Motorcycle glossary
All motorcycle technical terms explained simply.
A
A2 licence
Motorcycle licence category restricting riders to machines producing no more than 35 kW (47.5 hp) with a power-to-weight ratio not exceeding 0.2 kW/kg.
The A2 licence is the motorcycle licence category available from age 18 in France (and across the EU under Directive 2006/126/EC). It allows you to ride motorcycles with a maximum power output of 35 kW (roughly 47.5 hp) and a power-to-weight ratio no greater than 0.2 kW/kg. A more powerful bike can qualify if it’s restricted to meet these limits, provided its unrestricted output doesn’t exceed 70 kW (95 hp).
A2 restriction
Electronic or mechanical power limitation applied to a motorcycle engine to cap output at 35 kW (47.5 hp), as required by the A2 licence category.
A2 restriction (or A2 detuning) involves limiting a motorcycle’s power output to no more than 35 kW (roughly 47.5 hp), the ceiling imposed by A2 licence regulations. This allows an A2 licence holder to ride a model that, in unrestricted form, would exceed the category — provided the original power doesn’t exceed 70 kW (95 hp), i.e. double the A2 limit.
ABS
Anti-lock braking system that automatically modulates brake pressure to prevent wheel lock-up during hard braking.
ABS (Anti-lock Braking System) is an electronic safety system that prevents the wheels from locking up when you brake hard. Speed sensors on each wheel detect when a wheel is about to stop rotating. The ABS control unit then rapidly releases and reapplies brake pressure — dozens of times per second — so the tyre keeps rolling and maintains grip. This means you stay in control of steering even during emergency braking.
Airbox
Enclosed chamber upstream of the intake that filters, stabilises, and channels the flow of fresh air feeding the engine.
The airbox is a housing — usually made of plastic — positioned between the external air intake and the throttle bodies (or carburettors). It performs several essential functions that are often underestimated.
Air filter
Filter element inside the airbox that traps particles, dust, and debris before they enter the engine, protecting the cylinders and extending engine life.
The air filter is your motorcycle’s lung. Every litre of fuel burnt requires roughly 10,000 litres of air. That ambient air contains dust, sand, insects, and all sorts of particles that, without filtration, would scratch the cylinders, wear the piston rings, and damage the valves in very short order.
Aquaplaning
Loss of tyre grip caused by a film of water building up between the tyre and the road surface, preventing direct contact with the pavement.
Aquaplaning (also called hydroplaning) occurs when water accumulates in front of the tyre faster than the tread can disperse it. The tyre effectively lifts off the road surface and rides on a layer of water. During those moments, you have zero grip — no ability to brake, steer, or accelerate. The bike slides as if on ice.