Adjusting brake bias during driving

In some cars you can adjust it on the fly. How much difference does this make, and what is the basic principle of adjusting it?

AFAIK more front bias gives better stability, more rear bias more efficient braking (as long as you don't overdo it)? But are you actually supposed to do this on the fly, and if, how? I have never touched it during driving, because I have no idea if it has notable effect or when/how much adjust it.

 

more rear bias stops the car quicker but is more unstable entering turns if you are trail braking. It's different for each corner though.

That's the basics, there are also tyre wear and heat implications etc.

 

I have it assigned to 2 buttons on the wheel and use it quite a lot when I jump into a server and I have to quickly adjust the car, braking is so important that you have to get that sorted first of all I think. Of course if I had a decent setup done already I might use it less. Also, track conditions vary and you may find yourself locking the front or rear tires, in that case a quick tap at the buttons and you are again in a safer zone. Also, fuel load makes the car heavier and you may need to compensate for this, then when the car gets lighter you rebalance. Also, you may want to be more aggressive if you need speed (eg. move it to the rear) and then come back to a safer setting if you're just controlling the race. Quick guys may also change it on each corner.. I'm far away from that though.

 

It depends on car type, track etc but in general it can be approached in 3 "ways":
1) You go out on the track (possibly load your favorite setup) and then depending on how much grip and temperatures there is you fine tune the brake balance to suit it and then it remains constant to the end.
2) Reactionary to changing conditions - for example you follow a car very closely and overheat front tyres due to lack of downforce - bias helps controlling the temperatures, then you tune it back when you are in the clear.
3) On per corner basis - usually there are 1-3 important corners on track that can benefit a different than normal value, you change the bias lap after lap according to predetermined way. (This does require a lot of practice of the same combo to get right)

As for what's and when's the brake balance:

More front bias
- when braking downhill (Imola second to last turn) (reverse for uphill - but it's less important as brake distance is much shorter anyways).
- when anticipating oversteer mid braking (Imola T4).
- when rears start to overheat (to both control the car better with brake input mid corner, and to let them cool a bit more between the corners).
- when grip goes up (more grip = more weight on front less on rear during braking) (this works with downforce too - high speed braking wants more front bias, but it's usually not used as engine braking is doing the balance change already).

More rear bias
- to fully use grip of all 4 tyres (as 95% of cars in AC have default safe front bias) = braking better. (It's really car dependant - some cars have no problem locking rear first, others will snap as soon as there is underrotation on either rear wheel).
- when grip goes down (tyres wear out, overheat, even stuff like changing tyre compound between sessions (Qualy=Soft slicks -> Race=Mediums) etc).
- when front tyres overheat in long fast corners - to get better "turn in" before applying throttle and dynamically reduce the understeer. (to offset the change for braking itself you ease on downshifting)
- on cars that don't snap oversteer in trailbraking - to stop front inside from locking and get better turn in.

Also if the car has ABS with more forward brake bias, there is no big need to change it as it's possible to balance the braking (front-rear) on ABS alone by using brake pedal. (as you press the pedal at some point front stops gaining braking torque and the last part of pedal travel will only increase the rear braking).
Personally i do 1) always, 2) often and 3) only sparsely when there is actual time to be gained (~0.1+s) and i'm pushing for best laptime. Using G27 i have it on 2 of the red buttons on steering wheel.

 

In AC you can effectively put 100% braking on either axle, which I don't believe is correct. In reality you would never shove 100% of the braking force to just the front or rear. I'm pretty sure that in a race car it's lever operated and has maybe "10-15 stops" to shove the bias front or rear. So really the values should be something like;

Front min; 55% Rear max; 45%
Front max; 75% Rear min; 25%

 

hahaha what? why would you not want to put 100% of your braking on both (not either, you cant do that in AC... if you put 55% force to the front, ther rear will recieve 45%) axles (that is how it works in AC, it's why it is called bias)?