Grip budget
Each tire has a limited amount of grip. Cornering, braking, and acceleration share that budget.
One budget for every demand
A tire generates lateral force when cornering and longitudinal force when braking or accelerating. The total grip available for these demands is limited.
What sets the grip limit
- the road surface
- tire condition and temperature
- the load on each wheel
- how the load is distributed between the wheels
Slippery surfaces leave less grip
Wet road markings, metal, and gravel offer less grip than dry asphalt. At the same lean angle and braking force, a tire may start to slide.
How to read the diagram
The lateral force used for cornering and the longitudinal force used for braking or acceleration are jointly limited by tire grip. The closer a tire is to that limit, the less room remains to brake harder, add drive, or change your line.
Sources · 1
- Физические основы классической механики
Сухое трение и реакция опоры; PDF: с. 3.
Used for: Dependence of available friction force on load in the basic model.
Open source
Cornering
The more lateral force needed to hold a curve, the less grip remains for sudden braking or acceleration.
More lean leaves less in reserve
A large lean angle does not by itself mean a tire will lose grip. But as lean increases, less grip remains for harder braking, acceleration, or a tighter turn.
Braking while leaned over
You can brake in a corner, but build brake pressure progressively and account for your current lean angle. The more you need to slow down, the more useful reducing lean becomes, provided your line allows it.
Bringing the bike upright
As lean decreases, some of the grip budget becomes available for stronger acceleration or braking.
Sources · 1
- Motorcycle Operator Manual
Basic Vehicle Control, pp. 10–13
Used for: In a lean, less grip remains for braking.
Open source
Braking
Braking harder is easier at a smaller lean angle, when the tire is generating less lateral force. While leaned over, build brake pressure progressively and account for the grip you have available.
The rear brake and engine braking
The rear brake and the engine both slow the motorcycle through the same rear tire. Under hard braking, that tire becomes less loaded and can transmit less braking force. Adding too much engine braking to the rear brake can lock the wheel.
Throttle
Acceleration adds longitudinal demand at the rear tire. As the motorcycle comes upright, you can open the throttle further. At a large lean angle, an abrupt roll-on takes the tire toward its grip limit more quickly.
Change the load smoothly
Abrupt brake release or throttle opening quickly changes the loads on the tires and suspension. Release the brake and roll on the throttle smoothly so you can more easily feel when you are approaching the grip limit.
The wheels carry different loads
The rear tire provides drive during acceleration, while the front wheel usually carries more load than the rear under braking. One tire can therefore start to slide while the other still has grip in reserve.
Sources · 1
- Motorcycle Operator Manual
Crash Avoidance, pp. 26–28
Used for: Some of the grip in a turn is needed for lateral force.
Open source