simple 26 Pyga 160mm aluminium prototype