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# Reconciliation of ATV/UTV Handling Characteristics and the Operator

Author, co

- author ( Do NOT e nter this i nformation . It will be pulled from p articipant t ab in MyTechZone ) Affiliation ( Do NOT e nter this i nformation . It will be p ulled from p articipant t ab in MyTechZone )

Copyright © 201 4 SAE International



## A bstract

This paper examines the directional handling characteristics of several vehicles in their original condition, then examines modifications to a few of these vehicles to determine if the handling characteristics can be made more forgiving of normal operators without sacrificing utility and without substantial increases in cost. These analyses of vehicles are made in the context of what normal operators are capable of performing with regards to steering response.



## I ntroduction

Humans have a limited ability to control any machine. The operator perceives what is wanted and applies a control input to have the machine perform the desired operation. I n the case of vehicles that is a steering, throttle, or brake input. In this paper the concentration is on the ste ering input with the desired path of the vehicle as the machine output. Control of a vehicle begins with a decision regarding what direction the ope rator desires the machine to go. A steering input is applied, the vehicle responds, the operator observes the response and adjusts the inputs for any error that occurred between the steering input and the desired vehicle response. Through the last century, vehicle dynamic control has been the subject of serious study and applied to all vehicles on land,
sea, and air. The principles of dynamic stability apply in all three of the realms and are all limited by what a person can do with regards to perception, reaction, and response. Maintenance of dynamic control of a vehicle is paramount in the safe operation o f the vehicle. This paper reports on an examination of human control characterist ics and applies these to all

- terrain vehicle ( ATV ) and utility

- terrain vehicle ( UTV ) control.

In this pap er the handling characteristics necessary for human control of va rious ATVs and UTVs are presented. Most of these vehicles had handling characterist ics that traditionally have been found to not be conducive to vehicle control or safety . Several vehicles were modified to alter the oversteer/understeer characteristics to be consistent with accepted control parameters of automobiles . This was done to both determine if that can be done economically and without negatively affecting utilitarian functions and improve safety performance

. This paper reports t he modified vehicl es ’ measured handling characteristics and the rider heuristic evaluation of handling

. This is then compared to the traditional vehicle handling design to determine if there is a potential for improved safety through vehicle design.

First a short discussio n of the possible connection between control and crash frequency will be given. This will be followed by a description of how humans control vehicles and the vehicle characteristics that are most important for human control. Then the results of testing various vehicles from EI Consultants independent tests will be presented. The modified vehicles will be described and their handling characteristics will be given. Conclusions concerning the possible effects of traditional understeering on drivability and safety are presented.



## Crashe s and Control

ATV fatalities have been a major concern in the USA for many years, with the CPSC reporting 11,688 fatalities in the three decades 1982 to 2011 [ 1] . Of these approximately 25% were younger than 16 years of age. Similarly in Australia, ATV fatalities are a major issue, particularly on farms, with 124 fatalities in the period 2001 and 2010 [ 2 ]. Improvements in Quad Bike and SSV handling has been h ighlighted by authors such as Roberts [ 3 ] and others as being practical means to reduce crash and rollover risk. (Note: Australian for ATV is quad bikes and UTV is side by side )

In the CPSC study of 1989 they found that the ca use of 80% of ATV crashe s was affected by lack of “rider judgment” [ 4 ].Page 2 of 10 Fi gure 1. Percent of crashes and potential fixes based on Scheers, et al (1990).

From an engineering standpoint, it seems that r ather than rely ing solely on “improved judgment” by ATV operators to reduce ATV crashes , ways to improve vehicle safety through design should be examined. Certainly part of the fix to overturn crashes could be attributed to the rider’s judgment, but vehicle design also affects the ability of the rider to maintain vehicle control an d possibly prevent crahes . Since 1990

, efforts have been made to assist riders to improve their judgment through training and education. Frustration after attempting to improve judgment by training and education alone was expressed in a recent meeting i n Australia 1 . In the FAQs associated with a discussion paper released by Australia's Federal Minister for Employment and Workplace Relations in August 2012, the following statement was made:

" For over 20 years the focus on quad bike safety in Australia h as been on other approaches like training and education, awareness raising and helmet use to address the high number of fatalities and serious injuries sustained by quad bike riders. The time has come to focus on design and engineering controls for improv ing quad bike safety. ” Looking at handling characteristics of the existing ATVs and UTVs in light of operator handling capabilities could be a way of approaching the problem from another direction.

Controllability of the vehicle

, in conjunction with ridin g ability

, is linked to vehicle design characteristics that will assist in allowing the vehicle to be controlled by inexperienced riders or riders who are not intent on the act of riding . F armers and ranchers, and those who are confronted with emergency

s ituations and must react quickly and properly to avoid a crash are the individuals being considered . The first portion of this paper is about determining what vehicle characteristics contribute to human control of vehicles and how can these characteristic s be quantified by testing. Understanding these dynamic properties of a vehicle for predictable human control will allow the selection of a set of tests to measure the vehicles for human control compatibility. Due to space restrictions, only

1 http://www.safeworkaustralia.gov.au/sites/swa/whs

information/agriculture/quad

- watch/pages/quad

- bike

- safety

- forum one of these characteristics will be discussed here. The others will follow in future publications.



### Characteristics Affecting Human Control of **Vehicles**

Analysis of the control of any system by a human requires two things. Knowledge of the human ability to perceive, process, and react to events encountered by the vehicle as it follow s the intended path is one. T he system dynamic characteristics to receive a control input and respond in a stable manner and provide feedback to the human controller is the other. A bloc k diagram describing such an operator/vehicle sys tem is shown below [ 5 ].

Figure 2. Block Diagram of Driver/Vehicle System for Lateral Steering Control and Regulation [ 5 ]

The McRuer study was to determine “how the response of a vehicle to a driver’s steering input affects the driver’s ability to maintain precise control over vehicle path.” He went on to state in his opening paragraph of his report, “With this knowledge we can identi fy those vehicle steering response characteristics which may lead to imprecise vehicle path control and which may, in turn, lead to accidents.” Can the ATV/UTV be studied to yield similar results of vehicle characteristics? Would the handling characteris tics of automobiles, which must respond to inputs and give feedback to the same humans that operate ATVs/UTVs, be relevant to the study of ATVs/UTVs? Use of research regarding dissimilar vehicles as a starting point for improving and understanding vehicle control is not a new or novel endeavor. A 1956 study drew on the work concerning the stability of aircraft and ships to understand and improve the handli ng of road vehicles [ 6 ]. Milliken and Ollie also relied on aircraft stability studies to improve the handling and longitudinal stability of the modern automobile [ 7 ]. Similarly, the results of automobile/operator interface have been used in the study of the handling of ATVs [ 8 ]. Indeed, in the SAE Technical Paper "An Introduction to the Operational Cha racter istics of All

- Terrain Vehicles" [ 9 ] the authors argue: "...handling qualities include, in general, controllability which in turn involves ease of control, the ability to follow a desired path or make the desired maneuver, and the ability to suppress disturbance inputs, whether they arise from the environment or from within the system itself."

Control of any machine by a human requires that it resp onds quickly to a control input. T he human controller then perceives the effect of the control input thro ug h visual or tactile perceptions. He or she then analyzes the response, and determines any error wit h respect to the desired effect. T hen he/she adjusts the control input to correct for any error in the response. Control implies that the machine must r espond thePage 3 of 10 same way to a given control input, respond in a timely manner, and not change the response over time with constant control inputs . For dynamic systems such as vehicles

, the response time must be short enough to allow the controller to adjust th e control inputs to safely manage a high speed vehicle along a desired path. When the vehicle or machine ceases to respond or is random in its response then that vehicle is “out of control.”

There are mai n control characteristics that determine if a vehic le is controllable by a human operator . T he se are understeer/oversteer [ 6 ], the stee ring response time [ 5 ], and steering gain [ 5 ]. For off

- road vehicles, the vertical and yaw response to striking a series of bumps at the suspension harmonic frequency is also an element of concern [ 10 ]. For the scope of this paper only understeer/oversteer will be addressed. Pitch and bounce response, step steer response and steering gain will be addressed in later paper s

.



### Understeer and Oversteer

The first order of business is to differentiate between the

common usages of the terms understeer and oversteer which are results of specific driver inputs and the engineering use of the terms that describes a characteristic of the vehicle. A man

off

- the

- street

, discussing oversteer

, understands that word to be how he can cause oversteer . He causes oversteer by pulling on the parking brake or applying throttle to cause the rear of the vehicle to break away and swing out in a turn. These are maneuver s use d in racing and recreational riding

. The vehicles being driven in oversteer actually have an inherent understeering design characteristic. This driver induced “oversteer” is not what is being discussed here. Understeer is a measure of a handling charact eristic of the vehicle independent of the driver. It is measured using a circle test as described in SAE J266 (ISO 4138:2012 ) [ 11 ]. When the numerical value of the measured understeer of the vehicle is negative, it is then an oversteer vehicle, meaning t hat the yaw rate responses are diverging from the steering angle magnitude. This is a classic instability. To measure this characteristic a vehicle is driven in a circle laid out on a flat surface of consistent coefficient of friction . W hi le gradually i ncreasing speed , the steering angle and lateral acceler ation are measured. The plot in Figure 3 below shows the steering angle versus the lateral acceleration for a typical

, well behaving

, understeer vehicle. Figure 3. Understeer characteristic for a s table handling vehicle.

The vehicle described in this graph will require a continually increasing steering angle as the lateral acceleration increases. The yaw rate response is proportional and gradually decreasing as the steering increases. Understeer is quantified by the slope of the graph between 0.1 and about 0.4 g’s. For the vehicle illustrated in F igure 3

, that slope would be about 2 degrees per g. This vehicle would respond to a lateral force from a gust of wind or a change in road camber by dri fting away from the applied force . This would establish a new stable path without any effort by the driver. However if that slope of the above graph is negative, the vehicle is called an oversteer vehicle. If a road camber angle change occurred, the veh icle would tend to move toward the applied force or uphill to the slope of the road. T hat would then decrease the turning radius of the vehicle. That decrease in turning radius would in turn cause an increase in the lateral force on the vehicle. I t woul d respond by turning in an even smaller turni ng radius. This cycle would continue increasing the lateral forces which decrease the turning radius in an unstable manner. In an Advance Notice of Proposed Rulemaking (ANPR) for recreational off

- highway vehic les, the CPSC states

,
"If a vehicle oversteers in a turn, ..., the rear wheels lose traction and the steering wheel needs to be turned less to stay on the turn. This condition is directionally unstable because it can result in spin out or rollover of the vehicle. Controlling oversteer requires driver skill and knowledge in using acceleration and steering that is beyond the average driver" [ 12 ]

Conducting the same SAE J266 circle test and graphing the results as was discussed by the CPSC in 2009 [ 12 ] a nd b y Heydinger et.al [1 3 ] for a typical UTV or ATV will often yield a graph as shown in Figure 4 below.Page 4 of 10 Figure 4. Understeer characteristic for typical UTV

By contrast to the first vehicle’s understeer graph in F igure 3, this vehicle demonstrates too much u ndersteer at low lateral accelerations . This can be as much as 9 degrees per g

. R easonable handling vehicles have an understeer gradient between 2 and 6 degrees per g. At a lateral acceleration of 0.2 g, the vehicle transitions to oversteer

. At this po int what was once a severe understeering vehicle becomes a sever ely oversteering vehicle. The slope shown above is about

- 8 degrees per g. Due to the steep understeer gradient at the very low lateral accelerations the vehicle instability will be masked w hile driving straight at low lateral accelerations. However, any steer maneuver that would cause the vehicle to exceed a lateral acceleration of 0.2 g will move the vehicle response into the oversteer realm causing the rider to exert a significant effort to maintain control. These are all results consistent with what was found by Allen, et al [ 8

, 9

, 1 4 ], “Four wheeled ATVs with mechanical suspensions tend to oversteer under hard cornering conditions due to rear axle side force saturation... ” In addition, Heydinger et al. [1 3 ] concluded,

“ Several of the vehicles tested exhibit understeer at low levels of lateral acceleration and then transition to oversteer at higher levels of lateral acceleration.”

A recent paper suggested that an oversteering ve hicle for off

road or UTV handling characteristic was preferable to a slightly

u ndersteering vehicle [1 5 ]. The data from their testing actually suggests that a heavy understeering vehicle of 9 degrees per g is undesirable. That is understandable since 9 degrees per g is far higher than anything that has been found to be controllable or desirable. That vehicle was sluggish and difficult to control . The most desirable vehicle in the study was a stock Polaris RZR that illustrated a good understeer characte ristic and was preferred over the other vehicle configurations in the study. These results support what has been found in this study.



### Dynamic Testing for Understeer and Oversteer

Dynamic testing and analysis of various ATVs and UTVs has demonstrated that several stock, unmodified vehicles exhibit terminal oversteer often preceded by understeer at low lateral acceleration levels. It was found that the oversteer vehicle was difficult for riders to control . T he fact that the vehicle exhibits both understeer and oversteer depending on the lateral demands placed on the vehicle increases the unpredictable handling characteristics of these vehicles and the demand on the rider

.



### ATVs

ATVs are rider active vehicles . This means that the rider is free to move arou nd on the seat and can affect the handling of the vehicle by shifting his or her position. During the ATV testing, the rider remained as still as possible in a neutral seating position.

The testing summarized in this paper involved stock ATVs, modified AT Vs for which suspension layouts and components were changed, and tuned ATVs where existing geometries were used and the shocks and springs were tuned. General characteristics of the vehicles are shown below.

Table 1 . Summary of ATVs tested by EI Consultants

ATV A and ATV B are typical small ATVs with a solid axle rear suspension. The solid axle design creates a near infinite rear roll stiffness with the only rear compliance being flex in the mountings/bushings and from deflect ion of the tires. This massive roll stiffness differential between the rear and the front of the vehicle results in an oversteer vehicle

.
Testing of the vehicles both subjectively and quantitatively confirmed this prediction. The driver felt an initial p ushing from an understeer tendency at very low speeds then was forced to apply constant steering corrections by taking out steering as the test speed increased. This is mirrored in the test data. As seen with ATV A (Figure 5) , the initial positive slope of the data indicating understeer is seen at very low lateral accelerations. Before even 0.1 g is developed, the vehicle is a neutral steer vehicle with a transition to oversteer just beyond 0.1 g. The scatter of the data seen above 0.2 g is indicative o f the driver having to input and remove steering to keep the vehicle on course as the rear of the vehicle is losing lateral traction.

Vehicle Designation Stock/Modified /Tuned Year
Model Engine
Size Unladen Weight (lbs) Front
Track
Width (in) Rear
Track
Width (in) Wheelbase (in) Rear Suspension

ATV A Stock 2001 250 462 30.75 30.75 44 Solid Axle

ATV B Stock 2006 250 421 31.625 31.875 44 Solid Axle
ATV C Modified 2006 250 468 31.625 35.125 44 IRS with Spool

ATV D Modified 2006 250 468 31.625 35.125 44 IRS with Differential

ATV E Tuned 2012 700 745 35.625 36 53.625 IRS with Spool

ATV F Tuned 2012 800 854 36.25 38.75 57.625 IRS with SpoolPage 5 of 10 Figure 5. ATV A understeer/oversteer p lot

ATV B showed similar characteristics (Figure 6) . A difference between ATV A and ATV B is that there is more scatter in the ATV B data. This indicates a more unpredictable vehicle requiring more rider corrections to stay on course. The general trend for both vehicles is predictably similar.

Figure 6. AT V B u ndersteer/ o ver steer p lot

ATV C (Figure 7) and ATV D (Figure 8) were modifications of ATV B. A matching chassis (same year, make, and model) was modified with an independent dual control arm rear suspension with a wider track

. ATV C had a spool rear axle with an anti

- sway bar, whereas, ATV D had a differential and no sway bar.

The figure below shows the testing with ATV C with spool drive. Driver confidence was improved, and there was a decrease in the data scatter. Transition to oversteer occurred at a higher lateral acceleration than the stock vehicle

. Figure 7: Understeer/oversteer plot f or ATV C

The addition of an open differential allows the roll stiffness distribution to be tune d without the need of a rear sway bar to unweight the inside ti re. The open differential installed on the ATV gave much greater freedom when setting the roll stiffness distribution between the front and rear of the vehicle.

The driver’s confidence was much improved, and the vehicle response was much more predictabl e. The data shows a defined lack of scatter throughout the test. In addition the data shows that the vehicle is neutral to slightly understeer up to the limits of the test.

Figure 8 : Understeer/Oversteer p lot for ATV D

ATV B and ATV D were also compared in an off

- road environment. A small, oval course with a gravel surface was used for this comparison. This course consisted of two short straights and two sweeping curves of near constant radius connecting the straights. The course was driven counterclockwise meaning the rider was inputting turns that would cause the vehicle to enter and hold left

- hand turns. The track is shown below.Page 6 of 10 Figure 9. Gravel test course.

The handling differences between ATV B and ATV D were drastic on this course. The driver was much more confident with ATV D. ATV B was very unpredictable and constant sawing of the handlebars was required by the driver. Corrective steers required were so extreme that the rider was often inpu tting right steers to stay on the left curve.

The following figures demonstrate the improved handling from the modifications. The colored boxes in the figures correspond to the colored boxes in Figure 9 . These boxes show what part of the course the ATV is traversing on the data plot. Note that turning the handlebars to the left is indicated by a negative wheel angle and turning right is a positive angle. I t is shown from the first figure that the rider was alternately steering right (positive) and left (negative) to stay on the left curve. F igure 11 shows that the steering required to stay on course is less erratic and did not require the corrections necessary with the stock vehicle . Considering that the speeds are the same for both tests, it is clea rly demonstrated that improved on

- road handling stability translates to an off

- road environment.

Figure 10: Plot of ATV B steering on gravel c ourse Figure 11: Plot of ATV D s teering on g ravel c ourse

ATVs E and F have the original stock suspension geometry only the shocks and springs were replaced . Spring stiffnesses and damping rates were selected with the aid of computer modeling and tuning for flat ride over cyclical rolling bumps commonly known as “whoop

- di

- doos”.

I n addition to tuning the springs and shocks, the tires were also modified. The force versus deflection properties of the tires were measured at various pressures. Based upon this research, it was found that 10 psi was the optimum pressure for the tires t o transmit terrain forces to the suspension

. This will be discussed in a subsequent paper about the terrain effects.

A constraint was placed on the tuning by the fact that the spool drive was retained. As mentioned above, this made it difficult to obta in the desired front and rear roll couple and overcome the effects of the solid axle on understeer . Still, the final tuning of the vehicles resulted in predictable handling as felt in the constant radius testing. The constant radius tuning was also evalu ated in an off

- road environment to ensure that the understeer did not compromise the off

- highway mobility. The representative plot below shows the understeer/oversteer plot for the tuned ATV F. Notice from the plot that the vehicle is basically neutral s teer with a slight turn to understeer at higher lateral accelerations.

Figure 12: ATV F understeer/oversteer p lotPage 7 of 10 The testing of these ATVs demonstrated that tuning of the suspensions and components can result in predictable handling during testing on pavement. This improved handling on pavement was also reflect ed in the off

- road environment, both on the gravel test track

, where quantitative measurements demonstrated the improvement

, and through subjective evaluations at the EI Consultants test track.

The suspension tuning not only improved the handling during the on

- road testing, but also improved the handling in an off

road environment. Travel and clearance was not reduced, so no off

- road mobility was lost due to these adjustments . In addition, it is feasible to offer limited slip and lockable rear differentials yet provide improved under steer performance that increases rider confidence and reduces rider work load

.



### UTVs

UTVs are distinguished from ATVs in that the operator is seated on a more conventional bench or bucket seat and they are typically equipped with seatbelts and a roll cage . The driver operates the vehicle via a steering wheel and foot pedals. In addition, UTVs are not rider active as are ATVs. However, the suspens ion, tires, a nd drivetrain of UTVs are virtually identical to ATVs

. As such, UTVs demonstrate similar handling behavior to an ATV.

For the purposes of this paper, research and analysis of six UTVs are presented. Certain characteristics of the vehicles used in this st udy are summarized in Table 2 which is seen below.

Table 2 : Summary of UTVs t ested By EI Consultants

All UTVs tested had dual control arm independent suspension systems on the front and rear. All modified UTVs had suspension modi fications as well as spring and shock absorber tuning.

UTV A, a stock UTV, showed both understeer at low lateral accelerations and a transition to pronounced oversteer at higher ones. This placed a large burden on the driver to keep the vehicle under cont rol. The test driver lost control in a slalom maneuver due to not catching the oversteer response

. This total loss of control resulted in a tip onto the outriggers.

The understeer and oversteer are clearly seen in the data plot for the constant radius circle testing (Figure 13) . In addition, scatter is also seen as the driver is constantly correcting the steering so the vehicle remains on

- path. Figure 13. Understeer/oversteer p lot for UTV A

UTV B was also tested in stock configuration. This vehic le also exhibi ted a transition to oversteer . Test termination was often a tip

- up event. The vehicle starts understeer, quickly transitions to neutral steer, then becomes oversteer around 0.25 g. The oversteer range is also characterized by erratic steer ing inputs in order to keep the vehicle on course as evident by data scatter as seen in Figure 14

.

Figure 14. Understeer/o versteer for UTV B

UTV C and UTV D were direct modifications of UTV A and UTV B respectively. Modifications included suspension tu ning and increased track width . UTV C and D w ere modified to achieve a static stability factor of 1.0 with vehicle plus driver. The modification to meet these goals was a track width increase achieved by fabricating longer suspension arm s for UTV C and a dding wheel spacers f or UTV D

. In addition, UTV D was fitted with a rear differential.

UTV C’s suspension tuning consisted of replacing the OEM shocks and springs. Adjustable dampers were installed to tune the damping characteristics. Spring stiffness were altered based on mathematical calculations concerning ride rates and pitch characteristics discussed in reference [ 10 ] . In addition, new sway bar mounts and mounting points were fabricated allowing tuning of the roll stiffness on the front and rear suspension

. Vehicle Designation Stock/Modified /Tuned Year
Model Engine
Size Unladen Weight (lbs) Front
Track
Width (in) Rear
Track
Width (in) Wheelbase (in) Rear Suspension
UTV A Stock 2011 700 1320 44.25 46.625 74.75 IRS with Spool

UTV B Stock 2007 450 1107 43.5 42.5 75 IRS with Spool
UTV C Modified 2011 700 1321 51 55 75 IRS with Spool

UTV D Modified 2007 450 1113 51.5 50.5 75 IRS with Differential

UTV E Modified 2011 400 1178 52.5 49.25 74.75 IRS with Spool

UTV F Modified 2011 800 1232 51.125 46.625 74.75 IRS with Limited SlipPage 8 of 10 The dynamic handling characteristics of the modified vehicles were predictable and the driver demands were greatly reduced. The trend seen is increasing understeer up to test termination with very little scatter as evident in Figure 15 and 16

.

Figure 15. Understeer/o versteer p lot for UTV C

Figure 16. Understeer/oversteer p lot for UTV D

The modifications to UTV E and F were based on static analysis and computer modeling. The shock and spring specifications were based on mathematical and computer analysis again discussed in reference [ 10 ] . Slight tuning of the roll stiffness at the test track was achieved via adjustable rate sway bars.

Track width was increased on both vehicles by fabricating longer control arms. The track width values were based on static analysis and the design goal that the static stability coefficient, Kst

, value be 1.0 or greater with a driver.

Note the lack of scatter in both plots below (Figures 17 and 18) . Understeer is seen through out each test. Also note that the limited slip differential on UTV F allowed slightly more limit understeer to be tuned into the vehicle. Figure 17. UTV E understeer/oversteer p lot

Figure 18. UTV F understeer/oversteer p lot

As with the ATVs, the UTV testing demonstrated an inherent directional instability in the stock vehicles. The modified vehicles demonstrated more controllability as reported by the driver and less steering demand as seen in the data

.


## S ummary / Conclusion s

Human control of a vehicle requires that after a disturbance or control input, it establish a new stable trim. The handling characteristic that is easily measured and translates across to off road vehicles is the understeer gradient. Tests reported here illustrated that the predominate characteristic of ATVs and UTVs is a high understeer gradient at low lateral accelerations that transitions to oversteer at relatively low lateral accelerations.

It was shown that when the vehicles were adjusted to have

no minal amounts of understeer throughout the driving range the driver demand is reduced and steering variations required to maintain a circular path at el evated lateral accelerations

were reduced

. This was illustrated by the driver reports during the tests and the lack of scatter seen in the data as higher lateral accelerations were reached.

As can be seen from this paper, design constraints from drive trains and suspension s affect the ability to tune the suspensionPage 9 of 10 for an ideal configuration. However, as the oversteer/understeer curv e approached the form shown in F igure 3, controllability increased and driver demand decreased

.

It is underst oo d that the particular demands for control of off

road vehicles is more challenging than on

- roa d vehicles. Friction c oefficients are changing, the wheels of the vehicle are often not on the ground

, and the terrain is undulating and rough . However, these vehicles are often driven at high speeds on flat and sometimes paved surfaces. Providing designs that can manage in “ All” terrains is truly a challenging goal. This research has indicated that directional control instabilities do exist with many ATV and UTV designs. By adjusting these designs to follow well established principles of longitudinal stability

, the driver d emand is reduced and increase d rider confidence is gained while maneuvering the vehicle.

Improvements in Quad Bike and SSV handling has been previously highlighted by one of the authors and others [ 3 ] as being a practical means to reduce crash and rollover risk. The methodology presented in this paper has now been used by an Australian/US research team (that includes four of the authors) at Australia’s New South Wales government Crashlab facility to

assess the handling characteristics of eight typic al ATVs and five UTV designs used in the workplace, and three sports/ recreational type ATVs , as part of a safety rating program outlined in reference [1 6 ]. The results of these tests will be presented in a later paper.

This work should be the beginning of marrying on

- road and off

road design principles to improve the rider’s experience. As McRuer said about automobiles, “With this knowledge we can identify those vehicle steering response characteristics which may lead to imprecise vehicle path control and which may, in turn, lead to accidents. [ 5 ] ” The research presented here illustrates that l earning from the past vehicle design and development may assist ATV and UTV designers in “... focus [ing] on design and engineering controls for improving quad bike saf ety.”



## References

1. Garland, S., 2011 Annual Report of ATV

- Related Deaths and Injuries. CPSC, 2013. 2. Lower T, Pollock K & Herde E (2013). Australian Quad Bike Fatalities: What is the Economic Cost?. Aust N Z J Public Health. 2013 April; 37(2):173

- 8 3. Roberts A, “Dynamic Analysis of Side

- by

- Side Utility and Recreational Vehicles”, Paper No.09

- 0260

- O, 21st International Safety Conference on the Enhanced Safety of Vehicles, 2009 4. Scheers, N.J., Fulcher, D., and Polen, C., Four

- Wheel ATVs and Lateral Stability, Emergency Room Treated Injuries (1989) , U.S. Consumer Product Safety Commission, 1990. 5. McRuer, D. , Klein, R., “Automobile Controllability

– Driver/Vehicle Response for Steering Control,” DOT

- HS

801

- 407, Volume 1, 1975. 6. Segel, Leonard, “Research In the Fundamentals of Automobile Control and Stability,” Transactions of the SAE, 1956

. 7. Milliken, Milliken, Notes of Vehicle Dynamics

– Maurice Olley , SAE publications, 2004. 8. Allen, R., Szostak, H., Rosenthal, T ., Klyde, D. “ Steady State and Dynamic Properties of All Terrain Vehicles Related to Lateral Directional Handling and Stability ”, SAE 891105, 1989. 9. Weir D.H. and Zellner J.W. An Introduction to the Operational Characteristics of All

- Terrain Vehicles"; SAE 86022 5. Dynamic Research Inc, Torrance CA, 1986

. 10. Renfroe, D. , Fleniken, G., “Designing for Pitch and Bounce Motions of Single

- Passenger Off

- Road Vehicles, SAE 940273, 1994. 11. SAE International Surface Vehicle Recommended Practice, “ Steady

- State Directional Contro l Test Procedures for Passenger Cars and Light Trucks,” SAE Standard J266

, Issued January, 1996

. 12. US Consumer Product Safety Commission (CPSC), “ANPR for Standard for Recreational Off

- Highway Vehicles,” Federal Register/Vol. 74, No. 207, October 28, 2009. 13. H eydinger, G.J., Bixel, R., Jebode, H., Peterman, E., Sidhu, A., “Vehicle Characteristics Measurements of Recreational Off

- Highway Vehicles,” CPSC, April, 2011. 14. Allen, R.W., T.J. Rosenthal, and H.T. Szostak, “Steady State Transient Analysis of Ground Vehicle Handling,” SAE 870485, Nov. 1986. 15. Brown, Jeffrey C., Larson, R., Fowler, G., Kuhn, R., “Recreational Off

- Highway Vehicle (ROV) Handling and Control,” SAE 2012

- 01

- 0239, April 2012. 16. Rechnitzer, G., Grzebieta R.H., McIntosh A.S., and Simmons K. (2013)

. “ Reducing All Terrain Vehicle Injuries (A TV s) And Deaths

- A Way Ahead ” , Proc. 23 rd International Safety Conference on the Enhanced Safety of Vehicles, Soeul, Korea, May, Paper No. 13

- 0213.



## C ontact Information

David A. Renfroe; EI Consultants, LLC; dar@enginst.org

Alex Roberts; EI Consultants, LLC; alex@enginst.org

Raphael Grzebieta , University of New South Wales, r.grzebieta@unsw.edu.au

George Rechnitzer, University of New South Wales, g.rechnitzer@unsw.edu.au

Keith Simmons, KND Consulting Pty Ltd, keith_simmons@bigpond.com



## Definition s /Abbreviation s

ATV all

- terrain vehicle

U TV utility

- terrain vehicle

SSF static stability factorPage 10 of 10 critical speed on an oversteer vehicle, critical

s peed is that speed at which yaw rate tends to infinity

Kst static stability constant

ROV recreational off

- highway vehicle

ROHVA Recreational Off

- Highway Vehicles Association