4x4 Explained

Introduction to All Wheel Drive systems - By Eliot Lim

Consumer Considerations

Many potential buyers of all wheel drive cars wonder if the extra "stuff" would mean more problems or if the system would lead to heavy penalties in fuel consumption. Real world experience has shown that all wheel drive systems are not known for any kind of teething problems. The probability of an extra set of driveshafts failing has turned out to be as probable as a V8 engine failing because it has double the number of cylinders over an inline 4. This is a good analogy because with the power split over more wheels, the drivetrain is less stressed.

Those implementations that rely on ABS wheel sensors to lock differentials would be as likely to suffer from problems as any car with anti lock brakes. i.e. no greater than average.

In fact, many of the suspicions of all wheel drive come from the world of manually engaging part time systems where attempts were made to make four wheel drive engagement less cumbersome, with features such as automatically locking hubs and/or "shift on the fly four wheel drive". An all wheel drive system is always engaged and is actually simpler because it eliminates the need of these convenience "features" and their associated parts, which are the usual source of problems.

Accusations that four wheel drive wastes a lot of gas is only applicable to part time manually engaging systems. A full time system with a center diff has none of the tire scrubbing waste of the former. Furthermore, research by Audi showed that as tractive loads built up, the tire losses of two wheel drive exceeded the losses caused by the extra weight and inertia of a full time four wheel drive system. Tire losses were found to rise disproportionately with load. Consider the extreme case of the "burnout" or wheelspin scenario, where 100% of the tractive energy is converted to burning rubber rather than propelling the vehicle.

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