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. Rent it to mates for beer money.
If your bike has a rear derailleur, at some point it's going to get hit. This is a given of storing, transporting and riding a bike. 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. 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.
So far, so sacrificial. But you also want accuracy in shifting, along with quiet. Noise = lost watts, accelerated wear and justified derision from clubmates. 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. That's less than 0.4mm of room for error. And the derailleur has to be indexed. 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. All this while transmitting anywhere between 100 and 1000 watts of power and being jolted up, down and sideways by the UK's quality road 'surfaces'.
As Caroline Stewart (top mechanic and handy with a sword) puts it - 'Here Be Dragons'. 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. 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 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. 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. Sooner or later you're going to damage the hanger, hanger thread or bolt through repeated screwing and bending.
So you need a hanger alignment tool, or access to one via a friend, clubmate or bike shop. This is not an optional extra, a bike toolset nice-to-have – it's essential to achieving optimal shifting and minimising noise/wear. 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. If your shifting seems out and a basic check of the indexing doesn't resolve it, you need to confirm the hanger is straight.
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. Most bike shops will own at least one, and for home mechanics it represents a spousal-budget-approval-friendly addition to your pegboard.
How it works
The DAG-2 is effectively two tools in one. Firstly, it's a gauge to measure how far out of true your hanger is. Secondly, it's a strong lever to bend the hanger into true. At the threaded head there's a large-diameter bushing with rebuildable parts – as with most Park (Tool) tools, parts are available to extend the life of the tool. This is a good idea as the thread that screws into the hanger should always be in good nick – you don't want to risk damaging the soft thread through use of a worn tool, which will also be less accurate in use.
At the other end of the tool is a sliding gauge, with an arm that slides in and out to perform the measuring. This has two rubber rings on it to assist with repeated measurements.
The process of aligning your hanger starts with removing the derailleur after shifting into the smallest sprocket/ring to minimise chain tension. The DAG-2 is carefully screwed on, and the gauge is shifted to the nine o'clock position, the arm horizontal and rearmost. You spin your wheel to align the tube valve at the same spot, and keep this valve-gauge reference throughout the process. This means the trueness of your rim does not affect the end result – your rim could be out by a considerable amount around its circumference and, particularly with disc brakes, you might not notice.
Move the sliding rod back and forth, in and out until you get the tip just touching the centre of the rim sidewall. Push the rubber ring on the rod up to the body of the slide, where it acts as a marker for the next measurement. Then slide the rod back out, slide the gauge inward, and rotate the whole lot 180 degrees to the front of the wheel, just below the chainstay and repeat the process. Spin the wheel to shift the valve at the same time. If the tip of the rod is now more than 4mm too far in or out from the rim, you need to straighten the hanger. The distance you need to adjust is half that shown by the rod, as you will be adjusting the reference point at the previous location at the same time.
The process of bending the hanger is one you pick up quickly, and the secret is to start small – the malleability of hangers will be different across different materials and thicknesses. Bend, check, bend again, check again. Once you think it's right, reset the gauge at this new point and go back to the start to verify. The process is then repeated for the vertical plane, by starting at the bottom and progressing to the top, spinning the valve to follow each time.
The sliding rod means you can clear any mudguard or rack stays. With practice you can have a hanger aligned and the derailleur back on in a minute or two, satisfied that any subsequent work will be on an accurate base.
Prior to getting the DAG-2 for review I prided myself on my 9-speed gear setup. Always using slick, stainless cables and new outers every 1000km or so, perfectly lubricated derailleur pivots, indexed as per Shimano's instructions. What I didn't know was how inherently out my hanger alignment was, and what that meant for shifting. I was used to a certain level of shifting accuracy, speed and chain noise, thinking things couldn't get any better without jumping up a groupset or two.
Using the DAG-2 was a revelation. Immediately the shifting was noticeably faster in both directions, and the chain ran quieter. It was one of those 'I can't believe I waited so long' moments. Working on a friend's 10- and 11-speed bikes gave similar results. When paired with a fresh set of cables, what I had thought to be good shifting became great, and great shifting became almost telepathic.
A bike shop will charge you maybe £10 for a hanger alignment - and should carry one out by default as part of a new build-up, replacement mech or gear indexing (if they don't, consider finding a new bike shop). If you have a number of bikes, ride one or several often, mountain biking or road, and like a bit of DIY, then you should consider investing in a tool like the DAG-2. It will pay for itself in terms of bike shop savings, from beers earned lending to friends or checking their bikes for them, and from general smugness knowing that your drivetrain is working as best it can. And the alignment process is so quick you can do it pre-ride in a minute or so, should someone be concerned their shifting isn't quite right.
For 2016 Park has updated the DAG-2 to the DAG-2.2. The distance gauge and arm remain the same, the key difference is a redesigned head that affords better clearance for screwing into hangers where there's a lot of protruding metal nearby. Park has also increased the diameter of the shaft that screws into the hanger from 14.4mm to 16mm, and claims an improvement in accuracy. It has stuck with the same 4mm tolerance at the rim, though, and I couldn't discern any difference in use, so that benefit is moot. No one knows what happened to the DAG-2.1. Best not to ask really.
The rise in disc-braked bikes and associated thru-axle hangers makes clearance an issue that's not going away any time soon, so the DAG-2.2 is a timely update for this venerable workshop workhorse.
If you use traditional QRs and have a traditional-looking dropout area then the DAG-2 will do you right, while it's still available.
For performance at a palatable price, the DAG-2 (or 2.2) is hard to beat. Two notable hanger alignment tools in the 'Lust' category of tool geekdom are the Abbey Tools HAG and the Efficient Velo Tools Tru-Arc – but they cost £165 and £366 respectively and sport tolerances approaching 1/4 of 1/1000 of an inch (that's 0.00635mm in new money, or 'gnat's testicle' for the hoi polloi). For £63 the Park Tool DAG-2/2.2 will meet the needs of all but the pickiest of home mechanics.
For around £60 – or less – the Park Tool DAG-2/2.2 will meet the needs of all but the pickiest of home mechanics
Make and model: Park Tool DAG-2/2.2
Size tested: n/a
Tell us what the product is for, and who it's aimed at. What do the manufacturers say about it? How does that compare to your own feelings about it?
It's for anyone who rides, regularly, and wants the best-possible shifting experience but not at a bank-breaking price.
"The DAG-2.2 is an indispensable shop tool that can be used to both measure and straighten misaligned derailleur hangers solving a high percentage of shifting problems."
Tell us some more about the technical aspects of the product?
Gauge bar made of heavy gauge, chrome plated steel
Adjusts to fit 20" to 29"+ wheels
Replaceable threaded tip
Upgraded large inner shaft for added strength*
Tighter tolerances for improved accuracy*
Improved clearance and reach to fit more frame/hanger combos including low clearance thru-axle derailleur hangers*
It's built like the brick proverbial. Should zombies attack the workshop, this would be my go-to defensive weapon.
Performance in this regard equals accuracy. The DAG-2.2 does the job - not as accurately as the pricier options, but well enough for 99.999% of fettlers.
The only loss on durability is the black rubber rings – they are easily lost.
For the money, the DAG-2.2 is excellent value.
Tell us how the product performed overall when used for its designed purpose
Very well. Only very infrequently would I want for more accuracy or tighter tolerances to aid more precise bending.
Tell us what you particularly liked about the product
The overall vibe/value proposition. I like that for £60 it sorts even horrific shifting issues in a few minutes.
Tell us what you particularly disliked about the product
The slide on the gauge is pretty agricultural – sheet steel spring on metal. You quickly get used to it, but the more expensive options featuring machined sliders are much nicer.
Did you enjoy using the product? Yes
Would you consider buying the product? Yes
Would you recommend the product to a friend? Yes
Use this box to explain your score
'Perfect' in the world of hanger gauges is reserved for the likes of the Abbey Tools HAG or Velo Tools workshop candy. The DAG tools from Park are built very well, but still to an affordable price point – with compromises in the distance gauge assembly friction slide and rubber marker rings in particular. Therefore, four out of five. But don't be fooled – it will do the job, no problem.
About the tester
Age: 42 Height: 183cm Weight: 72kg
I usually ride: Charge Juicer My best bike is:
I've been riding for: Over 20 years I ride: A few times a week I would class myself as: Expert
I regularly do the following types of riding: club rides, general fitness riding, fixed/singlespeed, mountain biking, and Dutch bike pootling