Braking and turning in - Trail Braking

[raymondu999]

but I presume that would be more of overlapping brakes and throttle; rather than any actual purposeful use of the throttle no?

[bizadfar]

I've never fully understood trail braking but I'd like to. Its very popular in sim racing. Is it due to tire wear not being as much of an issue?

It's popular in sim and real racing because it's the quickest way around the track.

You get to carry the same amount of mid corner speed, same exit speed, and you get to brake later. Can't beat it.

With regard to the "blurred edge" analogy, that's not quite what I'm getting at. And while the "edge" does move based on downforce, temperature, whatever... I'd say the limit itself isn't that blurred. Exceed the combined limit on a front tire in trailbraking and you will lock it up and push. Exceed the combined limit on a rear tire in trailbraking and you will lock it up and have a good chance of spinning out.

But, when going through a corner... even a big sweeping constant speed corner... you can feather the throttle or put some pressure on the brakes, tip some load from the rear axle to the front, and get some extra yaw attitude or rotation. This is not necessarily limit behavior, and I'd say it's a trait that most anyone who's done any driving (autocross, sim, circuit, whatever) has experienced.

Incidentally, that behavior is the reason I picked the quote in my sig.

Tires and vehicle dynamics really aren't inherently that crazy and mysterious - but people let them be so with a hail of hand waving and vague terminology.

The inputs available to you are not just to point, accelerate and slowdown. They are there to exploit load transfer.

/thread.

[timbo]

but I presume that would be more of overlapping brakes and throttle; rather than any actual purposeful use of the throttle no?

No, more like a purposeful use.
Read this .pdf if you haven't seen
http://pdfcast.org/pdf/schumacher-vs-barrichello

[allstaruk08]

http://www.dellanave.com/files/f1racing.pdf
dunno if this is the same thing i read a while back i cant open your link timbo macbooks playing up, but its clear he over laps on purpose . i was just saying drivers want to be careful if they're going to start overlapping brake and throttle with the engine safety cut off.

[gold333]

I wouldn't necessarily agree with that assessment, no.

Tires are always operating at some amount of sideslip. Just because the car is a bit "hung out" doesn't mean you've exceeded the limit capacity of the tires. Just means you've done something to make one axle work at a higher sideslip angle than the other.

So where on the friction oval would you put Senna's 4 wheel drift technique in advancing the apex?

[Tim.Wright]

So where on the friction oval would you put Senna's 4 wheel drift technique in advancing the apex?

Have a read of my post on the previous page. The fact that everyone are alluding to is the boundary of the friction circle changes depending on the state of the vehicle with respect to slip angle AND load transfer.

Senna and Schumacher have found their own unique ways of presenting the vehicle into the corner such that the friction circle of the car is greater than others.

In short, there is no such thing as "exceeding" the friction circle - instead the goal is to make your friction circle bigger than everyone elses. Obviously part of this is the car, part of this is the driver.

Tim

[gold333]

So where on the friction oval would you put Senna's 4 wheel drift technique in advancing the apex?

Have a read of my post on the previous page. The fact that everyone are alluding to is the boundary of the friction circle changes depending on the state of the vehicle with respect to slip angle AND load transfer.

Senna and Schumacher have found their own unique ways of presenting the vehicle into the corner such that the friction circle of the car is greater than others.

In short, there is no such thing as "exceeding" the friction circle - instead the goal is to make your friction circle bigger than everyone elses. Obviously part of this is the car, part of this is the driver.

Tim

Isn't the friction coefficient of a tire in a particular direction (at a certain temperature, loading, PSI, asphalt condition, etc.) a set value?

I.e. a value outside of which the tyre has lost its adhesion and is sliding? That is a fact as far as I am aware.

The outer limits of these values (in forewards-backwards and side to side tire loading) create an oval. That oval is the performance limit of the grip of the tire at peak slippage as far as I am aware. The trick is to transition from complete aft coefficient (braking) to complete lateral coefficient (cornering) to complete foreward coefficient (accelerating), i.e. skirting the edge of the oval at all times.

I am sure you know this already but I'm reiterating it just in case.

The way I see it it is as if Senna and Schumacher can get closer to the edge of the (one and only) friction oval and not increase the grip coefficient values themselves and increase the oval as you say. I don't understand this enlarging the oval argument. The coefficient of grip at the edge of the friction oval for a particular tire is a given, a maximum and cannot be exceeded unless you use a different compound of tire or something.

Edit: I think I understand you, you are saying the friction oval depends not only on the tire itself but how the contact patch of the tire changes shape according to load, cornering style, etc. I am merely postulating that the friction oval is what is possible with a certain tire on a certain car period, if God himself were driving it say.

[Tim.Wright]

A couple of things;

1. The coefficient of friction of a tyre is not a set value. It is very dynamic and non linear and difficult to predict at any one time.

2. When I talk about the friction circle, I talk about it for the complete vehicle, not a single tyre. Therefore factors such as load transfer, slip angle, slip ratio, temperature and aerodynamics, all of which are dynamically changing on the track, cause the friction limits to change.

A simple example is comparing the acceleration capabilities of a slow corner to a fast one. An F1 car has a large friction circle at high speed because of downforce so the friction circle is larger at a higher speed compared to low speed.

On a more detailed level, the friction circle depends on load transfer which is affected by the drivers throttle, steer and brake inputs.

Tim

[gold333]

I see what you are saying now. The grip of the car can be changed by the driving style.

What I was saying was the same, the best drivers exploit the grip a car can offer to the maximum.

The interesting thing (and what we were actually discussing) is what type of tire loading is best for laptime? Schumacher's religious adherence to the early turn in (at the outer limits of the grip available in his version of the friction oval created by that style of driving)?

Or say a Senna like drifting technique for advancing the apex on slow nd medium speed corners (which appears to go beyond the limits of the friction oval for that style of driving).

[raymondu999]

Just found this video on YouTube which I found interesting:
[youtube]http://www.youtube.com/watch?v=NHgoij63Ae0[/youtube]

What I found very interesting was that in the more prominent braking zones, such as Turn 1 and 4; and when Mark was very clearly trail braking; the G-meter reads constant the whole way; basically having the same net acceleration, just that it shifts in direction from the car's longitudinal axis, onto the lateral.

But would I be right in saying that trail braking should only be done as the steering wheel is being turned? I don't see a benefit in braking while the steering angle is held constant.

[timbo]

But would I be right in saying that trail braking should only be done as the steering wheel is being turned? I don't see a benefit in braking while the steering angle is held constant.

Well, that makes sense and usually it really is how it's being done, however, with loads on wheels MASSIVELY change along the way, you can have a bit different reaction even if your steering angle is not changing.

[raymondu999]

No I mean... if you're holding the wheel at a constant angle; with no understeer/oversteer (relatively speaking) generated in the car; then surely that means, that at that given point in time; with the existing load transfers; the car is able to laterally accelerate enough to turn the car as such. Braking would just mean that you're using less and less of the lateral grip when you're not increasing the demand for lateral, no?

[timbo]

Braking would just mean that you're using less and less of the lateral grip when you're not increasing the demand for lateral, no?

But braking would change load transfer big time. So the conditions you stated won't hold.

[Jersey Tom]

No I mean... if you're holding the wheel at a constant angle; with no understeer/oversteer (relatively speaking) generated in the car; then surely that means, that at that given point in time; with the existing load transfers; the car is able to laterally accelerate enough to turn the car as such. Braking would just mean that you're using less and less of the lateral grip when you're not increasing the demand for lateral, no?

Think about this-

Let's consider how much steering it takes at the apex of a corner. Let's say for argument's sake it's 60 degrees of hand wheel angle. At that point - 60 degrees of steering - we know we're at 100% of the tires' lateral traction.

Consider that entering a corner you gradually add steering. You don't just immediately go from straight ahead to 60 degrees in a snap. So as you're turning in... all that time you're at LESS than 60 degrees steer for this corner, you're using LESS than 100% of the tires grip capacity. During that time you might as well use the remainder of grip for something useful - i.e. braking.

Bit of a simplified example but hopefully that gets the point across.

[raymondu999]

Yep I know; as in my post before the one you addressed - I was asking that in overly simplistic terms, you'd trail brake while turning the wheel; but while you were at a constant 60 degrees of steering then you'd maintain speed to just use 100% of lateral traction.

Obviously when load transfer comes into the game it complicates things a lot