Gears

 THE DEVELOPMENT, DRIVES AND GEARS

     The distance covered by one crank rotation is called the development. The more meters we want to travel, the harder we have to push on the pedals. (In England they use the gearratio in inches).

Most important parameters are rearwheel diameter, and the sprockets and chainrings used on the bike. Riders often talk about the gear ratio on their racing bike: "I rode the Cauberg with 42-18 ". Because the rear wheels of roadracing bikes have a standard size, you can  instantly compare the gear ratios. On the mountain bike this is more difficult nowadays. In the eighties and nineties we rode a standard size, a rim diameter of 559mm ; 26 inch as mountain bikers usually say. The current range of ATB's has also got extra large tyre sizes of 27.5 and 29 inch. Especially if you want to compare different gear systems or wheel sizes, a conversion to the distance travelled, is the best way to make that comparison. Things like Rohloff 14 speed hubs and Pinion 18 speed gearboxes can be compared using the Excel-files here.

Every drive has losses; an average derailleur about 5%. That percentage is often higher in geared hubs. This is a downside to planetary systems: all gears that are interlocking, rotating and transmitting forces. lose energy by friction. Usually the bearings of the planet wheels are plain bearings. The losses of friction by bearings and sprockets can add up to 10-20%. In some gears there will be many planetwheels enabled and in others less. The efficiency of the geared hub will therefore depend on the gear selection and the type of hub. An expensive hub like Rohloff, does use bearings; the efficiency is similar to a derailleur. The efficiency of Shimano Nexus 7-speed was very moderate, averaging 85%; the current 8-speed has been improved by using some bearings and another shifting pattern.

 THE DEVELOPMENT OF DERAILLEURS

Around 1895 in England a system is marketed with an expanding chain wheel. This "Protean 4 speed" had chain tensioner to take up the difference in chain length; an arm with an auxiliary wheel and pressure spring, which was supported on the rearfork. In that same year a Frenchman designed a system with such a chain tensioner, but it also had a swing arm with a fork, which could lay the chain from one sprocket to another: a real derailleur. Probably this was never produced, but the idea existed already.

   In FIG. 2a, 2b and 2 c we see designs from the 1930s. Until 1950 these are the most common types of gear changing in the sport of cycling. In Italy before the war, they used the Vittoria Margherita, see FIG. 2 c.  This is a similar construction, but it had the shifting fork reversed above the chainstay ; the rider had to pedal backwards to shift. This was also the case in the first Campagnolo systems (see FIG. 5a). At first the rear hub was disconnected. The rearaxle was dented, just like the dropouts (see FIG. 5b), it could move to take up the difference in chain length, see the YouTube video. 

But even before the war, there were more advanced models, like the Super Champion of FIG. 3 and the vulnerable Simplex of  FIG.4. The front derailleur of FIG. 3 was not used by racers, but by tourists and commuters. Racers had three sprockets on the rearhub; that used to be enough for a real man in those days.

Just after the war, Simplex and Campagnolo front derailleurs were operated by a lever on top (see FIG. 5b) ; it meant that the rider had to bend over deeply, what could lead to crashes, hence the nickname "suicide levers". In 1946 Navet patented the strange idea of combining shift and brake lever (FIG. 4a); it took a while before it became popular.

   From 1949 Campagnolo experimented with a rear derailleur on basis of a deformable parallelogram. In 1953 the final version came on the market. The shifters of the front and rear derailleur moved to the down tube. The Campagnolo Gran Sport is the most imitated derailleur ever ( FIG. 6a).

   It was not until 1964 that a new improvement was made by the manufacturer Suntour. They placed the parallelogram at an angle ("slant parallelogram"); see the right image in fig. 7a. The upper Jockey wheel remains closer to the gears and the derailleur is more accurate. The patent expired after 20 years and all the manufacturers like Shimano, Campagnolo, Sachs etc. design new series,  according to this principle. In the mid-1970s the shifters from Suntour don't use friction  but a ratchet system (micro-ratchet fig. 7b,); this was also copied by many other manufacturers.   

    Most derailleurs and Shimano shifters are interchangeable. An exception are the first 3 series of Dura-ace. The rear derailleurs from 1984 to 1993 can only be used with Dura-ace shifters. It doesn't matter if it shifts 6, 7, or 8 speeds; the rear derailleur is interchangeable. Shimano did a masterpiece in marketing policy: the derailleurs, gears and chains, all had to be from Shimano to get the best possible SIS action. Not only in road bikes, but also at the new fashion: the All Terrain Bikes. With the top groupsets like XT and Dura-ace they spoiled the cyclists, and after a testride, they did not want anything else.

    The standard was set! Each competitor had to be at least almost as good as the Shimano group in its price range, in order to remain on the market. Each renewal, like STI and Rapidfire (the shift levers), was introduced in the top group and then trickeled down in the cheaper groups. Suntour is gone, Huret and Sachs are bought by SRAM. In the roadracing market, Campagnolo is still playing a role, but the whole ATB-market was lost after 1 attempt. Shimano rules!

   The cablerouting on the rear derailleur is very inefficient. SRAM, M5 (U-turn-away) and Suntour, have made better desings. The framebuilders had to design frames with other dropouts for the Suntour S1 derailleur; that was just a step too far. Actually the Suntour S1 was a redesign of the Nivex and Altenburger from 1938 and the 50's.

    A new market for groupsets was found, designing the gravelbike. Just a single sprocket in the front, 12 or 13 cogs on the cassette, ranging from 9 or 10, to 44 or 48.

    The integration of brake handles and derailleur shifters has a long history; already in 1946 the Frenchman Navet applies for a patent, in which he places the derailleur switch on the brake handle. There were also such patents in the 1950s.Mavic had an electronic shifting system in the nineties; the UCI demanded, it should be selfpowered and banned batteries. Twenty years later Simano introduced their DI2 and there was no problem (?).

Chosing double planet gear ("stepped" see FIG. 9 ), it may be for example a second  gear ring . This extends the capabilities. There is a big downside to planetary systems: all gears interlocking, rotate and forces pass, lose energy by friction. Usually the bearings of the planet wheels are simple plain bearings. The sprockets are made via sintering of metal powder (pressed and baked). The surface is somewhat rougher (more friction). One advantage is that the lubricants better stick and attach in the cavities. The losses by friction of bearings and sprockets can really add up to 10-20%. In some gears there will be many wheels enabled and others less so. The efficiency of the gear hub will therefore depend on the gear selection. Only Rohloff used anywhere real bearings in the sprockets. Those wheels make them also through machining (only the SRAM Spectro P5 Cargo has also machined wheels). Usually there is one circuit in which the chain wheel to the hub home linked; the return is then maximum (96%).

The number of teeth on the ring gear is equal to the number of teeth on the Sun wheel, + 2 times the number of teeth of the planet carrier.

The ratio's between the gears determine the steps between the accelerations and decelerations. It depends if the  gear ring or the planet carrier powered, if we have an acceleration (> 1) or deceleration (< 1). If the  acceleration is 4/3 , then the deceleration is 3/4 . This is for example the case for the classic Sturmey-Archer AW and copie hubs, such as Hercules, Steyr, Suntour, Brampton, etc.

If the planet carrier is driven: the gear number = (teeth ring gear teeth + Sun wheel)/ teeth ring gear (> 1);  if the gear ring is driven: the gear number = teeth gear ring/(teeth ring gear teeth + Sun wheel) (< 1).

On the pictures below we see the inside of a SRAM Spectro P5 with 2 switchable Sun wheels, 3 stepped planet wheels in a carrier, and 1 ring gear. In fig. 14a we see the cams on the axle at B; These are engaged by the control pin pushing the sun wheels (the small sun wheel A or the big one C) . Both sun wheels are continuously connected with stepped planet wheels. There are two sets of pawls; on the right side on the ring gear (see fig. 14 c + e) and to the left side in the hub are the pawls of the planetary carrier (see top fig. 14f ). In fig. 14 d we can see the two rows of ratched cams in the hub, where the pawls connect.

    The operation of the gearchange is done the clickbox (4 in Fig. 15a). A cable operated camdisk pushes a control pin and a control tube to engage the sun wheels. The red plastic tube aligns the clickbox, between control markers. The steel control pin (1 in Fig. 15b) pushes to engage one of the sun wheels (A or C in Fig. 14a) on the clutch (cams B in Fig. 14a) . The aluminium tube around it (2 in Fig. 15b) is the coupler between the driver and the planetary carrier or the ring gear.

In the first two gears, the driver engages the wide spaced left ratchets on planet wheel carrier ; and in the other three gears the short spaced ratchets of the ring gear, see Fig. 14d .

The low gear is a reduction of 37% ; the second gear is a 22% reduction ; the third gear is the direct drive ; the fourth gear is a 28% increase and the fith gear is a 58% increase.
So the light gear is 63% of the direct drive ; the high gear is 158% of the direct drive. The total range in gearratio is (158/63) * 100% = 251%

The functioning of the 7-speed of SRAM is the same. The only difference is, that there are 3 switchable sun wheels and that the planet wheels have 3 steps.

The construction of the 7-speed from SA, is somewhat similar to the SRAM (both three sun wheels).

The construction of the Shimano 7-gearbox is totally different; with 4 Sun wheels, two ring wheels and two planetary carriers. Because there is no direct drive and the forces sometimes go through both systems, the yield in some gears is lower than 80%, and the average about 85%.

The 8-speed by SA works quite different. The first gear is the direct drive here. This means that all other transmissions are higher gears. So choose a low set up, like a 32 chainwheel and 22 sprocket on the hub. 

In the early 1990s Sachs worked on a 12 speed gearhub; This would be the great leap forward. There was a lot invested in development and automation, but the result was a relatively expensive and heavy hub. There were some technical and financial problems. This made Sachs vulnarable for the takeover by SRAM. After a year SRAM stopped the production, development and support for this product.

The Nexus 8-gearhub is a design with 4 down-gears, the fifth gear is a direct drive, and there are three up-gears. The planet wheels with needle roller bearings, and the fact that there is a direct drive, gives the average yield of this gearhub above the 90%. The range (the difference between the highest and lowest acceleration) of the 8-speed has risen to 307%, instead of the 244%  for  the 7-gearhub.

In 2010, the Shimano Alfine 11 gearhub entered the market. The weight is about 2 kg; the lubrication is done by an oil bath, the range is 409% and the price approximately 300 euro; This makes it a formidable competitor for Rohloff, which however scores better, on all points, except price .

More about IHG's can be found in other pages on my site :

1. A chronological summary of speedhubs     2.  Internal parts of gearhubs   3. Duomatics  4. Extra links  

COMBINATION DERAILLEUR AND PLANETARY SYSTEM

It is of course possible to combine a derailleur and a planetary system. In particular Sachs has applied this combination. The "Torpedo 2 x 3" was a three speed hub with coaster brake, combined with a derailleur and two sprockets. If you use the coasterbrake at first the derailleur is tensioned; this means an extra time delay before the brake works. 

GEAR SYSTEMS IN THE BOTTOM BRACKET

     Characteristic of all bottom bracket gearboxes is that the chainwheel can rotate faster or slower than the bottom bracket axle.  In a hub gear the torque is more than halved by the transmission, in a bottom bracket it is fully transmitted. 

    The Dutch bicycle manufacturer Phoenix has used a real 3-speed gearbox (no planetary system) type Mutaped (Swiss) for 20 years. Like most of its competitors, it needed  a special large bracket . Several German manufacturers had that too before the war. Bismarck, Wanderer and Brennabor made 2-speeds,  Adler a 3-speed, and Rappa a 4-speed. All were examples of German engineering (see figure 17a/b), sturdy but heavy. In France in 1949 the firm Vilex-B.U.E.C, made a 5-speed, fixed gear with drumbrake and freewheel in the bottom-bracket. 

    A modern bottombracket gearbox that has been around for a while (we see them hardly in the Netherlands), is the 2-speed of Schlumpf . You shift this 2-speed, by moving the crankshaft to the left or to the right. The steps between the gears are large; it is used in folding bikes (including Brompton) or recumbents (extra light or extra heavy gears).

Schlumpf also offers  a 2-speed (150%) front wheel hub and a crankshaft, type FSU, for unicycle or imitation high-wheeler; if the tyre choice is 60-787, you get a development of 4,27m. In the 1990s there was another epicyclic 4-speed transmission from Bridgestone (the FM-4). Quite popular in the USA and Japan, but never marketed in Europe. A comparable Shimano FM-5 from that period never made it past a few years at Miyata. The Strida folding bike sometimes uses a bottom bracket gear from Sun Race: the Sturmey-Archer KS3.

FIG.17c  Pre-war German 2-speeds  Brennabor, Wanderer and the Rappa 4-speed.

This gearbox is often combined with belt drive: http://www.gatescarbondrive.com/ ; a trend that we also see for hubgears like Rohloff and Shimano Alfine. The rear triangle of the bicycle must be divisible, because the belt does not split. Compared to a well lubricated chain, you have some extra losses.  A French look-a-like: https://www.effigear.com/en/114-gearboxes

FIG.18 /19 show a Shimano patent for a bracket derailleur-gearbox; which requires a special bracket too. Being a large OEM manufacturer they can push a new standard!  Het bolt patern is rumoured to be identical to their E-bike motor, which makes massproduction easier. The details of the patent point to a design for the mid-pricerange, but it is not clear if or when production starts. In fact it will compete with their Alfine 11 speedhub. The cassettes contain 7 cogs: 19-21-25-29-33-37-41 ; the cassette below  in FIG.20 can move one step to the left. Diagonal via D2, a derailleur moves along. For the chain on the cassette below there are two positions; the last cog only has one.So there are 13 speeds. The chain always runs straight ; the use of an oilreservoir will enhance the efficiency. It will be between a derailleur and a hubgear around 90-92%; the gearrange is 467%. The patent application can be found on the page.

  ELECTRONIC SHIFTING

The first company to introduce an electronic shifting system was Mavic in 1992. In 1999 the system even became "wireless" : the Mavic Mektronic. More than 10 years later, other manufacturers such as Shimano and SRAM have also entered that market. Campagnolo had applied for a patent for electronic shifting in 1994, see patent application. Mavic already used a small dynamo in a pulley wheel of the derailleur in 1992. A neat design that Campagnolo shamelessly also included in this patent, see FIG.21b at no.31.

   Electronic shifted internal gearhubs, like Classified , Rohloff and Shimano Alfine, are also available;  Pinion has one too.