ryoung

I'm the crewchief for our racecar, not the driver. Keeping that in mind ...

Yes, "trail braking" is continuing to brake after turn in. You never want to make sudden steering (or braking or acceleration) inputs into the car because it upsets the car's balance and because the very high instantaneous loads can overload the tires. Everything must be smooth turning in to a corner, you want to start with a small steering input, increase steering gradually until you reach the apex, and then gradually unwind, even when it's all done relatively quickly.

A tire is capable of ~1.0g of acceleration in any direction -- braking, cornering, acceleration, and most important ... combinations. Coming into Grattan's Turn 1, if you complete all your braking at 1.0g and then turn in, you won't be back to 1.0g until the apex of the corner. The result is that the car's tires are not at their maximum potential between turn-in and the apex, and the car could be going faster. You could be braking as you're turning, gradually releasing the brakes as you increase steering, off the brakes by the apex, and reverse the procedure with the gas pedal and unwinding in the exit. Theoretically, you can maintain the tires at the limits of the "friction circle" thru the entire turn, not just near the apex, and go faster thru the entire turn. Also, note that the reverse of trail braking is occurring in the exit, but it's much more natural as you unwind to increase the throttle just enough to stay on the desired line to the track out point at full throttle.

That was the easy part, now the hard part ... You're absolutely right, straight line braking is MUCH more comfortable than trail braking, and I usually straight line brake also. If you're braking too hard after turn-in, the car will spin! From the table, you can brake at -0.26g while cornering at 0.88g. With any more braking, you're outside the friction circle, oversteering, and spinning. Also, if you straight line brake, you always have a little reserve left in the tires between turn-in and the apex. If you miss the turn-in, you can tighten the line a bit and still get thru the corner. If you're trail braking at the limits of the friction circle and try to tighten your line, well ... you're screwed.

Having said all this, the most important turn on a track is the turn leading onto the fastest straight, not the turn off of it; and the most important part of a turn is the exit, not the entrance. Any additional speed you can carry exiting a turn is additional speed down the entire straight, not just the short segment at the end between turn-in and the apex. At Grattan, by far the most important turn is actually Turn 10! Since 11 and 12 can both be taken flat out, any additional speed exiting 10 is carried for about 3/4 of a mile at full throttle all the way to Turn 1.

Serious racers are trail braking where it's a benefit, especially when the slower speed at the entrance of a turn is the opportunity for someone to pass you! This is obviously not an issue at an Audi driving school, but trail braking is a good skill to develop. Don not only trail brakes, but he left foot brakes also. At the apex, the right foot can start adding gas as the left foot has finished releasing the brakes. There's no wasted time, or speed, when you're right foot is in the air doing neither.

<img src="http://www.audipages.com/on_track/grattan1.JPG">
<img src="http://pictureposter.audiworld.com/17157/weightdistribution.jpg">

PaulW

Thanks....puts it all in real work perspective!

mclarenm8d

I have to re-wire my driving when I go from a RWD car to the Audi and vice versa, because I always trail brake on the street.

On the street, to get a feel for this in the Audi, think to begin your turn-in first then lift off of the brake. So, one-two-three-four, one-two-three-four, off throttle-brake-begin steer-lift gently off the brake. You will quickly get acclimated to the benefits. Also, with quattro we can get on the throttle very quickly after braking is complete.

Randy implies some elements that you have to be careful about with braking hard and trail braking, so please don't try learning this at 9/10ths. You can feel the benefits on a lazy 90 degree turn at 20 mph. Also, I do the opposite after getting into a RWD car when getting acclimated to trail braking, I think to begin lifting off the brake first and then steer so I don't have the *** end swapping around on me.

There are some that completely argue against the benefits of trail braking with an Audi, but I think Randy's analysis is the most complete assessment presented on this forum of what is the best in what cases.

ryoung

I took my spreadsheet and plugged in the inputs for an M5 with it's 50/50 weight distribution, and it's very apparent why you have to re-wire your driving habits. Steady state cornering limits are higher, but without the wider tires in the rear, ANY trail braking results in oversteer and risks a spin. Corner exit is interesting also. At partial throttle, the car is near neutral with high cornering limits. At full throttle, though, things go very bad in a hurry. With all acceleration loads handled by the rear tires, oversteer sets in with a vengence. In Skiwi's Stasis link, Paul Lambert claims that he can get on the throttle in his A4 2-3 car lengths before any RWD car.

I want to reinforce your point that you don't want to trail brake at 9/10th's on the street, but I practice this a little differently. On an Interstate exit ramp, most of the time you'll complete braking in a straight line before turning in for a cloverleaf. For practice, do complete nearly all of the braking in a straight line, and then begin releasing the brakes quickly, but also very deliberately. Just before the brakes are totally released, begin turn-in. The "easier" turn-in will be readily apparent. As you get used to the car's response, you can begin turn-in with more and more braking, and still stay well below the limits of the car.

On the track, I find trail braking helpful where turn-in is difficult for some reason, such as when the track is downhill at turn-in. Grattan's Turn 5 is a good example of this. Not only is the track downhill, but the straight crests just about at the point where you'd like to start braking. To avoid braking just after going over the crest when the tires are almost off the ground, you either have to brake a bit before the crest, or wait till the car settles after the crest and trail brake thru the corner entry. I think Turn 5 was the only turn at Grattan where I normally trail braked.

barryl

Hey Paul,

You need more seat time, that's all.
Right now, your car has more ability than
you do. Since you started with a very competant
car, then enhanced it (suspension, wheels,
brakes), your car has lots going for it.

Regarding Randy's analysis, it is a good start,
but there are lots of assumptions. For example,
the ABS on the A8 is sophisticated, when braking
for a corner, the front gains grip and the
rear loses it, but the ABS allows each WHEEL to
brake as muc has possible.

The quattro also maximized grip when getting out
of the corner. Where a real wheel car would tend
to spin the inside rear wheel (without a limited
slip differential) the quattro will move the
drive to the wheel with the most grip.

Finally, using better tires will also increase
the grip from the levels listed.

I have run some laps with a data logger connected
to my race car, a Porsche 944 turbo. With Hoosier
R3S03 tires, I was able to pull 1.2G in braking,
and 1.3G in cornering.

Regarding trail braking, that is something for
advanced drivers, not beginners (and you are a
beginner until you have done at least 3-5 track
days). I am the chief driving instructor for my
PCA region, and I don't talk about trail braking
until the students have moved into the intermediate
run group.

Finaly, remember that just because a race car does
something does it does not mean that it is the
right thing to do in a driver school. When
you are racing your goal is NOT lap times, but
to get ahead (and stay there) of the other drivers.
Race drivers tend to early apex corners in a race
because if you don't, and there is someone behind
you, they can execute a 'drive bomb' pass where
they will stuff inside of you, preventing you from
driving down to the apex. So you have to drive
defensively, early apexing to take track position
away.

Take care,
Barry

PaulW

I don't think I'll be trail braking the first day at Road America, or the second day for that matter.

The one thing I have come to realize reading everything and being on the track is that the car has way more skills than I do driving it!

An experienced driver in my car could get around a track faster than an unexperienced driver in an RS6 (okay...I don't want to start a debate, you get my point though).

I love thinking about how I'm going to drive at Road America, and getting mentally prepared for it.

Once I get there, I'm like a kid looking up at the ski hill - scared ****less.

Then once I get on the track....I eat it up! It's so much fun....the most important thing is to remain calm and don't grip that damn steering wheel so hard!

I guess that's the level I'm at....two track days under my belt....hopefully it will be four in a couple of weeks.

BTW, how the heck to do you get all your posts to stop at about 250 pixels wide and go to the next line?

pw

mclarenm8d

And as always Randy, you add the voice of reason.

Relative to the analysis you provided, I should clarify two items about my earlier comments about trail braking on the street for those reading through these posts -

1. I am not "hard" trail braking, more a matter of being somewhere between hard trail braking and easing off the brakes relative to Randy's data,

2. Applying trail braking on the street in the interest of finding the limits of a car's traction is quit dangerous to innocent bystanders.

The reason I do this on the street is because if feels (and sounds) less abusive to the tires, and therefore feels right to me and is more rewarding during a daily commute. As an aside, one can usually note if a fellow driver is an "excessive" control banger and straight line braker by how badly the crowns of their street tires are worn.

Sarge

All you're doing, in a general sense, is bringing the rear of the car around by reducing the weight over the rear tires and increasing the lateral force (braking while turning). Increasing weight to the rear wheels (accelerating) is one of the 'outs', as are dialing out the turn.

SO practicing safely really just means having the space to accelerate and straighten the car.

I'd say the first thing to have a handle on is how your car responds to revocery attempts once you're headed out of control. In our case (quattro) adding throttle (if even only a little) along with some counter-steering will yeild the result you're looking for.

The best place to practice trail braking on the track are corners with safe run-out areas that can be approached from moderate speeds. Like skiing you have to have enough momentum to initiate the turns. And I'd say you'll want to try some ham-fisted manuevers at first just to get a real direct sense of the limits of your setup and the characteristics of recovery.

Then you can smooth out the 'ham' and increase the speed. You just have to have enough 'critical mass' (and momentum) to start with.

In my experiences with these cars, depending on whether it's wet or dry, either neutral (wet) on-throttle is what brings you back in control.

Just never give it more brake once you've started to bring the tail out unless you want more tail out. The brake is not a chicken out mechanism.

Randy and mclarenm8d have far greater knowledge than I do, I'm just trying to share a layman's perspective of 'the learning curve'.

Have fun! Wish I was there!!!

PaulW

Thanks, practiced on some back roads today - does significantly reduce understeer

Sarge

Going into a left hander, fake right, then go hard left while braking just long enough to get the tail out and hit the gas! Use the e-brake at your own discretion. (unfortunately the ebrake is a little abusive to the center torsen, so do it sparingly)...

YeeeHaw!

(Since moving to MS I have learned that the Dukes of Hazard may have actually been an early reality TV show.)