On a recent multi-day ride, a friend and I pulled off of the road into a the parking lot of an Italian restaurant buried in central Pennsylvania. Our chains were dry and shrieking for want of lubrication and it was sorta time for a lunch break too anyways. My friend rummaged through his panniers and happened upon the correct one with his repair stuff in it. As he removed everything to find a bottle of chain lube, I noticed something wrapped up in a grocery bag.
Me: "Is that a chain whip?"
Me: "I really wouldn't want to carry that."
Him: "Yeah, me neither. But what are you going to do if a drive side spoke breaks and you need to remove your cassette?"
Me: "Commit seppuku with a tire lever."
First off, I am not criticizing my friend. Both of our bikes (and wheelsets) have over 10k miles on them. We carry lots of heavy stuff in our rear panniers. We ride over things like rough trails, the cataclysmic streets of Baltimore, hippies, etc. Prime situations to break a rear spoke. And we do all of this often at great distance to a bike shop. If you break a spoke on the drive side of your rear wheel next to the cassette, you need to remove the cassette in order to replace the spoke. The usual necessary tools are a chain whip, a cassette lockring tool and a crescent wrench. Unless you're my friend who opted to carry these along, you're not likely to find such specialized tools outside of a bike shop while out touring.
I have always been aware of this potential situation. For many thousands of miles of touring, I simply adopted the "I hope that a rear spoke never breaks but if it does make it right by a bike shop" mentality and tried not to think how royally screwed I might be in certain places. Perhaps somewhere like Wyoming's Great Divide Basin. I assure you that I am not alone in this mindset. Actually, I'll bet that many cross country cyclists have never even considered the predicament I just laid out. But right then and there, in the parking lot, I promised my friend that I'd determine a solution. We had both heard of "emergency" lockring removers, but hadn't purchased one since they cost about $40 and we had no idea how they worked.
The only such tool in current production that I have heard of is the J.A. Stein Mini Cassette Lockring Tool. It's been recommended by other long distance cyclists, but I could not find anywhere that clearly explained how the tool operates. I ordered one through Harris Cyclery for $35.95 and I would urge you to call them and try to negotiate their $10 shipping fee since what I received could have been essentially mailed in an envelope. For your forty odd dollars, you receive a small plastic bag with several loose metal bits and you begin wondering if you've been swindled.
Now, I have the advantage of having removed my cassette a couple of times to replace it. I used the ubiquitous Park Tool Cassette Lockring Tool and Chain Whip and a crescent wrench. This gave me an overall expectation of what had to happen here. If you haven't removed a cassette using conventional means, it would probably behoove you to ask for a demo at your local bike shop before playing with the Stein tool. But once you look at the Stein tool, you will note that the larger plate has splines machined on it much like a conventional lockring removal tool. With your skewer removed, you engage the splined plate with the lockring on your cassette. Then with a 3mm allen key, you attach the smaller arm to the plate. With the wheel in your bike's dropout, you reinstall the skewer, clamping down the slotted end of the arm. As you rotate your crankarms in the easiest gearing, the tool rotates until it contacts the frame whereupon further crankarm rotation causes the lockring to be loosened by the now immobile tool. By changing the orientation of the tool slightly, you can tighten the lockring back on by rotating your rear wheel backwards by hand.
This may sound quite complicated. I assure you it isn't. It's just hard to put into words. If you have experience with a usual cassette removal procedure, you will be able to follow the directions that come along with the tool. You will need to be carrying your own 3mm allen key and if you are the type to carry an emergency cassette remover then it would stand to reason you're also packing a multitool. The tool worked fabulously once I read through the instructions. I had to remove a bolt holding one of the fender arms on that would have blocked the tool's rotation. In order to get the lockring to "break free" I sat on the bike and pushed down on a pedal with my foot. I doubt that handstrength on the crankarm alone would be enough force. And likewise, reinstallation of the lockring was a snap too (albeit with one caveat that I will describe below). I can absolutely recommend carrying the Stein tool along on bicycle rides that take you far away from the bicycle shop or your home workbench. Just remember to bring extra spokes as well, otherwise this is all for naught.
DISCLAIMER for Surly Long Haul Trucker owners: I have an LHT and by my observation, a heck of a lot of other cycletourists do too. When I went to reinstall/tighten the cassette lockring, the directions are at odds with the LHT dropouts. When reinstalling, you set up the tool with the arm pointing 180 degrees in the other direction and thus the arm contacts the frame by the chainstay, instead of the seatstay as in the loosening operation. If you look at the above photo where the tool is installed for the loosening operation, you'll see a flange of sorts where the chainstay meets the dropout. If you follow the tools directions, when you are tightening the lockring back on, the arm of the tool will ride up onto this flange and get bent. I know because I did it. I was able to hammer the arm back flat and I'm sure it will work fine in the future. What I would do next time is allow the tool to contact the back of the derailleur hanger instead of the chainstay. The directions clearly say that you should not do that as you may damage your derailleur. With that in mind, I would probably unbolt my derailleur first since it isn't necessary for the tightening function to avoid damaging it. Again, if you own an LHT and are using a Stein tool, this will make immediate sense when you're sitting there looking at it.