RUMoto Theory / Interactives

Track cornering line

One consistent example on a closed track. Not a line for a blind corner on a public road.

Left-hand corner · closed track

Reference Error comparison
TOP VIEW · MOTORCYCLE ENLARGED
Reference line for a left-hand corner Moving left to right on the straight, then turning left toward the top of the diagram. Entry from the outside, apex near the inside edge, and exit back toward the outside. BRAKING
Line logic

Wider entry.
Smoother exit.

Use the track width to connect the entry, apex, and exit with one smooth arc. Leave a margin from the edge.

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Approach

The motorcycle is upright at a steady speed, near the outside of the track. Braking and turn-in reference points were chosen in advance.

Compare entry
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Moving the slider pauses the run. The arrow keys change the position; Home goes to the start, End to the finish. Choosing a phase also pauses the run.

Playback uses a training pace. Speed, gear, and percentages are illustrative; they are not settings for a specific motorcycle.

Where the line goes wrong

Five errors, with different causes and similar consequences.

01 / REFERENCE

Early apex

The inside edge is reached too early. The error is where the line approaches that edge: it can happen even from the correct turn-in point if you steer inward too quickly. This leaves less room on the exit.

02 / ENTRY

Entry too early

Lean begins before the chosen reference. The motorcycle moves inside too early and reaches an early apex. There is then not enough radius left for a clean exit.

03 / ENTRY

Entry too late

The straight is extended too far, leaving less room for the arc. To reach the apex, the radius must decrease sharply or the line must be corrected. On the diagram, this appears as a tight arc and a cramped exit near the inside.

04 / SPEED

Too much entry speed

The same arc requires more lean, while grip reserve is limited. Running wide and overloading the tires are possible. Reduce most of the speed on the straight; braking while leaned over requires especially smooth control.

05 / THROTTLE

Abrupt throttle at the exit

Opening the throttle wide at a large lean angle uses up the rear tire's grip reserve and can cause a slide. The initial throttle input is gentle; noticeable acceleration builds as lean decreases.

This is a closed-track analysis, not a road-riding instruction. A line does not compensate for excess speed. Grip, visibility, and the margin from the edge matter more than instrument readings. Practice braking while leaned over gradually with a qualified instructor.

How the model works and its limits

In this model, most deceleration happens on the straight. A small amount of smoothly decreasing braking remains at entry: trail braking. The brake is released shortly before the apex; initial throttle begins after it. This is one consistent example, not a universal rule about where to release the brake or open the throttle.

Lean is calculated from speed and line curvature for an assumed flat surface. Movement of the center of mass relative to the motorcycle, tire profile, suspension, aerodynamics, and changes in grip are not modeled. The rider leans with the motorcycle; separate hanging off is not modeled. The two views show the same vector model; the “−” sign means left lean.

Brake and throttle are relative training scales, not percentages of available grip. The gears use fixed shift points. The red lines show the geometric consequences of errors; they do not model separate dynamics or predict a fall or inevitable outcome.