MotoGP crashes often come from a loss of tire grip while the motorcycle is leaned over in a corner. A lowside happens when one or both tires slide out and the bike falls toward the inside of the turn. A highside is more violent because the rear tire first slides, then suddenly regains grip and snaps the bike upright, launching the rider.
Understanding these crashes helps engineers design tires, suspension, electronics, and rider safety systems.
Key Facts
- Maximum tire friction is approximately Fmax = μN, where μ is the coefficient of friction and N is the normal force.
- Cornering force requirement is Fc = mv^2/r, so higher speed or tighter radius demands more lateral grip.
- Lean angle for steady cornering can be estimated by tan(θ) = v^2/(rg), ignoring tire width and suspension effects.
- A lowside occurs when required lateral force exceeds available tire friction and the bike continues sliding outward and downward.
- A highside occurs when rear tire slip reduces yaw stability, then sudden grip recovery creates a large restoring torque.
- Traction control reduces engine torque when rear wheel slip is too high, helping prevent rear-tire spin and highsides.
Vocabulary
- Lowside
- A crash in which the motorcycle loses grip and slides down toward the inside of the corner.
- Highside
- A crash in which the rear tire slides, suddenly regains grip, and violently throws the motorcycle and rider upward or outward.
- Lean angle
- The angle between the motorcycle and vertical direction while cornering.
- Coefficient of friction
- A number that describes how much grip exists between the tire and the track surface.
- Torque
- A turning effect caused by a force acting at a distance from a rotation axis.
Common Mistakes to Avoid
- Treating a highside as just a faster lowside is wrong because a highside depends on sudden grip recovery after a slide, not only on loss of grip.
- Ignoring the normal force is wrong because the maximum friction force depends on Fmax = μN, so load transfer changes available grip.
- Assuming more throttle always helps stabilize the bike is wrong because excessive rear-wheel torque can increase slip and trigger a highside.
- Forgetting that braking, turning, and accelerating share tire grip is wrong because a tire has a limited friction budget in all directions combined.
Practice Questions
- 1 A MotoGP bike and rider have a total mass of 250 kg and enter a 90 m radius corner at 45 m/s. Calculate the required centripetal force using Fc = mv^2/r.
- 2 On a dry track with μ = 1.6, estimate the maximum friction force if the normal force on the tires is 2450 N. Use Fmax = μN.
- 3 A rider begins sliding the rear tire while leaned over and then abruptly closes the throttle. Explain why this can increase the chance of a highside instead of smoothly recovering.