In the past, the issue of axle standards was much simpler. All wheels had a surface for rim brakes, and road hubs could be divided into two main types: Shimano and Campagnolo. Mounting was done using skewers also known as quick releases or QRs.
Front wheels fit forks with a hub mounting spacing of 100 mm. In turn, road rear wheels had a spacing of 130 mm (previously 125 mm), and rear wheels in MTB and cyclocross bikes — 135 mm. And that was the end of complicated standards.
QR skewers, usually based on an eccentric mechanism, wore out over time. In the pursuit of weight reduction, riders reached for very light skewers, e.g. titanium, which often led to the wheels loosening in the dropouts. The use of thru axles eliminated this problem and significantly increased the stiffness of the entire system. Thru axles dominate modern bikes.
In most road, gravel and cyclocross bikes:
• 12×100 at the front
• 12×142 at the rear
In most MTB bikes:
• 15×110 (Boost) at the front
• 12×148 (Boost) at the rear
A less popular solution in bikes with disc brakes are the mentioned QR (quick release) skewers:
• 5×100 at the front
• 5×135 at the rear
Some manufacturers use sizes 5×100, 15×100 or 15×110 for the front wheel and a less common 141×9 spacing at the rear, also known as 141 Boost. In this case, the rear freehub body is the same as modern MTB Boost hubs, with the difference that the wheel is attached to the frame using a QR skewer.
The Boost standard in mountain bikes has replaced thru axles with a spacing of 100 mm at the front and 142 mm at the rear. Hubs with wider spaced flanges are also found in gravel bikes and some road bikes (especially those with electric drives). However, it is important to note that this does not automatically mean that MTB Boost hubs are compatible with gravel bikes that use the Road Boost standard.
However, there are some MTB hub models that can be converted and adapted to the road or gravel Boost standard.
The axle standard can be checked in the bike’s specifications, but it is important to remember that it may change in different years of the same model. Bicycle manufacturers can be frugal with information, and the parameters of older models may be difficult to find online. In such a situation, apart from contacting a bicycle service to verify the axle standard, we are left with the option of self-verification “by eye”.
The name of each standard consists of two values separated by an “x” character. The lower value specifies the inner diameter of the hub axle, which is the hole through which the axle passes when screwed into the fork or frame. The higher value is the spacing of the hub mounting points, or the distance between the points where the hub contacts the frame or fork.
The freehub body standard determines cassette compatibility. Different models can be mounted on the following most common freehub body standards:
• Shimano HG (9/10s road and 11s MTB cassettes)
• Shimano HG-EV (11/12s road cassettes or 9/10s and 11s MTB with spacer)
• Shimano MicroSpline (12s cassettes from MTB groups)
• Sram XD (12s MTB cassettes)
• Sram XDR (12s road cassettes or 12s with spacer)
• Campagnolo (9/10/11/12s cassettes)
• Campagnolo N3W (13s cassette)
• Shimano 11s road cassette is compatible with Shimano 11s (HG-EV) freehub body.
• Shimano 12s road cassette is compatible with Shimano 11s (HG-EV) freehub body.
• Sram 12s road cassette is compatible with Sram XDR freehub body.
• Shimano 11s MTB cassette is compatible with Shimano HG (and HG-EV + spacer) freehub body.
• Shimano 12s MTB cassette is compatible with Shimano Micro Spline freehub body.
• Sram 12s MTB cassette is compatible with Sram XD (and XDR + spacer) freehub body.
• Campagnolo 9/10/11/12s road cassettes are compatible with Campagnolo freehub body.
• Campagnolo 13s gravel cassette is compatible with Campagnolo N3W freehub body.
• Cassettes compatible with the Shimano 11s HG standard can be mounted on a freehub body in the Shimano 11s HG-EV standard after installing a 1.85 mm spacer ring.
• Cassettes compatible with the Sram XD standard can be mounted on a freehub body in the Sram XDR standard after installing a 1.85 mm spacer ring.
There are some exceptions:
• Sram NX/SX Eagle and SunRace 12s cassettes are compatible with the Shimano 11s freehub body in the mountain standard (HG)
• There are also 11s cassettes with the smallest cog of 10t compatible with the Sram XD freehub body.
The Dandy Horse TCN, RTC and DT Swiss hubs, on which we build road and gravel wheels, have Shimano HG-EV standard hub bodies.
There are two main ways to attach brake discs to the hub: Centerlock (CL) and International Standard (IS), commonly called six-bolt.
Centerlock is the dominant standard in road and gravel bikes, and it is also gaining popularity in MTB XC. It features easier disc mounting and removal, as well as greater stiffness and better heat dissipation.
IS mounting is more common in heavier MTB variants and in budget road and gravel bikes, especially when the manufacturer uses the same hub model in different bike models in its range. This is a cheaper solution to produce, but less convenient to mount and remove.
Changing the mounting standard:
If you change a wheel with Centerlock mounting to IS, you can use adapters to allow you to use your existing IS discs. However, it is worth considering whether it is better to use the money to buy new discs for the Centerlock standard (the cost of DT Swiss adapters from CL to IS is around PLN 100 per wheel) instead of buying adapters. For mounting centerlock rotors, lockrings are used, available in two standards: one for a cassette lockring tool and one for a bottom bracket tool. Both standards are compatible with the hubs we offer. An exception is, for example, Fulcrum wheels, which use different lockrings compatible only with that manufacturer’s hubs.
Changing to a complete wheelset with a different disc mounting standard does not affect compatibility with the brake calipers on the bike, but may require caliper adjustment.
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