Issue: Low Speed Manoeuvring Front Tyre Skipping Phenomenon
Cause: Acute Ackerman angles employed to enhance driving experience
Action:This SSM is a guide to explain the phenomenon of front tyre skipping while low speed manoeuvring with full lock applied to the steering causing a feeling of a slight jump, vibration or noise from the front tyres.
This is NOT an error state. It is a result of geometry focused for higher dynamic higher cornering speeds, manoeuver, environment and tyre type.
Geometry
Tyre Selection
Changing the tyres from summer to all season or winter tyres may result in an improvement but there is a trade off in economy, road noise and tyre life. A customer experiencing this phenomenon can choose to fit an alternative tyre at their own expense.
A benefit of low Ackermann can be found at higher cornering speeds when the tyres are generating slip angles (represented in picture 1 by the green arrows).
More sports orientated vehicles have these lower levels of Ackermann specifically to improve tyre utilisation.100% Ackermann Geometry principle means that front lock angles allow for the radius of travel of both wheels to be defined by a common point through the rear axle. However in reality this principle cannot be achieved due to inner wheel lock angle constraints. Typically, vehicles have Full Lock Ackermann levels between 55 and 65%. More sports orientated vehicles have lower levels of Ackermann specifically to improve tyre utilisation.
Manoeuver
A benefit of low Ackermann can be found at higher cornering speeds when the tyres are generating slip angles. At very low speeds the tyres do not generate a slip angle which results in an aligning torque being applied to the tyres that is absorbed in the tyre. Tyre slip is exaggerated at high lock angles.
Environment
Tyre slip is more perceptible when the friction level between road and tyre is lower, I.e. when there is ice and snow, or when the road surface is wet. Or Brick, car park painted surfaces or concrete containing pea shingle may exacerbate the concern.
Tyre Selection
Changing the tyres from summer to all season or winter tyres may result in an improvement but there is a trade off in economy, road noise and tyre life. A customer experiencing this phenomenon can choose to fit an alternative tyre at their own expense.
A benefit of low Ackermann can be found at higher cornering speeds when the tyres are generating slip angles (represented in picture 1 by the green arrows).
More sports orientated vehicles have these lower levels of Ackermann specifically to improve tyre utilisation.
Cause: Acute Ackerman angles employed to enhance driving experience
Action:This SSM is a guide to explain the phenomenon of front tyre skipping while low speed manoeuvring with full lock applied to the steering causing a feeling of a slight jump, vibration or noise from the front tyres.
This is NOT an error state. It is a result of geometry focused for higher dynamic higher cornering speeds, manoeuver, environment and tyre type.
Geometry
Tyre Selection
Changing the tyres from summer to all season or winter tyres may result in an improvement but there is a trade off in economy, road noise and tyre life. A customer experiencing this phenomenon can choose to fit an alternative tyre at their own expense.
A benefit of low Ackermann can be found at higher cornering speeds when the tyres are generating slip angles (represented in picture 1 by the green arrows).
More sports orientated vehicles have these lower levels of Ackermann specifically to improve tyre utilisation.100% Ackermann Geometry principle means that front lock angles allow for the radius of travel of both wheels to be defined by a common point through the rear axle. However in reality this principle cannot be achieved due to inner wheel lock angle constraints. Typically, vehicles have Full Lock Ackermann levels between 55 and 65%. More sports orientated vehicles have lower levels of Ackermann specifically to improve tyre utilisation.
Manoeuver
A benefit of low Ackermann can be found at higher cornering speeds when the tyres are generating slip angles. At very low speeds the tyres do not generate a slip angle which results in an aligning torque being applied to the tyres that is absorbed in the tyre. Tyre slip is exaggerated at high lock angles.
Environment
Tyre slip is more perceptible when the friction level between road and tyre is lower, I.e. when there is ice and snow, or when the road surface is wet. Or Brick, car park painted surfaces or concrete containing pea shingle may exacerbate the concern.
Tyre Selection
Changing the tyres from summer to all season or winter tyres may result in an improvement but there is a trade off in economy, road noise and tyre life. A customer experiencing this phenomenon can choose to fit an alternative tyre at their own expense.
A benefit of low Ackermann can be found at higher cornering speeds when the tyres are generating slip angles (represented in picture 1 by the green arrows).
More sports orientated vehicles have these lower levels of Ackermann specifically to improve tyre utilisation.