Gas Pedal

Millbrook training days promote safe driving techniques for road and circuit. This year CAT travelled north of the border for an MLR training day at the Ingliston Showground. The training took place the day before the Ingliston round of the Sprint series. Many of the questions on the day regarding technique were track focused and included questions on skid recovery. This article reflects on one of the days questions.

In the last edition CAT’s Driving Clinic focused on observation – maintaining a long focal point when driving on circuit or the public highway is essential. We finished the article discussing the importance of “looking where you want to go” when recovering from an oversteer/understeer scenario. Let’s now polarise our thoughts on the subtle adjustment needed to the gas pedal to recover the situation.

We know an Evo has exceptional grip limit stability, predictable and safe when driven to its limit of adhesion. LSD’s, AYC & intelligent four wheel drive systems offer superior control, optimising tyre grip and cornering speed. That said these systems cannot defy physics, their function is to help the driver manage available grip. Irrespective of the complexity of the stability programme and drive train layout, we only have a finite amount of grip between the tyre and the road.

Tyre grip is governed by 3 key factors: 1 -the coefficient of friction between the tyre and the road surface; 2 – the contact area the tyre makes with the road; and 3 – the vertical down load or weight experienced by the tyre. If you have entered a corner too quickly and saturated the tyres available grip, the driver will need to make a correcting input. The gas pedal plays a key role in the correction process. When driving a vehicle at its limit of adhesion it helps to visualise the platform you are driving as having two ends: front and rear. If you are understeering the front of the vehicle is travelling at a higher speed than the rear. Oversteering, the rear of the vehicle is travelling quicker than the front.

If you too successfully micro manage the available grip, be aware that once at true grip limit, the gas pedal will steer your Evo more effectively than the steering wheel. Maintain a steady state steer and squeeze on the gas at grip limit through a turn and the front of the vehicle will understeer (push) through the corner. Ease out of the gas pedal at grip limit and the rear of the vehicle will oversteer. AYC adds to the experience. If you are smooth with the application of power, the system promotes a manageable four wheel slide. Logically this is a very efficient set up, all four wheels are travelling at the same speed. The gas pedal in effect through a corner is levelling the car, compensating for the frictional loss between the tyre and the road, and assisting in keeping all four tyre contact patches perpendicular to the road.

So what do you with the gas pedal if you’re all out of shape through a corner, under or oversteering and need to reduce terminal speed and yaw rate (slide angle)? The rule of thumb is to reduce the gas progressively, maintaining some! forward momentum with the gas is essential. If you snap the gas pedal shut you could induce lift off/roll oversteer. Why? The tyres on the loaded side of the vehicle are already buckling under the cornering forces of the over speeding vehicle – they are running on the sidewalls. Snap the gas shut taking away the levelling effect the gas has on the cornering forces and you will simply further over load the tyres, increasing slide angle.

It is counterintuitive to reduce the gas progressively and takes practice and often instruction to perfect. Another one of those driving conundrums: survival instincts urge you to slow down as quickly as possible. Engineering logic dictates reduction of speed must be graduated. We will focus on steering inputs next edition.

Safe motoring over the winter months.

Colin Hoad

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