Bump steer is best described as “a change of wheel direction without any input from the steering wheel”.
Initially this concept maybe a little difficult to grasp until a basic understanding of the coupling effect between suspension travel and the steering components is appreciated.
Much has been written about this subject and Elan and other Lotus owners still struggle to get this right.
In the past, inaccurate articles have been provide by UK Lotus clubs and other individuals that further confuses the subject.
In addition to this, authors who have written books about the Lotus Elan but still fail to understand what is involved.
One myth that gets recirculated is a static measurement that is taken between the top front suspension pivot spindle and the inner steering rack ball joint centre.
This is absolute nonsense as this single measurement does not take into account the following -
1) manufacturing tolerances of the chassis
2) pivot spindle positions
3) location of the steering rack platform
4) location of steering rack and mounts
5) manufacturing tolerances of the steering rack its self
6) and the possibility of a bent steering control arm...............to further compound problems
Its worth noting the internals of the steering rack do not run perfectly concentric with the external rack casing.
Just the one measurement suggested does not take into account manufacturing tolerances in the suspension upright or steering arm.
Elan owners carrying out this task, often make it difficult for themselves by placing bags of sand or people in vehicles to establish the required suspension heights.
So how can one static dimension take into account the dynamics of a compliment suspension system and steering rack?
Several years ago, Lotus Marques looked at this procedure to find a simple and accurate way to carry this out in our workshop.
Lotus Marques cannot take full credit for this solution but was inspired by a valued customers restoration project.
Part 2 of this document provides comprehensive details of all the necessary components required to make the bump steer measurements and adjustments.
A series of graph plots of the front suspension movement are shown with commentary to explain a logical approach to the sensitive adjustments.
Initially this concept maybe a little difficult to grasp until a basic understanding of the coupling effect between suspension travel and the steering components is appreciated.
Much has been written about this subject and Elan and other Lotus owners still struggle to get this right.
In the past, inaccurate articles have been provide by UK Lotus clubs and other individuals that further confuses the subject.
In addition to this, authors who have written books about the Lotus Elan but still fail to understand what is involved.
One myth that gets recirculated is a static measurement that is taken between the top front suspension pivot spindle and the inner steering rack ball joint centre.
This is absolute nonsense as this single measurement does not take into account the following -
1) manufacturing tolerances of the chassis
2) pivot spindle positions
3) location of the steering rack platform
4) location of steering rack and mounts
5) manufacturing tolerances of the steering rack its self
6) and the possibility of a bent steering control arm...............to further compound problems
Its worth noting the internals of the steering rack do not run perfectly concentric with the external rack casing.
Just the one measurement suggested does not take into account manufacturing tolerances in the suspension upright or steering arm.
Elan owners carrying out this task, often make it difficult for themselves by placing bags of sand or people in vehicles to establish the required suspension heights.
So how can one static dimension take into account the dynamics of a compliment suspension system and steering rack?
Several years ago, Lotus Marques looked at this procedure to find a simple and accurate way to carry this out in our workshop.
Lotus Marques cannot take full credit for this solution but was inspired by a valued customers restoration project.
Part 2 of this document provides comprehensive details of all the necessary components required to make the bump steer measurements and adjustments.
A series of graph plots of the front suspension movement are shown with commentary to explain a logical approach to the sensitive adjustments.