Oversteer overanalyzed: weight transfer & brake bias

Whether you’re talking about drifting, e-brake turns, trailing-throttle oversteer, or Scandinavian Flick, oversteer looks awesome. It’s not always the fastest way around a corner, but it’s the coolest. Unfortunately, oversteer often leads to spins and crashes. Understanding oversteer will make you safer and faster, so that’s the topic for a few posts.

First off, let’s define oversteer. It’s pretty simple really. It’s caused when your tires are sliding and your front tires have more traction than your rear tires. Assuming your car has 50/50 weight distribution (half the weight on the front tires and half the weight on the rear tires), when you start to slide, the front and rear tires will slide equally. But this assumes you’re not accelerating or braking. As soon as you accelerate, weight and traction shift to the rear. This causes understeer. As soon as you brake, weight and traction shift to the front, which causes oversteer.

Wait-a-goddamn-minute, if accelerating causes understeer and braking causes oversteer, how the hell does drifting work? That’s totally different and has nothing to do with weight transfer. If you spin your tires really fast, the friction starts to disappear. The rubber begins to liquify and gasses build up at the tire-road interface. That’s some slippery shit. But even drifters initiate their turns with weight transfer. It’s the key to understanding oversteer.

So how does one add weight to the front of the car while driving?

  • Brake
  • Hand brake
  • Downshift (RWD only)
  • Trailing throttle oversteer
  • Downhill

Brake

Probably the most obvious way to shift weight forward is by pressing the brake pedal. But what isn’t so obvious is how much of the braking effort is being done by the front wheels vs. the rear wheels. Generally, the front brakes are designed to do more work than the rears because the engine is in the front of the car and the weight is also transferring to the front. Adjusting the brake balance between the front and the rear can make the front or rear tires lock up first. If the brake balance is too far to the rear, the rear tires will lock up first, which will cause additional oversteer beyond the weight transfer. How can you change brake balance/bias? That’s a topic for later.

Hand brake

The hand brake does double-duty for oversteer. (1) It transfers weight to the front (2) It causes the rear wheels to lock up. Grabbing a fist-full of e-brake is one of the most common ways to make a FWD car oversteer. There are a couple reasons for this. First, FWD cars can’t liquify their rear tires, so that’s out. Second, FWD cars have most of their weight forward anyway, so locking up the rears gets them to pivot very easily.

Downshift (RWD only)

Engine-braking a RWD car slows down the rear wheels only. This effectively changes the brake balance toward the rear. Downshifting and feeding out the clutch is therefore a good way to cause oversteer because the weight is transferring forward and the rear brakes are doing more work. A sudden pop of the clutch is a lot like grabbing the hand brake.

Trailing throttle oversteer

Driving at constant speed requires some throttle to counteract air resistance and mechanical friction. As soon as you lift off the throttle, the weight shifts forward. This is called trailing throttle oversteer (TTO). It’s basically a milder form of downshifting.

Downhill

If you’re driving on a downward slope, there is naturally more weight on the front than the rear. The car wants to oversteer simply because of the geometry of the track. Downhill corners are therefore the most prone to oversteering (and spinning).

Quiz

See if you can determine why these crashes happened.

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