|
I hope this post will totaly define what bump steer is, why it is a concern, and what to do to repair it. First lets define bump steer:
Bump Steer
From Wikipedia, the free encyclopedia
Bump Steer is the term for the tendency of a wheel to steer as it moves upwards into jounce. It is typically measured in degrees per meter or degrees per foot.
On modern cars the front of the tire moves outwards, as the suspension is raised, a process known as the front wheels "toeing out". This gives roll understeer. The rear suspension is usually set up to minimize bump steer, where possible.
A typical value is two degrees per meter, or perhaps more, for the front wheels.
Excessive bump steer increases tire wear and makes the vehicle more difficult to handle on rough roads.
Solid axles generally have zero bump steer, but still have roll steer, in most cases. That is, if the wheels move upwards by the same amount, they tend not to steer.
Roll steer is an important part of the budget used to define a vehicle's understeer, known as a Bundorf analysis.
Difference between Bump Steer and Roll Steer
In a bump steer, both wheels rise together. In roll steer, one wheel rises as the other falls. Typically this produces more "toe in" on one wheel, and more "toe out" on the other, thus producing a steering effect. In a simple analysis you can just assume that the roll steer is the same as bump steer, but in practice things like the Sway bar geometry have an effect that modifies it.
Roll steer is usually measured in degrees of toe per degree of roll, but can also be measured in degrees of toe per meter of wheel travel.
Method of Adjustment
The linearity of the bump steer curve is important. If it is not straight then the length of the tie rod needs to be adjusted.
Bump steer can be made more toe out in jounce by lifting the rack or dropping the outer tie rod, if the rack is in front of the axle. The reverse applies if the rack is behind the axle. Usually only small adjustments (say 3mm) are required.
Now as it pertains to the LX specifically:
Defining Bump Steer as it Affect the LX Product line
STOCK SUSPENSION attachment 1
This is the graph showing the significant amount of toe change on a stock LX suspension. Notice at a 40mm jounce (compression, toe changes almost 10mm. And at a 40mm rebound (growth, toe changes a -6mm. So on a 80 mm total change ( 3.15 inches total travel), toe changed a total of almost 16mm ( .63 inches). This can contribute to significant tire wear, plus will require you to make steering corrections while turning, especially when hitting bumps, because this toe change is a self steering mode that will take away from your steering control and stability. If you drive twisty, bumpy roads, your tires may wear abnormally due to the serious toe changes,
BUMP STEER CORRECTION KIT INSTALLED. Attachment 2
This graph shows the toe changes under bump steer, after the EP2113 bushing was installed. Notice when the suspension jounces (compresses) 40mm, the toe changes 3mm. When the suspension rebounds (grows) 40mm, the toe changes – 1.3mm. So over a 80mm suspension travel, ( 3.15 inches), the toe will chane a total of 4.15 mm (.16 inches). That is a reduction of nearly 11.85mm (.47 inches). This is a substantial amount of toe change improvement. The LX already has a toe wear concern. Adding our cost efficient EP2113 bump steer kit, will not only reduce toe wear, but will increase handling through the twisties by a significant amount. This is a very big deal. Customers are also reporting better steering feel over repeating bumps, and better isolation of road vibration. Camber changes are also reduced!
some of the side benifits of our bump steer bush kit has to do with better control of the steering gear over bumps. This is what our customers tell us. Plus they tell us of a much better steering feel handling.
When you check out the graphs below, notice the vertical scale on the left side. This is critical.
thanks
mike
dms
|
07-04-2008, 04:28 PM
Linear Mode
