7/9/2018

SSM73928 - Low Speed Manoeuvering Front Tyre Skip / Jump phenomenon | TOPIx

Reference

SSM73928

Models

Discovery / L462
Discovery Sport / L550
Range Rover / L405
Range Rover Evoque / L538
Range Rover Sport / L494
Range Rover Velar / L560

Title

Low Speed Manoeuvering Front Tyre Skip / Jump phenomenon

Category

Chassis

Last modified

09-Jul-2018 00:00:00

Symptom

306000 Tyres/Wheels

Attachments

Picture 1.pdf

Content

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
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

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7/9/2018

SSM73928 - Low Speed Manoeuvering Front Tyre Skip / Jump phenomenon | TOPIx

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.

Technicians - Please rate this SSM and provide comments so that
future communications can be improved.
1 = Poor – Basic information provided – The SSM does not help me
resolve the customer concern.
3 = Average – Adequate information provided – The SSM partially
helps me resolve the customer concern.
5 = Excellent – All required information provided to resolve the
customer concern.

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