Step 1: copy the manufacturer’s geometry table We are going to calculate precisely by how much the geometry changes if a smaller 27.5' rear wheel is installed. The bike comes stock with 29' wheels front and rear. The bike that serves as an example is a Specialized Stumpjumper 2020 in size S4. In this section, I walk you through an example calculation in detail. However, the result will most likely remain a lifted bottom braked, slackened angles, reduced reach, and increased stack.Īssessing the Effect of a Mullet Setup on the Bike’s Geometry

Of course, some of the effect can be adverted by picking a lower travel fork. In that case, the larger front wheel diameter has a doubled effect: first for the bigger wheel itself and second for the longer fork to accommodate that bigger wheel. It depends highly on the geometry of the bike if the new numbers fall within normal rideable limits.Ī similar issue emerges if a 27.5' wheeled bike is fitted with a bigger 29' fork and front wheel. The stack grows a little while the reach shortens. If the bike is designed for 29' wheels, a smaller rear wheel will lower the bottom bracket and slacken the seat and head tube angles.

The geometry of the bike may be compromised if the bike was not designed for a mullet setup from the beginning.Ĭhances are that your current bike was designed for equally-sized wheels.Two different wheel sizes complicate stocking replacement tires, tubes, and rims.Inferior roll over behavior for rocks and roots.A stronger and at the same time lighter rear wheel.More space for increased tire clearance in the tightly spaced bottom bracket area.An effect which is often cited as the reason for a more nimble ride feel. Due to the smaller diameter, a smaller rear wheel has lower gyroscopic forces.Watch out for MX bikes, as this is the term that bicycle companies often use to market their mullet bikes. As a result, we see many companies starting to sell bikes with mixed-sized wheels. Naturally, that sparked the interest of the mountain bike media as well as the consumers. Since the UCI allowed mixed wheel sizes for the 2019 race season, many downhill athletes chose to run mullet setups in their competitions. The basic idea is to combine the good roll-over behavior and gyroscopic stability of twenty-nine-inch wheels in the front (where it matters most) with the nimbleness of a 27.5' wheels. It describes the combination of a large front wheel with a smaller rear wheel, typically 29' up front and 27.5' on the rear. Mullet bikes are a trending subject in the enduro and downhill mountain bike world. Mullet Bike Geometry Tutorial The Mullet Bike

Mtb geometry calculator