- 1
- Georgia
- Harribull
Brake Balancing 101
While tuning with my son I realized that many drivers do not understand the actual physics and or its effect on braking. Likely most younger people have never driven a real car without ABS, which is a lot livelier and frankly more on the edge of out of control in panic stops.
ABS brings a lot more control to the table than the old method of manually pumping your brakes ever could. People that didn't know to pump their brakes in a non-ABS vehicle would ride their brakes into what ever was in their path.
Depending on the vehicle, heavy brake controller settings such as 10/10 in GT5 without ABS on seems to assume your wheels are locked up even under very mild braking. I experienced this at Tsukuba testing the Mucielago LP 670-4 SuperVeloce '09 for the 9 hour Spec-A event.
Balanced Brake Controller Setting: This may not mean balanced braking, which is actually affected by the CG (center of gravity) limit of the vehicle.
The axle with the most braking force is going to tend to want to be in the front, which will result in a tendency to spin the vehicle around backwards if the rear axle's brake force takes the vehicle beyond its CG limit.
To verify this for yourselves, perform the following test:
Step One: Select your testbed vehicle.
Step Two: Center the car's balance with ballast (a neutral CG).
Step Three: Pick your test track.
Step Four: Turn all driving assist off including ABS
Note: Do not steer while braking for these test stops. Only brake when the car is traveling downhill in a stable straight line.
Test One: Set brakes 10/0. Start the test by accelerating to say 70MPH on down hill, slam on the the brakes, and watch what happens.
Test Two: Set brakes 0/10. Start the test by accelerating to say 70MPH on down hill, slam on the the brakes, and watch what happens.
Conclusion:
For balanced braking, you want to set your braking force bias so that in a straight-line, down-hill stop without ABS you have the maximum braking force you can apply to the rear axle without introducing uncontrolled spin or pronounced left or right yaw to your vehicle. Under optimal braking conditions there will be some minor yaw due to minute amounts of lateral G force introduced by differences in grip based on pavement and tire conditions (etc.). These conditions will also introduce a mild oscillation (or tendency for the car to wiggle) during braking.
Unless your intention is to introduce yaw to start a drift, or you desire to point the nose of the vehicle inside a turn by having the rear end tend to slide out, one should aim for as neutral and stable a result as possible when brake tuning. Then when you're done tuning, re-enable ABS . You should have the most effective, stable, and controllable braking your vehicle can produce.
The weight balance was just for this test. I am not suggesting you should balance every vehicle 50/50; though it can improve braking (dependent upon the natural balance of the vehicle), the performance penalty from correcting of bad balance by adding ballast can make you non-competitive. Even though you gain stability and performance points that may be utilized else ware in your tune provided the resources are available.
Off topic: The balance of your vehicle also greatly effects under-steer/over-steer conditions and can be used to correct them though, again, at a cost.
While tuning with my son I realized that many drivers do not understand the actual physics and or its effect on braking. Likely most younger people have never driven a real car without ABS, which is a lot livelier and frankly more on the edge of out of control in panic stops.
ABS brings a lot more control to the table than the old method of manually pumping your brakes ever could. People that didn't know to pump their brakes in a non-ABS vehicle would ride their brakes into what ever was in their path.
Depending on the vehicle, heavy brake controller settings such as 10/10 in GT5 without ABS on seems to assume your wheels are locked up even under very mild braking. I experienced this at Tsukuba testing the Mucielago LP 670-4 SuperVeloce '09 for the 9 hour Spec-A event.
Balanced Brake Controller Setting: This may not mean balanced braking, which is actually affected by the CG (center of gravity) limit of the vehicle.
The axle with the most braking force is going to tend to want to be in the front, which will result in a tendency to spin the vehicle around backwards if the rear axle's brake force takes the vehicle beyond its CG limit.
To verify this for yourselves, perform the following test:
Step One: Select your testbed vehicle.
Comments: I used a Daihatsu OFC-1 Concept '07 as the test bed vehicle because it is stable, light, and lacks the ability to overpower and spin on throttle alone. Raw power and weight will just muddy the waters with uncontrolled amusement park spins, and, while amusing with damage turned off, does not contribute anything but violence to the test.
Step Two: Center the car's balance with ballast (a neutral CG).
Comments: Use or configure a car with a neutral CG 50/50 balance.
(You can use a minimum amount of ballast to test by moving the ballast position as far towards the light end of the vehicle as possible (+or-50) then load only enough ballast to achieve a 50/50 balance.
(You can use a minimum amount of ballast to test by moving the ballast position as far towards the light end of the vehicle as possible (+or-50) then load only enough ballast to achieve a 50/50 balance.
Example:
Ballast Position +50 with a weight of 159kg = 50/50 for this vehicle.
The default balance for the OFC-1 = 40/60
Ballast Position +50 with a weight of 159kg = 50/50 for this vehicle.
The default balance for the OFC-1 = 40/60
Step Three: Pick your test track.
Comments: I selected the down hill segment of the Eiger Nordwand Short Track
Step Four: Turn all driving assist off including ABS
Comments: ABS has a dampening effect on brake balance.
Note: Do not steer while braking for these test stops. Only brake when the car is traveling downhill in a stable straight line.
Test One: Set brakes 10/0. Start the test by accelerating to say 70MPH on down hill, slam on the the brakes, and watch what happens.
Comments: The result will be your vehicle will stop in a straight line.
Test Two: Set brakes 0/10. Start the test by accelerating to say 70MPH on down hill, slam on the the brakes, and watch what happens.
Comments: The result will be your vehicle will spin around, and if you don't hit anything and you still have momentum, you will end up going down the hill backwards until you come to a stop. The faster you are going, the more spins you may experience.
Conclusion:
For balanced braking, you want to set your braking force bias so that in a straight-line, down-hill stop without ABS you have the maximum braking force you can apply to the rear axle without introducing uncontrolled spin or pronounced left or right yaw to your vehicle. Under optimal braking conditions there will be some minor yaw due to minute amounts of lateral G force introduced by differences in grip based on pavement and tire conditions (etc.). These conditions will also introduce a mild oscillation (or tendency for the car to wiggle) during braking.
Unless your intention is to introduce yaw to start a drift, or you desire to point the nose of the vehicle inside a turn by having the rear end tend to slide out, one should aim for as neutral and stable a result as possible when brake tuning. Then when you're done tuning, re-enable ABS . You should have the most effective, stable, and controllable braking your vehicle can produce.
The weight balance was just for this test. I am not suggesting you should balance every vehicle 50/50; though it can improve braking (dependent upon the natural balance of the vehicle), the performance penalty from correcting of bad balance by adding ballast can make you non-competitive. Even though you gain stability and performance points that may be utilized else ware in your tune provided the resources are available.
Off topic: The balance of your vehicle also greatly effects under-steer/over-steer conditions and can be used to correct them though, again, at a cost.
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