Trail Braking and the 911

[drsimonwong]

Trail braking and the 911. What is recommended with our special rear engined cars?

Actually can someone define 'trail braking' for me?

I understand this techique iof braking into the turn is not ideal in our cars.

Comments from those more experienced in driving would be appreciated.

Also hints on when the the seqence of events in the ideal turn would be helpful too!

Simon

[Paulporsche]

check this out

http://virtualracersedge.com/trail_braking.htm

It's tricky in our cars because that big mass of an engine also wants to help the car rotate.

[nostatic]

depends on the turn...

[robfike]

For rear engined cars (really any car) you normally want to do all of your braking in a strait line. Max brake, down shift (same time), turn in, accelerate, apex (full power), track out (full power).
Some think that using a measure of brake past the turn in point helps keep the car balanced.
Where people get in trouble with this is they are asking the tires to do too much at the same time. It is very easy to exceed the amount of available grip. When that is exceeded, the spin follows shortly thereafter.
Getting all of the braking done in a strait line, lets you use all of that grip to slow the car. Then you can use all of the grip to turn the car. This results in the corner taking the least amount of time.
A great book on this subject is: "Driving in competition" by Allan Johnson.

[Paulporsche]

AKA "Slow in...fast out".

[Zeke]

Originally posted by nostatic
depends on the turn...

What he said. There might come a time at an autox where you really need to hit a late apex and you need to rotate the car late in the turn. Like a decreasing radius tight turn. If you ride the brakes down into the turn, the car will overreact and you will have to catch it as you aim for your mark. Nice trick if you can do it w/o spinning out.

When you watch races and you see someone make a late pass at the turn entrance, that person is in need of the technique. Often times, you see the driver being passed re-pass at the exit due to his/her superior line and better exit speed. But, when it works, it works. For the accomplished driver.

[Jack Olsen]

Originally posted by nostatic
depends on the turn...

And it depends on the driver, too.

Too many novices think it's a kind of magic bullet they can break out early in the learning process. It's counterproductive to work on it before a lot of other skills are in place. Later, it makes sense in some conditions.

Often, novices find themselves doing it for the sole reason that they overcooked the entrance to a corner. It then continues, past the apex, as the tires scream and the tail comes swinging around...

[drsimonwong]

Thanks guys,

Robfike, so when you initiate turn in you are totally off the brakes- or are you easing off as you begin to turn?

Simon

[Superman]

One of the striking things I have found, and come nowhere near mastering, is that while our cars are very light in the front end and this gives them some trouble in the form of understeer (not enough traction on the front axle), you can get momentarily ENORMOUS traction by tapping the brakes. Of course, if you're going too fast, the car is going to swing like a frickin' pendulum. But if it's done right, you can tap the brakes, plant the front, turn with ABSOLUTE positiveness, and then use the throttle to get tremendous traction by shifting nearly the entire weight of the car onto the big rear wheels. It's a spin when done wrong. It's breathtaking when done right. This can get a Porsche 911 around a tight turn faster than you ever dreamed to be physically possible.

Oh, and this often requires that you have three feet.

[nostatic]

trailing throttle oversteer is the other big part of the equation. In general I try to avoid trail braking (like Jack said, it usually means I'm too hot into the corner...Tyson can do it in his sleep though), but you can use TTO on a 911 to great effect. For instance turn 4 at Willow is a horseshoe that is uphill in, downhill out. The big hp cars usually do the turn as a "V", going up high, braking hard, cranking the wheel, then heading down hill. In my car, I can stay tight, power up the hill, start the turn in, ease off the gas, and the rear end starts to swing around. When I'm pointing toward the track out, get back on the gas, the rear end plants and you're off.

That is one of the true joys of rear engine land...steering without the wheel.

[gchappel]

SporstsCar magazine- the scca pub- had an interesting article in the july issue on maximinzing the traction circle. They used an oval track and computerized data analysis- and also did some real world track testing. They talk about 3 lines:
The classic slow in fast out
A trail braking line, with a shallower entrance
An inside radius line- which gives the lowest lap times on sims.
The slowin fast out sifo- line was the SLOWEST
The trail breaking line was faster on every lap.
The trail breaking laps had slower max speeds, but clearly faster lap times- the differences may be as small as the shorter line around the corner with trail breaking.
One of the authors changed his line based on this data and put a honda civic on the 2004 national championship pole.
The sifo line is the easiest to drive- which is probably why I use it. It probably is not the fastest.
I can try to scan the article and post it if there is interest- I am allowed to do that?
I find it interesting that after 100 years of racing, we can still discuss and disagree on how to be fast- that is what makes this sport so interesting.
Gary

[masraum]

I'm sure we'd all appreciate that article. Thanks if/when you get a chance.

[robfike]

Drsimonwong, Yes- I am off the brakes at the turn in point. I break the corner up into seperate pieces. The first part is Brake and Down shift (Strait line), then Turn-in, after turn-in the throttle is coming back in so as to be at full throttle the same time the apex is reached. From there on it is a matter of continued acceleration from the apex to the track out point, and on to the strait.
Hope this helps, Rob

[dickster]

I find it interesting that after 100 years of racing, we can still discuss and disagree on how to be fast- that is what makes this sport so interesting.

It is but with all motor sport each driver has their own preferences. Same with the setups. Its comes down to what suits their driving/riding styles.

That's why I love watching Moto GP - the different cornering styles are more obvious.

[molsen]

Also try to be smooth w/ your control inputs. Some folks are overzelous

w/ their inputs & this slows them down. Take your time, set up your car,

get to know & use braking markers & reference points. Take baby steps

& build on your experiance. No substitute for track time; racers never

stop learning.

[sammyg2]

The only time I trail brake is when I am going into a tight turn and need to plant the front tires (reduce understeer). I'm just not good enough to use it to rotate the rear consistantly, but have pulled it off a few times.

Sometimes I will tap the brakes right after the turn in and immediately get on the gas, that helps rotate the car towards the apex and is easier to control for me but I wouldn't really call that trail braking.

IMO The thing that sets a 911 apart from a BMW or vette is the ability to change the car's handling with weight transfer.

[nostatic]

Originally posted by gchappel

The slowin fast out sifo- line was the SLOWEST
The trail breaking line was faster on every lap.
The trail breaking laps had slower max speeds, but clearly faster lap times- the differences may be as small as the shorter line around the corner with trail breaking.
One of the authors changed his line based on this data and put a honda civic on the 2004 national championship pole.
The sifo line is the easiest to drive- which is probably why I use it. It probably is not the fastest.

What cars did they test with? A Civic has very different dynamics than a 911.

[Bill Verburg]

A ZF type locking diff. will help, a split lockup PMS type will help even more

[Wrecked944]

Ooooh...TTO is super duper fun...and addictive like crack...after I first got it sort of vaguely under control I jumped out of my car in the AutoX paddock and hugged the roof yelling, "I love my Porsche! I love my Porsche!" It really is stupidly fun. Now I know why Henry Watts warns that it should be treated as a driving technique and not the driving technique.

But this thread is very timely for me. Like Superman said, the front ends of our cars are pretty light. And so I get very frustrated in AutoX when I brake hard going into a turn and then feed in the gas only to find the car understeering like a pig. Granted, my car has AWD which only makes it worse. But Superman's point suggests that all of our cars will tend to understeer when turning under acceleration. Is Trail Braking an answer to this?

[Randy W]

I use left foot trail braking more and more, but never in the same way on different corners. I sometimes even use it (gently) in the rain on medium speed downhill twisties to help plant the front end during initial turn in. It is faster, but takes about a year of autocrosses or track days to perfect and match to acceleration. You can end up going off line, spinning or crashing if you are not smooth enough. Like Jack, I would only recommend trail braking for slow and tight corners until you have mastered your car in a smooth and controlled way, including being able to hell/toe downshift and throttle steer without thinking about it. So my advise is to be cautious and practice at autocrosses where the risk is less.