Braking and turning in - Trail Braking

[raymondu999]

If you look at a lot of pole laps; or even onboard laps; you often see the driver braking until the apex; then rolling completely off the brake at the apex and getting on the throttle. What exactly is the advantage of doing this? Surely if you're braking; you would just be taking grip that could be used for centripetal force,for braking? I would surmise they decrease the brake pressure as they are still turning the steering wheel so as to not create understeer, so that more grip can be used for getting the lateral acceleration; rather than the backwards longitudinal acceleration.

My point being; wouldn't you be able to carry much more speed if you had used all of the grip for lateral acceleration; rather than using some of it for braking?

[NonNewtonic]

According to some ex-egineers its not wrong to brake early the key to et through the corner fast is get on the throttle as early as possible so by braking early drivers could be on the throttle and start sqeezing some power througout the corner

[raymondu999]

Upon watching the F1 Review DVD when you watch Turkey; when Lewis and JB are talking of their battles in Turkey 2011; JB told Lewis; that Lewis was always braking too late into Turn 9; while Button braked early and set the car up immediately for exit; and was flat for most of the 9-10 chicane; for a good exit. Here:
[youtube]http://www.youtube.com/watch?v=owQeF3RaR8Y[/youtube]

My point is; a lot of people do the braking+turn in thing. Some corners everyone does it; such as Abu Dhabi and/or Istanbul Turn 1. But some corners some do and some don't; for example at Portier. If you watched Kubica's onboard he brakes all the way until the apex and when he hit the apex; he rolled completely off and went on the throttle. I don't get it though; You'd be compromising your braking grip and getting less deceleration; but at the same time your turning is also compromised. Isn't it a negative double whammy?

[machin]

This makes use of something which is refered to as a "traction circle" (although it might not actually be an actual circle with many tyres). But for the moment imagine its a circle... The radius is the amount of grip,and the angle on which the radius is measured is the direction of the force, so a pure lateral load would be represented by measuring the radius from the centre of the cirlce directly outwards to the left or right. A pure acceleration or deceleration would be shown by a line purely on the vertical axis. So you can have 100% grip in lateral and 0% in longitudinal or 100% grip in longitudinal and 0% in lateral... ok, but what about the ponit where you have a bit of lateral and a bit of longitudinal? Well if the angle were measured at 45 degrees you can have 70.7% in lateral AND 70.7% in longitudinal!!! (cos 45)*100% and (sin45)*100%.

So you can see that you have higher performance if you smoothly blend between lateral and longitudinal forces(as opposed to the classical thinking where all braking is done in a straight line).

[raymondu999]

I was thinking of a traction circle analogy as well - I liken it to those old telemetry displays we see on onboard laps; i.e. this one:
[youtube]http://www.youtube.com/watch?v=tPs7k-0SaYg[/youtube]

Which let's face it is basically the same thing.

However I didn't exactly think of it in terms of Cartesian coordinates; but rather more like a polar graph - I don't remember if that's the correct term; but rather than looking at the distance from vertical and horizontal axes; we should be looking at the distance from the center. After all that was the point of it being a circle in the first place - it's used to describe a tyre that gives you the same amount of grip; whichever direction the force is being applied. I don't 100% buy that at a 45 degree angle on the traction circle they can use 70.7% of long and lat grip - where would the tires produce the extra grip from?

In his Brawn days for example, Jenson used to apply brakes while he was turning the wheel; and as he held the wheel steady; hold constant speed with part throttle.

[i70q7m7ghw]

Trail braking is a well known technique tbh.

[SiLo]

I think if they brake until the apex, they turn in early to compensate. It may be faster but it may also use the tyres more. That's the way I see it anyway. That video of Lewis and Jensen is interesting though, still having a laugh about fighting it out!

[timbo]

This is indeed a trail braking, and is widely used.
The main advantage is that with trail braking you can brake later. This stems from better exploiting the available grip from the tyres.
So, if you want to be fast you have to trail brake.
But there are many tiny details on how you do it -- as the braking and turning is combined you can manage the proportion and this is where driving styles are most different.
For example, both Schumacher and Hamilton are said to be preferring oversteering attitude of the car, but from my observation they use it differently.
Schumacher trail brakes a lot, starting to turn the wheel pretty early. Because of this he needs rather rear brake bias, so as too not lock the front wheels. By pushing front wheels right at the limit of grip Schumacher manages rear end instability -- so he actually has both four wheels at the limit.
Hamilton OTOH, does not combine turning and braking that much. He brakes on the straight line for a longer time, but that turns in more aggressively. He needs very grippy front end to promote faster yaw rate.

[machin]

I don't 100% buy that at a 45 degree angle on the traction circle they can use 70.7% of long and lat grip - where would the tires produce the extra grip from?

You can see this effect in the video you posted; at some points the G-force point is near the edge of the circle -but above the pure lateral line -showing that the sum of the lateral and vertical loads is higher than when the car is at peak lateral alone... just freeze the frame at some point and check out what the respective lateral and longitudinal loads are. Its a well understood phenomenom and is taught in all driver training programs. The classic "All Braking in a straight line" rule is wrong and out-dated.



In this frame Schu is achieving about 85% of his max lateral load at the same time as about 50% of his max longitudinal...

[timbo]

In this frame Schu is achieving about 85% of his max lateral load at the same time as about 50% of his max longitudinal...

To be fair he is at 85% of the graph, but not of his actual max lateral g-available.
But yeah, available g-g diagrams are actually not a circle, but are sort of squarish.

[raymondu999]

Ok now I can see where I (conceptually) went wrong. I was thinking that the source of grip was the tyre, and that produced a friction force in whichever direction. But what I'm getting from this discussion here is that I should view the longitudinal and latitudinal friction forces as two separate things. Gotcha.

[timbo]

But what I'm getting from this discussion here is that I should view the longitudinal and latitudinal friction forces as two separate things. Gotcha.

They are not completely separate, after all there's temperature buildup and both process heat the same tyre.
This is reportedly one of the quirks of Pirelli's, that they are not that good at combined grip.

[raymondu999]

Yes that is true. I wonder if that is hurting some of the more prolific trail brakers

[scuderiafan]

EDIT: Somebody already made a point about trail-braking.

[mep]

Don't forget load transfers from rear to front under braking.
This means you steer when you have more lateral force potential on the front.