I’m sure you hear a lot about being smooth and managing weight transfer (in fact, I’m sure I’ve already preached that to you myself), and in this installment, we will revisit the importance of both those things (and it won’t be the last time, either). We also spend a lot time talking about braking; when to brake, when to get off the brake, should I be trail braking? How much brake pedal pressure should I use? etc. etc. but rarely is how you get off the brakes discussed. This may seem trivial, but it plays a big roll in vehicle dynamics during turn in and mid corner, and can make an oversteer prone car understeer, and an understeer prone car infuriating to drive.
First, let’s think about what’s happening with the front suspension during a braking event. Upon the initial application of the brakes, weight is transferred to the front, which is translated to a downward force on the front suspension. This downward force compresses the front springs, and as a result, a large amount of elastic potential energy is stored. Once the force compressing the spring is removed (i.e. you begin to release the brake), this elastic potential energy will be released. According to the first law of thermodynamics, “energy is neither created nor destroyed.” This is notable because it tells us that the rebound (decompression) force of the front suspension when you release the brakes will have as much force as the compression of the front suspension. If you think about the amount of braking force you can produce and how much the front suspension deflects, this is a lot of force we’re talking about here! It’s easy to see how releasing the brakes too abruptly can cause an unloading of the front suspension and a loss of grip. This loss of grip will be especially noticeable in a vehicle with underdamped front suspension (i.e. stock suspension, or stock shocks with lowering springs), as a rapid unloading of the front suspension will cause oscillation. This unloading of the suspension can be an issue even in vehicles with properly damped suspension. The damper is designed to control the rate at which the spring is loaded and releases its stored energy. However, even in a car with a great set of coilovers that were well setup for the application (such as the Ohlins I had on my Evo X), there can still be some degree of unloading of the front end when releasing the brakes due the front end load accelerated upwards from the spring releasing its stored energy. The shocks can’t necessarily stop the mass of the front from accelerating upwards, although they will reduce it significantly.
To completely avoid the unwanted effects of the front suspension unloading, think of using the brake pedal as an additional shock absorber to control the front end loading. In general, you want to release the pedal somewhat slowly and as smooth as possible, especially towards the end of braking. As you gain a feel for how your suspension reacts to the release of the brake, you can begin to increase the speed of your release. Ideally, a passenger wouldn’t be able to pin point exactly when you let off the brake pedal by feel.
This is an important skill to master in a car that has a propensity towards understeer. For example, watch a few minutes of the video (link below) of me driving my Evo X at Watkins Glen (skip to turn 8 for a good example at 1:35). Notice the incredible amount of finesse associated with releasing the brake. If I were to come off the brakes any faster or more abruptly, the car would most certainly plow.