E-type derailers are commonly used on bicycles that have non-round seat tubes that are incompatible with standard clamp-type front derailers. E-type derailers do not provide any adjustment other than the high and low limit stops .
The benefit of this is that it is impossible to install one wrong. The downside is that they must be used only with the specific sizes of chainrings for which they were designed.
See also my Article on Front Derailers
A tandem synch chain runs between two bottom brackets, and the front bottom bracket is usually mounted in an eccentric. This is a cylindrical part with a large hole running parallel to its axis. This hole is sized and threaded to accept a normal bottom bracket assembly.
The cylinder mounts into an oversized shell located where a normal bottom bracket would be. The outer shell may use pinch bolts or setscrews to secure the moveable eccentric cylinder in position. Some eccentrics use a wedge bolt system, similar to that of a handlebar stem, so secure the cylinder. For more details on this, see my article on Adjusting Tandem Synch Chains.
Eccentric bottom brackets are sometimes used on single bikes too, especially because they permit adjustment of chain tension without moving the rear axle. This is useful if the bicycle is fitted with a rear disc brake or an internal-geared hub.
White Industries makes a rear hub with an eccentric axle, designed to permit use as a fixed-gear or singlespeed without a chain tensioner, on frames with vertical dropouts .
An "elastomer fork" is a suspension fork which uses elastomers as the active suspension element. Elastomers are also used in some suspension stems, seatposts and saddles.
Cyclists who pedal this way a lot of the time often do so because their saddles are too low, or their gears are too high.
See also the Spocalc Spoke Length Calculator on this site.
This system is explained in detail in my article on Tire Sizing
Extension (or "reach") is commonly measured from the centerline of the shaft to the center of the handlebar. Unfortunately, common industry practice is to measure this along the direction of the part that points forward. Since different styles of stems have different shapes, two stems with the same extension measurement may not have the same actual distance between the centerline of the handlebars and the steering axis.
Occasionally the term "extension" is used as a synonym for a handlebar stem, particularly one with a long extension.
Dia Compe invented bolt-on extensions that allowed Weinmann-type brake levers to be operated from the tops and middle of the handlebars, making this type of bar bearable for casual cyclists, since they never had to use the drops. This was so popular that Weinmann traded licensing with Dia Compe, so that each could copy the other's products.
(Stem shifters were also popularized around the same time, and for the same reason.)
This system has several drawbacks:
Other manufacturers produced similar systems, some of which addressed some of these difficulties.
Extenison levers are sometimes known as "safety levers." Since many people believe they actually reduce safety, the slang terms "death grips", "suicide levers" and "turkey wings" are occasionally substituted.
In the early 21st century, an greatly improved system of "interrupter brake levers " appeared, with all of the advantages and none of the drawbacks of the older extension levers. These also have the advantage of being compatible with modern "æro" brake levers which work a lot better than the older style levers that had the cables coming out of the tops.
The principal application in bicycles is the fabrication of aluminum rims.
Facing requires highly specialized milling equipment, among the most expensive of bicycle tools. Even minimal tools to do this job cost several hundred dollars.
Some fairings are designed less for ærodynamics than for the sake of protecting the rider from cold and rain.
A familiar example of metal fatigue is experienced if you open a pop-top beverage can then flex the top back and forth a few times.
Aluminum is more prone to metal fatigue than steel is, so aluminum parts have to be designed a bit stronger to make up for this characteristic.
Note, this is a very simplistic description of a rather complicated process.
In Britain and the Commonwealth countries fenders are called "mudguards."
See also Mike Rother's article on Fillet Brazed Schwinns on this site.
The fixed cup usually has a left-hand thread to prevent it from coming unscrewed due to the action of pedaling.
Bicycles with French or Italian threading have right-hand threaded fixed cups; these fixed cups must be tightened very firmly to keep them in position.
See the entry on "Track Hubs" for details.
The pedals of a fixed-gear bicycle revolve whenever the rear wheel turns; coasting is impossible. This type of gearing is usually associated with track racing.See my article on fixed-gears.
Most hubs in current production are "small-flange" or "low-flange" designs, where the flange is no taller than it needs to be to provide a suitable place for the spoke holes to be drilled.
"High-flange" or "large-flange" hubs have a larger flange, usually drilled out for lightness. They transmit torsional forces with less stress to the spokes than small-flange hubs do, but this is not a problem in practice with modern equipment. High-flange hubs can make a wheel with slightly greater lateral strength than equivalent small-flange hubs, because the spokes create a wider bracing angle to the rim. This makes them popular with track sprinters, who create greater-than-normal side loads on their wheels.
There is a special BMX variant of flip-flop hub which is intended to take a single-speed freewheel on each side. This type has a standard thread on one side, and a smaller thread on the other side, which fits special undersized 15- and 14-tooth freewheels. (There is not room to fit a freewheel mechanism inside of a 15-tooth or smaller sprocket, with a normal sized hub.)
Pedals with float allow you to rotate your heel inward or outward to some extent before disengaging the cleat.
See also Jeff del Papa's article on Forging, Casting & CNC Machining on this site.
The term "rear fork" is sometimes used to refer to the part of the frame that holds the rear wheel.
Joshua Putnam has a good discussion of forks and Bicycle Steering Geometry on his Web site.
Rear fork ends originally had the opening facing backwards, but in the 1930s, the "drop out" type fork end was introduced. With drop outs, the slot opens at the lower front, or, in the case of vertical drop outs, straight down. The advantage of this is that it makes for much easier wheel changes, since the chain does not need to be derailed before the wheel can "drop out" of the frame.
The old-fashioned rear-opening style fork ends are still seen on some single-speed bikes, mainly as a retro fashion statement. The revival of rear opening fork ends is an unfortunate fad, making the bikes that feature this design less versatile and less convenient than they would be if they used drop outs.
This is not to say that it is the ultimate, however. For some applications the cross frame is still viable, and for moldable materials, monocoque designs may yet eclipse the diamond. It is also not at all clear that the diamond design lends itself to suspension applications.
In my opinion, seat-tube length is not the most important frame dimension anyway. See my article on Frame Sizing for the details.
The only other type of hub that offers this feature is a coaster brake. Freecoaster hubs use a similar mechanism, only without the actual brake.
See also my article on Shimano Cassettes.
Freestyle bicycles usually are equipped with the "Potts modification" and a "rotor" which allow the handlebars and fork to be turned 'round and 'round at will without tangling the brake cables.
Freewheels are normally sold with the sprockets attached, so this term is frequently used as a synonym for a cluster.
A standard freewheel attaches to a hub by screwing on to external threads that are part of the hub. The action of pedaling tightens the freewheel down on the threads, so no tools are required to install a freewheel.
To remove a freewheel requires a special tool, commonly called a "freewheel puller" or "freewheel extractor"
This tool is a splined unit that may be mounted in a vise or turned with a wrench. The splines engage matching splines in the interior (non-rotating) part of the freewheel body. Different brands of freewheels have used different spline patterns, but there is a recent tendency to standard on the Shimano pattern.
Older freewheels had simple notches and matching extractors with two or four "bosses" (prongs.) This obsolete system was prone to failure, and it is easy to ruin the tool and the freewheel while trying to remove the freewheel. When using a boss-type freewheel puller, the tool should be secured against the freewheel by tightening down the axle nut or quick release skewer.
The standard I.S.O. thread for freewheels is 1.375 x 24 TPI, the same as for standard I.S.O bottom brackets.
|I.S.O.||1.375" x 24 tpi|
1.370" x 24 tpi
|34.92 x 1.048 mm|
34.80 x 1.058 mm
|French||34.7 x 1 mm||1.366" x 25.4 tpi|
|Italian||35 mm x 24 tpi||1.378" x 1.058 mm|
|Metric BMX||30 mm x 1 mm||1.181" x 25.4 tpi|
Newer French bicycles are built to Italian or I.S.O. standards For more details on this topic, see my article on French Bicycles.
If your bike has friction shifters, consider upgrading to a modern indexed system. This is a major, very worthwhile upgrade.
Front drive is slightly heavier, due to the greater length of chain, and in some cases the stoker's right crank may interfere with the chain. Front drive greatly reduces torsional stress on the frame: with rear drive, the stoker's bottom bracket is being pulled forward on the left by the synch chain, while being pulled to the rear by the primary chain. With front drive, the crossover takes place at the front bottom bracket, where both chains pull to the rear. Front drive also makes chainline an academic, not a practical concern. Since the chain run is so long, all gear combinations may be used without running the chain at a sharp angle.
See the 1982 Shimano Catalogue on this site.
In 1992, the axles were designed to be "field serviceable." FSA and FSC hubs can be dissassmbled with just two Allen wrenches , 5 mm for most models, 8 mm for the track hubs. You stick an Allen wrench into the cap at each end of the axle, and unscrew one from the other to release the axle assembly.
FSA Full Speed Ahead ® is also the brand name for a line of bicycle parts.
|Articles by Sheldon Brown and others|
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