Time of Session:
01:11:50 Glock sitting in the garage debriefing with his engineer, reports “for some reason” the quick-shift adjustment lever for brake balance is stuck “very hard” with him needing to “really hammer on it” to be able to move it. Engineer responds, “So, presuming you can’t do it with your left hand anymore, huh?” Glock replies can indeed move it, but only after pushing it “hard”
** Time of session is the session time at which the message was heard on the television broadcast, as radio communications are delayed from when they actually occur.
We often hear about drivers adjusting brake balance to compensate for rotor temperatures, KERS dynamics, or corner entry issues, but what really is it and how do they adjust it?
There are two separate master cylinders on two separate hydraulic circuits that actuate the brake calipers, with one master for the front calipers and another master for the rear calipers. Both cylinders are actuated together by the one single brake pedal. Any 4-wheeled car obviously requires more braking energy across the front axle to manage inertia of the mass of the vehicle, but how is more energy achieved at the front when there is only one single brake pedal?
The two separate master cylinder pistons are connected to the chassis from the brake pedal via a “balance bar” or also known as a “bias bar.” The balance bar mechanically dictates the ratio of piston displacement between the front and rear cylinder as the pedal is pressed. Basically, for any given distance the pedal is displaced, the front cylinder will be displaced more than the rear cylinder. With more piston displacement in the front cylinder, the front hydraulic circuit will experience a higher pressure than the rear which has less piston displacement. There are other means of fine tuning hydraulic pressure through piston and cylinder diameters, but we don’t need to discuss that for this basic explanation.
The balance bar is adjustable to mechanically alter the ratio of piston displacement. Mechanical adjustment is available to the driver in the cockpit as a “quick-shift” lever for large macro adjustments or a knob for finer adjustments. Levers can be set to make adjustments as large as 1.5% in one fast movement. The direction of lever actuation is usually intuitive for the driver to be able to use it without thinking too much about it or looking down at it. For example, moving the brake balance rearwards involves pulling the lever back, with pushing it forward to move balance towards the front. On in-car camera feeds, Schumacher is often seen actuating the quick shift lever multiple times during a lap from corner to corner.
What is the brake balance number we often hear about over the radio? Often when engineers request a driver to change brake balance, they not only ask for the percent of change, but also discuss the final total percentage. Formula 1 cars usually operate with a brake balance of approximately 56-60%. That percentage number is the ratio of total hydraulic pressure in both circuits, relative to the front axle. Basically, just keep in mind that it essentially means, 56-60% of the total braking force is being applied to the front brakes.
How is brake balance calculated? A hydraulic pressure transducer sensor is located at each master cylinder. Each sensor will thus have its own calibrated parameter in the data system. With the logged brake pressure data from each separate hydraulic circuit, we can then calculate brake balance with the follow basic equation:
First, let’s set up our 2 variables:
Fpress = Front Brake Hydraulic Circuit Pressure Rpress = Rear Brake Hydraulic Circuit Pressure
Brake Balance =
[(Fpress) / (Fpress + Rpress)] * 100%
As you can see, all the equation did was to determine the ratio of front force to the total force and multiply that number by 100 to present it as a percentage. On some in-car photos and videos, you can see the brake balance percentage designated on the steering wheel dash as “BBal.” Now you know how the data system and engineers measured and calculated that number we hear so often.