SUV Rollover Testing
Rollovers accounted for more than 10,000 fatalities in the USA in 1999. That's more than side and rear crashes combined. SUVs have the highest number of rollovers per 100 crashes of any other class of vehicles. More than 90 percent of rollovers occur after a vehicle runs off the road and strikes a curb, soft shoulder, grass, pavement edge, mud, guardrail, or other object that "trips" it, but the also shockingly rollover can happen on a flat roadway as well. "It's the fastest growing form of fatalities in motor vehicles today," says Clarence Ditlow, of the Center for Auto Safety. "And it's because we have sport utility vehicles that handle differently and we need a real world test that distinguishes how they do in the real world."
During a normal vehicular accident, vehicles are either rapidly slowed down by hitting an object or another vehicle or sent into in a different direction than they were originally heading. In these accidents the vehicle will slid, skid,spin crunch and even tip, but normally the vehicle does not roll over, unless it has been tripped or the design allows it to rollover due to it being top heavy. However, if a vehicle has a high center of gravity and is redirected (as when a driver steers in one direction and then has to quickly crank the wheel in the opposite direction) the vehicle can topple and roll.
"The public needs the numbers because more people are being killed, we're getting more vehicles out there on the road with higher rollover characteristics, and we don't know which are the good performers and which are the bad performers," says Ditlow.
All vehicles can roll over if the right conditions are present, such as a loss of control and sliding into a curb, ditch or other object and tripping into a rollover event. However, SUV's can and do roll over as a result of hard steering on flat, dry pavement, with no tripping device introduced..
SUV Rollover Testing - Center of Gravity Formula
From an engineering point of view, a vehicle's stability is measured by the formula:
In this rollover / stability formula, T is the 'track width' (center of the right front tire to the center of the left front tire) and h is the vehicle's center of gravity. When this number is 1.2 or greater, the vehicle is unlikely to roll. However, the further the ratio dips below 1.2, the greater the likelihood of roll over .
Rollover occurs because of the absence of a lower center of gravity and a wider track width, which allows automobiles to skid, spin and recover. In a normal evasive maneuver that passenger car drivers safety complete every day, rapidly corrective action (also called oversteering by police officers) causes SUVs to trip and roll. Rollovers occur with all sports utility vehicles but the condition seems is to be worse with the earlier Japanese vehicles. As the ratio approaches 1.0 the tendency for the vehicle to roll is increased. A ratio above 1.2 is considered safer.
The T/2H ratio for one Japanese SUV is approximately 1.05, when computed by the manufacturer with 80% gas, one driver, and no cargo. It is fair to assume that the test driver is 150# or less. Obviously the vehicle is designed to seat more than one and with all seats filled the T/2H ration is very close to 1.0. Add a full tank of gas and some cargo, in back, plus a roof top carrier and the likelihood of a roll at freeway speeds is assured when a driver makes an abrupt corrective move.
All current SUVs contain a rollover warning, but the warning provided do not mention that every bit of weight added to the passenger compartment, roof racks, and excessive passenger baggage increases the likelihood of a roll.
Basic Reasons for SUV Rollovers & Injuries
- Advertised to Carry Too Much Weight
- SUV's High Center of Gravity / Narrow Track width a Dangerous Combination
- SUV Absence of Roll Protection, Roll Bar or Roll Cage
- Faulty Seat belt protection in many SUVs
- Ejections in SUV Rollovers Due to bad door latches and lack of window glazing
- Seat Back Failures that allow occupants to come out of their seatbelts
- Lack of Rollover Warnings