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What is the tiny tap on the brakes whilst accelerating for?
Well, I know in NASCAR the announcers, including Jeff Gordon and Dale Earnheart Jr., always say they do it to make sure the brakes "are still there". The cars experience brake failure so rarely though so I don't really understand why they feel the need to check that they still work. Maybe they're tapping them to get just a little bit more heat into them before they apply the brakes fully?
After years of watching videos about driving fast on a track, the conclusion I took about brake application is that it’s not meant to be sharp.
People such as Rob Wilson speak about a progressive application so the car is not unsettled and the weight transfer is smooth.
Yet time and time again I see racing drivers just stamp the brakes as hard and fast as they can. For example:
Is that not a good racing driver, or is the smooth and progressive method flawed for lap time?
imho it doesn't make any sense to apply it smoothly. It may be better for consistency's sake, since you have some leeway to adjust the braking forces in the braking zone. But I don't think "unsettling" the car is an issue. And if it were, I would just make the brake pedal progressive. I.e. changing the pedal geometry to "map" a smooth curve on a linear pedal progression.
You are absolutely right, in the initial application of the brake you need to “set” the weight of the car forward before you can decelerate at the max.
But, all is relative. The harder the car is sprung, the faster this goes. Also, although it looks like in the video he slams on the brake, he doesn’t. Brake paddles have an initial travel where nothing happens, the travel of the pads etc, then, if you apply force, the travel is minimum. So, taking out the slack is super fast, your brake paddle is now hard (pads to the disk), then you apply the initial pressure to set the car (for instance, 300N), if the front suspension is at its lowest, you put more pressure on it, in the region of 600-1000N depending on the car, brakes, etc. This will happen very very fast. You won’t see the build up from 300-700N within a quarter second in a video.
If you don’t do this 300M phase, your front tires will lock before you hit 500N of pressure, because the weight is not yet on top of the front wheels and the suspension is not down yet. You will bounce off the track.
Generally, the softer your springs, the slower the weight transfer goes. You car really feel this well on motorcycles, which have, in comparison, lots of travel in the relatively soft suspension. Any biker knows that you have to be progressive on the brakes if you are really on it.
The tap on the brakes could well be a tic from the driver or in this particular car a way to take a bit of the first slack out of the paddle
... If you don’t do this 300M phase, your front tires will lock before you hit 500N of pressure, because the weight is not yet on top of the front wheels and the suspension is not down yet. You will bounce off the track.
.... Generally, the softer your springs, the slower the weight transfer goes.....
the weight transfer doesn't depend on suspension stiffness
(considering the car as a 'black box' how can it so depend ?)
some weight transfer is invisible because it is done by forces within damper and suspension linkages
some weight transfer is visible because it is done by compressing the suspension
weight transfer eg at 500N of 'pressure' is the same regardless of how it is spread amongst visible and invisible paths
....then you apply the initial pressure to set the car (for instance, 300N) ....
... If you don’t do this 300M phase, your front tires will lock before you hit 500N of pressure, because the weight is not yet on top of the front wheels and the suspension is not down yet. You will bounce off the track.
Generally, the softer your springs, the slower the weight transfer goes.....
the weight transfer doesn't depend on suspension stiffness
(considering the car as a 'black box' how can it so depend ?)
some weight transfer is invisible because it is done by forces within damper and suspension linkages
some weight transfer is visible because it is done by compressing the suspension
You are very right. Just more visual indeed. Also, softer springs have generally more travel and it takes a bit longer to transfer the load back into the tires.
On vehicles with anti dive, you can put pressure on the front a lot sooner.
The bit about progression being built into the brakes on purpose was something I never considered.
Don't forget as well, bespoke racing cars usually don't have assisted brakes like on your road car. They need a lot more pressure then what you know from what you drive on a day to day basis (but also gives a lot more feedback). Forces of more then 1000N are not unusual (in F1 its around 1500N max). In a road car, I think you already kick in the ABS around 200N
By the way, there is no progression build in to the system itself, all has to come from your upper leg strength. It's really set up as simple as possible. pedal goes straight on the master cilinders and those are directly connected to the callipers.
I forget the exact numbers but the boys on SKY said a couple of races ago that the amount of pressure needed on the brake pedal in an F1 car is extremely high. Higher than most civilians can even apply. What looks like "stamping" on the pedal to us is just the pressure needed.
Especially in the position they sit, F1 drivers need very strong leg muscles.
To achieve anything, you must be prepared to dabble on the boundary of disaster.”
Sir Stirling Moss
