Glossary

A | B | C |  D | E | F | G | H | I |  J | K |  L |  M |  N |  O |  P |  Q | R |  S |  T | U | V | W | X | Y | Z |

A

ABS:

Abbreviation for Anti-lock Braking System. First developed and used in the automotive industry in 1978 (Mercedes Class S), it was developed for the motorcycle in 1988 with BMW. Sensors located on the disks detect when the brakes begin to lock (due to the difference in rotation speed); in this case the brake fluid pressure is modulated so that the deceleration force is slightly reduced, and increases again when the wheel reaches a normal rotational speed. The ABS controllers are capable of detecting and repeating this operation several times each second. Some automotive manufacturers back up the ABS with a Coupled Braking System (CBS – Honda) or with an amplifier (EVO – BMW).

Aerodynamic turbulence:

physical phenomenon linked to an object moving through the air. In motorcycling, we make the distinction between that sustained by the driver (and possibly his passenger) and that appearing in the slipstream of the bike itself.

All-terrain:

Motorcycling in the natural environments (enduro, trial, rally-raid) or laid-out circuits (motocross, supercross, indoor trial). Requires an adapted motorcycle and equipment.

Apron:

protection covering the rider's legs and chest. It is fixed to the bike's frame and is ideal for winter riding. It generally comes with muffs which

B

Bike-jacking:

expression derived from "car-jacking": stealing a vehicle which is being driven by its owner, by force. You can be bike-jacked by one or more thieves who threaten you with a weapon at a road junction or when driving out of a garage, etc.

 Bi-xenon:

recent lighting method using gas discharge bulbs instead of traditional filaments. For the moment this method is mostly used in the automobile sector rather than in the motorcycle sector, but who knows, motorcycles may greatly benefit from it soon since so much progress remains to be made in this field.

Bubble:

convex surface made of plastic or PVC designed to divert the air pressure and give the rider some protection. It may be independent and fixed above the headlight, or be part of a larger protection element ("fairing bubble").

C

Chapters:

motorcycle clubs organized under the control of Harley-Davidson dealerships. The chapters are very well structured, their members have very varied duties (treasurer, road captain, safety manager, etc.). Their main aim is to promote motorcycling during group outings. They sometimes even organise charity events.

Chord point:

central point of a bend, after the entry phase and before the acceleration phase on the exit side. It is the moment when the tilt is highest and the speed lowest. Finding the right chord point is an essential part of trajectory science.

Compression ratio:

A high compression ratio is generally synonymous with a powerful modern engine. E.g.: 7.9 for a Royal Enfield Electra, 12.65 for a Triumph 675 Daytona…

Corrosion:

metal oxidation which results in a deterioration of the metal's molecular balance. Its most visible form is rust. It is the speciality of some motorcycles.

Custom:

literally, custom-built means "hand made, customized or unique". This term initially meant customized motorcycles, very often based on a Harley-Davidson. The term has now finally lost this strict meaning and covers all motorcycles, whatever their engine size, providing a driving position with large handlebars and the feet out front. A custom bike is covered in chrome and often impresses the man in the street but the connoisseur is more difficult to convince. Among the most distinguished of this large family of strange machines, a special mention must go to the Kawasaki 600 Eliminator (with its state-of-the-art four cylinder engine) and to the Aprilia 125 Red Rose (with its stinking two-stoke engine which belches out smoke like Renault 21 Diesel).

D

DOT standard:

 standard established by the US Department of Transport (although similar services issue national standards in other Anglo-Saxon countries: DOT in South Africa, Great Britain, Australia, etc.). It is a method of approval for various safety items ranging from helmets to tyres.

E

Enduro bike:

type of motorcycle designed for all-terrain use (special tyres, high-clearance suspension, high ground clearance), and not just for closed circuits. These bikes have the legal minimum equipment for road use (lights, flashers, number plate, mirror), but that does not make them easy to ride on the road!

Ergonomics:

 characteristic referring to the good grasp of all the controls which must be both intuitive, smooth, safe, and easy to operate. The equilateral triangle formed by the seat, footrests and handlebars is a good layout.

Ethylene glycol:

liquid which pushes the freezing point limit below zero degrees. It is therefore widely used in cooling systems. Disadvantage: it is viscous (slippery) and therefore prohibited for on-circuit racing.

 Expansion tank:

 bottle containing the coolant.

F

Friction:

effect of the resistance exerted by two moving objects in contact with each other. E.g.: the piston in the cylinders. The effects of friction can be limited by fine adjustment and lubricants.

G

Gravity type:

balance respecting the laws of gravity described by Newton. Applies to the motorcycle when stopped and at low speeds of less than 20 mph (30 kph).

Gyroscopic force:

 physical law applying to a moving object which tends to subject it to a centripetal force. All this seems complicated but it is what balances a moving motorcycle.

Gyroscopic type:

type of balance respecting the laws of physics affecting moving objects.

H

High-side:

a type of fall well known by those who don't sufficiently warm up their tyres or who accelerate too hard out of bends. Under the effect of excessive acceleration the back tyre reaches its grip limit and starts to slide. A fraction of a second later the rider normally instinctively closes the throttle (when he should keep some power applied and correct the slide by changing his body position and his position on the footrests). The effect is immediate: the bike suddenly gets some grip, and the rear suspension suddenly rises, throwing the rider off the bike. This fall is generally painful for the rider and destructive for the bikes.

Hoses:

sealed pipes carrying brake fluid and possibly clutch fluid. They are subjected to high temperatures and pressures and are often braided (or "aircraft type" on racing motorcycles).

I

Iridescent:

said of an object coated with an iridium treatment. Important: iridium coated visors are rarely approved and are unsuitable for night use.

Iridium:

reflective coating material for plastics (visors, fairing bubbles) to give them a "mirror" and coloured effect.

J

Jaso:

Japanese quality standard for lubricants (Japanese Automotive Standard Association). This standard is very severe and takes into account deposits and smoke emissions.

K

KKKK 
Progressive removal of material from a rubbing surface as evidenced by surface lapping caused by fine particles carried in the lubricant, fuel or air, or embedded in the surface.

L

L

M

Medium:

said of an "intermediate" tyre rubber, which is neither too hard (since it would take too long to warm up) nor to soft (since it would tend to wear quickly after a series of laps). This term is generally reserved for racing.

N

Neoprene:

synthetic material used in motorcyclist equipment due to its insulation and waterproof qualities.

O

Off-loading:

a motorcycle often has a high-clearance suspension and is often subjected to weight transfers (see glossary hyperlink below) during the acceleration phases (where it flattens on its rear suspension) or braking phases (where all the weight moves forward). Off-loading takes place when the forks rise during sharp accelerations (or when the bike is loaded with a passenger and luggage). This makes the steering less accurate and can even cause steering wobble.

Oxidation:

deterioration of metals due to the appearance of oxygen molecules which modify their chemical structure and weaken them. Therefore oxidised materials loose their strength.

P

Physiognomy:

said of a motorcyclist's corpulence and of his physical characteristics. The type of equipment chosen and the integration of the rider on his motorcycle largely depend on the rider's physiognomy.

Pivot point:

point where two physical elements are in a torsion phase. In the case of a motorcycle it can, for example, be the steering column.

Plates:

elements fixed on the frame, the role of which is to group together the foot controls: gear selector, footrest, brake pedal. They are easily broken during impacts. On racing bikes they are adjustable so the rider can find the most suitable position.

Polarising:

said of a material which reacts to the light. Polarising sunglasses can darken as the light increases. This is useful for motorcycling, to cover all driving conditions.

Q

Q

R

Reed valves:

specific type of inlet valves used in some two-stroke engines. Four stroke engines have normal valves. Reed valves are flexible blades which open under a fairly high depression, allowing the fuel mixture to flow into the cylinder(s).

Riding the clutch:

A clutch generally consists of a disk which, in its normal state, connects the engine to the transmission. When the motorcycle is driving along, the mechanism is released or "engaged". During a stop at traffic lights, the right hand lever is pulled in to "disengage" it. "Riding the clutch" means holding the point of friction, right at the point where engine and transmission are only just coupled. Excessive use of this technique can cause early wear of the mechanism.

Roadster:

type of motorcycle with no fairing or wind protection, and where the bike's engine and system components are visible. It came back into fashion at the start of the 90s as a tribute to past motorcycles. It is now a key style with subfamilies (basic, retro, urban, racing, etc.).

S

SAE:

standard defining a "viscosity grade" for lubricants. The higher the number the better the viscosity when the oil is hot.

Sidecar:

structure added to a motorcycle, resting on a third wheel, for carrying passengers. Rather dangerous for the nonspecialists, this type of vehicle has considerably developed over the last few years, with articulated sidecars which lean into the bend with the motorcycle, or even single-bodied structures like the Side-Bike.

Sintered brake pads:

asbestos-free brake pads made of sintered metal, with excellent friction coefficient and heat resistance characteristics.

Slicks:

tyres without tread grooves. They are strictly reserved to circuit use as they cannot eliminate water.

Sports bike:

type of motorcycle inspired by racing bikes. It has a powerful engine, very efficient brakes and tyres, a rigid frame and a very uncomfortable flattened driving position. However, it has a lot of fans attracted by its performance and safety.

SRA label:

 the SRA (French Automobile Safety and Repair Association) is a non-profit-making association which includes insurance companies and distributes information on vehicle safety and repair costs. For motorcycles, SRA is an approval label for antitheft devices which are recognised for their efficiency and covered by insurance policies.

Steering column:

front component of a motorcycle frame. The steering column consists of a tubular part into which a stem is inserted. This stem will support the forks. Its geometry is fundamental to a motorcycle's handling and dynamic characteristics. Its bearings must be regularly checked, otherwise roadholding will be affected.

Steering stop:

metal projections designed to limit the steering angle at fork tube level. To get a wider range of movement they can be filed down, as is the case with all driving school motorcycles.

Stiffners:

elements whose job it is to stiffen… On a motorcycle, they can be found on the forks, the frame or on saddlebags to prevent them flattening in the wind.

Stiffness:

state of limbs which have become stiff due to the cold or due to being in a restricting position for too long. It arises during long winter rides, or on uncomfortable motorcycles. In extreme cases, stretching a stiff leg can result in an unexpected inertia which may cause the rider to fall when he stops! Riders should stretch their limbs frequently, even on the motorways.

T

Trail bike:

type of motorcycle which first appeared in the early 70s, designed for polyvalent road / all-road use and a low budget. This is not so much the case now, since even 1200 cc monsters are defined as trail bikes, but they are still easy to drive, have a comfortable driving position and are polyvalent.

u

U

V

Velcro strip:

elastic strips with an adhesive material at the overlap point. Velcro strips are widely used in the motorcycle world: fasteners for jackets or pants, attaching saddlebags or tank bags, etc.

Viscosity:

term applying to a lubricant. Defines the liquid's coherence (the level of attachment between the molecules).

W

Weight transfer:

It must be noted that the BMW Telelever technology, which separates the steering and shock absorbing functions, limits body angle movements, flattening and off-loading to the maximum.

X

X

Y

Y

Z

Z