Why do we go in slow to go out fast

[PShipman]

I know because our instructors "told us so."

AND ... because it has been born out in corner after corner!

But it is, for me, counter intuitive. Anyone willing (perhaps an unemployed physicist or ???) to explain WHY slow in leads to fast out????

An inquiring mind wants to know!

[Kim Crosser]

Others feel free to chip in and correct me, but...

This is most important when the corner leads into a straight - a "Type 1" corner. Consider taking the corner three different ways - slow in/fast out, steady speed through, or dive in/brake late/then accelerate.

If you brake early ("in slow"), you get your speed down to the point where you can turn into the corner and immediately begin accelerating - even before you reach the apex of the turn. Thus, you are exiting the turn under hard acceleration into the straight. RPMs and torque are up and you are maximizing your speed in the straight (which is where you save ALL the time - turns are just to force you to think).

If you slow a little, so you can "coast" through the turn at maximum speed for the turn radius, it may seem faster in the turn, but you can't begin accelerating until well after the apex, so as you enter the straight, you are late accelerating and wind up entering the straight slower, costing you time.

Similarly, if you dive into the corner and brake late, you are still braking as you reach the apex, and cannot get back on the accelerator until too late to help with the next straight.

Note that if the corner is a "Type 2" (leading into another tight corner/chicane [a "Type 3"]), then "in fast, out slow" is actually the right way to take that corner.

"In slow, out fast" gives you the fastest entry into a following straight, maximizing your speed down the straight and thus minimizing your lap time.

When you are out corner working, watch and listen to the cars going around a Type 1 corner. You will see and hear the fast cars accelerating well before the apex, while the slower cars aren't on the accelerator until after the apex.

[Jad]

Kim is correct. Another simple way to think of it is:

When you enter the corner fast, you can carry the extra speed for 10-20ft? Thus you save hundredths or at most a 10th of a second. If you can exit with even 1-2 mph more speed, then the entire straight following the corner is taken at 1-2 mph faster which may be 1/4 mile or more at a track like Fontana which can add up to tenths or even a second or more saved.

Topics such as this will also be covered in the upcoming DE/TT school

[harnishclan]

This is especially true with low horsepower momentum cars such as 944. For a slow-in corner, I prefer to transistion from late hard braking to trail brake for the turn-in, to acceleration after the front tires take a set. All well before the apex of a given corner. For me, the key is not to be so abrupt. You can watch a car that is being accelerated hard, the back drops with a corresponding rise of the front thereby taking the weight off the front tires exactly when they need it most. The throttle is an analog device and I like to roll into it instead of stabbing it. Tends to lessen weight transfer and upset tires less.

In a 944 the key is keeping the momentum as high and smooth as possible. So you can accelerate WAY before you think you can, besides it takes a minute for the hamsters to get back on the wheel!

[Dan Chambers]

My take on this:

If you enter a late-apex-leading-to-a-fast section (referred to in San Diego Region parlance as "Type 1 Turn"), you want to slow the car enough to achieve a quick turn-in/rotation of the car, before the apex as Kim mentioned, and immediately return to the throttle to commence a steady, controlled excelleration through the apex (again, as Kim mentioned) using the throttle as steerage, and full excelleration ... sooner ... for the upcoming faster section. In effect, slightly earlier on the brakes, quick and efficient car rotation and straight-away excelleration. The straight or fast section is, in effect, "lengthened" to occur before the apex. Net result: faster overall travel through the straight / faster sections, as Jad points out.

I have found that this methods keeps the car settled, and allows for a smoother, quicker, more controlled travel through a turn ... and believe me, I've tried every other way (AKA lots of spins ).

Another, simple point: the sooner you're done turning, the straighter the wheels. Straight wheels go faster than turned wheels.

Come out to the DE/TT school and learn more about this ....

[Jad]

You can see examples of this if you watch good racing on TV. IF no blocking is allowed in the series, the lead car often drives the fast line, ie slow in fast out, but the overtaking car tries the fast in slow out approach and brakes late. What happens is the second car passes the first, but the first repasses as they enter the straight and has a bigger lead than when the corner started. So in racing, you do the fast in to pass, but then get in the way of the car you passed to prevent them from repassing with the slow in fast out straight lengthening method.

[PShipman]

Thank you all for clear responses. The explainations gave me a better handle on how to understand this viscerally.

Correct me if I am wrong ... if we took the directional vectors to an extreme example ... if the car is going down a road and must hang a u-turn at some set point ... coming up to that point fast leaves a log of momentum/energy pointed AWAY from the direction which I am u-turning to (in this case a 180 turn).

So ... when I killed the Eagle front tires at 3500 miles it was most likely because I was forcing them to bleed of a lot more energy to keep me from going away from where I was turning to.

I am not sure I am being clear (even in my own mind) but it feels like this is really about (as one of you pointed out) momentum management.

Hmmmm ... still think it is just on the edge of my mind ...

[PShipman]

And Jad ... due to my addiction to motorsports in the past on TV ... we no longer have a TV ... guess I'll just have to watch you fast guys more and take more ed classes such as the de school

[Dan Chambers]

So ... when I killed the Eagle front tires at 3500 miles it was most likely because I was forcing them to bleed of a lot more energy to keep me from going away from where I was turning to.

Correct. There is a definite traction/speed/inertia coefficient between the tires and the surface. Too much speed into the equation and loss of traction + too much inertia. UNDERSTEER! So, too fast, and the traction aspect is lost to inertia .... thus the understeer and scrubbing/reducing tread on the tires. Constant understeering = constant front tire wear.

The art of performance driving is finding the threshold of speed-to-traction coefficient from a relatively straight direction through the turn. knowing the braking needs of a turn help determine the speed you can gain from the exit. Yeah, that's right. Your skill at braking before the turn will determine your exit speed. Go figure. (This is why I like teaching the Braking exercise at the PDS. Braking skills determine speed.)

(Note: air pressure can also affect wear, but most front engined cars are tough on front tires when performance driving. All that weight up-front has an impact, especially when the majority of braking and turning are both delivered to the front tires.)

[Jad]

I agree with everything except that front engined cars are hard on the front tires. Your 944 should wear front to back pretty evenly UNLESS you are really hard on the gas and get power on wheel spin eating the rears OR if you are going in too fast, turning the steering wheel too much and scrubbing the tread off eating the front. In general, you should never turn the steering wheel more than ~1/2 a turn at an AX and less on a real track.

[ttweed]

Perhaps an oversimplification, but I think Sir Stirling Moss expressed it the best:

"It is better to go into a corner slow and come out fast, than to go in fast and come out dead."

TT

[Kim Crosser]

So ... when I killed the Eagle front tires at 3500 miles it was most likely because I was forcing them to bleed of a lot more energy to keep me from going away from where I was turning to.

I suspect that excessively shredding the front tires is usually due to understeer, which in turn is usually due to turning the front wheels too much. Going into the turn too fast isn't likely to be the primary culprit, unless you find yourself locking the brakes and sliding through the cones on the other side of the turn.
As Jad says, except for some insanely tight turns, you should not be turning the wheel too much.
Since we are tossing out aphorisms, one I like is "You start and end the turn with the steering wheel, but you execute the turn with the throttle." I.e., you turn the wheel (as little as possible) to initiate the turn, use the throttle to control the car's rotation through the turn, and then straighten the wheel as you accelerate out the exit.
A very common mistake I see is to "over-turn" the wheel on entry - if you turn the wheel, and then have to straighten it out a bit before the apex, you have turned it too far to begin with, which produces understeer and wheel scrubbing (and slow times).
Also, once you start feeling understeer there are only two things you can do to end it - straighten the wheels so they get rolling again (the preferred fix), or back off the gas to get more weight on the front wheels so they grip. Again - you should have had the wheels straighter in the first place.
Remember the 6-degree optimum slip angle (from the Performance Driving School) - if the wheels are cranked over more than a few degrees, they are probably scrubbing (or else you are going too slow ).

[PShipman]

if you turn the wheel, and then have to straighten it out a bit before the apex, you have turned it too far to begin with

Now how do I sink that into my "seat of the pants" ...

I want to thank all of you for this very enlightening discussion. A lot of "food for thought" here ...

I guess I can't be mad at Tirerack and Goodyear for having so little sympathy for my ruined front tires ...

Your skill at braking before the turn will determine your exit speed

I suppose that it is all experience (isn't that what Jerry said to Linda and I at our first autocross!) ... learning and retaining how much to slow down with braking so I can come around to give myself the most distance to accelerate ... and then applying that dynamicly to each turn (in turn ... LOL) ...

Again ... thanks to all for this very helpful feedback ... now all I need are a few more autocrosses in September (NOT) to get that experince!

[bibbetson]

My .02 cents.

I always like the saying "the driver who uses the most throttle wins". I like to use this when I'm looking at a track. The way to use the most throttle is to make every straight as long as possible (aka get on the gas early, slow in fast out).

I'll throw a different angle on Kim's comments on steering input. The most steering grip you will have (with a properly setup car) is the first turn-in due to weight transfer, however the added grip is temporary. I use this to my advantage by turning in hard and then straightening the wheel very slightly once the grip has diminished. This also helps get the rear of the car rotated. Another angle on this is the saying that your first steering input should be the largest input for the entire corner. This technique improves corner entry speed without sacrificing exit speed AND it promotes a late apex. This in general is pitch-and-catch just at a much slighter level.

On a track, type-1 corners are really interesting. You know you have done it right when your car's trajectory is set to drive off the inside of the track at the apex point and as you increase the throttle the car drifts out away from the apex. If you lift you will drive over the gator, if you push hard you will glide over it or just away from it and your speed down the straight will be much, much higher.

[PShipman]

... by turning in hard and then straightening the wheel very slightly once the grip has diminished. This also helps get the rear of the car rotated

??? is this correct ??? ... Martin/Jennifer, is this what you mean when talk about constant "little corrections for grip in the corner" ???

Bill ... Not that I would question anyone competing in KI ...