Single Chain Ring Considerations

A Canadian Peugeot with single chain ring and spider mounted chain guard.

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.

1947 Camille Daudon with single chainring

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.

Paul’s Chain Keeper

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.

Short People Got Nobody

1980s’s ALAN with 24 inch wheels

Randy Newman’s silly tune “Short People” was unfortunately taken literally rather than as its intended satire by the listening public when it was released back in 1977.  So, I heard this song all too often in the wrong context in those days – with people I knew laughingly singing the lyrics while mocking their friends of shorter stature, seemingly with full license from Randy himself.

But, the song was intended instead to mock those who held such discriminatory, narrow views of other humans who were ever so slightly different from themselves – a problem of human nature which seems to know no end or bounds (current events confirm this resoundingly).

The cycling industry is a casualty of such views, not only with regard to human stature, but also with regard to gender and race.

One of my quests has been to educate cyclists about the world they encounter when trying to find the appropriate bicycle for their needs.  In an ideal world, there would be no bias toward any particular size or type of bicycle.  Instead, bicycles would be manufactured according to the variation of human sizes, and according to their intended purposes (and that is to say that only a tiny fraction of bicycles would be “racing bicycles”).

1950 Raleigh Sports Tourist with 26″ wheels

The opposite was true for many recent decades.  Bicycles manufactured to fit only a certain taller human were offered, and all such bicycles were conceived as racing machines, since that is what appealed to the western, white male mass culture of the times.

The needs of daily riders, smaller cyclists, older cyclists, non-male, and non-white cyclists, and differently-abled cyclists were never considered.  Economic justice issues as they relate to transportation were not even in the vocabulary.

Meanwhile, let’s talk about what has changed and is changing in the industry, and how those changes address these basic inequalities:

1980’s Viner – converted to 650c

Wheel size:  the move toward smaller wheels for smaller frames is finally underway…again.  There was no bias in the early days of cycling toward any particular sized wheel.  Velocio” championed small wheeled bicycles from the late 1800’s through the early 1900’s as more efficient, even though he was of taller stature than most humans.  Georgena Terry is a modern day pioneer of small wheeled bicycles.  She continues to design frames around the anatomy of cyclists who are of smaller stature. Rodriguez Cycles, builder of custom frames in Seattle, also figured this out long ago, offering many frames designed for  650b, 650c and 26″ wheel sizes. Brompton, Bike Friday and other builders of small wheeled and foldable bicycles (which can be ridden by humans of any size) are also part of the solution.  Grant Petersen of Rivendell began offering smaller frames designed for 26″ and 650b wheels decades ago, well ahead of any current wheel size trends.

1990’s fillet brazed Terry Symmetry

Frame size, construction and materials:  While I love and prefer lugged steel frames, fillet brazed steel frames offer much in the way of customization for tube angles.  Georgena Terry’s smaller frames feature fillet brazing, with a sloping top tube.  Purchasers of her custom built frames can specify the degree of slope they prefer.  But one thing to remember is that for any cyclist who is actually riding a bicycle with appropriate sized wheels, they also need to carefully consider top tube length, which for me is the most important measurement on a bike’s frame.  The Terry that I include in my constellation of daily riders is a fillet brazed off the shelf Tange steel model from the 90’s.  The short 51 cm top tube means that I experience a comfortable ride, even on long hauls.  The 559 wheels allow for a large head tube – and that means an overall very comfortable ride, with more steel underneath the rider to absorb road shock.  Shorter cyclists should rule out most modern aluminum frames, as they will be much too stiff and uncomfortable due to their smaller overall size.  One exception is vintage ALAN frames (or any other bonded aluminum frame) from the 70’s to the 90’s.  These aluminum frames can actually be more flexible and comfortable than their steel counterparts.

Photo credit J. Maus

The crazy obsession with stand over height:  When was the last time you had an unfortunate encounter with your bike’s top tube?  Probably, if you are an adult, the answer is NEVER.  There really is no reason to fret over whether you have just the right amount of stand-over height for your bicycle (whatever that is) unless you are planning to use your bike for stunts.  It’s very easy to dismount a slightly taller bike than one you would normally ride and lean it over at stops.  If you have ever been to Portland, you’ll enjoy seeing the occasional tall bike making its way through traffic.  The rider has no chance of putting a foot down at stops, and instead learns to balance and maneuver their odd contraption, sans traditional bike fitting advice.

1980’s Panasonic Mountain Bike converted to City Commuter

1980 Meral custom frame converted to 650b

And, summing up:  if you are a shorter cyclist looking to get back in to cycling, or to find a bicycle better suited for your build, DON’T go to your Local Bike Shop (at least not initially).  Look at the bike you currently have:  can it be converted to a smaller wheel size?  If not, I advise purchasing an appropriate frame (or having it custom built), and then building it up to your spec’s from there.  Better yet, learn how to do this yourself by enrolling in the many bike maintenance classes that are available in your city.  Smaller lugged steel mountain bike frames make wonderful and inexpensive commuter bikes – but pay attention to the top tube length.  And, there are many lugged steel vintage 700c frames that are good candidates for conversion to 650b.

French Threaded Shifter Bosses

While I usually love all things French, I was perplexed to discover that the shifter bosses on the early 1980’s Méral Randonneuse I am currently restoring are not threaded “normally”.  What is normal threading for a shifter boss?  Well, it’s the same  5 mm x .8 that you will find on much of the rest of your frame:  bottle cage mounts, rack mounts, etc.

Courtesy of Park Tools.

Fasteners have several elements that help identify their size, the two most important of which are: thread pitch, which is the distance from the crest to the crest, and thread diameter which is the outer measurement of the thread crests.  English threading is designated by the frequency of how many threads are counted along one inch.  This is know as “threads per inch” or TPI.  Metric threading uses the direct pitch measurement in millimeters, measuring between two adjacent thread crests.  A fastener designated as TPI is “standard”.  Unfortunately, some fasteners are “mix and match”, with both a TPI and a metric size, such as Italian bottom bracket threads labeled “36mm x 24 tpi”.  There are standard coarse metric threads which are designated with the letter “M” followed by the thread pitch.  For example M6 = 6.0 diameter with a 1.00 mm pitch.

This Méral has a shifter boss on the seat tube – for engaging a bottom bracket mounted dynamo.  When I acquired the bike, the lights and dynamo had been removed from the frame.  So, I planned on reinstalling a BB dynamo hooked up to a friction shifter on the seat tube.  That’s when I discovered that the threads on the shifter mounts did not match any threads on any shifters I tried, even including some Simplex shifters from this era.

Simplex Shifter with 6 mm x .8 threading

That’s because these shifter bosses are tapped with 6 x .8mm threads (not 5 x .8), as you can see from the above nomenclature on the bike’s Simplex shifter boss bolts.  These Simplex shifters use a nonstandard threading on the boss. My research indicates that Simplex used a variety of threading standards for its shifters:  5 x .8, 5 x 1.0, as well as 6 x .8, shown above.  Classic Rendezvous has a discussion of these sizing anomalies.

Soubitez BB dynamo

Here is one idea for a BB dynamo for this bike – a Soubitez which is in good shape. I’ll need to set up the seat tube shifter, and given that the boss threading is non standard, it’s back to the drawing board for now.