Hub "Standards"

Standard. Boost. . . Super Boost??
Shimano. XDR. . . Microspline??

The world of Mountain Bike “standards” is changing quickly. Road, cyclocross, and gravel went through these same changes, and seemed to have settled on a standard for axle size and width. Chances are your new drop-bar disc brake bike has 12x100mm thru axle on the front and 12x142mm thru axle for the rear. Again, I said “chances are” as there are some outliers.

However, in the past couple years there have been a bunch of changes that affect your Mountain Bike. I’d like to go through all those changes, and what standards exist so as a consumer, you can make informed decisions about what products you are riding and what you need if you are looking at upgrading your wheels.

Back in the day all mountain bikes were equipped with Quick Release skewers. When we say “back in the day” it was not that long ago. Thru axle only started appearing on most mountain bikes around 2008. The top song that year was “Low” by Flo Rida featuring T-Pain. That was 12 years ago! I’ll let you stop feeling old now.

Before then there were two main standards. Road bikes were 100mm QR front and 130mm QR rear. Mountain Bikes were 100mm QR front and 135mm QR rear.

Thru axle changed those standards for MTB. Front hubs moved to a 15X100mm thru axle for the front, and a 12X142mm thru axle for the rear. This is what we still refer to as “standard” spacing.

Right around the same time that thru axles became the norm for mountain bikes, disc brakes became more prominent on cyclocross bikes. This happened just a few years ago around 2013. For cyclocross, most bikes started off as quick release, and then very rapidly moved to thru axle. This is where the fun began. At first, CX thru axle was also 15X100mm front and 12X142mm thru axle rear (same as the MTB “standard”).

Almost at the same development time, three things happened. More and more mountain bikes were using the 29er wheel size for more aggressive riding. To combat this, there was an introduction of “Boost” spacing which places the flanges wider to make for a stronger wheel. The Boost spacing increases the width of the hub to 110mm in the front and 148mm in the rear. The change in width is in the hub shell width. The end cap dimensions between “standard” and “boost” spacing remain the same.

Also, road bikes started coming with disc brakes. With road disc, the front axle moved to a 12mm thru axle as the strength (and weight) of the 15mm thru axle was not needed. Yes, those 10 grams are very precious!

For the vast majority of bikes, that is where we are now for axle and hub standards. Most road, CX, and gravel bikes come with 12X100mm thru axle front and 12X142mm thru axle rear. Most mountain bikes come with 15X110mm thru axle front and 12X148mm thru axle rear.

Very recently (starting around 2018ish), a few brands have wanted to go even wider with the rear wheel hub spec. This led to a new “standard” of “Super Boost. Like the change going from Standard to Boost, going from Boost to Super Boost only makes the hub shell wider. On our hubs, the Standard, Boost, and Super Boost hubs all use the same end caps.

Wow! It’s been a busy decade with a lot of changes.

There have also been a lot of changes in the freehub bodies for mountain bikes recently. Most mountain bikes until recently had both a front derailleur and a rear derailleur. However, with the rise of the new modern 1X chainrings, the cassette size on the rear wheel has changed dramatically. Whereas an older model mountain bike would have 2 gears up front, and an 11-40 in the rear, the newer 1X systems rely on having a much wider range in the cassette size.

This led to 11-46 range, which still fit on a standard Shimano Hyperglide freehub body (same style as road bike wheels). Sram around 2013 popularized a new 1X system that used a different type of freehub body, called the XD Driver. This allowed the use of a 10-tooth cog, and by also including a massive 50 tooth cog, the gear range was even greater than the traditional double chainring mountain bike. The only problem was that a cassette meant for an XD Driver could not work on a Shimano Hyperglide freehub body (and vice versa).

In 2018, Sram made a push for 12 speed on the road using the XDR freehub body, which basically allows for 12 speeds in road gearing to be used. This is also built around using a 10 tooth for the smallest cog. You can fit an XD spaced cassette on an XDR freehub body with a 1.8mm spacer. As of right now, no mountain bike cassettes are designed for XDR, but it’s only a matter of time which is why we are shipping all of our mountain bike XD driver wheels with an XDR freehub body and a 1.8mm spacer. In a few years when 1X13 is introduced (not guaranteed) your wheels will be future proofed!

Not to be outdone on the gear range for 1X mountain bikes, Shimano introduced the Microspline driver and a 12 speed 10-51 cassette (1 tooth more than Sram, take that!). Similar to how the Sram driver is only compatible with an XD style cassette, the Microspline driver is only compatible with the Microspline style cassette.

My prediction is the Microspline style driver will make its way to road, CX, and gravel groups from Shimano shortly. I would expect to see a GRX or Dura Ace 1X system on a Microspline soon. When that happens, we are already set up for that. We have Microspline, Sram XDR, and Hyperglide style freehub bodies available for both our Quest (road, CX, gravel) hubs and our Tripel (MTB) hubs. Our Tripel Mountain Bike hubs are available in Standard, Boost, and even Super Boost spacing.

How do I know which driver I need to order?

The driver for the wheels is going to be dependent on the style of cassette you want to run. Since the drivers are only compatible with the freehub they were designed for, you REALLY need to know what style of cassette you have. For example, there will never be a situation where you run a Shimano cassette on a Sram XDR freehub body. However, depending on what Sram cassette you have, it could either work on a Hyperglide or an XDR freehub body. Below is a chart that should help. This is effective as of April, 2020.

A couple quick hints. If you are running Shimano or Sram 12 speed, then you will need a Microspline or XDR Driver respectibely. If your cassette has a 10 tooth on it, then it can't fit onto a Hyperglide freehub body and you will need either a Shimano Microspline or a Sram XDR Driver.

In conclusion

We know the ever changing “standards” may be very confusing for a consumer, we keep very apprised of those changes, and work hard to make sure it’s as easy as possible to adapt to any new changes. We are also hear to answer any questions you may have about what freehub body you need. Worse case scenario, if you order the wrong driver, you can easily swap it out in just a few seconds with no tools required!

P.S. 
Campy exists. But that's a whole other article!