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Park DAG-1
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Key Search Terms: Park Tool, DAG-1, derailleur alignment, derailleur hanger.
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Product: Park DAG-1 derailleur alignment tool. Reviewed by: Rich Ries. Cost: MSRP is around $60; typical street/online price is $50 to $55. Recommended? Yes. A virtual necessity.
Executive Summary: A simple, cost-effective tool for eliminating the majority of shifting problems with at the rear derailleur.
Ratings
(1 is lowest, 5 is highest)
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Comments
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Effectiveness
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5
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Perfectly suited to the application.
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Ease of Use
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4
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Just follow the directions; use care removing and re-installing derailleur.
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Cost/Value
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5
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See TCO info in text.
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Disclaimer: this is not intended to provide complete instructions on the procedure of aligning a derailleur. Consult other sources for specifics and safety considerations.
Two conditions account for most rear shifting problems: cable tension and derailleur alignment. Most riders know that cable tension is modified by turning barrel adjusters (although they're often mystified by the direction and extent of required turns). But even if the cable tension is spot-on, rear shifting can be poor if the derailleur is out of alignment.
How does the derailleur get out of alignment? Normal wear and tear. Dropping the bike on the right side or even laying it down gently on that side. Some new bikes have poor rear derailleur alignment when the customer takes delivery. Derailleur alignment should be part of new bike setup but is often overlooked.
You can eyeball the alignment and try to make adjustments with Vise Grips or Channellocks, but that's a primitive approach that can result in more damage. A much better solution is to use Park Tool's DAG-1 derailleur hanger alignment gauge. Operation is simple: remove the derailleur; install the tool; check alignment and adjust as necessary, using the tool for leverage; remove the tool and re-install the derailleur. The DAG-1 comes with full, illustrated instructions which can also be found on Park's Web site.
There are three potential risks in the procedure. One is that you'll booger up the threads in the derailleur hanger. The risk is low as they are coarse, not fine threads, but the possibility exists. Grease the threads of the DAG-1 and the derailleur and take care to not cross-thread either. Two is that you'll break the derailleur hanger itself. Most hangers are aluminum alloy and aluminum alloy doesn't like to bend very far or very often. Push the hanger past its limits and it will break. It's a good idea to have a couple of spare hangers for each of your bikes. Put one hanger in your seat bag and leave one in your shop toolbox. There are several Web sites selling hangers if you can't get one through your local independent bicycle dealer. Three is that you'll not get the B screw properly aligned; see the photos below.
A word about cost: while the front-end cost of the tool is fairly high, the total cost of operation (TCO) is low. There is no maintenance. There are no wear parts. Tool use doesn't require a subscription or calibration or professional servicing. All of the cost is in the original purchase. Use the tool once and you have a $60 per use cost, which is quite high. Use it 60 times and you have a $1 per use cost, which is absurdly low for the resulting improvement to shifting.
And you probably will use the DAG-1 60 times, or 600 times. It's a well-built, shop-quality tool, made of steel, and chrome plated. It'll be part of your estate some decades from now. Besides, in my experience servicing my bikes and others' bikes, poor derailleur alignment is far more prevalent than incorrect cable tension, at least after the first few hundred miles of riding with new cables. I check the alignment of my mountain bikes three or four times a year and of my road bikes at least twice a year. I've never attached the DAG-1 to a bike and found alignment unnecessary.
If you're moderately adept at mechanical things and even slightly interested in crisp, accurate shifting, a Park DAG-1 is a must-have.
The Park DAG-1 derailleur hanger alignment gauge is elegant in its simplicity. With the rear derailleur removed from the bike, the tool is attached using bolt A. Thumbscrew B allows the rod holder to move up and down the arm and the rod C to move in and out.
Derailleur removal is simple as long as you work gently and support the derailleur with one hand. Shown is a typical removal where a 5 mm hex wrench is the only tool required. The arrow points to the B tension screw, which we'll get to in a minute.
With the DAG-1 mounted, the rod is moved until it just contacts the rim or the knurled nut on the valve stem. The rubber O-rings on the rod provide a reference point when the rod is retracted so that the tool can be swung to another orientation. This is the 6 o'clock position. The wheel is turned and the alignment rechecked with the valve stem at the 12 o'clock position and adjustments are made until the rod is the same length from the holder to the rim or valve nut in both positions. Alignment is then checked at the 9 o'clock and 3 o'clock positions. Additional text and photos can be found on Park's Web site.
When re-attaching the derailleur, make sure the B tension screw (A) clear its shelf on the derailleur hanger (B). The wheel has been removed in this photo for the sake of clarity.
To do this, turn the mounting bolt just enough to ensure that it has properly engaged the mounting hole in the hanger. Stop turning the bolt just before the B screw contacts the face of the hanger. Use your free hand to rotate the derailleur back, in the direction of the arrow, until the B screw clears its shelf on the hanger, then finish tightening the derailleur mounting bolt to the torque specified by the manufacturer.