analysis of motorcycle impacts

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Forensic Engineering Analysis of Motorcycle Impacts Using Rotational Mechanics and

Fork/Vehicle Deformation

By Jerry S. Ogden, PE (NAFE 561F)1and Katrina M. Kloberdanz, PE (NAFE Correspondent 430C)2

Abstract

Methods of reconstructing motorcycle collisions have traditionally been limited to speed

from skid marks, speeds from scrapes or gouges, speed from rider ejection, speed from linear

momentum, or sometimes speed from witness observations. Oftentimes, the data necessary for

analysis is either misunderstood or misinterpreted. This paper tests the applicability of using

rotational mechanics and specific models for motorcycle front fork deformation and vehicle

deformation when determining motorcycle impact velocity. Additionally, the results of these

methods are statistically tested for significance and reliability against independent motorcycle

impact test data.

Key WordsForensic Engineering, Fork Deformation, Motorcycle Impact, Rotation, Yaw Moment of Inertia.

Rotational Mechanics

According to the principles of rigid body mechanics, when a collision force is applied to

a vehicle or object such that the resultant force does not pass through the center of mass of one or

both of the colliding objects, a moment is applied that tends to produce rotation to one or both of

the colliding objects. The force applied (F) offset to the center of mass of the object by some

distance (d), will produce a moment (Fd) about the center of mass of the object. This moment, in

turn, will produce both translational (linear) and rotational motion of the object.

For the purposes of rigid body collision analysis, rotational motion involves a property

called mass moment of inertia (I). The mass moment of inertia of a rigid body is a measure of the

resistance that a body has to angular acceleration, and is a function of the shape and mass of the

rigid body. The vast majority of motor vehicle collisions, to include motorcycle/vehicle impacts,

can be analyzed in two-dimensions, and therefore, the yaw moment of inertia describes the

resistance of a vehicle to rotate in yaw (clockwise or counterclockwise about the vertical axis

through the vehicle center of mass).

The determination of mass moment of inertia for a homogeneous geometrically shaped

object is quite straight forward. However, because of the complicated shape and mass

distribution of motor vehicles, the yaw moment of inertia is best determined from experimental

data, rather than by assuming a motor vehicle is a completely homogenous parallelepiped object.

1Jerry S. Ogden, PE (NAFE 561F), PO Box 621519, Littleton, CO 80162-15192Katrina M. Kloberdanz, PE (NAFE Correspondent 430C), PO Box 621519, Littleton, CO 80162-1519


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The derivations of the rotational energy/work equations for motorcycle impacts are quite

lengthy and outside the scope of this paper. However, several resources show these derivations

for those interested (Keifer, et al. 2007, Daily, et al. 2006). The following equations determine

the impact speed of a motorcycle, as well as the velocity change of a motorcycle and the struck

vehicle resulting from an offset collision that produces rotation of the impacted vehicle, Figure 1:

Figure 1: Moment Diagram

Equation 3: Motorcycle Impact Velocity

Equation 4: Motorcycle Velocity Change

Equation 5: Target Vehicle Velocity Change:

Where, VMC= impact velocity of motorcycle (ft/sec)VMC= velocity change of motorcycle (ft/sec)Vcar= velocity change of car (ft/sec)

Icar= yaw moment of inertia of struck vehicle ()Wcar= weight of struck vehicle (lb)WMC= weight of motorcycle (lb)

di= distance from impact to center of mass on vehicle (ft), see Figure 2

= angular rotation of vehicle (radians), see Figure 2

n = rotational friction coefficient

WBcar= wheelbase of car (ft)

x

y

Fimpact Fimpact

di

diFimpact


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If the motorcycle riders body collides with the side of the target vehicle, then the full weight of

the rider is considered with the motorcycle weight at impact. If there is evidence of handle bar or

tank deformation due to motorcycle rider contact and no contact with the vehicle, then adding

1/3 to 2/3 of the riders weight to the weight of the motorcycle at impact is appropriate,

otherwise, the weight of the rider is omitted if the rider is ejected without contacting the vehicle

or the engaging with components of the motorcycle during ejection. Figure 2 demonstrates the

measurement of the distance di(perpendicular lever arm) and the vehicle rotation angle ().

Figure 2: Rotational Diagram

Rotational friction takes into account the weight distribution of the vehicle as well as

whether the wheels are locked or free-rolling as the vehicle rotates due to the impact force.

Keifer, et al. (2007) established a curve for determining the normalization factor for increasing

amounts of rotational displacement () for vehicles that do not have the brakes applied at impact.This normalization factor is then multiplied by the full roadway friction to determine the

rotational friction value (n).

Figure 3: Relative Rotational Friction Normalization Factor Curve (Keifer, et al. 2007).


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Application to Independent Test Data

Adamson, et al. (2002) conducted seventeen motorcycle crash tests into vehicles and

barriers at speeds ranging from 10 to 49 mph. For the motorcycle into vehicle impact tests, they

used nineteen early 1989 to 1993 Kawasaki 1000 police motorcycles and two 1989 Ford

Thunderbirds. Tests 8, 9, 10, 11, 12, 13, 18 and 19 from the study produced rotational data thatcan be analyzed to test the validity of the rotational mechanics analysis methods discussed in this

paper. Additionally, Craig (2009) reported the results of 7 high speed motorcycle crash tests into

vehicles at speeds ranging from 44 to 67.5 mph. Only tests 1, 3, 5 and 6 contained impact data

that documented rotation of the target vehicle due to the impact by the motorcycle. These tests

used various 1980s Honda and Yamaha cruiser-type motorcycles colliding with 1991 Mercury

Sable station wagons, 1989 Ford Taurus sedans and a 1979 Dodge B100 full sized van.

For each of these tests, the relevant rotational analysis parameters were determined from

scaled diagrams of the impact tests, and the impact velocity of the motorcycle was calculated

using Equation 3. Table 2 provides a summary of the overall results when applying the rotational

mechanics analysis to the test data. The results were analyzed using the -squared test of fit

(=0.99) and the paired t-test (=0.01), both to a 99% confidence interval. The calculated impact

velocity for the motorcycle was determined to have no statistically significant difference between

the measured impact velocities and the calculated impact velocities of the tests by the chi

squared test of fit (2= 0.903,

2critical= 3.053, for = 11), and with the same results for the

paired t-test (t= -0.714, t-critical= 3.106, for = 11). The analysis of this test data indicates that

determining the impact velocity of a motorcycle for impacts producing measurable rotation to

the target vehicle should provide statistically reliable analysis results. The error rate using

Equation 3 ranged between +6.31% to -9.90%. The chart that plots Calculated versus Expectedanalysis values for Equation 3 indicates the data has an excellent correlation of R

2= 0.9925. The

dashed lines on this chart represent a 10% variance, demonstrating that all data points would fit

within that spread or less.


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Test Number Calculated Impact

Velocity

Reported Impact

Velocity

Absolute

Difference

Adamson #8 43.7 mph 46.0 mph -2.3 mph (-4.93%)



Adamson #11 22.5 mph 25.0 mph -2.5 mph (-9.90%)Adamson #12 27.7 mph 30.0 mph -2.3 mph (-7.57%)

Adamson #13 44.6 mph 42.0 mph +2.6 mph (+6.31%)

Adamson #18 46.9 mph 45.0 mph +1.9 mph (+4.17%)


Craig #1 46.2 mph 45.5 mph +0.7 mph (+1.54%)

Craig #3 45.4 mph 46.0 mph -0.6 mph (-1.30%)

Craig #5 45.5 mph 46.0 mph -0.5 mph (-1.09%)

Craig #6 68.2 mph 67.5 mph +0.7 mph (+1.78)

Means 42.57 mph 42.92 mph -0.35 mph (-0.81%)

Table 2: Overall Results for Rotational Mechanics Analysis

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0

TestSpeed(mph)

Calculated Speed (mph)

Calculated versus Expected (Equation 3)

R2

= 0.9925

-10%

+10%


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The following two examples demonstrate the application and analysis results for a

representative test from the Adamson, et al. (2002) and Craig (2009) test data.

Adamson, et al. (2002), Test #9

Adamson, et al. (2002) Test # 9 is a typical example of the application of rotationalmechanics for determining the impact speed of a motorcycle. Figure 4 is actually from the

resource, but the measurement of angular change for the vehicle and the perpendicular lever arm,

di, for the motorcycle were measured by this author from the scale diagram. This impact

involved a Kawasaki 1000 police model motorcycle colliding with the drivers side rear of a

1989 Ford Thunderbird. The Australasian & South Pacific Association of Collision Investigators

(ASPACI) provided the following photographs of this collision and shows the setup and

aftermath of the test.

Vehicle specifications taken from Expert Auto Stats, version 5.0.4, indicate the 1989 Ford

Thunderbird has the following dimensional properties:

Overall Length (L) = 16.58 feet Overall Width (b) = 6.08 feet

Loaded Mass (mloaded) = (3590 pounds)/g Curb Mass (mcurb) = (3559 pounds)/gKG= 13.8 KM= 0.769

From this data, and while using Table 1 values for a car, the yaw moment of inertia was

determined for the Ford using the Neptune methodology of Equation 2.

= 2510.2 ft*lbs*sec

2yaw moment of inertia


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Figure 4: Test #9 from Adamson, et al (2002)

(Red lines and text represent variables di= 7.05 feet and = 54.6o, measured by author)

Adamson, et al. (2002) reported that the friction of the test surface was measured by the

Texas Transportation Institute at =0.72. From analysis of Figure 4, as well as determining the

normalized rotational friction factor using Figure 3, the impact speed of the Kawasaki

motorcycle was determined using rotational mechanics through the application of Equation 3 as

follows:

= 56.6 fps = 38.6 mph

Where, Wmc= 620 pounds, weight of test Kawasaki 1000Wcar= 3590 pounds, weight of test Ford Thunderbird

Icar= 2510.2 ft*lbs*sec2, yaw moment of inertia of Ford Thunderbird

= 54.6o= 0.953 radians, rotation angle of Ford Thunderbird

di= 7.05 feet, perpendicular moment armWBcar= 9.42 feet, wheelbase of Ford Thunderbird

= 0.72, reported test surface frictionn = 0.42, normalized rotational factor from Figure 3


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The actual impact velocity of the Kawasaki motorcycle reported for this test was 39 mph. When

considering a 10% range about the answer, the model predicts the impact speed of the

Kawasaki to be 38.6 mph 3.86 mph.

Craig (2009) Test #6

Test 6 of this collection represents the highest velocity impact test into a target vehicle.

The analysis results for this test were also typical of the other tests within the Craig (2009) study.

Figure 5 is the plot of the data from the study, from which the analysis was completed. The study

reports the weight of the 1979 Dodge B100 van at 3630 pounds, and the 1981 Yamaha Virago

motorcycle at 510 pounds. The following photographs show the impact test setup and results as

obtained from the cited resource.

Vehicle specifications taken from Expert Auto Stats, version 5.0.4, indicate the 1979 Dodge

B100, long wheelbase passenger van has the following dimensional properties:

Overall Length (L) = 16.42 feet Overall Width (b) = 6.58 feetLoaded Mass (mloaded) = (3630 pounds)/g Curb Mass (mcurb) = (3630 pounds)/g

KG= 12.3 KM= 0.642

From this data, and while using Table 1 values for a van, the yaw moment of inertia was

determined for the Dodge using the Neptune methodology of Equation 2.

= 2869.6 ft*lbs*sec

2yaw moment of inertia

Craig (2009) reported that the friction of the test surface was measured by the test team

to be a value of =0.84. From analysis of Figure 5, as well as determining the normalized

rotational friction factor using Figure 3, the impact speed of the Yamaha motorcycle was

determined using rotational mechanics through the application of Equation 3 as follows:


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Figure 5: Test #6 from Craig (2009)

(Red lines and text represent variables di= 2.20 feet and = 18.4o, measured by author)

= 100.0 fps = 68.7 mph

Where, Wmc= 510 pounds, weight of test Yamaha Virago

Wcar= 3630 pounds, weight of test Dodge B100 VanIcar= 2869.6 ft*lbs*sec

2, yaw moment of inertia of Ford Thunderbird

= 18.4o= 0.321 radians, rotation angle of Ford Thunderbird

di= 2.20 feet, perpendicular moment armWBcar = 9.42 feet, wheelbase of Ford Thunderbird

= 0.84, reported test surface frictionn = 0.30, normalized rotational factor from Figure 3


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The actual impact velocity of the Yamaha motorcycle reported for this test was 67.5 mph.

Again, when considering a 10% range about the answer, the model predicts the impact speed of

the Yamaha to be 68.7 mph 6.87 mph.

Motorcycle Front Fork and Maximum Vehicle Deformation Analysis

Over the decades, researchers have attempted to correlate the impact speed of a

motorcycle with the amount of wheelbase reduction produced upon the motorcycle due to

rearward bending of the front forks from an impact. The first such study was conducted by

Severy, et al. (1970) when they attempted to correlate the damage to Honda CB350 motorcycles

with spoked wheels for impacts into rigid barriers and 1960s vintage automobiles. This resulted

in a fairly simplistic linear regression between limited data points for correlating wheelbase

reduction of the motorcycle with impact speed. Whereas this study may still have applicability to

barrier-type collision events, the Severy, et al. (1970) study, however, did not account for

damage to the struck vehicle. Adamson, et al. (2002) attempted to correlate wheelbase reduction

with impact speed using a linear regression analysis as well, and compared their results to thoseof Severy, et al. (1970). Adamson, et al. (2002) also did not use vehicle damage as a factor in

their regression model, but also attempted to correlate the fork deformation of their tests with

motorcycle impact velocity. Bartlett, et al. (2009) reported results of testing conducted during the

2004 CAARS conference and the 2008 ARC-CSI conference, as well as utilizing the data from

Adamson, et al. (2002) and Severy, et al. (1970) in presenting models that uniquely accounted

for not only wheelbase reduction of the motorcycle, but also maximum intrusion into the target

vehicle based upon whether the impact was into a hard zone (i.e., wheel or structural member),

or a soft zone (i.e., door panel, fender or quarter panel). Bartlett, et al. (2009) found no

correlation between the composition of the motorcycles front wheel and fork/vehicle

deformation relationships, in that the consideration of both wheelbase reduction and vehicle

damage applies to both spoke wheels and cast wheels on a motorcycle. It is these latter two

analysis methods that appear to have the greatest utility and will be the scope of investigation for

this presentation.

The following formula was developed from testing completed during the ARC-CSI 2008

Conference, which accounts for wheelbase reduction of the motorcycle, maximum damage depth

on the struck vehicle and whether the impact was into a hard zone (axle/pillar) or a soft zone

(door panel, fender or quarter panel):

Equation 6: ARC-CSI Fork/Vehicle Deformation Analysis

, Where, A= 1.4534 mph/in, for soft zone

1.5875 mph/in, for hard zone

B= 10.124 mph, for soft zone

14.720 mph, for hard zone


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WB= Change in motorcycle wheelbase, inchesCmax= Maximum penetration into vehicle, inches

The following formula was developed from testing completed during the CAARS 2004

Conference, which accounts for wheelbase reduction of the motorcycle, maximum damage depth

on the struck vehicle and whether the impact was into a hard zone (axle/pillar) or a soft zone(door panel, fender or quarter panel):

Equation 7: CAARS Fork/Vehicle Deformation Analysis

, Where, A= 2.0 mph/in, for soft zone


B= 1.8 mph/in, for soft zone


D= 2.0 mph, for soft zone4.5 mph, for hard zone

WB= Change in motorcycle wheelbase, inchesCmax= Maximum penetration into vehicle, inches

The following formula was reported by Severy and was developed from motorcycle

impact tests into a fixed barrier and 1960s vintage automobile, and attempts to correlate

motorcycle wheelbase reduction only with motorcycle impact speed:

Equation 8: Severy Fork-Only Deformation Analysis

,Where, A= 2.18 mph/in, for all conditions

B= 10.3 mph, for all conditions

WB= Change in motorcycle wheelbase, inches

Application to Independent Test Data

The application of the three fork deformation based models discussed will be applied to

the impact tests reported by both Adamson, et al. (2002) and Craig (2009). Additional tests are

available regarding the application of these models. From the Adamson, et al. (2002) study, tests

8, 9, 10, 11, 12, 13, 14, 16, 18 and 19 are motorcycle-to-vehicle tests that report both wheelbasereduction and maximum extent of damage on the struck vehicle. From the Craig (2009) study,

tests 3, 4, 5 and 6 contained motorcycle wheelbase reduction and maximum vehicle damage data.

Table 3 reports the results from application of the ARC-CSI equation, Equation 6.

The results for Equation 6 were analyzed using the -squared test of fit (=0.99) and the

paired t-test (=0.01), both to a 99% confidence interval. The calculated impact velocity for the


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motorcycle was determined to have no statistically significant difference between the measured

impact velocities and the calculated impact velocities by the chi squared test of fit (2= 3.81,

2critical= 4.11, for = 13), and with the same results for the paired t-test (t= 0.18, t-critical=

3.01, for = 13). The analysis of this data using Equation 6 indicates that determining the impactvelocity of a motorcycle for impacts producing both measurable wheelbase reduction to the

motorcycle and maximum deformation to the target vehicle should provide statistically reliableanalysis results. The error rate ranged between +16.86% to -15.21%, however, the vast majority

of the data remained within a 10% range. The chart that plots Calculated versus Expected

analysis values for Equation 6 also indicates the data has a reasonable correlation at R2= 0.9593.

The dashed lines on this chart represent a 10% variance, demonstrating that most data points

would fit within that spread.


Velocity

Reported Impact

Velocity

Absolute

Difference

Adamson #8 45.4 mph 46.0 mph -0.6 mph (-1.37 %)


Adamson #10 32.3 mph 34.0 mph -1.71 mph (-5.03 %)Adamson #11 29.2 mph 25.0 mph 4.21 mph (16.86 %)


Adamson #13 44.6 mph 42.0 mph 2.58 mph (6.14 %)





Craig #3 46.5 mph 46.0 mph 0.45 mph (0.98 %)

Craig #4 45.7 mph 46.0 mph -0.28 mph (-0.60 %)

Craig #5 47.6 mph 46.0 mph 1.55 mph (3.37 %)

Craig #6 69.5 mph 67.5 mph 2.00 mph (2.95 %)

Means 42.05 mph 41.89 mph 0.16 mph (0.38 %)

Table 3: Overall Results for Fork/Vehicle Deformation using ARC-CSI, Equation 6

To date, there is no public domain data regarding impact tests of motorcycles designedwith aluminum frames, or equipped with stiffer upside down forks found on many modern

sport motorcycles. Additionally, there is an absence of public domain testing of motor scooters

or other motorcycle surrogate vehicles. However, just as with the difference between a castwheel and a spoke wheel for a motorcycle is unlikely to have an effect on speed analysis using

this motorcycle fork/vehicle deformation model, this model is expected to account for the

difference in frame design and motorcycle components that stiffen the motorcycle during

dynamic loading in the same manner; i.e., the stiffer the motorcycle becomes, the greater themaximum penetration into the struck vehicle will become, thus balancing the energy dissipation

distribution of the impact.


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Table 4 reports the results from application of the CAARS equation, Equation 7. The

results for Equation 7 were also analyzed using the -squared test of fit and the paired t-test. Due

to the wider variance of data when using Equation 7, the results for the -squared test of fit didnot meet the demands of a 99% confidence interval, but were within a 65% confidence interval

(=0.65,2= 10.28,

2critical= 10.53 , for = 13), much too low for statistical significance.

Since the variations of data did not affect the overall mean comparisons, the t-test was still

satisfied at the 99% confidence interval (=0.01, t= 0.30, t-critical= 3.01, for = 13). Theanalysis of this data using Equation 7 indicates that determining the impact velocity of a

motorcycle for impacts producing both measurable wheelbase reduction to the motorcycle and

maximum deformation to the target vehicle is not as reliable as when using Equations 3 and 6.The error rate for Equation 7 was much more significant than the other two models considered,

and ranged between +22.28% to -35.75%, however, the vast majority of the data remained within

a 15% range. The chart that plots Calculated versus Expected analysis values for Equation 7

also demonstrates a wide spread in the analysis results, however, it still has a reasonablecorrelation coefficient of R2= 0.9603. The dashed lines on this chart represent a 10% variance,

demonstrating that many of the data points would fall outside this spread. It is the opinion of

these authors that the variance while using Equation 7 alone would be far outside a reliablerange, but if used in conjunction with Equations 3 and 6, and other analysis methods, may still

provide some utility.

0

10

20

30

40

50

60

70

80

0 10 20 30 40 50 60 70 80

TestSpeed(mph)



-10%

+10%

R2= 0.9593


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Velocity

Reported Impact

Velocity

Absolute

Difference




Adamson #11 25.2 mph 25.0 mph 0.20 mph (0.90 %)Adamson #12 19.3 mph 30.0 mph -10.73 mph (-35.75 %)






Craig #3 49.3 mph 46.0 mph 3.30 mph (7.17 %)

Craig #4 48.9 mph 46.0 mph 2.90 mph (13.04 %)

Craig #5 50.1 mph 46.0 mph 4.10 mph (6.30 %)

Craig #6 76.7 mph 67.5 mph 9.2 mph (13.56 %)

Means 42.34 mph 41.89 mph 0.45 mph (1.07 %)

Table 4: Overall Results for Fork/Vehicle Deformation using CAARS, Equation 7

0

10

20

30

40

50

60

70

80

0 10 20 30 40 50 60 70 80 90

Testspeed(mph)



-10%

+10%

R2

= 0.9603


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Table 5 reports the results from application of the Severy equation, Equation 8. The

results for Equation 8 were also analyzed using the -squared test of fit and the paired t-test.Equation 8 produced the least linear and the least representative data for motorcycle-to-vehicle

impacts of any of the models presented. The results for the -squared test of fit did not meet the

demands of any statistical confidence interval (=0.99,2= 4.11,

2critical= 68.43 , for = 13),

showing no statistically significant relationship between the test data the analysis results usingEquation 8 for motorcycle-to-vehicle impacts. The variations of data were random enough to

affect the overall mean comparisons, such that the t-test was not satisfied at the 99% confidence

interval (=0.01, t= 6.36, t-critical= 3.01, for = 13). The analysis of this data using Equation 8indicates that determining the impact velocity of a motorcycle for impacts producing both

measurable wheelbase reduction to the motorcycle and maximum deformation to the targetvehicle is not reliable when using Equation 8. The error rate for Equation 8 was significantly

greater than all other models considered, demonstrating a trend to under-predict the impact speed

of a motorcycle by as much as nearly 50% (-49.21%, Craig test 6), and an average error rate of-32%. The chart that plots Calculated versus Expected analysis values for Equation 8 also

demonstrates a random and wide under-prediction spread in the analysis results, resulting in a

correlation coefficient of only R2

= 0.6638. The dashed lines on this chart represent a 10%variance, demonstrating that nearly every data point produced while using Equation 8 for a

motorcycle-to-vehicle impact fell below the -10% error spread boundary. It is the opinion of

these authors that the variance while using Equation 8 is so significant as to render this analysis

method unreliable for motorcycle-to-vehicle impact events. However, the model does tend toprovide reasonable results for motorcycle impacts into fixed, immovable and/or massive objects.


Velocity

Reported Impact

Velocity

Absolute

Difference



Adamson #10 28.3 mph 34.0 mph -5.7 mph (-16.8 %)Adamson #11 22.6 mph 25.0 mph -2.4 mph (-9.7 %)







Craig #3 35.4 mph 46.0 mph -10.6 mph (-23.1 %)

Craig #4 40.8 mph 46.0 mph -5.2 mph (-11.3 %)

Craig #5 29.4 mph 46.0 mph -16.6 mph (-36.1 %)

Craig #6 34.3 mph 67.5 mph -33.2 mph (-49.2 %)

Means 28.50 mph 41.89 mph -13.39 mph (-32.0 %)

Table 5: Overall Results for Fork-Only Deformation using Severy, Equation 8


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In order to demonstrate the convergence between rotational (Equation 3) and fork/vehicle

deformation analysis results (Equation 6), Test #9 from the Adamson, et al. (2002) and Test #6

from Craig (2009) will again be used as application examples. Since Equation 6 shows the best

relationship and statistically significant results between the data and the analysis results, only

Equation 6 will be used for the fork/vehicle deformation analysis of these examples.

Adamson, et al. (2002), Test #9

Adamson, et al. (2002) Test # 9 involved a Kawasaki 1000 motorcycle colliding into the

left rear quarter panel of a 1989 Ford Thunderbird within the area between the left rear wheel

and the rear bumper. This area constitutes a soft zone impact location. The following results

were obtained when analyzing this impact test with Equation 6.

= 53.5 fps = 36.5 mphWhere, A= 1.4534 mph/in, for soft zone

B= 10.124 mph, for soft zoneWB= 7.63 inches, measured change in motorcycle wheelbaseCmax= 10.5 inches, measured maximum penetration into vehicle

The motorcycle velocity reported for this test was 39 mph. While using the 10% application to

this data, Equation 6 produces a motorcycle impact speed range of 32.9 mph to 40.2 mph,

between which the actual test speed of 39 mph fits between.

0

5

10

15

20

25

30

35

40

45

0 10 20 30 40 50 60 70 80

TestSpeed(mph)



R2

= 0.6638

-10%

+10%


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Craig (2009) Test #6

Test 6 of this collection represents the highest velocity impact test into a target vehicle.

The study consisted of a 1981 Yamaha Virago motorcycle traveling at 67.5 mph when colliding

into the B-pillar on the right side of a 1979 Dodge B100 van. This impact represents a hard

zone impact location. The following results were obtained when analyzing this impact test withEquation 6.

= 101.9 fps =69.5 mphWhere, A= 1.5875 mph/in, for hard zone

B= 14.720 mph, for hard zone

WB= 11.0 inches, measured change in motorcycle wheelbase

Cmax= 23.5 inches, measured maximum penetration, vehicle centerline

The motorcycle velocity reported for this test was 67.5 mph. While using the 5% application

to this data, Equation 6 produces a motorcycle impact speed range of 66.0 mph to 73.0 mph,between which the actual test speed of 67.5 mph fits between.

Conclusions

Three separate analysis models were presented. The first model relied upon rigid body

mechanics and rotational kinetics in order to determine the impact speed of a motorcycle with a

motor vehicle when rotation of the target vehicle is produced. The second and third models were

based upon linear regression (best fit lines) analysis of impact data for motorcycles striking

motor vehicles and producing measurable motorcycle fork deformation and maximum vehicle

inward deformation. These models were tested against independently reported test data, so thatthe accuracy and applicability of the models cold be evaluated.

The results of this study indicate that analyzing motorcycle-to-vehicle impacts using

rotational mechanics when the necessary data is available, provides the most accurate and

reliable impact speed determination for motorcycles colliding offset from the center-of-mass of a

target vehicle such that rotation to the target vehicle is produced. The data analyzed was not just

limited to side impacts of motorcycles into a target vehicle, but also contained a motorcycle

striking head-on (Adamson #18), as well as into the rear of a stationary vehicle (Adamson #10),

both of which showed good correlation between the test impact speed and the calculated impact

speed using Equation 3. One observation from the data was for angles of rotation below 3degrees, the analysis became very sensitive to the accuracy of the measurement of the

perpendicular moment arm. While precision and accuracy was achieved when analyzing rotation

below 3 degrees for this data set, it should also be recognized that the data available from these

studies was sufficiently documented as to allow for an accurate determination of the rotation of

the target vehicle and the perpendicular moment arm to within two significant digits, which may

not always be obtainable for rear-world collisions. Caution should be exercised when analyzing


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real-world collisions where rotation of the target vehicle is less than 3 degrees, and it is

recommended that such an analysis be accompanied in conjunction with other speed

determinations, such as using linear momentum, fork/vehicle deformation or some other

applicable methodology. The results of this study indicate that with the consideration of the

proper data, a motorcycle-to-vehicle impact that conforms to the conditions of Equation 3 is

expected to result in motorcycle impact speed determinations that are statistically significant to

within a 99% confidence interval.

The results of this study determine that the analysis of motorcycle impact speed while

using Equation 6, where both motorcycle fork and maximum vehicle deformation are considered,

produces accurate, reliable and statistically significant results to within a 99% confidence

interval. When the fork/vehicle deformation model of Equations 7 is considered alone, it is not

reliable enough for an accurate determination of motorcycle impact speed by itself, but should be

used in conjunction with other more reliable methods. Equation 8 tends to significantly, as well

as randomly, under-predict motorcycle impact speed. This is likely due to the fact that it does not

consider the energy losses due to vehicle deformation, which become more significant as the

front forks of a motorcycle are compressed further rearward and into the engine block and/or

frame, changing the relative stiffness of the motorcycle and thus producing greater deformation

into the vehicle.

When rotational analysis of Equation 3, and fork/vehicle deformation analysis using

Equation 6 and 7 are completed concurrently, the forensic engineer is assured of not only

accuracy, but has a means by which cross-check of the results of a forensic motorcycle impact

speed analysis is accomplished. The authors have utilized these techniques in actual forensic

cases that were subject to cross-examination. The ability to demonstrate the correlation between

the test data and the models, along with the crosscheck that is provided by using two or more of

the presented methods is a critical part in justifying the applicability, reliability, and accuracy of

these analysis techniques when applied to real-world motorcycle collisions.

To date, there is no public domain data regarding impact tests of motorcycles designed

with aluminum frames, or equipped with stiffer upside down forks found on many modern

sport motorcycles. Additionally, there is an absence of public domain testing of motor scooters

or other motorcycle surrogates into other motor vehicles. Impacts with motorcycles so equipped

would have no influence upon the rotational analysis method presented. However, analysis of

motorcycle impact speed while using Equations 6 and 7, where both motorcycle fork and vehicle

deformation are considered together, should account for the effects of a stiffer motorcycle

structure by increasing the maximum penetration into the struck vehicle, thus balancing the

energy dissipation distribution of the impact.

Future work should investigate the appropriate parameters for uniform projectile motion

and/or other approaches for considering the flight of ejected motorcycle riders and passengers

that commonly result from motorcycle impact events. Considerations for determining the


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appropriate ejection angles, fall heights and ejection distance for use when compared to impact

testing should be undertaken. Since it has been observed by these authors that many analysts

attempt to apply empirical pedestrian vault equations to motorcycle collision events, it should

also be investigated to determine if a relationship between pedestrian projection and cycle rider

ejection actually does exist, and if not, why they differ. Additionally, the relationships between

vehicle force-deflection and energy dissipation properties (often referred to as A and B

stiffness values), along with the work-energy principles of bending the front forks of a

motorcycle should also be investigated to determine if correlation with motorcycle impact test

data exists. It is anticipated that the results of these additional investigations will provide not

only a more accurate determination of motorcycle impact speeds resulting from real-world

collisions, but also provide greater understanding of motorcycle and other two-wheeled cycle

collision events.

References

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Exposition (WREX 2000), College Station, Texas, September 2000.

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Crash Investigation and Reconstruction, Santa Rosa, California, 2004.

Bartlett, Wade. Motorcycle Crush Analysis. Accident Reconstruction Journal Volume 19, Number 2,March/April 2009, 2009 Accident Reconstruction Journal.

Craig, Victor.Motorcycle High-Speed Crash Tests. Accident Reconstruction Journal Volume 20, Number

1, January/February 2010, 2009.

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Institute of Police Technology and Management, 2006.

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Crash Reconstruction.Institute of Police Technology and Management, 2007.

Neptune, James. Overview of an HVE Vehicle Database.SAE Technical Paper Series, no. 960896,

1996.

Obenski, Kenneth, and Paul F. Hill,Motorcycle Accident Reconstruction and Litigation.2nded. Lawyers

& Judges Publishing Company, Inc, 1997.


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Ogden, Jerry. Forensic Engineering Principles of Motorcycle Accident Analysis and Motorcycle Impact

Speed Analysis Mathematics Appendix and Applied Problems.National Academy of Forensic Engineers

Education Committee Special Seminar, July 2010.

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1970 SAE International.

analysis of motorcycle impacts

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