Super Boost Plus & Boost in MTB: Explaining Hub Sizes and Hub Widths
Technological progress demands new standards: Boost increases the stiffness and stability of MTB wheels. Find out why this was necessary here!
The Boost standard has been a staple in the cycling world for over ten years. The reason for the development of a new hub standard was the growth of MTB wheel sizes from 26" to 27.5" and 29" in the early 2010s. The larger wheels were often less laterally stiff, so a solution was needed. The new Boost hubs were built six millimeters wider in the rear and ten millimeters wider in the front compared to standard hubs. The spoke flanges moved outward. The spoke angles became flatter. Thus, even larger wheels could become as torsionally stiff as their smaller counterparts. Some manufacturers went a step further and offer Super-Boost-Plus rear wheels with a hub width of 157 millimeters in the enduro and gravity segment – this is, by the way, the same installation width that was used for 26" downhill wheels. Unlike 157DH, with Super Boost Plus (also known as Super Boost or simply SB+), the spoke flanges also moved outwards to improve wheel lateral stiffness.
100 mm axle width was previously common for MTB as well.
The Boost standard has an axle width of 110 mm at the front wheel.
Hub widths in mountain biking – an overview
Although Boost has become the most common installation size in the MTB world, there are of course other sizes. Here's an overview:
| Legacy | Non-Boost | Boost | Super-Boost | |
|---|---|---|---|---|
| Quick Release | Thru-axle | Thru-axle | Thru-axle | |
| Front Wheel | 100 mm | 100 mm | 110 mm | 110 mm |
| Rear Wheel | 135 mm | 142 mm | 148 mm | 157 mm |
What exactly does the Boost standard offer?
The increased lateral stiffness of Boost wheels lets you steer more precisely through corners and maintain your intended line easier than with a Non-Boost wheel. Even the hardest braking maneuvers have less impact on the line of the front wheel, and spoke cracking due to hard pedaling becomes less common. And in the end, a more favorable spoke angle and increased stiffness also mean less wear, such as of the spoke nipples, thus fewer spoke breaks.
Moreover, the Boost standard offers more tire clearance, making enough space for Plus tires. FYI: Plus tires refer to tires with widths from 2.8"-3.25".
What changes were made to the front wheel and fork?
The introduction of the Boost standard increased the installation width of the front wheel from 100 millimeters to 110 millimeters. The spoke flanges of the Boost front wheels were symmetrically moved outward by five millimeters. This shift not only achieved the already mentioned stiffness and stability advantages but also made the fork wider and thus increased tire clearance.
Changes from the previously "normal" front hub to the Boost front hub
What changes were made to the rear wheel, frame, and crank?
At the rear wheel with Boost, both spoke flanges were symmetrically moved three millimeters outward. Thus, the installation width of the rear wheel increased by a total of six millimeters, from 142 to 148 millimeters. With Super Boost Plus, the installation width grows by another nine millimeters, thus to a total of 157 millimeters. To be able to accommodate the respective wheel, the frame's rear build also has to have the corresponding width – and this improved tire clearance. The wider chain line (more on that below) with Boost and Super Boost also allowed for the use of larger bearings and the design of wider bearing points, making the rear build stiffer.
The drive is affected by Boost as follows: Because the spoke flanges were shifted outward by three millimeters, the cassette was also moved out by the same amount. This, in turn, shifted the chain line to 52 millimeters. This also improved tire clearance in relation to the chain. To keep the Q-factor (the horizontal distance between the two crank arms at the level of the pedal attachment) the same as with the old hub standard, Boost cranks set the chain rings out by three millimeters. That means only the spider (in English, “spider") or, with direct mounts, the chain ring is adapted to the changed chain line with Boost cranks, otherwise, they do not differ from Non-Boost cranks. With Super Boost Plus, the cassette is pushed even further out, and the chain line lies between 55 and 56.5 millimeters depending on the bike. The chain ring is usually set out by six millimeters and therefore you need Super-Boost-compatible cranks. The Q-factor remains unchanged for enduro and gravity bikes.
Changes from the previously "normal" rear hub to the new Boost rear hub
