Friday, 28 October 2011

How many gears? - Part 2a: two-speed bikes

This time, I will start by looking at two-speed hubs, then discuss other two-speed systems after that, such as the two-speed Brompton derailleur system and the Schlumpf crankset systems, then briefly mention older, obselete, systems.

Two-speed hubs

Two-speed hub gear mechanisms in continental Europe (i.e. except the United Kindom and Ireland) are dominated by the Fichtel and Sachs Torpedo Duomatic.
Backpedalling lightly changes the gear - firmer backpedalling engages the rear hub-brake.
Sturmey-Archer currently produces a variant of this type of hub, with versions with or without a coaster brake (rear backpedal brake).
  • no cables for control - it is controlled by backpedalling
  • allows a decent gear for "normal" riding, while providing a lower gear for hills (although, officially, the gears are classified as "normal speed" and "fast speed")
  • compact and very low-maintenance
  • easy to enclose in a full chain-case
  • Sturmey-Archer 2-speed hubs are available in a 36-hole hub.

  • F&S hubs almost all have a 28-hole hub, as these were usually fitted to 20" folding bikes
  • Only two gears - top gear is 1.36x bottom gear for the F&S hub, 1.38x for the SA hub (compared with the 1.77x spread for an SA 3-speed hub)
  • F&S hubs all have the coaster-brake
  • F&S hubs are designed for a rear-wheel spacing (a.k.a. "O.L.D." - "Over Locknuts Dimension") of 112mm, the SA hub with the coaster brake is designed for an OLD of 116mm, the SA hub without the brake has two versions, designed for OLDs of 110mm and 120mm, while a typical modern "MTB" or "Hybrid" bike has an OLD of 135mm!!
    Older bikes (and a lot of folding bikes) had smaller OLDs, much closer to that of these hubs, while newer bikes will need the frame modified
  • if buying new, an SA 2-speed hub costs almost the same as an equivalent SA 3-speed hub
Bendix, in America, also made a lot of two-speed hubs. There seems little reason to recommend their cable-operated two-speeds (all the work of a three-speed, without the third speed!), but most of their production was two speed "Automatic" hubs, with variously 20, 24, 28, 36 or 40 spoke holes in the hub. The "Automatic" hubs had coaster brakes, and the mechanism to change gear was much the same as the F&S and SA hubs. They were widely fitted to Schwinn bicycles. The spread of the gears is larger than the F&S and SA hubs at 1.5x.

The Sturmey-Archer hubs seem to be the only ones currently available "new", and as such, will have full parts availablity via regular sources and local bike shops.

Other two-speed systems

As well as two-speed hubs, there are a couple of other oddities available, such as the Brompton two-speed derailleur, which Brompton claim is much lighter than a three-speed hub - indeed, Brompton claim that their two-speed derailleur bike is 550 grams (about 1 pound 3 ounces) lighter than their equivalent bike with a Sturmey-Archer three-speed hub! For a folding bike that you might be lugging up and down stairs, or (bagged up) on and off buses and other forms of transport, that extra half-a-kilo, or so, can really matter!
The gear ratio between the high and low gears on the two-speed Brompton is 1.33x, which is similar to the F&S and SA hubs.
Again, given the modest distances that Bromptons are typically cycled (although some folk cover HUGE distances on them!), the addition of the two-speed derailleur (which weighs only 188 grams, that's about six and a half ounces!) seems to give a big benefit over the single-speed model for only a small increase in weight.

The other unusual system one might encounter is the Schlumpf two-speed bottom-bracket gear system. That's right, it is not in/on the rear wheel at all, but is between the pedals!
It is a bit pricey (at c. 500 Pounds Sterling), but can be fitted to many machines, including a special variant for the Brompton. It's going to push the weight up, though.
Three variants are available, and they have a 1.65x overdrive (the "Speed Drive" model), a 2.5x overdrive (the "
High Speed Drive" model), and a 2.5x underdrive (that is to say the second ratio LOWERS the gearing, and is called the "Mountain Drive").
It all works with an epicyclic gear system built into the crankset (a bit like a rear hub gear, but built into the bottom bracket!),
and you change between the two gears by pushing a fat button on the end of the crank arm with your heel.
An interesting concept that can be combined with a multi-speed rear hub
now that eight- eleven- and even fourteen-speed rear hub gears are available, it seems a little pricey for most users.
With a heavy cargo bike, or a velomobile (a kind of pedal powered car!), the 2.5x ratio models could combine quite nicely with a tough hub like the Sturmey-Archer three-speed or the SRAM P5 Cargo to increase the gear range while having a very strong gear system.

Older two-speed systems

Historically, a number of other two-speed systems were employed in bicycles. Back before the First World War, Sunbeam made a two-speed crank gear (not unlike the principle of the modern Schlumpf system), and Eadie (as the "Fagan" model), BSA and Sturmey Archer all made two-speed hubs, along with various other manufacturers. The relative rarity of these systems now and the lack of availability of spare parts (the Sturmey Archer design has changed since those pre-WW1 days!) for them makes them of very limited practical use nowadays.

Summing up

It is probably best to avoid "improving" modern bikes with two-speed hubs due to the problems of hub-width (a.k.a. O.L.D.) unless deliberately building a "retro" bicycle, fitting to an old bicycle, or restoring an older machine.
Although two-speed hubs (with the exception of the cable-operated two-speed from Bendix) are even lower maintenance than a three-speed hub, it is hard to recommend a two-speed over a three-speed, with the exception of the lightweight Brompton system, where the weight saving over a three-speed (an SA hub) is important for many users, or a bike where the cables get in the way (such as a "seperable" bike, that takes apart into a front piece and a rear piece, or a folder where the cables may hang out when folded, making it look untidy and making it likely to catch on any obstacles).

The three-speed hub, for me at least, summarises the whole point of having more than one gear,
BUT if you want to see how a two-speed hub performs, then:
a) if you have a derailleur-equipped bike, choose a couple of lowish gears with a gap between them. Third and fifth gear will probably fit the bill. Just use these two gears, and no others.
b) if you have a three-speed hub, just don't use third :-)
c) if you have a five speed hub, just use second and third gear, not first, fourth or fifth.

I've been running my three-speed in "two-speed simulation mode" for a couple of weeks (basically, I just use 1st and 2nd gear!), and, to be honest, it isn't that much different for the type of cycling I do.

  • Where I miss the third gear is when I cycle on the road on the flat or downhill (or with a tailwind).
  • Most of my cycling, however, is on tarmac (asphalt) cycle paths and dual use pavements (sidewalks), and then I only lose a tiny bit of speed - not enough to worry about really.  
  • I coast a bit more than when using all three speeds
  • 95% of the time, my cycling is exactly the same using two speeds or three speeds.

Having said all that, choice is a personal thing, and if you want a two-speed, then go ahead and get one.
Despite my reservations, back when I rode an employer-owned single-speed, often carrying a load of about 20 kg uphill, I would have swapped it for a two-speed without hesitation!
I suppose it all depends how you ride.
Thirty years ago I used to ride a bike with ten gears (double chainwheel, and five-speed derailleur), and I almost always only used 3rd gear and 8th gear! So I kind of used it like a two-speed, anyway.
Nowadays, I ride a three-speed, and would use all three speeds on most journeys.
But, after experimenting for the last couple of weeks with not using the top gear, my three-speed is usable enough when ridden as a two-speed. It takes a bit longer to get places, as I just spend more time coasting, and enjoying the view, which is not necessarily a bad thing :-)

If one is only riding modest distances, and/or it is relatively flat where you live, a two-speed is quite usable enough, and much easier to ride than a single-speed bike.
Folding bikes don't, on the whole, get ridden long distances, and less cables means there is less to get snagged, so maybe F&S knew what they were doing after all!

Brompton, cables and all, use their unique two-speed derailleur to give a significant benefit (two gears, rather than one!), without adding much weight to their folding machines, which, folding smaller than many other folders, and being a good bit lighter, too, are one of the best for multi-modal transport in circumstances where the bike needs to be zipped into its carrying bag and passed off as a slightly odd-looking suitcase for part of the journey (e.g. on a bus/coach/autobus, or on a peak-hours train).

A new market also appears to be opening for two-speed bikes - aimed at folks who like the minimalist look of a single-speed bike, but want something that is more practical and easier to ride. An example of this trend is the Marin Ignacio, with a list price of about 650 pounds (call it 1000 US dollars or a bit over 800 euros) - big money, especially compared with a used 2-speed folder one might find on e-bay!
More realistically priced is the nostalgic Pointer Comfort Transport, which is available as a with a two-speed SA Duomatic hub for 390 euros (more like 500 US dollars).
So clearly there is still some life in the idea of a "no cables" two-speed hub!

For me, though, the only two-speed system I would think about paying serious money for would be the unusual two-speed derailleur on the Brompton light weight folder. If I was to get a job in a London office, I would almost certainly commute by train, using a Brompton for the stage beyond Maryleborne station, enjoying the light weight and both of the two speeds all the way!

If I was looking to get a "cheap and cheerful" bike, however, I would much prefer a two-speed over a single-speed, especially if there wasn't too much difference in cost. The second gear makes a BIG difference. But if a three-speed was available for a similar cost, I would buy that instead!

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