Motorcycle Dynamics - A Case Study
By Greg Du Val
understanding of motorcycle handling and braking dynamics are
critical for the accident reconstructionist. These skills are
learned through a combination of riding experiences, motorcycle
training classes, classroom studies, and available literature.
experiences do not always teach good riding habits. Many riders
have fears of front brake use. Many riders do not know how
to steer a motorcycle. Some riders try to steer a motorcycle through
leaning only. Fortunately, motorcycle training classes such as
those taught by the Motorcycle Safety Foundation are
available and improve a riders skills.
study such as the Investigation of Motorcycle Crashes
through IPTM teach useful topics covering many facets of motorcycle
handling and braking dynamics. Books and magazine articles are
available about related topics through numerous other sources.
of the above can prepare the accident reconstructionist to provide
more accurate evaluations of motorcycle accidents. This article
cannot cover the many aspects of motorcycle accident analysis
but is written to help one understand how these tools were applied
to an unusual case.
the fall of 1995 I was contacted by the rider of a Harley Davidson
motorcycle asking me to reconstruct his motorcycle accident. After
listening to him, I was interested enough to take a look at the
rider, Mark A. had been north bound on SR-189 in Provo Canyon,
Utah. Provo Canyon is a very scenic highway bordered by the Provo
River, Bridal Veil Falls, the antique coal burning Heber Creeper
Railroad, and Sundance Ski resort.
A., a 42 year old local resident had left his home to take a leisurely
ride up the canyon on a 1994 Harley Davidson Heritage Soft Tail
Classic. Approximately 10 miles later, he negotiated a right hand
curve on the roadway leading over Deer Creek Dam. The next thing
Mark A remembered was waking up under the front of a Ford Taurus
driven by Barry E.
A. was transported to a local hospital where he had back surgery
to repair badly damaged vertebra. While Mark A. was recuperating
from the surgery, he was provided a copy of the police accident
report. The narrative stated:
1 (a 1987 Chevrolet Nova driven by Quinten H.) was south bound
on SR-189. Vehicles #2 (Mark A.) and #3 (Barry E.) were north
bound on SR-189. Driver of vehicle #1 stated that vehicle #2 a
motorcycle went out of control causing vehicle #2 to go into a
slide. The driver of vehicle #2 (Mark A.) slid away from vehicle
#2 going onto the north bound lane where he stopped.
#2 crossed into the south bound lane hitting into the left front
and side of vehicle #1.
of vehicle #3 stated he was following vehicle #2 when vehicle
#2 went out of control and slid into the on-coming or south bound
traffic lane hitting vehicle #1. The driver of vehicle #2 was
thrown back into the north bound lane of traffic. Vehicle #3 stopped
over the top of driver #2. Driver #2 was not certain as to what
investigating officer did not take any photographs of the accident
scene. He did make some field measurements. Several witnesses
were interviewed with different observations not totally consistent
with the police narrative.
A. asked that I look at the evidence, evaluate it, and see if
the police report was accurate. The accident was only weeks old
and much of the evidence was still available for inspection.
had been transported from the scene on a flatbed wrecker to Salt
Lake Harley Davidson. The motorcycle was placed on a dolly in
a protected area.
wheel and fender showed obvious contact damage from where the
motorcycle had impacted the Chevrolet Nova. The damage was more
pronounced on the right side of the front wheel and fender. Behind
this area, there was no damage on the right side of the motorcycle.
The left side
of the motorcycle showed different damage. The left floor board
was bent upward and had asphalt embedded on the bottom side. The
left saddle bag was scraped as well as the primary cover and left
side of the handle bars. The left rear signal light was sheered
off. All of this damage was associated with sliding on the left
side prior to impacting the Chevrolet Nova.
piece of damage but later to be determined as critical to the
analysis of this case was the condition of the rear tail light.
The tail light showed a distinct black smear on the right side
corner. The tail light was also crooked from a force pushing up
the right corner of the tail light. The paint underneath the tail
light was scratched showing where the tail light had been pushed
upwards. The height of the tail light was measured.
drive train mechanics of the motorcycle including the transmission
and drive belt were found to be in working order. The brakes were
found to be in good working order.
Motorcycle Left Side
Left Side Floorboard
Front Rim bent by impact with the nova
left front wheel. Fender damaged by body
Tail Light View
Closer view. Black smear on corner. Paint scratch from upward
Nova Inspection and Driver Interview
I called Quinten
H. to inquire as to what had become of his vehicle after the accident.
He indicated his car had been towed to a salvage yard as it was
H. told me during our conversation he had been south bound on
the dam when he observed a motorcycle on its side sliding
into his lane. He never saw the motorcycle lose control. He never
saw the motorcycle rider in his lane. Quinten H. swerved right
and applied his brakes skidding into the motorcycle. Upon exiting
his vehicle after the accident, he observed the motorcycle rider
underneath the front of a Ford Taurus adjacent to him on the other
side of the road.
car was inspected at the salvage yard. The only damage was low
on the left front wheel and fender area. It was clear from the
vehicle inspection that the motorcycle was down on its side
when it collided with the Nova.
no evidence of any type of rider contact into the front or side
of the Nova.
Inspection and Driver Interview
called Barry E. asking him if I could photograph his car. He agreed
and a meeting time was scheduled. The inspection took place as
agreed upon. The Ford Taurus had a dark gray front bumper cover.
The cover showed many small nicks and scratches on it. There was
nothing from an outward appearance that showed obvious contact
with the motorcycle or rider. The height of the bumper cover was
Barry E. mentioned
to me at that time and later in a deposition that he had been
following the motorcycle at 30-35 mph near where the motorcycle
lost control. He had been following the motorcycle approximately
3 car lengths back when for no known reason, the motorcycle lost
Survey, and Photographs
son had gone to the accident scene the day after the accident
taking pictures of some of the evidence he thought important.
The pictures were provided to me. I traveled to the accident scene
where much of the evidence was still visible.
made by the investigating officer of the vehicles final rest locations,
skid marks, and the gouge mark from the motorcycle sliding into
the Nova were still visible. The gouge mark from where the motorcycle
first went on its side was still very clear from its
beginning point to the impact point with the Nova. The skid marks
from the Nova were still very visible.
was surveyed to prepare a scale diagram for further analysis.
Photographs were taken showing the evidence still visible.
evidence began at the end of the right hand curve. The gouge mark
from the motorcycle going onto its side began 9 feet prior
to crossing over the double yellow center line. The gouge mark
continued 42 feet into the south bound lane to the impact point
with the Nova.
Looking north bound towards the accident location
1. Start of m/c gouge; 2. End gouge; 3. LF Skid
1. End of gouge, impact of m/c into LF Chevy wheel
2. Skidmark LF Chevy
this same curve many times on similar motorcycles, the described
travel speed of 30-35 mph would not cause a motorcycle to lose
control. The speed at which Mark A. negotiated this curve was
very normal, if not low.
scale diagram, the curve radius was found to be 386 feet. At speeds
of 30-40 mph, a motorcycle would only lean 8.8-15.4 degrees during
the turn. This degree of lean would be very comfortable for a
To lose control,
some other event had to occur. The mechanical inspection of the
motorcycle showed there was nothing wrong with the motorcycle
to cause some type of wheel lock-up. The motor had not seized
nor the transmission locked up. Nothing such as loose clothing
had fallen into the drive train or wheels.
Side or Slide Out?
In order for
the motorcycle to go down as described, some other event had to
precipitate the gouge mark. Mark A. nor Barry E. described the
motorcycle wobbling back and forth as the motorcycle began to
exit the curve. Mark A. was an experienced rider.
then arose, could the motorcycle have slid out of control? The
low travel speed would not have caused the motorcycle to slide
out of control. If high speed was involved, the rear wheel would
have begun to yaw clockwise in a right hand turn. In most yaw
type cases, the rider does not brake so the motorcycle slides
out in front of the rider. The motorcycle would go onto the right
side in this scenario.
supported a yaw or slide out. There were no yaw marks. The motorcycle
speed was too low to yaw anyway.
aspect was that the motorcycle had fallen onto the left side,
opposite that of a slide out. Some other type of event
would have to cause the motorcycle to go onto its left side.
but possible explanation was that of a high side.
If a rider brakes and locks up the rear brake with little or no
front wheel braking, the rear of the motorcycle will begin to
rotate outward. As the rear continues to rotate outward, the motorcycle
will start to slide out. If the rider releases the rear brake,
the rear wheel will begin to free roll. The motorcycle will attempt
to regain gyroscopic stability up-righting the motorcycle. There
is no mechanism to stop the motorcycle from continuing through
the up-righting process so it catapults forward violently onto
the leading side. This violent motion throws the rider forward
of the motorcycle.
did not support a high side. There were no skid marks
preceding the motorcycle going down.
no evidence of the motorcycle rider ever being thrown forward
of the motorcycle. There were no contact marks showing the motorcycle
rider had ever impacted any portion of the Nova or the Harley
Mark A. was
found perpendicular to the Nova. There was no force vector that
would have re-directed Mark A. towards the area he was found.
There was not enough force if there had been a high side to direct
Mark A. towards the Nova, impact the Nova, and then bounce to
a location near where he was found.
Mark A. did
not have any injuries consistent with sliding any distance. There
was no evidence on the Nova that he had struck its side.
There were no marks from a person sliding on the ground or fabric
grinding across the asphalt.
supported either a slide out or a high side. Some other event
had to have occurred.
mark provided more useful information. There was no indication
that Mark A. had traveled with the motorcycle towards the Nova.
If he had done so, he would have slid into the south bound lane
within 1/4 second based on mathematical equations. Therefore,
within that 1/4 second from when the motorcycle went down, Mark
A. was being re-directed in the Ford Tauruss path.
smear on the right corner of the tail light then began to play
an important role in concluding what had occurred. Only one explanation
Barry E. had
to lightly contact the rear tail light of the motorcycle just
as Mark A. was completing his right hand curve. The light impact
damaged the rear tail light of the motorcycle. No other event
was ever found that would have damaged the tail light.
pushed the motorcycle onto its left side. The motorcycle
slid into the path of the Chevrolet Nova where the two collided.
Mark A. was
caught by Barry E.s Ford Taurus and moved forward to the
point he was found.
commenced in this accident. Barry E.s insurance carrier
accepted liability and settled for policy limits.
to May 2003 Newsletter