On a bicycle, the cassette or cluster [1] is the set of multiple sprockets that attaches to the hub on the rear wheel. A cogset works with a rear derailleur to provide multiple gear ratios to the rider. Cassettes come in two varieties, freewheels or cassettes, of which cassettes are a newer development. Although cassettes and freewheels perform the same function and look almost the same when installed, they have important mechanical differences and are not interchangeable.
A freewheel (also known as a block) consists of either a single sprocket or a set of sprockets mounted on a body which contains an internal ratcheting mechanism and mounts on a threaded hub. Threaded rear hubs were available in different thread patterns depending on the country of manufacture, French and British threads being the most common. The British Cycle Engineers Institute (CEI) thread was adopted as the international standard[ when? ] and is now known as British Standard Cycle (BSC). It is a standardized right-hand 1-3/8″-24 TPI (M34.925×1.058 mm) thread onto which a standard freewheel is screwed. [2] This allows different brands of freewheels to be mounted on different brands of hubs.
The major disadvantage of the multiple sprocket freewheel design is that the drive-side bearing is located inboard of the freewheel, and as sprockets were added over time, the bearing moved inward, farther from the drive-side axle support. This resulted in more flexing stress being placed on the axle, which can bend or even break. Multiple speed freewheels were common on quality high end bikes until the late 1980s. [3] Suntour — Maeda Industries (Japan) introduced a compact 6 speed freewheel which reduced the spacing between the sprockets and was the same width as a standard 5 speed freewheel but required a narrower chain than the standard. The concept was copied by European freewheel manufacturers Regina (Italy) and Maillard (France). [4] As the number of sprockets on a multiple freewheel increased, and became physically wider, the freehub design overcame the axle/bearing problem associated with threaded hubs and began to supersede the freewheel design. Today[ when? ] it is rare to find a freewheel on a new bicycle with more than 7 speeds. Some new single-speed — especially BMX and utility bikes — and lower-end multi-geared bicycles continue to be manufactured and sold with freewheels.
Pedaling forces tighten a freewheel onto the hub, so no tool is required to install one. The ratcheting mechanism prevents the freewheel being loosened when the sprockets are turned counter-clockwise. A freewheel can be removed from the hub with one of the many specific freewheel removal tools that engages a spline or set of notches on the outboard end of the freewheel. Removal often requires considerable effort due to the large torque that tightens the freewheel during pedaling, and some freewheels cannot be removed intact. Future removal of a freewheel is facilitated by grease on the freewheel threads before installation.
Cassettes are distinguished from freewheels in that a cassette has a series of straight splines that form the mechanical connection between the sprockets and the cassette compatible hub, called a freehub, which contains the ratcheting mechanism. The entire cassette is held on the hub by means of a threaded lockring. Some cassette systems from the late 1980s and early 1990s use a threaded small sprocket to hold on the larger splined sprockets. Cassettes resemble freewheels when installed, but are clearly different when removed as they do not contain a freewheel's internal ratcheting mechanism.
The sprockets in a cassette are usually held together by three small bolts or rivets for ease of installation. These keep the sprockets and spacers in the correct order and position when they are removed from the freehub body. When the sprockets need to be replaced due to wear or the user wishes to change gear ratios available, only the sprockets are replaced, not the ratchet mechanism. Cassettes also allow the use of sprockets with fewer teeth, as in micro drive systems. [5]
The ratchet mechanism, known as the freehub body, is still replaceable on most hubs, but forms a structural part of the hub. Cassette systems have a major advantage in that the drive-side axle bearing can be out near the frame, rather than being back towards the centre of the axle behind the freewheel. This greatly reduces the stress on the rear axle, making bent or broken axles extremely rare.
Since their introduction in the late 1970s [6] cassettes have been used on increasing numbers of bicycles, starting at the high-end and over time becoming available on less expensive bikes. Today[ when? ] the vast majority of bicycles with derailleur gears use this newer design.
Over time, the number of sprockets in a cogset has increased, from 3 or 4 before World War II, to 5 used from the 1950s to the 1970s, up to the 8, 9, 10, 11, 12, and even 13 in the 2010s [ when? ] found on modern bikes. As more rear sprockets were added, the combination became wider, and the sprocket spacing narrower. One of the ways to make space for this was the axle length (measured as the over locknut distance — OLD. [7] ) was increased, necessitating more dish on the rear wheel drive side with a threaded hub to centre the wheel in the frame. The hub flanges spacing was not shortened on threaded hubs, rather the axle length increased from 120 mm OLD (5-speed/compact-6) to 126 mm OLD (6-speed/compact-7) through to 130 mm OLD (threaded 7-speed) for a road bike. MTB rear spacing is normally 135 mm OLD. Another advantage of the Shimano cassette hubs introduced from 1978 was that the rear hub flanges were wider apart than those of a threaded hub, so built a stronger wheel with less dish and without the problem of increased bearing stress or axle failure.
Before the introduction of indexed shifting, the width of a 5-speed or compact-6 freewheel was approximately 32 mm; the introduction of indexed shifting supposedly made standardized sprocket spacing necessary. Shimano and Campagnolo both came up with independent standards, and SRAM later followed Shimano's lead in respect to sprocket spacing and cassette width. The width of early Shimano 6- and 7-speed cassettes was 36 mm, and early 8-speed 40 mm wide. Shimano then changed again and standardised 8-11 speed cassettes on 41.5 mm and second generation 7-speed to 38 mm. The widening of the sprocket carrier on the cassette hubs to 41.5 mm resulted in a decrease in the distance between the hub flanges.
For Shimano and SRAM the cassette spacing developed as follows. Early Shimano 7-speed cassettes are 36 mm wide, with sprocket spacing of 3.65 mm, but levers and rear derailleurs are not compatible with later Shimano 7-speed cassettes, which are 38 mm wide and have 3.2 mm sprocket spacing. An 8-speed cassette is wider at 41.5 mm than a second generation Shimano 7. This results in functionally compatible shifters, but specific freehub bodies, or necessitating the use of a spacer with a 7-speed cassette on an 8-speed hub. 8- and 9-speed cassettes and freehub bodies have the same width (41.5 mm), yet the sprockets on the 9-speed are closer together; as a result the shifters are not compatible, but they use the same freehub bodies. This development continued with 10-speed cassettes, but branched out for 11-speed cassettes. With them, new freehub bodies emerged which were either wider (Shimano road 11-speed) or entirely different (SRAM XD, XDr, which differ in width and both provide the space for a 10-tooth cog). For 12-speed, Shimano introduced a new freehub body as well (Microspline).
This progression has provided more fine adjustment of gear ratio, however the use of thinner metal parts has had the effect of shortening the life-span of the chain and sprockets due to so called "stretching" of the chain. This is caused by frictional abrasion of the load-bearing surfaces of the chain causing elongation. As such, the chain and sprockets of a 9-speed system require more frequent replacement than an 8-speed system.[ citation needed ] The narrowing of the hub flanges has created more dish in the wheel, which weakens the wheel if all other factors are the same, but improvements in the strength and reliability of spokes and rims has more than balanced this out, and wheel strength is generally higher despite the increased dish.
Shift ramps are complex tooth profiles, in the rear sprockets and front chainrings, designed to pick up and drop the chain during shifting. They allow for shifting under greater load than was previously possible, and for smoother and cleaner shifting. The different systems are branded Hyperglide by Shimano, UltraDrive by Campagnolo, and OpenGlide by SRAM. The chain itself is specifically manufactured for ease of shifting, and to interface with a particular manufacturer's shift ramps; using a different type of chain may result in sub-optimal shifting.
A mountain bike (MTB) or mountain bicycle is a bicycle designed for off-road cycling. Mountain bikes share some similarities with other bicycles, but incorporate features designed to enhance durability and performance in rough terrain, which makes them heavier, more complex and less efficient on smooth surfaces. These typically include a suspension fork, large knobby tires, more durable wheels, more powerful brakes, straight, extra wide handlebars to improve balance and comfort over rough terrain, and wide-ratio gearing optimised for topography, application and a frame with a suspension mechanism for the rear wheel. Rear suspension is ubiquitous in heavier-duty bikes and now common even in lighter bikes. Dropper seat posts can be installed to allow the rider to quickly adjust the seat height.
A bicycle wheel is a wheel, most commonly a wire wheel, designed for a bicycle. A pair is often called a wheelset, especially in the context of ready built "off the shelf" performance-oriented wheels.
A derailleur is a variable-ratio bicycle gearing system consisting of a chain, multiple sprockets of different sizes, and a mechanism to move the chain from one sprocket to another.
A hub gear, internal-gear hub, internally geared hub or just gear hub is a gear ratio changing system commonly used on bicycles that is implemented with planetary or epicyclic gears. The gears and lubricants are sealed within the shell of the hub gear, in contrast with derailleur gears where the gears and mechanism are exposed to the elements. Changing the gear ratio was traditionally accomplished by a shift lever connected to the hub with a Bowden cable, and twist-grip style shifters have become common.
Shimano, Inc., originally Shimano Iron Works (島野鐵工所) and later Shimano Industries, Inc. (島野工業株式会社), is a Japanese multinational manufacturing company for cycling components, fishing tackle and rowing equipment, who also produced golf supplies until 2005 and snowboarding gear until 2008. Named after founder Shozaburo Shimano and headquartered in Sakai, Osaka Prefecture, the company has 32 consolidated and 11 unconsolidated subsidiaries, with the primary manufacturing plants based in Kunshan (China), Malaysia and Singapore.
The crankset or chainset is the component of a bicycle drivetrain that converts the reciprocating motion of the rider's legs into rotational motion used to drive the chain or belt, which in turn drives the rear wheel. It consists of one or more sprockets, also called chainrings or chainwheels attached to the cranks, arms, or crankarms to which the pedals attach. It is connected to the rider by the pedals, to the bicycle frame by the bottom bracket, and to the rear sprocket, cassette or freewheel via the chain.
A bicycle chain is a roller chain that transfers power from the pedals to the drive-wheel of a bicycle, thus propelling it. Most bicycle chains are made from plain carbon or alloy steel, but some are nickel-plated to prevent rust, or simply for aesthetics.
In mechanical or automotive engineering, a freewheel or overrunning clutch is a device in a transmission that disengages the driveshaft from the driven shaft when the driven shaft rotates faster than the driveshaft. An overdrive is sometimes mistakenly called a freewheel, but is otherwise unrelated.
Sturmey-Archer was a manufacturing company originally from Nottingham, England. It primarily produced bicycle hub gears, brakes and a great many other sundry bicycle components, most prominently during its heyday as a subsidiary of the Raleigh Bicycle Company. In the past, it also manufactured motorcycle hubs, gearboxes and engines.
A single-speed bicycle is a type of bicycle with a single gear ratio. These bicycles are without derailleur gears, hub gearing or other methods for varying the gear ratio of the bicycle.
A fixed-gear bicycle is a bicycle that has a drivetrain with no freewheel mechanism such that the pedals always will spin together with the rear wheel. The freewheel was developed early in the history of bicycle design but the fixed-gear bicycle remained the standard track racing design. More recently the "fixie" has become a popular alternative among mainly urban cyclists, offering the advantage of simplicity compared with the standard multi-geared bicycle.
SR Suntour is a Taiwanese manufacturer of bicycle components, formed in 1988 when Osaka based SunTour (Maeda) went bankrupt and was purchased by Sakae Ringyo Company, a major Japanese maker of aluminum parts, particularly cranks and seat posts. SunTour's sales and commercial success peaked from the late 1970s to the mid-1980s.
A freehub is a type of bicycle hub that incorporates a ratcheting mechanism.
The Rohloff Speedhub is an epicyclic internal hub gear for bicycles, developed and patented by Rohloff AG. It has been manufactured and marketed by that company since 1998. The Speedhub 500/14 has 14 equally spaced, sequential, non-overlapping gear ratios operated by a single twistgrip. The overall gear range is 526%, meaning the highest gear is 5.26 times as high as the lowest gear. Individual gear shifts when shifting up give an increase of about 13.6%.
A front freewheel or freewheel crank is a freewheel mechanism used on some bicycles which enables the drivetrain of the bicycle to continue spinning while the rider rolls, but stops pedaling, or coasts. Unlike regular bicycles, a front freewheel can make it possible to shift gears using a derailleur while the rider is coasting if paired with a fixed rear hub or a freehub with a slight resistance in the freewheel mechanism, which causes the chain to continue spinning with the wheel rotation.
Bicycle gearing is the aspect of a bicycle drivetrain that determines the relation between the cadence, the rate at which the rider pedals, and the rate at which the drive wheel turns.
Hyperglide is the name given by cycling component manufacturer Shimano to a sprocket design in their bicycle derailleur tooth cassette systems. It varies gear tooth profiles, and/or pins along the faces of freewheel or cassette sprockets, or between the chainrings in a crankset, to ease shifting between them.
Flip-flop hubs, also called double-sided hubs, are rear bicycle hubs that are threaded to accept fixed cogs and/or freewheels on both sides.
Bicycle drivetrain systems are used to transmit power on bicycles, tricycles, quadracycles, unicycles, or other human-powered vehicles from the riders to the drive wheels. Most also include some type of a mechanism to convert speed and torque via gear ratios.
Currently with a cassette hub you can run as small as an 8t sprocket. The smallest a freewheel hub can go is 13t.
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