Birzman Rotor Truing Fork

The Birzman Rotor Truing Fork is a well-made and precise tool for getting your rotor rub-free.

If you run disc brakes (and why wouldn't you?) it's almost inevitable that at some stage you will find yourself in need of a rotor truing fork. Learning how to true a rotor – whilst bothersome – is a rite of self-help resourceful-cyclist-growth passage not dissimilar to learning how to mend a puncture.

Disc brake rotors are anywhere between 1.5 and 2mm thick, and 140-200mm in diameter. Or, 'very thin' in common language. This thinness makes rotors very susceptible to bending, even by leaning a bike down in thick grass.

The 'rule' used to be that you only ever laid your bike down drive side up – to protect the fragile rear mech and hanger. With the advent of disc brakes this is less applicable, as mechs and hangers have become more robust, better protected and more inboard. Yes, the mech side has more potential for expensive repairs being needed, but that's rare compared with the almost-certainty of bending a rotor laying your bike down wrong on the brake side. Basically, be careful whatever side you're laying a bike down on.

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Clearance inside the calliper between rotor and brake pad is usually measured in fractions of a millimetre – so you can see how even the slightest knock can induce a rubbing rotor. This is not only annoying, it will prematurely glaze and wear the pad on the rubbing side, leading to uneven pad wear and need for earlier replacement. Not good for your wallet, bike time or the planet.

I have mechanic colleagues who swear by a 'fingers-only' approach to rotor straightening – on the assumption that a rotor bent beyond what fingers can straighten is too far gone to recover. If you're trying this, be sure to do so wearing clean gloves – no contaminants on your rotor, please.

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Sometimes it's just the slightest of tweaks that's needed to silence a rotor, and therefore a tool can be overkill, inducing too much bend the other way and leading you into a disheartening cycle of see-sawing back and forth between rubbing sides. There's a special technique I've developed, which uses 5mm hex tools inserted through the joining piece to effect the right amount of bend either way.

But for most solid-metal rotors, a tool like the Birzman Rotor Truing Fork is what you need.

Laser-cut from steel alloy, with two slots for deep or shallow engagement and with a polymer-coated handle, it's nicely presented. The long slot – the one used most often – is offset by 10 degrees, positioning the handle away from the spokes for ease of use. With great leverage comes great responsibility – and the inclination can be to go too far with the initial bend. Having such a long handle does allow for small adjustments to be made; there's certainly no need for more than a few fingers on the tool to effect sufficient bend.

It's hard to get too excited about variations on what is a very basic tool. So long as it's not rusty and the slots are straight, pretty much anything will do. For the last decade I've been using a rotor truing tool made by a friend from thick stainless steel sheet in his garage. It's perfectly usable and has personal sentimental value too.

But do you need such a tool – when an adjustable spanner set to the appropriate gap can suffice? Yes, is the answer. I've used a spanner in this manner when nothing else was available. It's effective, but certainly not couth. And there's a very real risk that the spanner might have contaminants like oil or grease on it – in which case you've swapped a rubbing rotor for a contaminated one, likely to either shriek, not work, or both.

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Value-wise, at £16 Birzman's tool sits in the middle of the road, between the high-end Park Tool Rotor Truing Fork DT-2 at £21 and a plethora of £9-£10 clones available online. Yes, the Park Tool one has a lifetime warranty – but how you'd ever wear a rotor fork out or damage one is beyond me. So yes, there's probably a few quid in there for the Birzman brand, if that matters to you.

If you want to become self-sufficient in the rub-free rotor game, the Birzman Rotor Truing Fork is a good, if somewhat overpriced for what you get, shout.

Verdict

Well-presented, decent enough tool, if slightly pricey