Axle standards explained

Our resident mechanic Al explains axle standards. Know your thru-axle from your Super Boost spacing.

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Skewers are for the BBQ

In the not-so-distant pas, hub axles sat in slotted or open frame or fork dropouts and everything was tied together by a skinny quick release skewer that passed through the axle and when tightened against the outside of the dropouts they clamped everything together best as they could. A thru-axle hub is similar but the dropouts are closed and threaded on one end and the much larger diameter thru-axle locks everything in place, often with the aid of a quick release lever. The action of removing a wheel is now slightly slower but we have bikes that are stronger, more responsive due to increased stiffness and also much safer.

And then there was Boost

Old quick release hubs and 142 x 12mm thru-axle hubs have the same widths between the hub flanges so there is no change in terms of hub flange positioning and wheel strength and stiffness. Boost gives a 148 x 12mm spacing which allows for the hub flanges to be further apart which gives a potentially stronger and stiffer rear wheel.

What’s better than Boost? Super Boost!

This is more of the same – with wider flange spacing Super Boost’s 157 x 12mm spacing gives even wider hub flange spacing so potentially even more wheel stiffness and strength. Will it catch on? Do we need it? Who really knows.

What should I get if I’m buying a new wheelset?

Your fork dictates the front axle you buy so that’s easy, just but the manufacturer’s recommended option – Maxle for Rock-Shox, QR15 for Fox etc. Just make sure you replace with the correct length so 100mm for a regular fork or 110mm for a Boost fork. On the rear there are a multitude of options. First of all consult the frame manufacturer’s spec’s. With any luck they will state the type of axle you require. Failing that give them a call/email and speak with their tech support staff. The differences between axles are so numerous these days that you’d be daft to take a guess. Axle length, diameter, thread length, thread pitch, the interface between the axle and the dropouts and whether the securing thread is part of the frame or a separate nut that comes with the axle make this a ridiculously complicated component to replace or upgrade.