Brake bias

[varley16]

ive noticed drivers adjusting there brake bias on certain corners.

why?
what are the advantages?
whats better for the hard braking slow corners?

thanks.

[mep]

That’s my theory about it:
I think the reason is aero and speed related.
The downforce mainly comes from the front wing, the rear wing and the floor.
The front and rear wings have different size and coefficient of lift so one wing will produce more downforce than the other.
Downforce is a square function of speed so when your speed goes up the wing producing more downforce will do so more and more. This will move the cars center of pressure (CoP) towards this wing at a given speed.
The CoP shift then will be multiplied with the tire friction coefficient making the effect bigger. This means your grip situation of your tires changes with your car speed. When you want to get max use of it you adjust your brake bias accordingly.

On the graph you see the effect. Don't look to close to the figueres they don't fit to an F1 wing.
FW =front wing
RW = rear wing


Uploaded with ImageShack.us


(I wonder if anybody will complain that I am to theoretical again )

[timbo]

The main reason for changing of brake bias is the profile of the braking zone. When you're braking in a straight line, with little trail braking, you may want to exploit front weight transfer to the maximum and also have very stable car, which means front brake bias.
But if you're braking and turning simultaneously some of the traction budget of the front wheels is gotta be needed for turning, so you would want relatively rearward bias.

2mep — what you say is definitely true. At high speed you have a lot of DF and drag, so you're able to pull more g's when braking, which causes more weight transfer to the front. So ideally you want brake bias to move from front to rear while braking.
However, it is almost impossible for driver to precisely control balance WHILE braking (however, it seems like some used throttle to do just that). But @ espionage hearing 2007, it was told that Ferrari used simple mechanical system to delay the onset of rear wheels braking.

[marcush.]

it was very often stated that you cannot lock the brakes at high speeds .... the question will be is there much weighttransfer when you hit the brakes at this elevated speeds and of course the downforce levels maybe increasing and cop shifting through the increase of angle angle of attack and rake ... would this mean you would want significant bias movement during the braking itself ...
initially you would retard the rise of the brake pressure at the rear witht the weight shift forward but as this is done you could surely move brake balance progressively to the rear and stop this as the downforce comes down only to have as much as needed to the rear to help turn in


I used such a mechanical brake delay valve 10 years ago already ...made in USA by Stewart components..itwas a simple device that only retarded the rise of the line pressure but not the pressure itself...simple bleed piston with spring actuation opening the port .

[timbo]

I used such a mechanical brake delay valve 10 years ago already ...made in USA by Stewart components..itwas a simple device that only retarded the rise of the line pressure but not the pressure itself...simple bleed piston with spring actuation opening the port .

That's probably very close to what Ferrari used.

[tinhouse]

However, it is almost impossible for driver to precisely control balance WHILE braking (however, it seems like some used throttle to do just that). But @ espionage hearing 2007, it was told that Ferrari used simple mechanical system to delay the onset of rear wheels braking.

I've always wondered if I imagined this but I'm sure I read years back of braking systems where the driver could finely control brake balance by rocking the pedal from side to side. From the article I got the impression that it was common in F1 cars, although I don't think I've ever seen it repeated anywhere so I've come to think that I might have misunderstood something ....

Matt.

[autogyro]

I used such a mechanical brake delay valve 10 years ago already ...made in USA by Stewart components..itwas a simple device that only retarded the rise of the line pressure but not the pressure itself...simple bleed piston with spring actuation opening the port .

That's probably very close to what Ferrari used.

Back in the 70s they had a brake compensator valve on the early mini Cooper S.
We used to modify it and make it driver adjustable inside the car.

[raymondu999]

We often see drivers deciding on a brake bias, then they decide to brake later/harder, and turn the brake bias. I wonder which way they turn the bias...

[marcush.]

I used such a mechanical brake delay valve 10 years ago already ...made in USA by Stewart components..itwas a simple device that only retarded the rise of the line pressure but not the pressure itself...simple bleed piston with spring actuation opening the port .

That's probably very close to what Ferrari used.

Back in the 70s they had a brake compensator valve on the early mini Cooper S.
We used to modify it and make it driver adjustable inside the car.

that was a modified original equipment piece of the mini...it is a piston augmented by a spring ,to effectively restrict line pressure to the back .,by making the spring preload adjustable to a degree riar bias was adjustable...although only a reduction of rear hydraulic force was possible...with the minis rear drum and front disc arrangement it was of course a bit of an issue with baraking performance as the brakedrum rears are much easier to block than the discs and they tend to overheat quickly when you start to put seriously brake with the drums...

the concept of delayed presure buildup as I described is completely different to this restricted line pressure ...you can use a lot more rear brake bias when you build up brake force at the rear later (depends as well on (anti)dive /lift characteristics when you hit the brakes as well ..)

[747heavy]

We often see drivers deciding on a brake bias, then they decide to brake later/harder, and turn the brake bias. I wonder which way they turn the bias...

if they decide to brake "harder" - most likely more forward brake bias, as you will get more load transfer to the front of the car. Therefore less load on the rear tires.
But it will depend on the general layout of the car in terms of downforce and weight distribution. IMO

Another reason is that locking up the front is a "safer" more "stable" condition then locking up the rear. Especially when you brake and turn in (late braking).

[747heavy]

@ markus

Hi Marcus,

I´m not sure Ferrari wanted to/has retarded braking on one axle with their system.
I think it was a dynamic change in brake bias during braking.

If you don´t mind to share, why would you want to retard (delay) pressure built up in one circuit?
Thanks !!

[speedsense]

ive noticed drivers adjusting there brake bias on certain corners.

why?

Of the many reasons to adjust brake bias, two tend to be at the top. One is the grip of the racetrack. The higher the grip of the track, the more percent of front bias is needed. Lesser grip and the adjustment goes to the rear. For instance, when Monaco practice starts the brake bias will be changed towards the rear. As the weekend progresses the brake bias will be moved towards the front as the grip level increases.
Heavy rain will almost always be the highest percentage of rear brake bias.
In some cases on the same track, some braking areas may have less grip than other places (even with the same top speed) which may require a change in bias for optimum braking, at that perticular braking area.
2) With wings and the speed attained, at the initial strike of the brakes, the wings drag "can" create an imbalance of braking grip on one end of the car or the other (depending on the wing types and DF numbers). Ideally the brake bias needs to "match" this imbalance. As the car slows down, and the wing drag decreases this imbalance will change to the mechanical balance and move the required balanced to the other end of the car. (A lot of times, this is the rear that needs more bias moving towards the front as the car slows down)
Ferrari built a system a few years back (called "Quick change") that moved the bias during braking towards the end of the car that needed it, after the wing drag declined. It was setup as three settings, one for high speed braking (the highest top speed of the track) and two other "speed" adjustments for lower speed (less wing drag) corners. The driver had "preselected" settings for bias based on speed and a method to move the bias automatically as the car slowed in the braking area.

IMHO

[Tec5nical]

Now my question is, am I right in this conclusion?
Drivers should be cautious to not to lock the rears by not over-downshifting. Cuz the resultant engine braking sums up with the disk braking and as the result endangers the rear end's stability.
On the other hand, ideally, it usually is better for the car to have more braking bias in start of braking and transfer it the rear axel as they slow the car down.
As far as I've noticed Lewis Hamilton and Robert Kubica tend to go much later on downshifting during a braking period, but as they start to it, they do it much faster. I wonder whether if in fact they are using engine braking to improve their desired actual changeable braking-bias path (algorithm) they want to, during the braking period?

[Belatti]

Another ingredient missing in the soup here is the fuel load. Now it vary way more than in the refuelling years...

[wrcsti]

@ markus

Hi Marcus,

I´m not sure Ferrari wanted to/has retarded braking on one axle with their system.
I think it was a dynamic change in brake bias during braking.

If you don´t mind to share, why would you want to retard (delay) pressure built up in one circuit?
Thanks !!

While i doubt the validity of tht claim i can see on a long straight having tons of rear brake bias at the start of braking and it progressing forwards as rear downforce is decreased to keep from locking the rears or wheel hopping.
That being said brake bias adjustment has little to do with downforce, not everything in an F1 car has to do with downforce. Its mostly to maximize the tires grip all around without locking them. It also if properly set and driver dependent can be used to control turn in agressiveness.
The reason you see so many adjustments is to get the max out of every corner.