Editors Note: This article was written by Art’s Cyclery web content editor Brett Murphy, who uses his mechanical engineering background to explain the latest industry advances and breakdown component design. The original post can be found here.
By now you have heard about the new Boost 148 hub standards. But what exactly are they and what do they mean to you?
I previously wrote an article that discussed axle standards. You can see that there are a dozens of different standards, but when discussing the latest Boost 148 and Boost 110 hubs it is more important to just look at a couple of the older mountain bike standards.
In the beginning mountain bikes generally had quick releases with 100mm spacing in the front and 135mm spacing in the rear. Within the last 10 years, QR’s have given way to the thru axle. The thru axle offers a much stiffer and more secure platform for bigger hits and harder cornering. On most mountain bikes, we now see 15mm or 20mm thru axles in the front and 12mm thru axles in the rear.
With the increasing popularity of thru axles, we saw the introduction of the 142x12mm hub and axle standard. These new 142mm hubs replaced the 135mm standard that had been around for years. But there is one important thing to remember about this standard: The distance between the two dropouts on the frame is still 135 millimeters, with an extra 3.5 millimeters of inset on each side built into the frame dropout. This 3.5 millimeters is used to guide the hub into the frame and self-center the wheel, making thru axle installation easier.
Most hub manufactures offer replaceable hub end caps to convert their hubs between 135mm and 142×12. So while frame designs changed, the hubs for these two standards still have the same spoke flange spacing and other dimensions.
Now that we have some background on hub spacing, lets talk about wheel size. Originally everything was designed and engineered in the mountain industry around 26” mountain bike wheels. However, we now have 27.5” and 29” wheels, but the hubs are still the same width. With larger diameter hoops, spokes become longer. These longer spokes mounted in the same width hub create smaller spoke bracing angles.
The spoke bracing angle is the angle formed between the spoke and the vertical plane. Larger spoke angles are able to balance a larger component of the lateral forces exerted in the horizontal plane during loading. So the end result is that 27.5” and 29” wheels are weaker than 26” wheels with current hub standards.
Enter Boost 148 and Boost 110. These two hubs move hub flanges outward. By moving the hub flanges outwards, spoke angles increase, creating a more stable base. So Boost standards maintain the ratio of spoke length to bracing angle seen in 26” wheels resulting in, “26” stiffness from a 29” wheel.”