Road Access for Disabled Americans
Links to more Information about Bumps and Traditional Suspension Systems
- Car Talk,
Click and Clack Talk Cars: September 1993
"Speed bumps are one of those things that can really turn a car to junk."
How Things Work,
Louis A. Bloomfield, Professor of Physics, The University of Virginia, Spring 1998
"If the train track gets bumpier in effect with increasing speed,
why is it that your car bumps less when you go over a speed bump fast
instead of slow?
"Actually, if you drive fast over a real speed bump, it's not good
for your wheels and suspension. The springs in your car do protect
the car from some of the effects of the bump, but not all of them.
However, imagine driving over a speed bump on a traditional
bicycle--one that has no spring suspension. The fast you drive over
that bump, the more it will throw you into the air."
- Does your car do this?,
by Charles Ofria, 1999
"When I drive over a speed bump or a dip in the road, my car bounces
2 or more times before settling down.
This condition is usually caused by worn or broken shocks or struts.
This condition happens gradually over the life of the shocks and it is
hard to notice the change, but when they are replaced you should notice
a big difference in the ride and stability of your car."
Automobile Ride, Handling, and Suspension Design,
Robert Q. Riley Enterprises, 1999
"Obstacles impart a vertical acceleration to tires that
increases in proportion to the forward speed of the vehicle
and the size of the obstacle. The greater the accelerated mass
(unsprung weight) the greater the kinetic energy. In a sense,
a raised obstacle throws tires away from the roadway. A
depression causes the surface to rapidly drop away leaving the
tire to follow along when inertia can be overcome by the downward
pressure of the springs. Both occurrences reduce the tire's
contact-pressure and tires can actually become airborne if the
forces are great enough."
"The forces generated by roadway irregularities (bumps)
must be overcome by the springs in order to keep tires in contact
with the road. The force of the springs comes from the compressive
load imposed by the weight of the vehicle. The lighter the vehicle,
the less compressive force is available, and the easier it is for
the vertical motion of the wheels to overcome the inertia of the
sprung mass and transfer motion to it as well. The ideal combination
occurs when the ground pressure is maximized and inertial forces
are minimized by a high sprung-to-unsprung weight ratio. A high ratio
keeps the tires more firmly in contact with the road, and it also
produces the best ride."
The sections titled, Ride Comfort,
Implications of High Payload-to-Vehicle Weight Ratio
and The Ratio of Sprung to Unsprung Weight discuss
issues related to:
- high frequency vibrations
- low frequency bounce and rebound movements,
- lurches and pitches during acceleration and braking,
- oscillations that will cycle according to the natural frequency of the system
(and human sensitivity to ride frequency)
- variations in payload
- Of interest to engineering enthusiasts -
Robert Q. Riley Enterprises Homepage
More Technical Papers
Potholes of Opportunity, Larry Carley,
Tire Review, February 1997
"benefits that result from proper
wheel alignment ... reduced tire wear, improved steering stability
and tracking, better traction and reduced rolling resistance for
better fuel economy."
Investigation into Air Bags Inflating Unexpectedly,
Car Today, South Africa, April 16, 1998
"US Federal investigators are examining over 14 different car
models after some 350 complaints of potentially dangerous airbag
deployment. The crash-sensors in some Mazda, Subaru, GM and Chrysler
cars are under particular scrutiny to find out if their sensors might
be too sensitive and trigger an airbag if the vehicle hits a pot hole
or speed bump, or if water has got into the sensor mechanism."
| Fire & EMS
February 7, 2000 / last update: May 2, 2000 (Version 1.c)