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INTRODUCTION

REDUNDANCY

TRANSMISSIONS

STEERING

WEIGHT

MISCELLANEOUS

SUV STABILITY

DIALOG

FEEDBACK


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Page Nomenclature
c.g. = center of gravity H = height of c.g. above datum, in.
SF = rollover safety factor SUV = sport utility vehicle
T = wheel track, in.  

 

Conclusions

It can be stated now as an axiom, a vehicle's stability on a curve, that is, its tendency to slide vs. tip over and its directional behavior leading up to slide or tipover is solely determined on the drawing board by selecting the proper combination of loaded vehicle c.g. height, H and wheel track, T, based on applied physics. Nothing can compensate for improper choices; not springing, not tires, not shock absorbers, extra weight, or any other engineering solution.

At this point, it should be clear to any rational analyst that the first choice for passenger car use, is a front wheel drive car with a low and forward biased c.g. I believe that most current designs (i.e.. sedans, hatchbacks, vans, and small pickups) can and should be better designed to achieve anti-overturning stability. However, the current trend of increasing H, perhaps as a styling gimmick, is very alarming. Millions of excessively high SUVs have been sold to the public and these are literally time bombs, accidents waiting to happen. The recent rash of SUV rollovers due to sudden tire failure is one good example; a tire failure on a straightaway should never by itself cause a chain of events leading to vehicle overturn. Given a sufficient safety factor SF, a tire blowout should merely result in a safe coast-down to a stop. Except for off-road or farm use, vehicles designed for passenger use on smooth roads do not need excessive frame height and its subsequent ill effects on c.g. height.

It is infinitely better to sacrifice ground clearance in favor of lower c.g. as had been the trend for decades, until reversal took hold in recent times. For clearance in adverse conditions, such as snow, the option to temporarily raise the frame by means of pneumatic or hydraulic means should be investigated. Remember, much of the excess height of SUVs is not effective in improving true ground clearance because the rear member (differential housing) is usually the lowest part and is usually fixed on a solid axle at the axle centerline. Seldom is more than eight or nine inches true clearance obtained, as compared to typically five inches for a standard passenger car; the extra three or four inches ground clearance of the SUV is accomplished at the expense of eight inches or more increase in c.g. height. The HummerŪ achieves 18 inches or so ground clearance by means of a unique drive train which is mounted high off the surface. Conventional SUVs do not have that luxury built in.

Recommendations

I will now make a series of recommendations for the SUV problem. These apply to all parties: drivers, passengers, buyers, manufacturers, and government regulatory agencies.

 

  • Safety Factor, SF should be provided by the manufacturer and be published on the new car sticker. It should be color-coded for ease of understanding by the lay public.

  • Placards should be put in place for the unwary driver and passengers. The driver's side placard should  read "Caution: Vehicle subject to upset during extreme maneuvers". The passengers' placard should state, "Vehicle not rated safe for routine passenger use".

  • No new model should be allowed for sale with an SF in the orange or red zones, except a commercial vehicle over 80 inches in width. It too should be placarded.

  • Designers should limit power on rear axle drive vehicles. Rear wheel drive cars are much more benign when power is limited to about 30 pounds/b.h.p. or so.

  • Proving test results should be summarized and available as an appendix to the owner's manual as well as part of the sales presentation literature. Of particular interest is whether or not the car model tested stable (understeering) in turns and remained controllable in accident avoidance maneuvers.

  • c.g. studies should be performed by each manufacturer for its entire range of models and those makes and models for which SF falls in the red or orange zones should be removed from further production.

  • In the interest of public safety, legislation should be considered prohibiting the modifications of vehicles which may affect c.g. location adversely or cause structural or operational compromise. Included would be the installation of "lift kits" and unauthorized wheels and tires, both over and undersized.

  • In the case of SUVs that have a calculated SF of 0 or less, manufacturers should brace themselves for potential claims, including demands for replacement or refund for inherently defective automotive design. After all, it was realized more than 90 years ago that high c.g. is hazardous to driving. Prior knowledge of inherent design deficiency and then ignoring or dismissing it exposes those who should know better for the inevitable claims that will result from unnecessary accidents.

  • Insurance companies should familiarize themselves with SF and apply it for the purposes of underwriting. It is not recommended that policies be written for any vehicle whose SF falls in the red or orange zones as it is a high risk for tipover and a driver of such a hazardous vehicle could face possible additional exposure to public liability due to his limited ability for accident avoidance.

  • Attorneys for plaintiffs injured either directly or as third parties should consider petitioning courts for punitive damages in addition to actual loss for injury or property damage. The theory being prior knowledge of inherent defect and total disregard of traditional design principles and standards of performance. We have witnessed a retrograde class of vehicle produced in great quantity and promoted as family safe, possibly transcending six or seven decades of actual progress.

Death, personal injury, and property damage should no longer be the result of improper automotive design. The state-of-the-art of sound engineering practices should always be the first consideration, not the whimsy of stylists and promotional personal. A well designed vehicle must sell itself on its merits; nothing should compromise engineering excellence.

This concludes the presentation. An extra appendix page is included for those who wish to take a follow-up look at the Safety Factor Chart.

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