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You are a bike mechanic. Whether or not you’ve ever thought of it that way, you possess skills that most people don’t. At the very least, maybe you think those skills start and end with changing a tire, but I disagree. You know the angle your brake levers should be at, and how to get them there. You know how your saddle clamps to your seat post and how to adjust it. You at least know your left pedal is reverse thread. From my years of being a professional bike mechanic I can tell you that this makes you more qualified to fix a bike than most of the human population. And if you’re reading this article, it means you probably know what a derailleur-hanger alignment gauge is, and that rockets you well into the top 1%.
But very few of us own one. The hanger gauge is the sort of thing most of us let bike shops worry about. They’re bulky, they’re rarely used, and most notably, they’re expensive. The benchmark is the Park Tools DAG-2.2, and it’s $80. For a tool that you might go a year or more without needing, that’s a lot of cash to have hanging on the pegboard, if you even have pegboard. But when you need a hanger gauge, you need it. So, what about a cheap one? How bad could they be? Well, that’s exactly what we’re going to find out.
Coherny Professional Bicycles Hanger Alignment Gauge Alignment Ranging Tool for MTB and Road Bikes: $38.92
You can see where this is going. That’s literally what this thing is called on Amazon. But it’s not the only one. There are look-alikes out there from “SYCOOVEN” (yes, all caps) or one on AliExpress that’s just called “AG 2.0,” which is even a few bucks cheaper than my trusty Coherny.
The first thing I noticed about this tool is how well put together it feels. It’s entirely lathe-spun aluminum, and it’s oddly satisfying to slide the two telescoping elements in and out. It ‘s hard to tell scale in a photo, but it is not undersized or flimsy-feeling. It’s also significantly lighter than the Park DAG-2.2, and far more compact. Not that this is the sort of tool you’d pack on a trip to Whistler, but it wouldn’t be a bad luxury item to take on a road trip. It even can be quickly broken down to three narrow parts and would fit in a small toolbox.
Having used the very differently configured Park DAG-2.2 during my near 20 years of shop life, I was surprised how familiar it was to use the Coherny. I had expected the telescoping motion to be a problem, in that it would be loose or sloppy, but there’s actually a bit of smooth resistance that keeps the outer end steadily at a constant distance from the axis so you can follow the rim. In fact, it was a little smoother than sliding the probe of the Park DAG-2.2 up and down its arm. Similarly, sliding the probe in and out on the Coherney was also easier because it is held in place by a tight plastic bushing, whereas the DAG-2.2 relies on a thumb screw that is best tightened and loosened every time the probe is slid in and out.
But on the other end, the “axle” that threads into the hanger, there is a considerable amount of play. You can’t tell when it is off the bike, but magnified by the length of the tool, there is about 17 millimeters of wobble, and it makes getting an accurate reading a little more difficult. I needed to set the probe to hit the rim at one end of that wobble and go from there, putting some pressure on the tool as I did my rounds looking for the direction of the bend. I didn’t sense any further inconsistency in the rate of wobble as I went around, and this method did get me a straight hanger after checking it against the more robust DAG-2.2. It is imperfect, clumsy, and requires the extra step of flexing it towards the rim to actually know the shape of the hanger, but I have to admit that it’s better than eyeballing it.
Park DAG-2.2 $80
Your local bike shop probably has a couple of these above its workbench. We often forget that Park is not the only dedicated bike tool brand out there, but they are the biggest and most popular. While there are several fancier gauges on the market (the $185 Abbey Bike Tools gauge is an absolute treat to use, and Park has a new DAG-3 for $120), the DAG-2.2 offers the most bang for the buck.
Part of that is its simplicity, albeit simplicity that might make you question the $80. But like 85% of Park Tools, the DAG-2.2 is made at Park’s headquarters in St. Paul, Minnesota. And as I learned using the apparently not-so-dialed Coherney alignment gauge, it’s not easy to do this right.
The axle assembly is what makes the DAG-2.2 stand out. It’s the heaviest part of this already heavy tool. The thick steel around the axle is meant to survive years of professional use, and the occasional professional fall to the shop floor. It also is designed not to stretch, flex or deflect under load. The Coherney tool seemed tight as a drum until the force was magnified by a 14-inch lever. The DAG-2-2 that I tested, which I’ve had for two years, had barely two millimeters of play compared to 15 on the Coherney.
The probe on the DAG-2.2 is probably the only slightly frustrating bit. If it were held in place with constant friction like the Coherney or that Abbey tool I once had the pleasure of using, it would make one rather frequent action in the process of hanger alignment a lot easier. Hanger straightening needs to be done slowly, especially in the era of thru-axles, when hangers are far stronger and take far more force to straighten. It’s done in small steps, so the probe needs to be re-positioned a couple times during the process. But as we established already, this is a tool that most of us won’t use that often. A few seconds of fiddling is worth the accuracy if you want it done right.
As for which of these two tools is the right choice for a de facto bike mechanic like yourself, I really have to say it’s worth it to pony up for the Park. Although a cheap gauge eventually did get me good results, I had to put a lot of thought into it on the way. And that’s coming from someone who worked in bike shops for nearly two decades, using a hanger gauge several times a week. For the vast majority of us who will not be using it often, a tool that gives accurate, reliable results will make a crucial task (which is as crucial as ever in the era of 12 speeds and 52-tooth cogs) far easier and more repeatable. It’s worth it.