127 replies to this topic

[Remco Hitman]

Here's the simple explanation: Four wheel drift is the summum of the adage "Throttle comes on, steering comes off".
This is the best advice in car control: the more throttle you use, the less steering input you should give.
Put differently, less steering input allows for more throttle.

If you can negotiate a stretch of non-straight while maintaining little to no lock, you will be as fast as you can be on that particular stretch, basically because it allows for more throttle.
Combine this with the fact that tyres sure love a bit of slip angle and you're golden.

[John Woods]

Throttle on, steering off.
Great adage.
Thanks Remco.

Just as true whether drifting or not.

Way back when someone else also much wiser than me on a long gone forum noted there are only three modes to worry about: acceleration, coasting, and braking.

For years that was pretty much all I knew for sure.

Nice when things are that simple.
Its like, well okay, at least we got this far.

All the rest is detail, where it never seems so easy and everything seems counter-intuitive and complex.

BTW, seems to be no history and little or no definition of the term "lock" as it applies to driver technique, when it seems to become a verb and have a different meaning than "full lock" and "lock-to-lock."

Try searching for "steering lock."


Has the term lock been used since stage coach days?
"Driver Plan B: To avoid going off cliff, apply some lock and whip the horse to full run."
Is its lineage nautical?
"Lock her down and rig all sails tight. We'll outrun this puppy and beat them all to Tortuga!"

Sorry for having too much fun.

What is locked up? Is something locked up?

To negotiate a constant radius turn, (refer to diagram at post #70), steering is held almost straight, pretty steady, and sort of firm.
Its only constant radius btw on a flat surface like an airport circuit or Skid Fun.
On any surface the car takes the line of least resistance.

The biggest lockup is that steering and throttle hold the suspension out away from static CoG hopefully with sustained intent somewhere near maximum lateral load.

Seems appropriate to describe its use as in "to place a car into lock," or "applying a little lock," and that it means to countersteer in response to coast induced oversteer, or just oversteer?

So the three phases of drift thru a turn could then be 1) entry into lock, 2) in lock, 3) exit out of lock?

Please don't forget...its questions and guesses.

PS to JonnyA, yes it is amazing reading Taruffi confirms experience with Grand Prix Legends.
Now have a lot more confidence blathering on about things I thought were new to me that without understanding it I knew all along because of GPL.

Edited by John Woods, May 22 2018 - 08:25 AM.

[Remco Hitman]

Maybe it's just me but to me "lock" means any amount of steering input greater than zero. To which you will surely reply "Is zero steering input any input at all?"

"Full lock" means maximum allowed steering input so some lock isn't quite as much.

Remco Hitman, on May 22 2018 - 11:29 AM, said:

"Is zero steering input any input at all?"

It is, by the way.

Edited by Remco Hitman, May 22 2018 - 11:31 AM.

[fajanko]

"Lock her down and rig all sails tight. We'll outrun this puppy and beat them all to Tortuga!"

[John Woods]

Hey JP, hope all things are well.



Zero input is input?

Think I understand.
Zero input is when you let go of the wheel?


Isn't applying lock more specifically counter-steering, with the intent to put the front at a specific angle of slip?

So it could be zero steering input or, maybe theoretically, even with the direction of the turn as long as its balancing against the rear that is itself going toward being in slip?

Just my humble guess you first have to know what the rear will be doing before tossing it against some patch of track camber and expect to match its motion with a quick spot on flick of the steering wheel, all at the proper instant.

Amazing when you get it right.
Curious it seems sometimes the Ai up ahead syncs in and advances in unison?

Edited by John Woods, May 31 2018 - 05:51 PM.

[John Woods]

Another bucket list must read checked off...thanks Grand Prix Legends.

Finally after many years of dumb procrastination, forgetfulness, and occasional wishing about it, now have a re-print paperback copy of Denis Jenkinson's c1958 classic, The Racing Driver, The Theory and Practice of Fast Driving.

First time thru it is kind of a slow sloggy read with too long paragraphs of uncertain direction all bundled into a rambling jumble of way too much detail, side stories, and occassional apparent inabilities to stay on point or get to one.

Then later, maybe days later, something clicks and that chapter has to be read all over again, now that it is starting to make some sense why he went on so long about some peculiar aspect of sidecar riding that is of particular interest to the professional F1 driver.

Then on and on and on about slip angles after summing it all up with the simple declaration that science and engineering confirm the optimum slip angle for a racing car is designed to occur when 15deg of steering lock is applied.

Have to wonder if that's still the case.
(Thinking probably not).

There's a graph to prove less is not enough and more is too much. It was also noted, if the driver is not getting out there to 15degs of lock at the tire patch that they are not going fast enough. Apparently the optimum speed is just past way too fast to get thru the turn otherwise. Better get it right.

Two things that are interesting in his analysis of a racing driver's skill, (entirely unlike mere mortals), is first, compelling a car at will to demonstrate an oversteer or understeer attitude regardless of its predisposed inclination, and unlike the rest of humanity, do it with incredibly focused nonchalance within a few fractions of a second at the precise micro-second the move must begin and end, and second, doing it at somewhere over 180mph where there is zero tolerance for error.

Also clearly no doubt in Jenkinson's view any use of steering input, even zero lock, can be "applying lock."

Paying attention to use of the term lock has narrowed the search for a reasonable practical definition to "the use of steering input to direct the car away from the line of minimal resistance," to a line of greater resistance and greater grip.

Note the line of minimal resistance is where the car would go if the driver released the steering wheel and let the car roll. It is the same as the line of least resistance, as others use the term, and the fastest way thru a turn if that line is available from entry thru exit. If not available at the speed that must be maintained, it is time to try a little lock.

"Lock" is a verb. It means "to hold in position." So where the steering wheel is relative to zero at 12 o'clock, or any number of degrees either way, is secondary to the art of applying lock to set the car on a certain line.

In the context of suspension dynamics, is it more appropriate to think of the steering wheel as a lever, that pivots off the rack, to keep the suspension steady out near the break-away limit of no more marginal returns?

How do we reverse engineer 15deg of tire patch lock into Grand Prix Legends setups?

BTW, Denis rode professionally on winning sidecars and rode with Stirling Moss to win Mille Miglia. Many of the side stories used as examples, (like a book within a book), are about his many years of very special direct experience with racing and race drivers.

Then it finally hit, on a sidecar the rider is the active suspension.
On the Mille Miglia, the rider is as much a part of the car as its driver.
Stirling could not have made a better choice, and together they proved it.

This post could have been much longer if all the scope of this book had been covered.

Forgot to note the two turns DJ mentions as being especially suited to serious applications of lock are Abbey and Woodcote, (nice they are on the same circuit), and also the last turn before the front straight at Rouen.


Read this book, then read it again and again and again...

Maybe it won't help you be faster.
It will help you become a better driver and better understand firsthand what it was all about back then.

Attached Files

•  DJ The Racing Driver.png   1.1MB   9 downloads

Edited by John Woods, Jul 12 2018 - 09:13 AM.

[Remco Hitman]

Slip angle is not measured by steering wheel input. Slip angle is the angle of the roll center of the tyre compared to the direction it travels at.
Grip builds up as the slip angle increases (but not linear) until a certain point after which it falls away again (though not a steeply as some sims will have you think). It is generally believed the optimum slip angle in GPL is somewhat high, allowing for quite aggressive sideways driving without taking it beyond the optimum. This is aided by the lack of tyre (temp) degradation.
Front tyres push the car around the corner at a greater angle than required to keep the car following the radius, thus developing some slip angle and increasing grip. The rear tyres follow suit. The momentum of the car pulls the car outward, creating a friction in the rears which acts as a slip angle.
In a controlled slide, the slip angle of the rears is increased as the body of the car is set at an angle to the direction of travel. The increased slip angle yields some extra grip which can be used to put more power on the road.

[gliebzeit]

[John Woods]

Hi Remco, appreciate your insights and another perspective that helps understanding.
Howdy Greg, thanks for checking in.


There is an essential to the era driving technique that has been described in very specific detail by Taruffi and Jenkinson. It is the technique of quickly making a single-motion counter-steering input to lock the front in exact and simultaneous correspondence to coast-induced slip on the rear.

Ferrari's description of his surprise, shock, and fear while first riding with Nuvolari at racing speeds through a series of turns includes a similar although almost frantic analysis of this technique.

Jenkinson in 1958 points out the optimum slip angle is 15degs and notes F1 drivers from Fangio to Moss (his reference) consistently caught the rear by tossing the front tires out near 10-14 degrees of slip.

By 1975, Niki Lauda noted in The Art and Science of Grand Prix Driving that then current tire technology had reduced the optimum slip angle to a range of 8 to 10 degrees.

The wider the tire patch, btw, the less slip angle at maximum grip.

It follows that the tires, while enjoying the approach to optimum slip, are doing so in coincidence with a symmetrical rotation of the car around its CoG.

Seems the setup idea then, especially if interested in exploiting this technique, should be to help the car rotate to optimum slip and no more.

Related to this is knowing when to put the car in coast and at the same time, (all within 4/5sec), how far on period-correct hard tires to turn the steering wheel in response, so the car "sets" itself and the driver then has only to comfortably accelerate with confidence on the resulting, hopefully the preferred, line of travel.

Rather than, otherwise, fighting with throttle and steering to keep the car close to some minimum line of maximum grip, even if that is another talent that separates the best race drivers from the rest of us.

The key is a dynamic setup that compliments the technique and yields a car eager to slide upto into and outof optimum slip.


We can dream.

Edited by John Woods, Jul 18 2018 - 01:09 PM.

[Remco Hitman]

It's the other way around. You don't catch the rear by increasing front grip but by decreasing it. By countersteering into a slide the slip angle decreases, thereby stopping the (over)rotation of the front of the car. (Note: in all Papy sims including iRacing, the same effect can be reached by rapidly steering the other way, depleating front grip and sliding the fronts to right the car. This is BAD).
Again, slip angle is not the steering wheel position or the front wheel angle. You can't see it just by looking at the tyres or the steering wheel.

[John Woods]

Forgive me Remco, sure you know my preference to is get things exactly wrong.
(Maybe we're talking about two different things)?

This is the technique Taruffi describes to negotiate the constant radius turn, (alleged by science and engineering to be the fastest way around a flat 90deg bend), but the slowest way around a circuit, which is why its kept to the minimum.

When going off throttle and dropping into coast, (as Taruffi describes), the rear swings out. He makes a point of emphasizing the significance of this initial motion and both he and Jenkinson describe the technique of immediately thereupon applying counter-steer and lots of throttle.

Pretty sure both of them are talking about using lock to increase front slip angle to just-at the break-away point. The difference between this and catching a slide to right a car is that the point in this case is to cause an almost slide, not to stop one.

Jenkinson maybe sort of describes the modern sim technique Remco details when he refers to what drivers have to do with a really poorly handling car, noting that some will resort to slamming the brakes and skidding the front to get it to break loose.

Agree we do not see slip angle...do think you hear it tho and could use tire sound to guess what is happening.

Certainly would agree that with wider tires than way back then, wider lower cars, better suspensions, brakes, aero slipperiness and downforce hugginess etc, that the technique itself is now almost lost to history.

If a modern driver were to want to measure change in slip angle at the steering wheel one way to do that, (just a guess), would be to place a piece of tape at 12 o'clock and note its position while going thru a turn over several laps?

Although, have to say, all this is technical stuff is very confusing to me.

Edited by John Woods, Jul 21 2018 - 03:40 PM.

[gliebzeit]

"Again, slip angle is not the steering wheel position or the front wheel angle. You can't see it just by looking at the tyres or the steering wheel. "

It's an invisible vector that is the direction that the car is moving at a given instant.

Edited by gliebzeit, Jul 22 2018 - 06:29 PM.

[Saiph]

gliebzeit, on Jul 22 2018 - 05:35 AM, said:

"Again, slip angle is not the steering wheel position or the front wheel angle. You can't see it just by looking at the tyres or the steering wheel. "

It;s an invisible vector that is the direction that the car is moving at a given instant.

Slip angle is an invisible vector that is the direction that the tyre is moving at a given instant, relative to the track surface. The front wheels may not be in line with the body of the car, so the steering lock angle has to be taken into consideration to arrive at the true slip angle.

Edited by Saiph, Jul 22 2018 - 06:14 AM.

[John Woods]

A short reminder courtesy of Mr. Clark, in his own words...

"...but I prefer to cut into the corner early and even with my brakes still on to set up the car earlier. In this way I almost make a false apex because I get the power on early and try to drift the car through the true apex and continue with this sliding until I am set up for the next bit of straight."

At which point, the car would have been "righted" back close enough to zero slip.
Seems exactly the technique Taruffi describes.

For a few more words refer to post #67. Note there that Clark refers to three distinct approaches to taking a turn, represented by the opinions and driving styles of Chapman, Clark, and Hill.

More like a story of what happens when you ask three experts a simple question.

Slip btw is real. Lateral forces and the track cause slip.  As I understand, you do not get maximum grip when slip is zero.

Edited by John Woods, Jul 22 2018 - 08:22 PM.

[gliebzeit]

Keith, the tires are of course attached to the car, most times.  
So, the slip angle vector will be the same for the subset of tires and the super-set of the car.
I think that you are saying  slip angle is not the same for the tires as for the nose of the car.

[John Woods]

Just spent way too much time watching YT selections on slip angle.
Even more experts saying confusing counter-intuitive things.

"Displacement causes lateral force."
Its not that lateral force causes displacement?

"Turning causes a lateral force toward the inside of the turn."
Why does this not make sense?
Guess the math proves it.

This video so far however did make sense and has some entertaining info about slip angles, enough to keep me watching, (30plus min). Notes that slip angles on F1 cars are now typically less than 3deg.

https://www.youtube....h?v=y5Y-w4zGW00

Edited by John Woods, Jul 23 2018 - 08:06 AM.

[John Woods]

Howdy Saiph.



There is a definition of slip angle that refers to the difference between the direction the tire is heading and the direction it is pointing and equates slip angle to heading as if we could substitute the terms and as easily say heading angle.

At any given moment, the tire is not heading anywhere, but really I don't care about that.

If Taruffi, Jenkinson, Clark, Hill, and Lauda, say you need slip to get some grip that's good enough. Just tell me how to get it and what I want to do with it.

Edited by John Woods, Jul 24 2018 - 08:16 PM.

[Remco Hitman]

gliebzeit, on Jul 22 2018 - 05:35 AM, said:

"Again, slip angle is not the steering wheel position or the front wheel angle. You can't see it just by looking at the tyres or the steering wheel. "

It's an invisible vector that is the direction that the car is moving at a given instant.

Hi Greg, check your PM!

[Remco Hitman]

John Woods, on Jul 22 2018 - 09:12 PM, said:

"Turning causes a lateral force toward the inside of the turn."
Why does this not make sense?
Guess the math proves it.

That's exactly the point. If you turn the wheel, the front tyres develop an angle with respect to the direction of travel, thereby pushing on the road. And the road pushes back (action is reaction) and takes the car off-course.
It's this slip angle that creates the action and invites the reaction. It's the road pushing back to takes you around the corner!

[John Woods]

The inward lateral force is not something that pops from nowhere out of a point in the center of a slip angle diagram?

How is any of this helping me learn how to drive like Jimmy?

Edited by John Woods, Jul 24 2018 - 03:23 PM.