Why do we go in slow to go out fast

[Jad]

911's do not drive like 944's, Bill's technique will work better for your balanced smooth car, whereas constant throttle and steering inputs are required to keep a rear heavy 911 going in the right direction as Martin and Jennifer have said. Also, with a street suspension, constant corrections do not work well as there is too much flex and mush in the car, you need to know what the car will do with a given input, do it, then wait and trust the car to do what you told it. Again, Martin has 500-600 lbs springs, Bill has ~280-300 lbs springs I would guess so Martins car will respond quicker to small corrections.

[Kim Crosser]

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

I suspect that they are really referring to trying to keep the car "hooked up" with all 4 wheels (or at least a critical few!) in a turn. If you are in a turn at (or near) the limit of adhesion of the tires, you will need to make some small corrections to keep from losing control.

After you have started the rotation, even if you are on steady throttle to exit, the actual torque at the rear wheels is constantly changing (see your engine torque curve) and consequently the acceleration vectors are changing and the weight distribution is changing. Plus, you are changing the slip angle dynamically as you straighten out the exit. Thus, the traction of the tires is changing throughout the turn. If you are starting to understeer (from too much front wheel angle, or from unweighting the front due to acceleration), OR if you are getting some power-on oversteer (something I rarely experience in the Boxster ), you need to be straightening the wheels to keep the car under control.

(Ok - highly simplistic, and doesn't address effects of increasing/decreasing radius turns or how torque is transfered to the inside (unweighted)/outside (weighted) wheels with or without a limited-slip differential, but I think you get the picture.)

Also, unless you are driving on a flat skidpad with a clean uniform surface, your car/suspension/tires are having to respond to camber and elevation changes, and friction changes (asphalt vs. concrete vs. paint vs. patches, etc.).

If you try to "lock" the wheel in one position and you are at the limits, you are probably going to lose it. Instead, small (emphasize SMALL) steering inputs will allow you to keep that steady acceleration while maintaining control.

I have found the following exercise on the street to be useful (for those of us who come down and play with our "daily drivers"): On any halfway decent curve, pick a turn-in point and a desired apex point and try to turn the wheel smoothly at the turn-in point, then hold the wheel steady to the apex. If you have to make additional steering corrections to hit the apex, you haven't quite got the "seat of the pants" feeling for how the car reacts to steering inputs. While the actual turning will be different at higher speeds on the track, having that gut feel for the car will help you adjust quicker.
Caveat - try not to scare other drivers, and any following law enforcement personnel may want to stop and ask why you were going from side to side of the road - don't try this after a few drinks.

Finally, at the risk of this becoming my Master's thesis, a note on the physics of understeer and why your tires may have suffered an untimely demise.
When understeer begins (tires transition from grip to slide/scrub), the tires literally begin forming a liquid layer of molten rubber on the surface. This further reduces the grip, increasing understeer and thus further eating up your tires. If you don't straighten the tires (so they begin rolling and gripping again) or increase grip by transferring weight forward (lift or brake), you are literally melting your tires. I suspect frequent and prolonged understeer is the most common cause of shortened front tire life.

[LUCKY DAVE]

Briefly discussed above is the effect rising torque has on how the car (mis)behaves. Those of us who compete in turbocharged cars have a large torque "hit" to deal with...the engine is weak as a kitten before boost, and suddenly too strong mid corner when boost arrives.
Murphy's law states that this always happens in the least desireable track location....that the powerband conspires against keeping the tires hooked up exiting the slipperiest -but most important for a fast lap- corner leading onto the long straight.
The steep rise in torque requires the driver to lift the throttle at the same rate that torque increases to get the best drive, the turbo muffles the exuast pulses enough to make the rpm hard to hear, and the driver is too busy to look at the tach. Practice laps are partially used just to learn the timing/location of the "hits"
This is true of any "pipey" powerband, not just turbos, motorcycle road racers have their hands full in this respect.
Good reaction time helps....anybody know where I can buy some?

[jenniferreinhardt]

You guys are great w/ this in-depth discussion. Jad and the on-board camera caught me scrubbing 2 times so far out of the 7 times I have autocrossed the 911, and the tires did not lie either. Increasing the steering input has helped me to have more control of the car at greater speed. Now, as Jad said I have to work on throttle input.

Perry, you willl not repeat this as a serial tire killer again now that you are well-aware of the feeling - sort of like scratching on a chalk board.

Can anyone explain the wheel turning and string pulling the foot visual? Thanks in advance.

[ttweed]

Can anyone explain the wheel turning and string pulling the foot visual?

Jennifer-
That is related to the friction circle diagram talked about above, and the fact that you only have a finite amount of grip. You can use it for turning, braking or accelerating, but once you have used up 100% of your "grip budget", it is gone. It is also related to the saying about "the straighter the steering wheel, the faster you can go."

I heard Steve Dente use the "string to the foot" visual in the PDS many times, in relation to unwinding the wheel and applying throttle when exiting a corner. Since your tires are using up some of their grip from the lateral forces of cornering, he cautioned against applying too much throttle until you were straightening the steering wheel, so that you didn't exceed your grip budget due to the added effect of acceleration. He suggested that you imagine a string tied to the steering wheel and connected to the accelerator pedal. As the steering wheel unwinds on corner exit, the string becomes more slack, and you can push down more on the gas pedal.

He also used it in explaining the corrections needed to recover from rotating the rear end in the "pitch and catch" exercise, where the mantra was "turn/lift/straighten/gas". As you straightened the wheel in the recovery phase, you would apply gas linearly, as if the two were connected.

This is of more concern in higher-powered cars where you might actually have enough torque to spin the rear wheels from stepping on the gas (at least in dry conditions).

TT

[jenniferreinhardt]

Thanks for clarifying it Tom, I remember him showing this in the PDS but did not quite understand it.

[PShipman]

Guess what I learned today ... there are page 2s of some discussions! I wondered why it kept saying other folks had posted but I couldn't find them!

When understeer begins (tires transition from grip to slide/scrub), the tires literally begin forming a liquid layer of molten rubber on the surface. This further reduces the grip, increasing understeer and thus further eating up your tires. If you don't straighten the tires (so they begin rolling and gripping again) or increase grip by transferring weight forward (lift or brake), you are literally melting your tires. I suspect frequent and prolonged understeer is the most common cause of shortened front tire life.

Great explaination ... I now have a better feel for why the "turn away from the turn" makes sense ... more turn of the wheel will just cause more "lubrication" to be laid down!

Perry, you willl not repeat this as a serial tire killer again now that you are well-aware of the feeling - sort of like scratching on a chalk board.

Darn ... it was kinda fun to feel sorry for myself ... now I have NO excuse ...

[PShipman]

Jad ... you talked about how stiffer suspension in the front improved wheel input response ...

What are some of the things that a S level car/driver can do to utilize the slower response to the best of its ability ... earlier turn in or ???

[ttweed]

What are some of the things that a S level car/driver can do to utilize the slower response to the best of its ability ... earlier turn in or ???

I'm not Jad, but I did stay at a Holiday Inn last night and think I know what he would say about this.

With a softer suspension, you need to be progressive with your steering inputs. When you initiate a turn, do it a little ahead of time with a small initial input, letting the car roll over to the outside and the weight transfer to the outside wheel before dialing in more steering. The tire will bite better once the lateral weight shift has occurred. To some extent, you must drive "ahead of the car"--anticipating the turn, or series of turns (as in a slalom) and get the weight transferring smoothly from side to side a bit ahead of the time when you need to really change direction.

With a stiff suspension, the weight transfers from side to side more quickly, and steering reaction is much more immediate. In that case, you can wait longer to initiate the turn, and in some cases, may want to give a stronger initial input (still smoothly, but stronger and quicker, without upsetting the car or overpowering the available grip) and correct back to a straighter wheel as soon as the car reacts and sets in an arc, then correct with smaller, quicker inputs as necessary to complete the turn on the correct line, or even use the throttle to do the rest of the steering thru the turn.

TT

[PShipman]

With a softer suspension, you need to be progressive with your steering inputs. .... With a stiff suspension, .... and in some cases, may want to give a stronger initial input

So the worst of all possible worlds with soft suspension would be strong, wrenching inital inputs??? That would induce, as I understand Kim, quick induced slip followed by liquification of rubber followed by MORE percieved need for steering input???

So what are some good methods for a type A guy to teach himself earlier turn ins with slower more progressive inputs?

[ttweed]

So what are some good methods for a type A guy to teach himself earlier turn ins with slower more progressive inputs?

The first one is to learn to calm down! No, really! It is easy to get caught up in the adrenaline rush when things happen so quickly on course and get too excited, losing focus on what is important, becoming re-active instead of pro-active.

One of the best mental exercises for enforcing smoothness in transitions I learned from Steve Grosekemper. He often suggests to his students to imagine a bowl glued down on the dashboard, or hood, with a ping-pong ball in it, rolling around freely. Then he tells you to try to drive so that the ball will stay in the bowl, and not go flying out of it. Harsh movements of large magnitude will throw the ball out, while smaller, progressive movements will allow the ball to climb the walls of the bowl, but stay inside it. See, Grasshopper?

You also need to study and learn the course as much as possible, beginning with the course walk, and you need to think and look ahead while driving it. You need to eliminate any distractions (such as rolling around in an unsupportive seat with insufficient restraints and having to physically brace yourself against sliding), and be able to feel how the car is responding to your inputs, being careful with the weight shifts in transitions so as not to upset the car by asking too much of the tires.

You have to see the course far enough ahead to put the car where it needs to be for the next corner, not the one you are in, once you have committed to it, and to turn the wheel as little as possible and still make it around the course.

Oh yeah--one more thing--here it is in a nutshell: go slow in the slow parts of the course and fast in the fast parts. The only way you know which is which is by analyzing the course ahead of time and trying to remember where you are and where you are going at all times. You need to be aggressive to be quick, for sure, and not leave any time out on the track by loafing anywhere, or coasting, but it needs to be a smooth and controlled aggression. If you make a mistake, you need to leave it behind you and get your focus back on what's coming up. When you finish your run, then revisit your mistake mentally while in the grid and debrief yourself--try to figure out where you went wrong and fix it on the next run.

HTH,
TT