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Sheldon Brown's Bicycle Glossary L

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Labyrinth Seal, illustration by Nicholas Flower Labyrinth Seal
A bearing seal that adds no friction, because there is no seal contact between the revolving part and the stationary part. Contaminants can't easily enter the bearing because the baffles of the labyrinth seal deprive them of a straight route inward.

Labyrinth seals work very well as long as the bearing assembly is not immersed.

The illustration shows a standard hub, but similar seals are used on some other bearing applications as well.

Lady's Bicycle
In the Victorian era, when the bicycle had its first popularity, women were forced to wear long skirts, which prevented them from riding conventional diamond-frame bicycles. This led to the development of the "lady's bicycle" which eliminated the top tube from the frame, adding a second down tube for strength.

Since hardly anybody rides in a skirt anymore, this inferior design is pretty-much obsolete. Conventional diamond frames have several advantages over the Victorian lady's bicycle. They are:

  • Lighter
  • Stiffer
  • Stronger
  • Easier to pick up and carry over stairs, etc.
  • Roomier, to mount useful accessories: bottles, pumps, locks, etc.
See also "mixte."
laprade type seatpost Laprade Seatpost
Laprade was originally a brand name, but has become a generic term for seatposts with a built-in clamp that uses a vertical Allen bolt to clamp the saddle rails. Typically,, the tilt of the saddle is adjustable by loosening this same bolt so the convex, toothed underside of saddle-clamp assembly can be slid backward or forward on a matching, concave, toothed surface. This type of seatpost is much easier to adjust than the classic Campagnolo two-bolt seatpost, but can be adjusted only in (small) steps.
Lateral Stays
Thin tubes that run in pairs alongside the front part of a frame, and typically extend past the seat tube to the rear fork ends. These are most commonly seen on mixte frames and on older tandems, although they are also used on a few large-sized diamond frames intended for heavy-duty use.
Lawyer Lips, Lawyer Tabs
Because some bicycle users are competent enough to remove their front wheels but not competent enough to secure them properly when they reinstall them, virtually all new bike purchasers have been deprived of the handy function of quick-release front wheels.

This has been done by encumbering fork ends with extra hardware, ridges or lumps that keep the wheel sort-of attached even if it has been installed by someone who doesn't know what he or she is doing. Unfortunately, this means that the quick-release mechanism must be re-adjusted each time it is used, seriously slowing down the operation.

Since this extra stuff was installed as a defense against frivolous lawsuits by ambulance-chasing shysters, the extra bumps are sometimes known as "lawyer lips" or "lawyer tabs."

As "lawyer lips" have become the norm, they have gradually become more important than they originally were, for two reasons:

  • The prevalence of these secondary retention systems in front, and vertical dropouts in the rear has caused the proliferation of inferior skewer designs that are cheaper to manufacture, but much less secure than traditional skewers.

    See my Article on Quick Release Skewers.

  • The introduction of disc brakes has caused increased vulnerability of the front axle and skewer, due to the disc brake applying an ejection force that tends to pull the axle out of the fork.

    See James Annan's article on disk brake wheel ejection.

LBS
Local Bike Shop
LED
Light-Emitting Diode, a solid-state device which generates light when an electric current is passed through it. Light-emitting diodes can be far more efficient than incandescent bulbs, increasing battery life and light output of bicycle lights. The first practical LEDs for bicycle lights produced red light and were used in taillights. There was an unintended and unfortunate side effect, that many bicyclists, out of convenience and because of fear from the rear would use only a taillight and no headlight. Beginning around 2005, high-efficiency white LEDs became available, LED headlights became common, and more bicyclists began using headlights.
Left (Hand) Thread
Most threaded fasteners are right-threaded, so you turn them clockwise to tighten them. Some parts which are used in conjunction with rotating shafts would tend to unscrew themselves if they threaded normally, so they are threaded in the opposite direction. This is called a "left thread," "left hand thread" or "reverse thread."

Left-threaded fasteners are turned counter-clockwise to tighten them.

Left threads are found on left pedals, some bottom-bracket parts, internal parts of freewheels, and sprockets that thread onto older freewheels from the left side.

Left-side pedals and right-side bottom bracket cups use left-hand threading because of the phenomenon called "precession." It is somewhat counterintuitive, because the direction of rotation caused by the precession is opposite the (much smaller) torque exerted by bearing friction.

See the Pedals entry in this Glossary , and Jobst Brandt's article on Left-Hand Threads on this site for a detailed explanation of precession.

Spoke nipples and the expander bolts that hold bar-con shifters in place often appear to have left threads, because they are approached from the opposite direction of most fasteners.

L.F.
Large-Flange or Low-Flange (hub). This is a source of confusion, since these two meanings are opposite. For clarity, this abbreviation should be avoided.
Lightweight
Traditional U.S. bicycle industry term for bicycles with tires narrower than about 1.5".
Limit-Stop Screws
The limit stops are two screws that set the limits of how far the derailer can move from left to right. They are usually located on the back of the parallelogram; sometimes they face outward to the bicycle's right. The end of a screw bumps into internal parts of the parallelogram when the derailer has moved all the way in the direction controlled by that screw.

derailer

See my article on Derailer Adjustment for more details.

Linear-Pull Brake
Another term for a direct-pull brake.
Locknut
A nut which is tightened against another nut to keep it from loosening up. Often, but not always, there will be a key washer between the locknut and the cone or other part it secures.

Locknuts are used to secure bearing adjustment of most hubs, headsets, pedals and sidepull brakes. Most hubs use locknuts to secure the cones so that they will stay in adjustment. These locknuts are the outermost parts which are screwed onto the axle, and their outer surfaces press against the insides of the fork ends of the frame. The locknuts are therefore the reference point by which axle width and dishing are measured.

Lockring
A thin locknut used to keep A threaded assembly from coming unscrewed. Conventional bottom brackets use a lockring on the adjustable cup to make it hold its adjustment.

Fixed-Gear (Track) Hub Lockring Threading (Left-hand thread):

English/ISO 1.29" x 24 TPI
Campagnolo/Phil Wood 1.32" x 24 TPI
Old French 33 mm x 1.0 mm
Star, Split Lockwashers Lockwasher
A washer with directional sharp edges to make a nut or bolt less likely to loosen up due to vibration. The edges are angled to work sort of like pawls, permitting the fastener to be tightened without undue friction, but biting into the fastener and/or surface of the part when the fastener tries to rotate in the loosening direction.
Loctite ®
A liquid adhesive for screw threads. Loctite and similar "threadlockers" are liquid as long as they are exposed to oxygen, but when you put them on screw threads and screw the parts together, oxygen can no longer get to the Loctite, so it hardens up, keeping the threads from loosening up to vibration and the like.

Threadlockers are mainly used for threads that are not intended to be fully tightened: adjustment screws and the like.

There are very few good applications for threadlockers in bicycle work. They include:

  • Cantilever brake mounting bolts (front especially.)

    If these are overtightened, they can "mushroom" the ends of the cantilever bosses, causing the brake to bind up.

  • Fixed bottom bracket cups on French or Italian threaded frames

    French and Italian fixed cups are threaded in the wrong direction, so there is a tendency for them to loosen up in use.

  • Mounting rings for some cartridge bottom brackets

    Many mounting rings are tightened only against the ends of the bearing cartridge rather than having a shoulder or lockring that bears against the end of the bottom-bracket shell.

  • Radial spokes.
Look ®
A French manufacturer of bicycle components, accessories and carbon-fiber frames and forks. Look made the first clipless shoe-pedal system that was successful in the market. Look caters mostly to the road-racing market.
Lost-Wax Casting
See investment casting.
Low (Gear)
A low gear is one in which the pedals move rapidly compared to the speed of the wheels.

Low gears make the pedals easy to push, but you need to turn them faster to get the bike to move at a good speed.

Low gears are achieved by using small chainwheels and large rear sprockets.

Low gears are used for climbing hills, or for starting up from a stop.

Low-normal/High-normal
Modern derailers are spring loaded, pulled one way by the spring and the other way by the control cable. A "low-normal" derailer is one in which the spring pulls it toward the lower gear(s). If you release the tension on the cable, it will shift to the lowest gear.

Up until the late 1950s, all spring loaded derailers were low-normal. Campagnolo's pioneering parallelogram-type rear derailer was high-normal, and most rear derailers made since then have been of the high-normal type.

The major advantage of high-normal rear derailers is that, when used with a low-normal front, both levers move in the same direction for double shifts. This makes it easier to perform a double shift with down-tube shift levers.

The major advantage of low-normal derailers is that they generally downshift a bit better than high-normal units.

Since the late 1990s, Shimano has attempted to revive the low-normal rear derailer design, using the trademark "RapidRise." This has met with increasing acceptance by cyclists.

Sun Tour used to make high-normal front derailers. The principal advantage of this was that the front and rear shift levers moved in the same direction to either raise or lower the gear, less confusing for beginner cyclists.

Low-Profile
  • Low Profile Cantilever Brakes

    Traditional cantilever brakes have arms that stick out fairly far to the side. These protruding arms sometimes get in the way of pannier bags, and the rear brakes sometimes interfere with the rider's heels on smaller frames.

    As mountain bikes became popular in the 1980s, the heel clearance issue became a serious problem, because mountain bikes generally used smaller frames than traditional designs, placing the seatstays lower. The riders' heels; banging into the ends of the brake cantilevers became a real concern.

    The industry responded with a re-designed cantilever whose arms were angled up higher, and didn't stick out so far to the side. This fixed the heel clearance problem, but introduced problems of its own.

    With low profile cantilevers, the mechanical advantage decreases as the brake shoe moves inward toward the rim, an undesirable characteristic which causes the braking performance to deteriorate sharply as the pads wear down.

    See also my article on Cantilever Geometry.

  • Low-Profile Cranks

    Traditional cranks run roughly parallel to the bicycle's centerline from the bottom bracket to the pedal.

    Most newer cranks use the "low-profile" design: the bottom bracket is made shorter, and the crank runs outward at an angle from bottom bracket to pedal, giving improved heel clearance for riders who tend to pedal splay-footed.

    Note: That a crank is "low-profile" says nothing about its tread width (a.k.a. "Q factor.") In fact most "low profile" cranks have fairly wide tread, but this has nothing to do with the "low-profile" design.

    The trend toward wider tread resulted from the wider chainstays introduced with mountain bikes, and also the additional clearance required to keep the right crank from rubbing against the cage of the front derailer (newer front derailers optimized for triple chainwheels require more crank clearance than older front derailers did.)

Lowrider
  1. Lowrider racks are front pannier racks designed so that the panniers attach below the top of the front wheel, so that their center of gravity is low and close to the steering axis of the fork. The purpose is to improve stability compared with the typical earlier setup that used high-mounted rear panniers. Lowrider racks were first sold by Blackburn Designs, and their design was based on experimentation by Jim Gentes, who went on to found Giro. See article by John Schubert
  2. Lowrider bicycles are a fad design of bicycles, inspired by the wheelie bikes of the 1960's with very long wheelbases. They are built purely as an exercise in styling, with no real concern for riding qualities. Some of them, in fact, are not rideable, because the cranks are so close to the ground that the pedals cannot turn around. They commonly feature lots of chrome or gold plating, 72 spoke wheels, sometimes steering wheels instead of normal handlebars, and springer forks. These toy "bicycles" should not be confused with recumbents, which are real bicycles.
Lug
A lug is a socket that forms the junction between two or more frame tubes. Traditional bicycle construction uses steel tubes and lugs, joined together by brazing or silver soldering so that the space between the tube and the lug fills up with molten brass or silver alloy. Some aluminum or carbon fiber bicycles also use lugs, with glue instead of the brass or silver.

Some frames use internal lugs, with a necked-down section that fits inside of the tube, rather than having a socket that the tube fits into.

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