Most of my bikes have multiple chainrings – double or triple. I’ve gotten so used to the shifting patterns on my bikes, that I don’t think much about the double rear shifts that might be required to maintain cadence when shifting the front ring, nor do I worry that I might have to trim out the front derailleur from time to time (I use friction shifting for the most part). But, that is not normal. I am a geek, and the vast majority of cyclists are not (no offense to the wonderfully geeky readers of this blog). Non-geeky cyclists are probably drawn to the seeming simplicity of a single chain ring up front. Less shifting equals better riding, right?
The only bike in my constellation of daily riders with a single chain ring up front is my 1987 Panasonic MC 7500 – a bike I acquired as a frame and fork and then built into a city commuter. Even though it’s the heaviest bike I ride, it’s the one that gets the most daily use. One of the reasons for its appeal as a commuter bike is the simplicity of its equipment. It has a rear freewheel with 6 speeds and plenty of range, plus a single chainring up front. I installed a $7 ratcheting no name friction shifter on the handlebar to move the rear derailleur, and the shifter works intuitively with the lower end but perfectly decent Shimano Acera long cage rear derailleur. At first, I didn’t use a chainkeeper, but experienced the chain jumping off on a few occasions, so decided to install Paul’s chainkeeper. Chainkeepers are designed to keep the chain from falling off either side of the front ring of a single chainring bicycle when shifting vigorously or oddly, as can happen when unexpected events occur while cycling, and especially while commuting.
After a few mishaps with Paul’s chainkeeper, the most recent of which caused me to re-locate this device, as shown above (it is now a “fender keeper”), I have been thinking about the way returning cyclists, as well as those not mechanically inclined might have dealt with my recent near disaster.
I was cycling home after a day at work, heading downhill when suddenly my cranks would not turn. Since I was still freewheeling I knew that the problem was at the front of the drive train and I immediately suspected that the chainkeeper had become dislodged and contacted the chain. I pulled over immediately, and after confirming this was true, disengaged the chainkeeper, as shown above. I rode home with no further issues, but shifted very gently, hoping my chain would not jump off the front ring, and all went well. It is unlikely that the average cyclist would have been able to diagnose this problem, much less solve it. Nor should they really need to. Instead, the marketplace needs some much better solutions to the single chain ring challenge.
Vintage bicycles with single chain rings don’t need chain keepers. Why? The rear freewheel will have only 3 to 5 speeds for the chain to navigate, causing the chain movement to be very manageable as compared to modern drive trains with 8 – 11 speeds at the rear. For commuters, it’s not necessary to have tons of gears, but instead to have enough gear range to accommodate the hills you encounter on your commute. So, 3 to 5 speeds might be all you need, if the gear range is appropriate.
The problem with many chainkeepers, such as Paul’s, is that they work TOO well. Since they are designed to prevent chain movement, there isn’t enough clearance to provide for even the slightest change in chain angle, and they require extremely precise adjustment that can go out of whack with even a small mishap.
One solution is to put a spider mounted chain guard on the crank, and then use a seat tube mounted chain watcher on the other side. Or, you can put two spider mounted chain guards on the crank – on either side of the chain ring. Sheldon Brown published an article for Adventure Touring Magazine in 1999 which deals with chainring issues for touring bicycles, but he also includes some good advice on anti-derailment devices that can help prevent the chain from dropping off a single chain ring.
If you are going to convert your bike to a single ring up front, here are some points to consider:
Shorten the Chain – you will want to remove links from your chain in order to accommodate the switch to a single ring up front. This will help to prevent chain slap and chain jump.
Decide about a chainkeeper vs. chainwatcher vs. chainguard(s): Depending on the width of your rear cassette or freewheel, you’ll need to think about the demands you are placing on the front ring. If you are trying to go with an 11 or 10 speed system at the rear, then you’ll need something to help deal with the extreme angles that the chain will experience at the front ring.
Make sure the rear derailleur can handle the range: when switching to a single ring up front, you often need to increase the range of your rear cassette or freewheel. If you do so, make sure that your rear derailleur can handle the the bigger cogs. You may need to adjust your b-screw, or invert it (a la Sheldon Brown) to get the clearance you’ll need for the larger cogs.
Or – shift carefully and don’t worry about any of this. Occasionally your chain may fall off, and then, you’ll put it back on again.