Mullet™ Bike Technology

How the 29 Front and 27.5 Rear Wheel Combo Changes Handling

The most critical aspect of a bike’s handling starts with its contact to the ground. Bike Geometry is a standard of measure used to market how a bike is supposed to handle. However, geometry plays a very small part in how the bike’s tires contact & react to the ground while in motion. As geometry changes on a bike, it affects how a bike steers, how forces impact the bike, and how the rider fits into that equation with regards to fit, handling, and pedaling efficiency. Little to nothing can be done outside of tire design to change how the tire’s contact is affected when the axle heights are the same because they pivot off identical axle heights. Suspension aids in keeping the tires in contact with the terrain but does nothing with regards to how that contact behaves.

Past attempts of changing wheel sizes focused on front wheel roll-over and rear wheel acceleration. While these things held true, 69er wheels were too far apart in size and resulted in an awkward handling bike that tended to wheelie on climbs. When 27.5 wheels gained popularity, no major attempts were made to develop a mixed wheel bike as it was still thought of as a niche that would ultimately fail.

One major factor left out of traditional bike design is how the rear wheel turns & reacts with the terrain. Since not much can be done short of changing the chainstay length on a bike with symmetrical wheels, the rear wheel’s Force Vector & Scrub Radius were never worth considering. While in motion, the relationship between each wheel’s axle height determines how the rear tire reacts with the terrain when the front wheel turns. In this case, Scrub Radius relates to the turning arch of the ‘fixed’ rear wheel created when the front ‘non-fixed’ wheel is turned while in motion. Force Vector is the direction force travels based on the magnitude of something driving it and what disrupts the rear wheel’s contact as it is being forced to turn.

Scrub Radius & Force Vectors are crucial elements of bike design, but the rear wheel is left out of the equation because it simply cannot be manipulated on bikes with symmetrical wheels.

Bikes with identical wheel sizes

When you have two wheels of the same size, the identical axle heights pivot the front & rear wheel on the same axis when turning. This forces the rear wheel to fight the direction it wants to go in and considering 70% of a rider’s weight is over the rear wheel, a significant amount of resistance is generated. (it slows you down!) Since nothing can be done to change (improve) a rear tire’s scrub radius when the axle heights are the same, geometry, suspension travel & tire design must compensate for it.

Bikes with mixed wheel sizes

When the front axle height is slightly higher than that of the rear’s, the two wheels pivot from two different points. As the front wheel of a mixed wheel bike turns (while in motion), the rear wheel’s lower axle height tosses in an additional factor which causes the tire to roll over more into the turn according to the direction the front wheel drives the bike.

Think of it like a boat trying to turn while it’s completely horizontal vs when its nose is slightly raised. As soon as the nose of the boat is higher, the rear of the boat can roll side to side into a turn with ease. A mixed wheel bike accomplishes this, essentially freeing up the rear wheel to play right along with whatever the front wheel is doing with that same rocking motion.

Improving how both tires react to the terrain while turning reduces rolling resistance, improves traction, and enables the bike to handle better when Dirt Bike Geometry™ is applied.

Other Mixed Wheel Factors

Larger Front wheel – Superior rolling resistance, roll-over & traction

Smaller Rear Wheel – Quicker technical handling & acceleration

Better Cornering – Front & rear wheels work together for better turning performance & predictability

Better Geometry – Due to changes in axle path, improved scrub radius, and a 29/27.5 wheel combo, taking extreme measures with a frame’s geometry is not needed to compensate for a symmetrical wheel bike’s handling

Improved Descending – Slightly raised axle path decreases the bike’s chances from tipping forward during steep descents while handling turns faster

Faster Climbing – While still maintaining optimum ergonomic pedal position, a smaller rear wheel aids in acceleration during steep climbs and the front stays planted

Improved Hardtails & Full Suspension Performance – With the correct geometry & suspension design, a mixed wheel bike performs & handles better without having to overcompensate with extreme geometry and over-engineered suspension designs

 (Copyright 2021 Mullet Cycles LLC. All rights reserved. This material may not be published, broadcast, rewritten or redistributed without permission)

© 2021 Mullet Cycles LLC