Saturday, November 8, 2008

Front Wheel Drive Mini Cooper

A distinctive feature of the new MINI Cooper, as with the classic Minis that inspired it, is that the engine drives the front wheels. For the purpose of making a car that is small and maneuverable while having lots of interior room, that is a good thing. For the purposes of getting the car around the track or autocross course quickly, or being good on the highway, well…let’s just say it is different.

We all know that the fastest cars on the track all have their drive wheels on the rear, so we can assume that there isn’t any inherent advantage in racing a front wheel car, but nevertheless, if you learn to drive the car well, you can find ways of making that front drive do some pretty amazing things.

So what’s the problem with front wheel drive? The first part of the problem is that the car has to be steered and powered by the same wheels. This means that if you’re going fast in a straight line, using the traction of the front tires to pull you along, they aren’t going to be as effective in making the car change directions. That’s the oversteer problem we discussed above.
Likewise, if you’re turning the wheels and using their traction to hold the car in the corner, they are not going to be able to absorb very much forward push. In addition, since a car tends to lean back as it accelerates, it is more difficult in a front-wheel drive car to really put the power to the pavement. As a result, the front wheel drive car isn’t as fast out of corners as a rear-wheel drive car with the same engine torque.

The second part of the problem is that as you accelerate or brake, these issues get worse. When you accelerate, you’re taking weight off the front wheels, making them less effective at steering the car. Likewise, when you put on the brakes the weight shifts to the front of the car, making the understeer even more of a problem.

So, what can we do to overcome these problems. There are some changes that can be made to the suspension and brakes to reduce the difficulties, and we’ll discuss them later. But there is a lot that can be done by the way you drive.

First, if you’re coming into a corner too fast and the car is under steering—refusing to go the way you want it to go—if you simply let off on the gas a little bit, the weight will transfer to the front end and give the front wheels more traction which will help the car steer around the corner.

Following the same principles of physics, if you find the rear end starting to get loose, especially as you come out of the corner, you don’t want to let off on the gas, or worse, hit the brakes. If you do, the car will pitch forward even more, and the rear end will come around with a vengeance. At that point, you may find yourself facing backwards as you slide off the track. Instead, what you want to do is use that power on the front wheels to pull you through the curve. Keep the throttle even, maybe even accelerating a little bit, as you drive your way out of the skid.

Mini Cooper Forum

This ability to put the power to the front wheels on corners was what made classic Minis so much fun to watch on the track in the sixties. Experienced drivers would power into the curve, then turn the wheel and briefly release the throttle, or even tap the brakes, to break the rear end loose. As the car rotated and was aimed in the proper direction, the Mini driver would get hard on the power and scoot off down the road, leaving the rear-drive cars wondering where he had gone.

Rally drivers found the MINI’s ability to rotate its rear end and then power out of corners particularly valuable in rally driving. On a rally route, the surprise of a tight corner might cause a traditionally powered car to slide off the road with the power wheels unable to get traction. Mini drivers, like Paddy Hopkirk for example, would simply let off the throttle and give the handbrake a yank to release the rear end and bring it around the corner, then get on the power to drive the car out of the corner. Today, this cornering technique is a standard feature of rally driving; in those days it was revolutionary.

However, right now you’ll probably be happiest if your car simply goes around the corner with you in control, without understeering or oversteering. So let’s talk about turning corners.

1 comment:

Michael said...

Thanks, that was a big help. I did my first autocross recently, and the understeer on turnarounds was something I couldn't figure out how to handle.