Secondly, it's a strong lever to bend the hanger into true. Firstly, it's a gauge to measure how far out of true your hanger is. The DAG-2 is effectively two tools in one. Most bike shops will own at least one, and for home mechanics it represents a spousal-budget-approval-friendly addition to your pegboard. With an rrp of £62.99 for the new 2.2 version (and prices online of around £40 for the DAG-2), the DAG sits in the middle ground of alignment tools. If your shifting seems out and a basic check of the indexing doesn't resolve it, you need to confirm the hanger is straight.
Checking and aligning your hanger is the very first thing to do when launching into drivetrain work without a straight hanger, everything else – derailleur adjustment, cable replacement, gear indexing – they are all going to be built on an inherently inaccurate, misaligned base and will never work in an optimal fashion. This is not an optional extra, a bike toolset nice-to-have – it's essential to achieving optimal shifting and minimising noise/wear. So you need a hanger alignment tool, or access to one via a friend, clubmate or bike shop. Sooner or later you're going to damage the hanger, hanger thread or bolt through repeated screwing and bending. Yes, you can swing it back and forth with a large wrench or a 5mm Allen key stuck into the derailleur bolt, fitting and re-fitting the derailleur to see if you've got it right this time, but this is guesswork, and somewhere a Bike Workshop Fairy just died. If your hanger is radically bent it might be possible to assess alignment by getting behind the bike and eyeballing it compared to the rim, but the problem is your hanger must be aligned both vertically and horizontally – and as the hanger is much narrower back-to-front than up-and-down, this is simply impossible to do by eye. The design tolerance of a hanger if extended all the way out to the rim is 4mm, but the problem is they are only 3cm long – so you're trying to spot 0.4mm of vertical hanger misalignment. If your drivetrain is making unfathomable noises or won't index no matter how much you swear at it, tweak the limit screws or twiddle the barrel adjuster, chances are your hanger is bent. All this while transmitting anywhere between 1 watts of power and being jolted up, down and sideways by the UK's quality road 'surfaces'.Īs Caroline Stewart (top mechanic and handy with a sword) puts it - 'Here Be Dragons'. And the top jockey wheel needs to feed that chain onto your smallest sprocket at nearly 100 joining pins per second if you're maxed out in top gear on a modern compact drivetrain. That's less than 0.4mm of room for error. An 11-speed cassette has just 2.18mm between sprockets, with overlapping chain plates totalling 1.8mm needing to fit between, without excessively rubbing against the sprocket it's on or either neighbour.
Noise = lost watts, accelerated wear and justified derision from clubmates. But you also want accuracy in shifting, along with quiet. You'd much rather replace a £20 hanger than a £500 frame, right? Hence it's usually made of a softer metal than your frame. The derailleur is perfectly positioned to catch door frames, gates, roots, rocks, kerbs and a multitude of other immovable objects, be banged against other bikes, be dropped or crashed, and it's attached to a part of your bike that's nowadays usually designed to bend so your frame doesn't - the derailleur hanger. This is a given of storing, transporting and riding a bike. If your bike has a rear derailleur, at some point it's going to get hit. Find your nearest dealer here Buy this online here The Park Tool DAG-2 (or the newer 2.2) is a shop-quality derailleur hanger straightening tool that will help keep your gears changing perfectly.
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