Speed Bump -ve- Alignment Debate

[Tony-Bones]

The following is my opinion born from over 25yrs in the chassis industry and hopefully i can answer some common questions regarding why Alignment changes.

We have three dimensions X, Y, Z within the chassis, this equates to left/ right, forward/ backward and up/ down. Every car made allows correction for X.

Historically it's globally recognized the front Toe will change, in fact the entire Geometry is subject to change but for now lets concentrate on longitudinal Alignment.... why and how is it displaced?

In the old days the Toe position was around 0 give or take a foot or two, nowadays with modern technology and advances in suspension the tolerances have reduced so that the car can perform as promised my the manufacturer, so rather than give or take a foot it's give or take 1/10th of a millimetre or 1/100th of a degree decimal.

Wear and tear

With the advent of multi-link suspension and it's satellite bushings it's inevitable wear will become part of the Alignment factor.... It's a bitter pill but small amounts of wear is no longer inconsequential. Although this reads depressing actual wear and tear can be recognized and compensated for assuming the wear is not to advanced.

The common criminals

With the advent of traffic calming the public have assumed a physical enemy to explain why Alignment is displaced and that criminal is the speed bump. This simply is not the case! The accent of the bump should be at a reasonable speed and assumes the wheels are in the dead ahead position. The tyre and suspension are more than able to absorb this compression.

Another argument is the "narrow bumps" these are the ones you need to stride the wheels either side off. The argument here is that the tyres are forced to deflect the contour of the bump forcing the Alignment to change. I have to disagree. The pneumatic deflection is retained within the tyre sidewall. Simply put the tyre does not have the strength within the internal structure to transport this energy into the chassis.

Off road parking

Assuming this is done at a reasonable speed then the tyre sidewall is more than able to absorb the transition between road and curb.

So what's the criminal?

We are looking for something able to compress/ stretch/ bend the chassis and something that effects us all, and that criminal is.................. The pothole. The inertia of the car plus the momentarilly impact has the energy to complete the inevitable change in the chassis, ever more painful since the tolerances are so small.

Solution

Ready for this........ There isn't one. It's a pants deal i agree but we are the victims of the highways agencies funding and i expect this condition will become worse before our voice becomes heard, so until then "mind those holes".