A mullet (or MX) runs a 29 front and a 27.5 rear. The smaller rear wheel lowers the rear axle by about 20 mm [ESTIMATED]: that drops the bottom bracket, slackens the angles and shortens the effective chainstay versus a dual 29. The result: more agile and playful at the rear, better tight-corner handling, without losing the roll of the 29 front. You pay for it in pedal strikes and a little composure at speed — and it only works cleanly if the frame is designed for mullet or has a flip chip.
A mullet isn't just a downhill trend: it's a whole-body geometry change triggered by a single part, the rear wheel. Understanding what it moves stops you converting a bike and ending up with the BB on the floor.
Why does the same bike "corner differently" just from swapping the rear wheel? Because that wheel doesn't move alone: it drags the axle, the bottom bracket and the angles with it.
A 27.5 wheel has less radius than a 29 — on the order of 20 mm [ESTIMATED] with comparable tyres, though it varies with the rubber. Put that wheel at the rear and the rear axle drops by that distance. Since the rear axle drops but the front doesn't, the whole bike tips slightly rearward. That tip is what slackens the head angle and seat angle, typically 0.3–0.5° [ESTIMATED] depending on wheelbase, and drops the bottom bracket a few millimetres. It's the same physics, reversed, as raising fork travel: move one end and the whole geometry rotates.
At the rear: more agility, the tail tucks in and out of tight corners with less effort, and there's more clearance between tyre and body with the dropper down — key for shorter riders. At the front: you keep the roll, composure and "rolls over everything" of the 29. The cost: the BB drops, so there are more pedal strikes in technical terrain, and on very rough, fast ground the 27.5 rear rolls slightly worse than a 29. Weight distribution and saddle height also shift, so you may need to reset sag and position.
It makes sense if you want agility and tight-corner handling without giving up the 29 front, if you're shorter and a dual 29 buzzes you with the dropper down, or in enduro and downhill where the rear clearance helps. Think twice if your terrain is open, fast and rough — the dual 29 usually wins there — or if your frame offers no way to correct the geometry the small wheel will change.
A 29 front and 27.5 rear. It blends the roll of the 29 with the agility and clearance of the 27.5.
Yes, but you drop the axle ~20 mm [ESTIMATED]: the BB drops and the angles slacken. Without a flip chip to correct it, expect pedal strikes and slacker angles than intended.
Riders who want more agility without losing the 29 front, shorter riders, and enduro/DH. On open, fast terrain a dual 29 usually rolls better.
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