A rollover test, particularly on-road dynamic roller test, is conducted by the National Highway Traffic Safety Administration (NHTSA) essentially on SUVS, minivans and pickups. Taller vehicles such as SUVS, pickups and minivans are more likely to rollover after a collision or sudden curving movement than the usual cars due to their high center of gravity or because these kind of vehicles are top heavy.
A rollover happens when there is a dramatic effect on the vehicle balance after vehicle traverses a curve which eventually shifts the vehicle center of gravity to one side.
Each car’s reliability including the strength of the vehicle pillars holding the roof is determined in every rollover test. The pillars, as tested, should resist load they receive during a dynamic impact or when rolling after severe turning maneuvers.
The fishhook test
The rollover test conducted by NHTSA subjects vehicles to a handling maneuver called a fishhook which is a term used for quick left-right turn at speeds ranging from 35 to 50 miles per hour. The operation is a simulation of the driver overdoing the vehicle steering usually happens during emergency situations.
The test vehicle passes the test when vehicle body slides out. The test vehicle fails when two wheels of the vehicle at the same side leave the ground or tip up.
Rollover ratings
NHTSA introduced a dynamic rollover test or vehicle in motion rollover test for 2004 models, with the results used by the agency to supplement its vehicle rollover ratings. Scores are determined from one to five star rating system.
NHTSA also provides separate ratings for two and four wheel drive models of SUVs, but as of now, no car or minivan has failed this test.
Static Stability Factor
NHTSA has also conducted on the road rollover tests in two sedans for each year and also provided star ratings for vehicles based on the vehicle static stability factor (SSF). SSF is a static measurement of the shape of the vehicle and the vehicle weight distribution as well.
Swedish VTI rollover test
VTI or Swedish National Road and Transport Research Institute is an agency that conducts stability and rollover testing on heavy vehicles such as buses, agricultural machinery, fire engines and lorries.
The destructive testing requires the vehicle to be tipped sideways against a hard surface from a certain height prior to analyzing of vehicle deformation particularly on buses in accordance to penetration into passenger compartment. This technique allows the determination of the practical strength of the vehicle body.