Applied Motorcycle Dynamics - A Case Study
By Greg Du Val

The 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.

Riding experiences do not always teach good riding habits. Many riders have fears of front brake use. Many rider’s 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 rider’s skills.

Classroom 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.

All 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.

In 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 accident.

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.

Mark 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.

Mark 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:

“Vehicle 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.

Vehicle #2 crossed into the south bound lane hitting into the left front and side of vehicle #1.

Driver 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 happened.”

The 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.

Mark 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.

Motorcycle Inspection

The motorcycle 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.

The front 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.

One subtle 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.

The normal 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 contact.	Tail Light View
Closer view. Black smear on corner. Paint scratch from upward force.

Chevrolet 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 totaled.

Quinten H. told me during our conversation he had been south bound on the dam when he observed a motorcycle on it’s 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.

Quinten H.’s 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 it’s side when it collided with the Nova.

There was no evidence of any type of rider contact into the front or side of the Nova.

Ford Taurus Inspection and Driver Interview

I 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 measured.

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 control.

Scene Inspection, Survey, and Photographs

Mark A.’s 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.

Paint marks 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 it’s side was still very clear from it’s beginning point to the impact point with the Nova. The skid marks from the Nova were still very visible.

The scene was surveyed to prepare a scale diagram for further analysis. Photographs were taken showing the evidence still visible.

The accident evidence began at the end of the right hand curve. The gouge mark from the motorcycle going onto it’s 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 Chevy

1. End of gouge, impact of m/c into LF Chevy wheel
2. Skidmark LF Chevy

Accident Analysis

Having ridden 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.

Using the 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 rider.

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.

“High 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.

The question 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.

No evidence supported a yaw or slide out. There were no yaw marks. The motorcycle speed was too low to yaw anyway.

Another unusual 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 it’s left side.

A different 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.

Several factors did not support a “high side”. There were no skid marks preceding the motorcycle going down.

There was 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 Davidson.

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 it’s side. There were no marks from a person sliding on the ground or fabric grinding across the asphalt.

No evidence supported either a slide out or a high side. Some other event had to have occurred.

The gouge 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 Taurus’s path.

The black smear on the right corner of the tail light then began to play an important role in concluding what had occurred. Only one explanation was found.

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.

The impact pushed the motorcycle onto it’s 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.

Side Note
Litigation commenced in this accident. Barry E.’s insurance carrier accepted liability and settled for policy limits.

By Greg Du Val
gduval@ix.netcom.com

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