Staggered wheel fitment is a term for the rear wheels being bigger and/or wider than the front wheels. Like rear wings, this only works on rear wheel drive cars, where the bigger rear wheels can put more power onto the pavement, and at the same time be chosen to improve the cornering ability of the vehicle. As most performance and racing cars are rear wheel drive cars, staggered fitment has for many people become synonymous with performance styling, which can be a serious mistake for owners of front- and 4-wheel drive vehicles. More on that below.
Changes in the relationship of wheel dimensions between front and rear on a RWD car changes the balance of the vehicle. The classic Porsche rear-engine cars are perhaps the best examples of how staggered fitments can be used to optimize performance. Porsche engineers have developed suspension settings and staggered fitments to perfection, making these inherently instable designs some of the most well-balanced and entertaining sports cars in the world. A rear-engine car is tail heavy. This makes the car "oversteer", i.e. only a slight turn of the front wheels makes the rear end swing out. This can be countered partly by the way the suspension is set up, but also by fitting bigger wheels in the rear than in the front. The staggered fitment, with bigger wheels on the rear axle, not only puts more power on the pavement, it also counteracts the tendency for the rear to swing out by putting more rubber on the road in the rear, thus providing more friction in the rear than the front. This makes the rear and front wheels reach the slipping point at nearly the same time. If the front loses grip before the rear, the car "plows" straight ahead, it "understeers".
This is typical for front-heavy cars, in particular for front-wheel-drive cars. Front-engine, rear wheel drive cars can shift quickly from under- to oversteer if the driver doesn't handle the accelerator with care. Quick changes in the speed of the driving rear wheels can cause wild spins. Whether a driving wheel is braked quickly or accelerated quickly, the change of speed can make it lose its grip on the tarmac. Choosing the right staggered fitment wheels minimizes these problems. Most drivers prefer the rear wheels to start skidding slightly just before the front wheels lose their grip. They want a little "oversteer". This way they can feel in the seat of their pants when the car is about to break loose, and can drive the car to the limit of its ability. They can steer the car with the accelerator, regulating the slip of the rear wheels to help the car turn exactly on the line they have chosen through a bend. Absolutely perfect balance is actually very scary. If a car is balanced to complete perfection, all four wheels will lose their grip at the same time, without providing the driver with any signs of warning. When this happens, there is very little the driver can do to regain control until everything has slowed down, hopefully without the vehicle crashing into anything.
If you have a rear wheel performance vehicle, finding the staggered fitment that is right for your driving style, your vehicle, your choice of tires, for the particular road you are driving on, and for the weather of the day, will keep you occupied for the rest of your life. The search for perfect performance is always fun, and the experience of trying out the best possible staggered fitment will give you endless exhilarating driving entertainment.
Fitting different size tires front and rear on a four-wheel-drive vehicle can be downright dangerous. Not to mention the fact that it makes the owner of the vehicle look foolish to car experts, as staggered wheels on a 4WD proves that the owner doesn't know even the most basic things about his vehicle. Staggered fitment on a 4WD can wreck the powertrain of the vehicle and it can cause the vehicle to perform in very strange and unexpected ways. On a front wheel drive vehicle a staggered fitment might not be dangerous, but it looks silly to car buffs who can tell a FWD vehicle apart from a RWD. It will also cause already understeering cars to perform even worse.