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AutoX, DE and Racing Discussions All discussions related autoxing, DE, amateur and professional racing activities |
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#16
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Re: How To Brake?
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brad 24-year PCA member and PCA national DE instructor |
#17
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Re: How To Brake?
I too fall more into the "ramp up the brake pressure" rather than the "hit it hard" technique, but for a few as yet unmentioned reasons. First, if you've ever driven an non-ABS car, you will appreciate the additional rear brake bias that you can run when you don't initially pitch the car on it's nose. Secondly, how "fast" you can actually ramp up the pressure depends on how stiff your car is. With a softer suspension like a stock GT3 has, you have to allow time (a few milli-seconds) for the front to dive under initial application. This will prevent excessive pitching and actually allow for greater initial braking. Even with full race suspensions, I have found it better to squeeze on the brakes rather than just pound on them. The more evenly you can keep pressure on all 4 tires the more grip that you will have, and the harder you can brake.
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Larry Herman 2002 GT3 Cup 2006 Boxster S 2006 Cayenne S National PCA Instructor Past Flames: 1994 RS America Club Racer 2004 GT3 Track Car 1984 911 Carrera Club Racer 1974 914/4 2.0 Track Car |
#18
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Re: How To Brake?
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For example, we see pro drivers with very abrupt steering and throttle inputs, not to mention how they use the brakes. Nothing I see in vids can be classified as "smooth" driving from the input perspective. So, if you are in a corner with increasing lateral Gs, which increases lateral weight transfer and vertical and lateral loads on tires, the slip angles of the tires will change and that change is constant. To manage to stay at the optimum slip angles that generate the most grip, you have to modulate steering and throttle constantly as well. That is why we see such rapid and abrupt steering inputs. Similarly, the harder you accelerate, the more abrupt the throttle, when you lift off, the more weight will transfer to the front at a faster speed. If you do execute this at the right moment, the less brake you'll need to use. But again the input is not smooth, but the resultant action creates higher grip when needed and smoother output. Of course this is all in my very humble interpretation of car dynamics and driving theories.
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Fatih Selekler 997.2 GT3 |
#19
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Re: How To Brake?
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Sprint racing you can beat the crap out of the car, ^ Endurance racing you have to be smooth, and preserve the car. You'd better believe the latter are very smooth with their "inputs", otherwise the race is over early. I think you need a session or two with Hurley versus some of the curb hoppers. |
#20
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Re: How To Brake?
This is a great discussion. I've always been taught that smoother is faster. An illuminating place to learn about braking and suspension response is on a motorcycle.
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#21
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Re: How To Brake?
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Some driving schools (I once heard that Jackie Stewart was a big proponent of this) use a car with a punch bowl bolted to the hood that contains a tennis ball on a string - the objective is to go as fast as you can while keeping the ball in the bowl. I will say this - many times when you see in-car views of pros racing, they're doing these kinds of inputs because they're not on the line... when I'm doing W2W racing, and making passes, I'm spending a huge amount of time off the line in order to make headway through a lot of slower cars, or just trying to find a way around someone. Driving off the line, and in the klag, might necessitate these kind of inputs, but for fast qualifying laps or time trialing, a smooth transfer of weight, and keeping those transfers to a minimum is much preferable, and ultimately faster in my experience.
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brad 24-year PCA member and PCA national DE instructor |
#22
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Re: How To Brake?
Smoother IS faster. What's also faster is keeping the wheel straight for as long as possible as opposed to having some steering input. And having little or to no toe either front or rear (keeps the chassis from binding, putting heat in wheel bearings creating hot spots).
I race laydown karts and road race sprint karts on big tracks, you had better believe steering input slows you down. Chassis setup is paramount for control. We watch everything from scrub radius to alignment almost every practice session- we can gain 1/10sec from more power, but literally a second or two if we can get closer to ideal chassis setup. Of course all this is for naught if you can't drive... Smooth inputs at all times, smoothly to threshold braking, smoothly on throttle to WOT, smooth steering inputs to get into and out of corners quickly. Just because a car/kart can be darty does not mean that's how it's meant to be driven. |
#23
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Re: How To Brake?
No doubt smooth is faster, but I am putting an argument as to whether the input or output need to be smoother, or are they the same?
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Fatih Selekler 997.2 GT3 |
#24
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Re: How To Brake?
Obviously if you stay within the traction circle you won't lose any traction, but to stay within that circle requires you to not exceed the chassis capabilities- those capabilities determine the size of the circle.
Ultimately we are concerned with getting through turns quicker, right? Instead of thinking of turns as brake-throttle input-turn in-track out-more throttle input, concern yourself with how to get to maximum speed as early as possible by track out. That usually means forgetting you have a ton of power, carrying far more speed into and thus out of the corner on a very stable chassis, and using far less brake than you thought you needed. I noticed my car is very neutral if the chassis is balanced, so if I don't give it any input via throttle, brake or steering the car is very settled and predictable. However, giving it throttle will lift the front, reducing the traction circle for the that end, and lifting the throttle will increase it. Braking will cause a more abrupt shift in weight transfer and really reduce the rear traction circle. So, if you are smooth on ALL your inputs you will always be able to maximize the size of the traction circle on the end of the car that needs it most. Now what you do with that traction, and whether you can use it to the limit, is another matter. Of course, there are instances like in AX that you violate that concept to induce oversteer, but even AX requires a good pointy front end. I'm sure I'm oversimplifying a lot of my concepts but the gist is there. |
#25
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Re: How To Brake?
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The point of my previous post, which I didn't manage to state very clearly, is as follows: the car being a dynamic system of the spring/mass/damper kind, needs sinusoidal inputs in order to generate linear - i.e. smooth - outputs. Sinusoidal meaning slowly initially, then accelerating to fairly quick, then decelerating input to the steering, the throttle, and in case of this thread, application to the brake. I like this theory because it encompasses most of the comments from from different people, and it seems to work in real life too! -Christian
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2004 Porsche 911 GT3 Black, 2010 - Current, Parked at home 1993 Porsche 968 Club Sport M030 White, 2002 - Current, Parked at Nürburg Ring 2003 Porsche 911 GT3 Club Sport Silver, 2003 - 2005, Sold 1998 Ferrari 355 Spyder Red, 2000 - 2004, Sold Last edited by FTS; 06-08-2011 at 12:01 PM. Reason: corrected one spelling :) |
#26
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Re: How To Brake?
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The first time I went in a car with a professional racing driver, what was most striking wasn't how "exciting" it was. On the contrary it was how "calm" it all was - despite going incredibly fast. That was the first time I really got an insight into what smooth was, and how important it is to be even more relaxed the faster you go! -Christian
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2004 Porsche 911 GT3 Black, 2010 - Current, Parked at home 1993 Porsche 968 Club Sport M030 White, 2002 - Current, Parked at Nürburg Ring 2003 Porsche 911 GT3 Club Sport Silver, 2003 - 2005, Sold 1998 Ferrari 355 Spyder Red, 2000 - 2004, Sold |
#27
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Re: How To Brake?
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#28
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Re: How To Brake?
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My driving experience, as with most that replied to this thread, certainly collaborates this statement. My data also collaborates this statement. The part that is not collaborating or making sense to me is why would some professional drivers that I talked with advice me to be abrupt, especially under braking. The same thing happened during my recent PSDS visit too, which the coaches were in the camp of what Mr. Neil Roberts states. There is no questions, I put out posts that are argumentative to generate discussion, but at the end I am trying to find out what is the next level of driving I need to be shooting for. I think the answer right now for me is the sinusodial approach (Christian, you should trademark the term "sinusodial driving" ); keep collecting data and analyze it until I can hit certain lap times while being absolutely smooth with inputs and observing the smooth outputs Thank you.
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Fatih Selekler 997.2 GT3 |
#29
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Re: How To Brake?
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But......how you use the brake to achieve balance seems to vary depending on the corner. I'd love to hear opinions on when you want a flat chassis vs a loaded nose vs early throttle? For some reason, I developed a bad habit of maintaining some brake pressure on ALL turn in's; a habit of trying to keep the nose down for good grip. But I'm fighting that habit and realiziing I've got to try different things. T10 at VIR and T12 at Mid Ohio come to mind as examples of where I want straight line braking and off the brake early enough to insure a flat chassis at turn in. Both seem to have some postive camber at first and then flatten near apex.......so does flat apex = flat chassis??? If so, why does T1 at VIR seem to require a lot of trail brake? It has some positive camber on the entry but goes flat near the apex.... I assume it's because you're approaching at high speed, trying to maintain speed at long as possible with a relatively low speed exit? Yes? Or does it have more to do with the radius? I understand a lot has to do with the car but are there any rules of thumb or opinions on proper chassis attitude relative to track surface (elevation/camber/radius)? I like this thread, thanks! |
#30
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Re: How To Brake?
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For some corners like at Road America's Carousel, a long sweeping slightly downhill righthander that literally lasts 10 seconds or more, a neutral throttle will help keep the car in shape, a slight lift will tuck the nose back in (gain front traction from moving polar point forward plus camber gain from front end suspension compression that results from caster amount, PLUS a larger tire contact point at the front left wheel), and a slight acceleration will push the front a bit (scrub off lateral force if you've turned in a bit too much). Again, I'm simplifying it quite a bit, there's a lot more going on- for example, LSD locking/unlocking, the rate at which it locks/unlocks, etc. But for the most part, I think I'm not too far off in concept. Quote:
Brakes on a racecar (or street car on the track) are not for actually stopping- you never want to actually stop. Brakes are for modulating speed- a tool to get the car to behave the way you want it to BEFORE you get to the apex. I've noticed that most people tend to overbrake because they thing threshold braking into corners is the fast way- probably read it in books, but never really properly taught by someone. The function of threshold braking is far more difficult to execute CONSISTENTLY- you may be able to do it 20% of the time, maybe even 70% of the time, but to drive effectively on the track you have to learn to execute each action as close to 100% as possible. Most people I know who threshold brake to the apex (like what they teach in the Skippy books) are incredibly bad at it, tending to overly slow down their cars- you can hear their mistakes when they release the brake and get on the throttle very abruptly. Even the pros make mistakes doing this- every time you see a racecar go straight and miss the apex, the driver is probably fighting braking forces (getting the car slow enough to get within his turning traction circle). Quote:
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