Mitsubishi Lancer Evolution MR vs. Subaru WRX STi; by Frank Rizzuti. Click image to enlarge
By Jim Kerr; photo by Frank Rizzuti
Photo Gallery: Evo vs. STi
I recently took a drive in Subaru's Impreza WRX STI. It has a 305-horsepower, turbocharged and intercooled four-cylinder boxer engine, so there is ample power to bring a smile to any enthusiast's face. But, of course, it takes much more than power to make a good car. That is where Subaru's all wheel drive system and rally car experience takes that smile and turns it into an ear-to-ear grin.
There are other rally inspired cars on the market: Audi and Mitsubishi have used their rally experience to build fine handling cars. Simply put, a rally car is all about handling over any road conditions. A street driven vehicle may not need the ultimate capability of a rally car, but the better it handles, the safer and more fun it will be to drive.
You may have read about "balanced" handling in vehicle reports and articles. There are very few vehicles on the road with perfectly balanced handling. Most cars push a little bit - and some push a lot! The easiest way to think of balanced handling is to imagine a car driving in a big circle around and around. As the vehicle speeds up, the tires start to lose their traction and the vehicle slips outward. If the car was perfectly balanced, both front and rear tires would loose traction at the same time and the car would drift sideways.
There are several factors that can quickly change how even a well balanced car handles. Let's start with a front-wheel drive vehicle. Front-wheel drive uses the front tires for both steering input and traction. Do anything that reduces that traction such as turning the steering wheel or accelerating, and the front tires slip before the back tires lose traction. The front end of the vehicle "pushes" out. This is often referred to as understeer and many cars have this characteristic because it is fairly forgiving when it happens. When a driver feels the car start to push or not turn, the natural reaction is to take your foot off the throttle. This causes more weight to transfer to the front wheels so they get traction back and the car begins to turn.
Oversteer is the exact opposite. Oversteer means the back wheels lose traction first, causing the vehicle to quickly spin out of control. When oversteer occurs with a front-wheel drive vehicle, backing off the gas pedal will actually make the problem worse, as the vehicle weight is transferred from the rear to the front tires.
Rear-wheel drive vehicles are usually designed to "push" as well, simply because it is safer for most driver reactions. A rear-wheel drive car can be made to oversteer fairly easy though by applying power or engine braking to the rear wheels. This reduces rear tire traction and the back end of the vehicle quickly tries to pass the front end. Skilled drivers can usually react fast enough to control oversteer. Do it right and it can be a lot of fun, but for most of us oversteer happens so quickly it is very difficult to control. Spinning into oncoming traffic is no fun for anyone.
Both front-wheel drive and rear-wheel drive vehicles can have more balanced handling by equalizing the weight on the both vehicle axles. Moving the battery to the trunk, positioning the engine back further in the chassis, using light weight materials for larger components are all techniques used both by factory engineers and performance enthusiasts to help balance car handling. There is another way: all-wheel drive.
The Subaru WRX STI's all-wheel drive system provides traction to both front and rear tires as equally as possible, and uses a computer-controlled centre differential to help balance that traction. In automatic mode, the computer senses cornering forces and wheel speeds to vary the traction from front to rear - all to balance the handling. All-wheel drive systems will help balance the handling in any car, but for the performance driver, the WRX STI control system allows manual control of the transfer case centre differential torque split. A skilled driver can then fine tune the traction balance to the road conditions and vehicle load with the push of a toggle switch on the console.
Excellent vehicle design can produce both front-wheel and rear-wheel drive vehicles with very fine handling characteristics, but all-wheel drive can do it much better for the everyday driver. Some think all-wheel drive is just about getting out of that mud puddle or snow bank, but it is really all about safe, controlled vehicle handling.
Jim Kerr is a master automotive mechanic and teaches automotive technology. He has been writing automotive articles for fifteen years for newspapers and magazines in Canada and the United States, and is a member of the Automotive Journalist's Association of Canada (AJAC).
