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Disc brakes : the ins and outs of axles

Disc brakes are much more powerful than rim brakes and exert their forces in a different way. The braking force can remove any wheel that is not securely clamped within the frame or fork, with potentially lethal consequences. This is obviously something to be avoided at all costs!

There are now several different axle standards, each with their own benefits. Quick-release hubs are still very common despite evidence that they lack the clamping power to resist the forces created by powerful brakes with large rotors and at the speeds which longer travel bikes allow riders to attain. If you’re running quick-release skewers with disc brakes, use robust, good-quality skewers. Shimano and Mavic are both excellent – and ensure that the mechanism is clean and well lubricated. ’Lawyer tabs’ are now standard on quick release forks, and though the little protruding lips below the drop-out mean you have to undo your quick release that much further to get the wheel in and out, they make it harder for the wheel to be accidentally removed if the quick release is not secure, for whatever reason. They are not a substitute for ensuring that your quick releases are in good working order and done up correctly. If you’re not sure how to do them up, then refer for instructions, and if in doubt please ask your friendly local bike shop for advice as this is not the time to experiment yourself.

Disc brakes - the ins and outs of axles

Shimano disc brake

The alternative to the quick release is the bolt-through hub (or through-axle). There are several different standards currently in use but the most common are the 20mm and 15mm versions. Bolt-through used to be the domain of the downhill bike only but they are becoming more popular on lighter, shorter travel forks now, too. As well as offering significantly improved security for disc brake users, they also make the front end of the bike much stiffer, improving steering on demanding terrain. A few manufacturers are also starting to experiment with bolt-through rear ends in search of the same benefits, and it’s likely that this too will become more common as technology progresses.

You will need to make sure that your hub matches your axle, as both standards require specific diameter axles. However, if you want to switch forks to a model that uses a different-sized axle you won’t necessarily need to buy a whole new wheel. Several hub manufacturers offer conversion kits that allow you to use one hub with different fork standards, which can be useful if you’re running several bikes and need to swap parts between them too. One drawback of bolt-through hubs used to be that you needed tools to remove them, making fixing punctures or loading onto car racks even slower and more fiddly tasks. Thankfully those same designers who are now looking at bolt-through rear ends have already lavished plenty of attention on the forks and have come up with a variety of devices that make the bolt-through axle easier to use. Essentially Rock Shox’s Maxle, Fox’s QR15 and similar systems are just overblown quick releases that fit through one fork leg and the hollow hub shell before screwing into the opposite fork leg and tightening into place with a cam lever. Check the instructions for your particular model if in doubt, though – you should be able to find these in the fork manual or on the manufacturer’s website if you don’t have the manual to hand.

Whatever system you’re running, you should check that your wheels are fitted securely before each and every ride, and even during a ride if you’re ever in doubt about their status (being careful not to touch the disc rotor, which will be very warm indeed if you’ve just been braking hard!). If a strange knocking noise or rattly feeling occurs halfway through a technical descent, stop and make sure that your bike is safe to ride. It’s a task that takes moments but it could save you from serious injury.