Attorney
- Client Privileged and Confidential Off Road Vehicle Division



# J - Turn DiscussionAttorney
- Client Privileged and Confidential Off Road Vehicle Division



## From safecar.gov Website
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# NHTSA Rollover Definitions

TRIPPED ROLLOVERS NHTSA data show that 95% of single - vehicle rollovers are tripped

. This happens when a vehicle leaves the roadway and slides sideways , digging its tires into soft soil or striking an object such as a curb or guardrail. The high tripping force applied to the tir es in these situations can cause the vehicle to roll over. UN - TRIPPED Un
- tripped rollovers are less common than tripped rollovers, occurring less than 5% of the time, and mostly to top
- heavy vehicles. Instead of an object serving as a tripping mechanism, un
- tripped rollovers usually occur during high - speed collision avoidance maneuvers.Attorney
- Client Privileged and Confidential Off Road Vehicle Division



## NPR Ay Requirement Can Not Prevent Tripping Rollovers
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# Off Road Vehicle Tripping Condition

Environment Sand Soil Berm Rock Tree Stump Incline Resistance Center of Gravity

Sliding Force Moment Of Inertia Force = Mass times Acceleration (Spike Load Condition) Can easily exceed 2G Tipping Force



## Off Road driving conditions can result in a tripping condition http:// www.safercar.gov/Vehicle+Shoppers/Rollover/Types+of+RolloversAttorney
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## Video shown at half speed – actually traveling 25mph
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# Sand J - Turn VideoAttorney
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### Off - road behaviors can vary greatly from on - road – unintended consequences
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# Off - Road Testing

Notes: 1) On pavement, the locked differential is oversteer and the open differential is understeer 2) In sand and gravel, the understeered vehicle rolled much easier than the oversteered vehicleAttorney
- Client Privileged and Confidential Off Road Vehicle Division



### Off - road behaviors can vary greatly from on - road – unintended consequences
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# Off - Road Testing

Notes: 1) On pavement, the locked differential is oversteer and the open differential is understeer 2) As the surface roughness increased, less steering angle was 

### required and the differential position had less effectAttorney
- Client Privileged and Confidential Off Road Vehicle Division



## Sliding Begins Well Below 0.7 G, Tripping Occurs Well Above 0.7G
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# Lateral Acceleration Comparison

Sand (Peak Ay @ 1.1) Gravel (Peak Ay @ 0.9) Pavement (Peak Ay @ .72)

All runs shown ended in roll:

• Off
- road runs begin sliding at less than 0.3G and can reach lateral accelerations well above 1.0

• Spikes are noticeable of the tire tripping/skipping over the ground

• Once the vehicle begins sliding, well below 0.3G, it really doesn’t matter what its Ay on pavement is because it will trip and spike well above that value 0.7G 0.7G

0.7G
Tire Slip

Tire Slip Tire SlipAttorney
- Client Privileged and Confidential Off Road Vehicle Division



## Sliding Begins Well Below 0.7 G, Tripping Occurs Well Above 0.7G
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# Lateral Acceleration Comparison
Plowed Dirt (Peak Ay @ 0.96) Rough Grass (Peak Ay @ 0.87)

0.7G 0.7G Pavement (Peak Ay @ .72)

0.7G

Tire Slip

All runs shown ended in roll:

• Off
- road runs begin sliding at less than 0.3G and can reach lateral accelerations well above 1.0

• Spikes are noticeable of the tire tripping/skipping over the ground

• Once the vehicle begins sliding, well below 0.3G, it really doesn’t matter what its Ay on pavement is because it will trip and spike well above that value Tire Slip Tire SlipAttorney
- Client Privileged and Confidential Off Road Vehicle Division



## Steer input on Pavement Is A Better Pass/Fail Metric
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# Vast majority of Off - Road rollovers are tripped On - Road J - Turn does not predict tripped rollover resistance Off - road terrain causes tires to slip well below 0.7g, proposed threshold is not connected to the terrain failure limit Once tires begin to slip, a tripped rollover is highly likely 

## Lateral acceleration at trip is well above .7g 

# Steer input at roll consistently higher off road vs on pavement 

# Focus vehicle designs to increase slip resistance & improve handling predictability 

# Summary