Sam Francis Fitness

Archive for September, 2009

It happens like this:You buy a new four-wheel-drive sport utility or pickup, take it out yonder, and promptly bury it in some mud- hole or strand it on a steep talus trail. Now you’re in for a really nasty surprise: It can easily cost several hundred dollars to hire a guy to pull the truck free.What gives? The truck is four-wheel-drive, right?
Not necessarily. By design, the majority of stock part-time four- wheel-drive systems don’t provide true four-wheel drive. Sure, you get power to the front and rear axles, but the vehicle’s standard “open” differential splits that power to the right and left. Doing so allows one wheel to go slower in order for the vehicle to negotiate a corner, but it also shunts all the power to the wheel that’s spinning when you get stuck.
Most outdoorsmen have addressed this problem over the years by ordering an optional limited-slip differential for the rear axle. (The option is not normally available for the front axle because it affects steering.) A limited slip is a big help, but as the name implies, the benefits are limited. You may get 40 to 50 percent more traction, but you’ll never get full power to both wheels in difficult situations.