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Sticking out in the wind, controlling your rear gears and just waiting to be bent. The rear derailleur sits in a precarious position and so the little hanger it’s bolted to is commonly designed as a weak point. Best ruin a replaceable piece of aluminium than write off an expensive derailleur, or worse, the frame.
Derailleur hangers are designed to be sacrificed but that also means they’re prone to bending, which manifests as dodgy and inconsistent shifting that no amount of cable-tension adjusting, limit-screw fiddling or chain cleaning will solve. A derailleur hanger tool is not only extremely useful for diagnosing that your hanger is, in fact, bent, but also making it straight once again.
Dave Rome investigates the options when it comes to derailleur hanger tools.
A hanger tool was previously thought to be a shop-only item, especially as it only requires occasional use. However, as cassette sprocket spacing has gotten tighter, and frames have become lighter, such a tool has become all the more common to use. In fact, I’ve worked in shops where the policy was to check every single new bike sold, and any quality bike being serviced.
Truthfully, about a third of new bikes straight out of the box would display hanger alignment issues, which were then carefully rectified.
How they work
Derailleur hanger gauges may seem like a complex shop tool, but the function is quite simple. Typically, the tool threads in place of the rear derailleur to provide a pivoting gauge that is used to measure the distance of the arm from the rim of the rear wheel.
As long as the derailleur hanger is tight, the wheel is true, and the hub axle straight, the hanger tool effectively measures how parallel the derailleur hanger is with the rear wheel. When the gauge is equidistant from the rim at the 6, 9, and 12 o’clock positions, the hanger is perfectly aligned.
Using a hanger alignment tool is therefore a matter of lining up the gauge with the rim at the 6 o’clock position, then swinging it up to 12 o’clock. If the gauge doesn’t line up with the rim then the hanger is bent. The arm of the tool provides plenty of leverage for gently “persuading” the hanger back into alignment. Once the 6 and 12 o’clock positions line up, check the 9 o’clock position and bend as needed until these three positions line up evenly with each other, as shown in the sequence below:
Both Park Tool and Shimano state that a variation of up to 4mm at the rim (equivalent to ~0.75° deviation from true) is acceptable for properly functioning shifting. Others, such as Jason Quade of Abbey Bike Tools, state that top-tier drivetrains can benefit from being even more accurate.
There are a few common things to be wary of when using a hanger tool. First, always make sure the wheel rear is perfectly seated in the dropouts and is tight. Make sure the hanger itself is tight as well. And if your wheel isn’t perfectly true, then simply use the valve stem as a consistent reference point, rotating it around with the derailleur hanger tool’s alignment gauge.
Lastly, be extremely careful to not overstress the material you’re working with. Aluminium work hardens with repeated bending, meaning it becomes increasingly brittle the more you fiddle with it. If the hanger requires anything more than the gentlest tweak, you’re best to replace it entirely – preferably with a high-quality machined unit (from a third party, if necessary) if the stock bit is noticeably soft.
Be cautious of the frame material, too. Some recommend, and most caution against, using a hanger tool with certain carbon frames. If in doubt, check with the frame manufacturer.
What to consider in a hanger tool
Perhaps the most important aspect of any alignment tool is its accuracy, and for hanger tools, the difference between the cheapest and most expensive tools is obvious due to the amount of lateral play at the pivot point of the tool. The cheapest hanger tools tend to wiggle a lot, making it very difficult to accurately measure the alignment of the hanger. Remember, you’re aiming to be within 4mm for adequate shifting, so even a small amount of lateral play at the pivot point can undermine the accuracy of the tool.
Frame clearance is another important aspect to consider, where the arm must be able to clear the stays to rotate to different positions around the wheel. Bikes with thru-axles can sometimes challenge the utility of older hanger tools, so new designs have emerged. The HAG from Abbey Bike Tools was perhaps the first to address this issue with a longer, narrower tip that can clear virtually every dropout arrangement, while Park Tool recently added extra clearance to its DAG-2.2.
There are smaller issues to consider with a derailleur hanger tool, too. Ease of use is always something to keep in mind, and be aware of a tool’s size and weight if you intend to travel with it.
Three of the best hanger tools for home workshops
It is difficult to judge the accuracy and utility of any tool without putting it to use, so I’ve gathered what I feel are three of the best hanger tools for home workshops from Lifeline, Park Tool, and Abbey, with each one satisfying a different price point.
To help understand the difference in the accuracy of each tool in this comparison, I set up a dial calliper at a consistent length and measured the free play in each tool. While this test was subject to material flex, the numbers that I recorded correlated closely with the amount of play I could detect in each tool.
To this, I measured the weight of each tool, as well as the amount of clearance available at the pivot point. This last point is more relevant to disc-equipped bikes with rear thru-axles than frames with traditional quick-release rear wheels but it’s something to consider nonetheless.
Lifeline Derailleur Hanger Alignment Gauge
LifeLine is Wiggle’s in-house brand of tools and the design is essentially a copy of Park Tool’s DAG-2, a popular and proven tool that can found in shops across the world. Interestingly, this tool can also be bought under the X-Tools brand at Chain Reaction Cycles, but I suspect the original creator was SuperB.
The Lifelife hanger tool offers chromed steel construction with a spring-loaded gauge that slides up and down the arm. I found the gauge needle was easier and faster to use than Park’s design but I’m not a huge fan of the (removable) circlips that stop the needle from falling out of the tool. I’d recommend removing them so as to avoid any risk of them scratching the rim.
This tool weighs almost 1kg (910g) and doesn’t collapse for storage. The threaded tip makes no concession to dropout or stay clearance, so there’s a risk that it may not work with some frames. And it exhibited the greatest amount of play in the pivot, which I measured as 2.11mm at the indicator needle.
Lifeline’s hanger tool is a generic design with perhaps too much lateral play, but it is still highly affordable so it’s a good choice for light duty in a home workshop.
Price: US$35/~AU$43 (often found for less)
Park Tool DAG-2.2 Derailleur Hanger Alignment Gauge
The DAG is a common sight in bike shops across the globe and now the American-made staple is in its third generation.
The overall design hasn’t changed much across three generations, with a familiar square steel tubing construction providing a rail for the gauge needle. A simple threaded knob allows adjustment and locking of the gauge needle, while o-rings provide a basic but effective holding point if the needle has to be moved to clear a pannier rack or similar obstacle.
As the latest version, the DAG-2.2 offers improved frame compatibility by way of a longer threaded tip, which provides 30mm of clearance. Park Tool has tightened up tolerances for more accurate adjustment with the new version, and added serviceable components (such as a replaceable threaded tip) to increase the longevity of the tool.
The DAG-2.2 weighs in at 918g and I measured 1.16mm of lateral play, a significant improvement over the previous generation that suffered 1.81mm of play.
Overall, the DAG-2.2 does exactly what it needs to with greater accuracy and wider frame compatibility than a generic option like the Lifeline. All that is really lacking is the refined build quality of a more expensive tool, but buyers can expect a long service life from the DAG-2.2.
Price: US$75/AU$145 (often found for less)
Abbey Bike Tools HAG Hanger Alignment Gauge
Based in Bend, Oregon, Abbey Bike Tools create a limited range of cycling tools in small batches. The HAG is an example of the brand’s WorldTour start, and is commonly spotted in the toolboxes of many WorldTour mechanics. Of the three tools tested, the HAG is the if-money-is-no-object winner.
The HAG offers high precision in a beautifully compact package that is also quick to use. The tool comprises two parts: an arm and pivot body that threads into the hanger, and a body with the gauge needle that swivels and telescopes on the arm of the tool. It’s a design that makes it easy to take measurements while still getting around stays, racks, and brake callipers.
The whole tool telescopes down to a minuscule 273mm in length (compared to 410mm for the DAG-2.2), and the gauge needle stores safely inside the body when not in use. Frame compatibility shouldn’t be an issue since the HAG has a 15mm extension above the thread, and the tolerances are superb. My testing jig measured just 0.48mm of play 30cm away from the pivot point – less than half that of the DAG-2.2.
At 522g, the HAG easily trumps the other tools in terms of weight, yet it still managed to feel more solid under hand, which I count as an impressive achievement.
While the HAG was originally designed to fit inside the compact toolboxes of travelling professional mechanics, it has found favour amongst numerous bike stores and keen home mechanics. That said, it’s priced well above simpler options, so it’s one for those that appreciate quality tools.
Worthy of mention
While I stand by my three choices above for the home mechanic, there are other options for the professional. The most notable one is from E.V.T, which arguably stands as the very finest available provided weight, cost, and storage space are of no concern. Shimano’s derailleur hanger tool is another impressive item, too, although Brett at E.V.T. played a strong role in its creation.
Meanwhile, many veteran mechanics will swear by the classic Campagnolo hanger tool. While I can’t deny its function on a classic road bike, it certainly lacks the wide bike/frame compatibility found in the latest tools tested.
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