Six sections, twenty pieces

Everything a motorcycle does in a corner starts with an input that feels wrong. Three pieces on what the machine is actually doing when the rider pushes the bar away from the turn.

• 01

  Countersteering

  Above walking pace you turn by pushing the bar away from the corner and the machine falls into the turn.

• 02

  Gyroscopic precession

  A spinning wheel resists being tilted and responds ninety degrees later, which is part of why the bar input works.

• 03

  Camber thrust

  A leaned tyre generates side force from its own conical contact patch, independent of slip angle.

Four numbers settle how a machine behaves before anyone chooses an engine: head angle, trail, wheelbase and where the mass sits. All four are measured at rest and none of them stays put.

• 01

  Rake and trail

  The head angle and the distance the contact patch trails behind the steering axis decide how willingly the machine turns and how hard it resists.

• 02

  Wheelbase

  Long is stable and slow to turn, short is quick and nervous; almost every other decision is negotiated against it.

• 03

  Weight distribution

  Front-to-rear bias decides which end lets go first, and it changes with fuel load and a passenger.

• 04

  What a number hides

  Static geometry is measured at rest; under braking the fork compresses and every figure changes.

The telescopic fork asks one pair of tubes to spring, damp, steer and take the braking load. Three pieces on why that survives, what it costs, and what was tried instead.

• 01

  The telescopic fork

  Almost universal and structurally poor: it bends under braking and its damping fights its own suspension duty.

• 02

  Alternatives that lost

  Hub-centre and leading-link systems separate braking from suspension and keep failing commercially.

• 03

  Dive

  The nose-down movement under braking is geometry changing while you are using it.

An engine is a packaging decision before it is a power figure. Where the cylinders point decides width, height, wheelbase and how willingly the machine leans.

• 01

  The flat twin

  Cylinders in the airflow and mass carried low, at the cost of width and a torque reaction when you blip it.

• 02

  The L-twin

  Narrow and long, which pushes the wheelbase out and puts the rear cylinder where the airflow is not.

• 03

  The inline four

  Smooth and wide, and it sits high because the crank has to clear the ground.

• 04

  Firing order and feel

  Uneven firing intervals change how the tyre is loaded and how the machine feels at the edge of grip.

A frame exists to hold the steering head and the swingarm pivot in a fixed relationship while everything else tries to move them. Three pieces on how that is done and what each method costs.

• 01

  The Featherbed

  The McCandless brothers' 1950 frame was stiff enough for power that already existed, and the handling difference was immediate.

• 02

  Trellis and spine

  Triangulated tube against a single large-section beam — two ways to reach the same stiffness with different mass and different access.

• 03

  The engine as a member

  Bolting the motor in as a stressed part deletes tubes and makes servicing worse.

Handling was a matter of rider report long before it was a matter of data. Three pieces on instruments, on riders, and on what each of them can and cannot see.

• 01

  Damping the steering

  A damper masks an instability rather than fixing it, which is why what it hides matters more than what it does.

• 02

  Instrumented testing

  Strain gauges, potentiometers and data logging turn feel into numbers that can be argued with.

• 03

  What riders report

  Subjective feedback is data with a wide error bar, and it still finds things instruments miss.