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Brake Pressure Sensor Analysis

maxresdefaultBrake pressure sensors are a logical addition to any data logging, whether it be for club level competitors or professional teams. The information we gather from them can help us with both driver and car development.

 

Analysis

Some of the most useful information to be had concerns driver performance and coaching. Braking is the one aspect of car control that goes against the accepted wisdom of smooth driver inputs. Aggressive braking is the key to both fast lap times and the tactical advantage needed to make passing moves stick. This is especially true of cars that produce a meaningful amount of down force. At high speeds these cars typically have much more grip available than the brakes could ever overcome. This means the driver can brake much harder at higher speeds than he can at lower speeds. The other facet to braking performance is the release of the brake pedal, once described by Jackie Stewart as one of the hardest things to learn how to do properly in a race car. As the road speed decreases, so does down force and braking ability. Some brake pad compounds will also increase in friction over the period of the braking event. Therefore, we need to be gradually decreasing the brake line pressure as we approach the corner to avoid unnecessary lock ups and to ensure that the car is balanced and can transition smoothly into the cornering phase.

Case Study One - Three drivers, one car

The track is the fabled Mount Panorama and the corner is turn 23 or Murrays Corner. The car is GT car with quite a lot of aero down force and excellent braking performance. This corner is located at the end of conrod straight that has a terminal velocity of around 220kmh, slowing down to a 90kmh left hander.It also has a downhill approach, levelling out at the turn in point. The braking area is smooth and the corner is well sighted with numerous visual references and braking markers so picking a braking point is usually no problem.

Murrays Corner

 

 

Fig 01

The data was collected over two qualifying sessions on the same car, a current spec GT3. All three examples were taken from the same numbr of laps out and all were verified from the video footage to be clear corners with no traffic to hamper the braking zone.

 

The first driver is a seasoned European professional with a mountain of experience, especially in this type of car. His approach and initial phase show the hall marks of an aggressive left foot braker. The brake pressure rise crosses over the throttle as it closes so that by the time the throttle is shut, the brake line pressure us already 54 Bar, rising to a peak of 137 bar.

 

Also of note is the tapering of the brake pressure as the car approaches the corner. This allows the front tyres to have some excess tractive ability at the point of turn in, improving grip in the initial phase of the corner.

 

 

Fig 01a

 From the numbers above, we can see that peak pressure is achieved within 0.19 seconds of initial brake application for a spped drop of 23kmh in 11 metres. Remember those numbers. This is essentially how you out brake anyone in a modern race car. Braking performance has become so reliable and attains such high levels of retardation that it's the little details that make it.

 

 

 

 

Fig 02The second driver is a seasoned  competitor with multiple national titles to his name, all in touring cars. His initial input is slower and the magnitude is not as much as driver 1.The brake pedal modulation is also not  as good with another spike right near the turn in point.

 

 

Fig 02a

The stats for this are s imilar speed drop to Driver 1 but it's taken nearly twice as long and covered twice as much ground. In fact, he's lost 1 - 2 car lengths........

 

 

Fig 03The third driver is a retired V8 Supercar driver with quite a bit of sports car experience. His initial input is just as quick as driver 1 but he doesn't quite match him for the magnitude of pressure, peaking out at about 90 bar.

 

Fig 03a

 His speed drop is only 10kmh over 21 metres and 0.35 seconds. So he's gotten to peak braking force as quickly as Driver 2, but due to the big gap between the throttle coming off and the brake pressure rising to it's peak, the car has rolled without slowing. This is quite evident in the speed trace which has a fairly round shoulder compared to