Mountain Hub Spacing: The 6-Millimeter Conundrum

Black and white dramatic image of man adjusting bike wheel

To Boost or not to Boost, that is the question! These days, hub spacing can be a confusing topic. We can help.

Within this post we will clarify hub spacing of modern mountain bikes, including the names of different spacing, what’s compatible with what, and how you can adapt prior generation Roval mountain bike wheels to modern spacing. This feels important because a lot of you have let us know that that this proliferation of sizes is confusing. Meanwhile, the changes in spacing standards have left us with a few highly versatile, adaptable, capable, REALLY AWESOME wheelsets that we’re looking to find homes for (at up to $1,200 off).  This piece will help you figure out if the wheels we’re selling will work with your bike.

If so, you win! And, if you want to save yourself some scrolling, the short message here is: Yes!

You can convert Roval 142 and 142+ wheels to Boost spacing. You can even run Torque Tube Control SL wheels on most current Rockshox forks. For a more detailed explanation, read on!

One of the most recent changes to come along in mountain biking is the shift to “Boost” hub spacing. Introduced in 2015, Boost spacing is generally referred to as follows: 148mm rear hub spacing with a 12mm rear axle, 110mm front hub spacing with a 15mm front axle, and a chainring/chainline of 52mm as measured from the center of the bottom bracket shell. Boost spacing allows for wider hub flange spacing, which correlates to better spoke bracing angle and dish when building wheels (this makes the wheels stronger). The brake rotor sits 3mm outboard of where it did before, as does the rear cassette. Boost also pushes the chainline outboard slightly, which can reduce chain/tire interference when trying to cram big tires, wide-range 12-speed cassettes, and ultra-short chainstays into the same very crowded real estate.

Closeup of red bike with hubs and spokes on wheels

Prior to Boost (148mm) spacing, performance mountain bikes had evolved after decades of 135mm spacing and pinner quick release axles to where they were generally running 142mm rear spacing, and 100mm spacing up front. Axle sizes were the same as Boost, 12mm in the rear, and 15mm up front. So, if you bought a high-end mountain bike somewhere between 2013 and 2015, it most likely had 142 spacing. Between 2015 and 2017, the high-end market was a mix of 142 and Boost, and since 2017 almost all performance bikes are running Boost.

Diagram of wheel hubs

Here’s where the word “compatibility” rears its complicated head. Now, if you have a real nice set of 142/100 wheels (or are considering the purchase of some), like say a 142mm Traverse SL wheelset, you’ll be pleased to know you can painlessly adapt them to work in a Boost frame. We offer Boost Conversion Kits so you can easily adapt your wheels and enjoy their lightweight yet stout and durable performance into the future.

Diagram of Roval Torque Tube front hubs

As for Roval Torque Tube front hubs (these were sold to be used with RockShox RS-1 inverted forks), since the spacing is 110mm, you MIGHT be able to run them on your Boost fork. It depends on the fork – they’ll work with RockShox Reba, Pike, Lyrik and Yari forks, simply by installing a 2mm spacer between the hub and brake rotor. Oftentimes the brake caliper has enough lateral adjustment range to get away without the spacer, but in case it doesn’t, the 2mm spacer gets you to spec.

Now, if you have a brand new Boost wheelset that you want to retrofit backward onto your existing 142/100 frame, that’s not going to go so well. If you are currently riding a 142/100 bike and eyeballing your next ride, undecided as to whether or not you want to commit to Boost, but also thinking it’s about time you got some new wheels, then opt for versatility – get the 142/100 wheels and enjoy the option of adaptability to fit either way. And if you are still rocking a 135mm Q.R setup, upgrading to a new bike will be a totally eye-opening experience. You’ll be stoked.

Closeup of USA female rider riding down hill

How much do these changes impact our riding out in the real world? If you are a big, strong, aggressive rider who is constantly destroying your 29” all-mountain wheels, then Boost is great news for you. For the rest of us, it makes wheels stronger and stiffer, but it’s not as monumental as say, the invention of the electric lightbulb. It’s a good evolutionary step, but if you are currently happy with your 142x12 spacing, you have every reason to stay happy with it.

This is a highly dynamic time as far as bike evolution is concerned. There will always be the concern that change is just happening for the sake of change, but it’s not. The market these days is too competitive to experiment around with trends and proprietary technology just for the sake of being different. We don’t want to be different, we strive to be better. And, when we pull back and recall all the broken handlebars and sheared off cottered cranks of our childhoods, when we remember what a royal pain in the ass it was to adjust cantilever brake pads so they wouldn’t eat our tire sidewalls, when we wince at the thought of stripped threads at the end of tiny wire quick release skewers, we realize that we are living in a really exciting and good time right now.

Speaking of memories, if you want to take a long walk down memory lane and get some insight into the specific evolution of bicycle hubs, we recently took a little dive here.

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