|Date added||June 16, 2014|
|Category||2014 CMRSC XXIV Vancouver|
|Tags||Research and Evaluation, Session 5C|
|Author/Auteur||Micky Gilbert, Brad Stolz|
|Stream/Volet||Research and Evaluation|
There have been a number of untripped rollover accidents involving Sport-Utility Vehicles
(SUVs). Accident data shows that these vehicles are unstable when subjected to emergencytype
steering maneuvers, and the physical characteristics of the vehicle are known to have
great impact on the vehicle’s ability to resist rollover. The automotive industry and automobile
handling/stability engineers have studied the effect of vehicle design on rollover for decades.
Published papers from the 1960-1970’s discuss basic vehicle geometry as a primary factor on
rollover resistance. Track width and center of gravity height are referred to as first order metrics
with respect to a vehicle’s lateral force capacity by almost every auto manufacturer in the world.
This means that a wide and low vehicle has more rollover resistance (and higher lateral force
capacity) than a tall and narrow vehicle. Static Stability Factor (SSF) also known as T/2H (track
width divided by two times the center of gravity height) is currently used by the National
Highway Traffic Safety Administration (NHTSA) to assign vehicle rollover performance ratings.
At the same time, the well-established automotive aftermarket has been providing custom wheel
and tire packages for decades, and for vehicles of all types including SUVs. While some
previous research has evaluated the consequence of the “plus-sizing” concept (wherein the
overall diameter is kept as close to original as possible), little work has been done to evaluate
the potential consequence of installing wheels and tires that have notably different dimensions
than stock (both in terms of physical dimensions and other characteristics). For example,
modifications to an already unstable vehicle that result in raising the center of gravity height
and/or narrowing the track width (or both) will result in a more unstable handling package in
terms of resistance to rollover.
This paper will present data from instrumented rollover testing of an SUV with very low rollover
resistance with the intent of observing the effect of larger and heavier wheels. The purpose of
our testing was: (1) to test/document the rollover threshold of the stock 1992 Ford Explorer XLT
4x2 with accepted industry handling maneuvers, and (2) to test/document the rollover threshold
of the 1992 Ford Explorer XLT 4x2 modified with aftermarket 22-inch wheels with 18mm offset
and 265/35R22 102V tires with the same accepted industry handling maneuvers. A comparison
of the two test setups will be used to establish a relationship between the change in the
wheel/tire condition and the dynamic roll resistance of the vehicle as a whole.
Micky Gilbert, Brad Stolz