128 replies to this topic

[John Woods]

How about Dellis?

Awhile back asked if a steering wheel is really a lever.

Link to steering wheel maker who seems to think yes: https://www.steeringw...eel-theory.html
Check out the ProPak Program under Support/FAQ.

Edited by John Woods, Jul 29 2018 - 07:08 PM.

[gliebzeit]

Keith, ya caught me with a mouth full of coffee.  Hahahahaaaaaa ....

Good one!

[John Woods]

Edited post so Victor checked out.


Spent the last several evenings re-reading Bob Bondurant On High Performance Driving, with John Blakemore, c1982, Motorbooks International.

Bob Bondurant started racing as a kid in 1950s Southern California. He became one of Shelby's team drivers and with Dan Gurney won GT class at Le Mans in 1964, then drove for Ford to win the Manufacturer's Championship in 1965.

He was a technical consultant for the movie Grand Prix, drove for BRM, Ferrari, and Eagle F1 teams, raced at Targa Florio, drove in the Can-Am series and drove a factory Porsche at the Ring.

Heck of a resume. Left stuff out like his 18/20 wins and two seconds in one season as a SoCal regional Corvette driver.

A second very high speed wreck, racing a privateer Can-Am McLaren, after an earlier 150mph loft off thru the trees outside Curva Grande, while having flat out test day fun in an ATS F1, suggested maybe time had come to think seriously about his idea of starting a high performance driving school.
At Monza he credits no seat belt to saving his life by being thrown out of the then instantly shredded car.

He taught a bus load of Hollywood celebrities how to drive race cars while they made movies about racing.
Good idea for us he thought of a driving school, as we now have a couple generations of pioneering influence on race team heritage and his book about how to drive.

Bob recommends two other authors...Taruffi and Jenkinson.
His book should be essential reading as well.

From start to end it is an easy very interesting read.
It is in plain language and it moves along.
Sentences make sense the first time thru.


Just like here.

Attached Files

•  BondurantHPDriving.png   3MB   15 downloads
•  DSCN3973.JPG   89.39K   14 downloads
•  DSCN3972.JPG   97.11K   14 downloads
•  DSCN3975.JPG   59.21K   8 downloads
•  DSCN3980.JPG   91.68K   9 downloads
•  DSCN3979.JPG   118.56K   12 downloads
•  DSCN3976.JPG   78.72K   9 downloads

Edited by John Woods, Aug 01 2018 - 08:56 AM.

[John Woods]

Lately, after years and years of ignoring good advice, have been focusing with extreme concentration on the tire patches, slip angles, and toe settings.

When on a curving trajectory slip angles are the controlling functional driver/setup induced net effect variables that describe/represent the line of the car's direction.

Note by pretty much universal recognition of fact and by definition when slip angles are greater in front a car is understeering.

Seems to make some sense to back engineer setup variables from the apparent effect at the tire patch, which means, with primary attention to slip angles because at the tire patch that and heat is all there is.

A few days ago while touring Road Atlanta the logic of a madman suggested there is a direct connection between appreciating changes in slip angle simulation and the FBB latency setting found in core.ini.

Had always thought latency was time it takes to get effect from tire patch to steering wheel.

What is being transmitted?
Changes in slip angle.

Obviously it has to take some milliseconds for the tire to twist away from its straight lne orientation with respect to the rim.

Even if not very many fractions of a second, it is this twisting effect and the time it takes that is the critical feedback effect altogether, whether virtually or real, that is transmitted thru the suspension to the steering wheel.

But setting latency to zero, as many do, means there is no time component in the equation that represents slip angle transition effects?

No idea really because impression of what is happening is too much subjective fantasy.

Yesterday setting was 0.0185. Been increasing it incrementally and it is now 0.0385.
Seems maybe easier to keep the car stable and on line out near the edges, but what do I know?

New theory: Latency = time it takes to reach maximum slip angle?
Or something like that.

Plus, for a bit more insight, there's this from Lee...

Quote

https://srmz.racesimcentral.net/inde...727

GPL's FFB curve has its maximum force occurring a few degrees prior the the maximum grip slip angle.  As a result, you should be able to feel when the steering wheel force goes light which means you are approaching the maximum grip slip angle just as real world drivers can do.

Edited by John Woods, Oct 02 2018 - 07:11 AM.

[John Woods]

(copy/paste starts here)
Relaxation length
From Wikipedia, the free encyclopedia




Plot showing lateral force building up as a bicycle tire rolls forward at a 2.4º slip angle. The results from three separate test runs are superimposed.
Relaxation length is a property of pneumatic tires that describes the delay between when a slip angle is introduced and when the cornering force reaches its steady-state value.^[1] It is also described as the distance that a tire rolls before the lateral force builds up to 63% of its steady-state value.^[2] It can be calculated as the ratio of cornering stiffness over the lateral stiffness, where cornering stiffness is the ratio of cornering force over slip angle, and lateral stiffness is the ratio of lateral force over lateral displacement.^[1]
(c/p ends here)

So...new theory > relaxation length = FFB latency?



(red font added)

Edited by John Woods, Oct 06 2018 - 05:22 AM.

[John Woods]

"You feel the car move. You can sense the slip angles," Bentley says.
Excerpts from an article in Road & Track.



Slop angles...get it?

Attached Files

•  Bentley On Slop Angles.png   324.06K   13 downloads

Edited by John Woods, Oct 07 2018 - 04:34 PM.

[John Woods]

A little housekeeping sort of...

Somewhere here in the threads posted this pic awhile back.
Now not sure where so here it is again.

The idea of it is to conceptually diagram the line of the instant CoG as it transitions in response to the track surface and driver inputs.

It is based on some analysis of the technique of a well-known GPL on-line racer.

Given similar cars, the difference between drivers and their lap times is measured in their transitions.

Also, here is a page link to Paul Frere and Stirling Moss describing how to take a turn:

https://srmz.racesimcentral.net/inde...showtopic=12701

Attached Files

•  virtualspace.png   17.28K   18 downloads

Edited by John Woods, May 21 2019 - 07:29 AM.

[John Woods]

Been slowly reading and re-reading the two books featured in this post.

The Design of Racng Sports Cars by Colin Campbell, Bentley Books, 1976 edition.

Racing Car Design and Development by Len Terry and Alan Baker, Robert Bentley Inc, 1973 edition.

As with the other books reviewed here on this thread the interest has been in finding the keystone gems of understanding that help connect all the dots together to form an accurate and appropriate idea of what the heck it is we are trying to accomplish.

Unlike other reviews that highlight the insights revealed by drivers and driving instructors, these books reference the engineer's POV and rely on their expert authority.

Note the cover jackets of each book recommends the other one.

In the attached section on stability in corners, Campbell describes how traction enables steering a RWD car with the throttle.

Len Terry designed the Indy Lotus for Colin Chapman, the AAR Eagle for Dan Gurney, and the P126 Tasman car for BRM. Read about it in the book. In the attached appendix he describes how wheel rate and spring rate are established.

In Grand Prix Legends btw, something to consider, due to efficiency of physics model, wheel rate and spring rate are the same thing, mainly because there is no actual spring and no actual suspension from which to lever and pivot.

Nonetheless, for those with interest in experimenting with the physics model, Campbell's description of how to steer a car with the foot and Len's notes on spring rate calculation might provide a lot of opportunity.


On word thru the fog


Important edit: The Len Terry pics are displayed in reverse order even though they were loaded in order and the editor shows them in proper order. Please note the pic names show the order to be read. (Figured it out but don't want to mess with it yet).

Attached Files

•  DSCN4565.JPG   94.56K   13 downloads
•  DSCN4567.JPG   89.06K   16 downloads
•  1DORSC.png   1.16MB   14 downloads
•  2DORSC.png   1.25MB   13 downloads
•  3DORSC.png   1.01MB   18 downloads
•  DSCN4574.JPG   143.21K   22 downloads
•  DSCN4575.JPG   123.98K   23 downloads
•  DSCN4576.JPG   107.43K   18 downloads
•  Len Terry RCDD4.JPG   553.35K   15 downloads
•  Len Terry RCDD3.JPG   538.95K   13 downloads
•  Len Terry RCDD2.JPG   544.54K   10 downloads
•  Len Terry RCDD1.JPG   546.36K   10 downloads

Edited by John Woods, Sep 25 2019 - 02:53 PM.

[John Woods]

Maybe it is possible to explain in a few words the fine art of countersteering to bring the front into optimum slip?


Thought it might be a good idea to begin with some humor.

Or just start out from scratch and try to finish...


"Traction" is grip on the rear caused by throttle input which, when modulated, can be applied to steer the car by causing the car to rotate around its center of gravity, (CoG).

Traction causes oversteer when the rear is already swung out, (pour tourner à l’arrière), by lifting the throttle momentarily and allowing the diff to go into coast, maybe while tapping the brake just enough to set the car in comfortable stance for acceleration.

If the rear is not swung out, (nicht ausgeschwenkt), traction can easily cause more tendancy to understeer, while the car is pushed into track camber. In this case, turning the steering wheel when accelerating does not prevent the car from wanting to go off on the outside.

All GPL differentials, just like in the real world, cause power side understeer.

To compensate for the diff, many drivers often prefer, as they gain experience, to tune out diff-induced power side understeer as much as possible, so it is easier to steer the car, especially at speeds slower than typical of those involving any sort of high speed drift.

This is where the most interest in neutral steering comes from, because from there, at slower speeds, as the car accelerates, traction increases grip at the same time traction is steering the car into oversteer that carries the car around the turn.

Given a moment of neutral steering, as soon as traction is applied the car will be oversteering as the rear will seem to swing out behind the driver.

This is a very important moment.

The rear has to swing out and roll over far enough to load up the outside tire and twist the rear tire into optimum slip.

If not, there is grip to gain.
And if not, there is time, speed, and distance lost.

In the mid-to-late 60s, with big innovations in tire technology, optimum slip had advanced down to about 8 to 10 degrees of slip required to yield maximum grip before the tire begins to slide with no grip.

This is when they invented the square wheel, 15inDIA by 15inW, which proved there is a practical limit on tire tread width relative to diameter.

In the 50s optimum slip angle per tire was around 15degs. Beginning in the 70s optimum slip evolved rapidly to now an F1 car with hot track and tires is looking for 3deg or less of optimum slip.

As slip angles were reduced by advances in tire technology, over time steering wheel diameters, reflecting by radius the leverage required to twist a tire patch off its rim, got smaller and smaller.

Steering wheel shapes changed dramatically while their significance as suspension levers diminished and significance as system control panels increased.

A rule-of-thumb for Grand Prix Legends could be, (pick a reasonable number), say 8-degrees at optimum slip.

There have been reports by a pretty quick on-line driver of Replay Analyzer recording Papy 67s slip angles of nearly twice that, with the average being between 8 and 13, which suggests a whole lot of grip and loading is possible.

This means to get to optimum slip the car has to, (it will and does every time), twist and roll its way off and around its center, (static CoG), some number of degrees while the tire patches are skewed out of alignment with their rims, until they get twisted or not into optimum slip and maximum grip.

As soon as the rear hops out to 8degs or so of slipped-off its static center, due to traction and the diff, the front goes rotating off in the opposite direction, and the driver wrestles with oversteer, as the car seems to want to drop off track camber and dive off into the inside of the turn.

This is exactly what is supposed to happen except for one thing.

While the rear of the car seems to be swinging out searching for maximum load, optimum slip, etc, the front is taking the path of least resistance, and will never get anywhere near optimum slip if the driver does not turn the wheel to the outside, forcing the front tires into the track surface camber.

The front must be set with enough front roll to be steered into the track camber with sufficient leverage to twist the tire patch away from the rim and bring it close enough to the same slip angles as the rear...and vu-ah-la, high speed neutral steering.

(Neutral steering: when slip angles are equal or cancel out to zero and car maintains undiminished path of current intended trajectory with increasing throttle input).

Just guessing this might require a little more steering wheel input than 8degs, but not much?
Probably varies with steering ratio, wheel settings, grip level, track camber, speed, spring rate, tire temp?

The driver only has to effect an 8deg slip angle on the front. The rear is already going there. This often requires very little leverage on the steering wheel.

When countersteering into track camber to increase front slip angles to match the rear slip angles, FFB is telling you exactly how much lateral force is being caused by setup, track camber, and by throttle.

If for example the steering wheel is turned 40degs to begin and hold a line, compensating for traction induced oversteer might find that FFB level of resistance in the wheel at somewhere around 32degs?

Ok, probably not 1:1, but concept of it is the point. There is a direct relationship between front slip angles and steering input.

Rear traction oversteer plus front countersteering understeer equals zero slip angle difference between front and rear.

Constant radius optimum slip turn across track camber = traction + steering input = (-8F) + (+8R) = 0, (or the other way around). If less than optimum slip, the trajectory is maintained by (<0) + (>0) = 0.

An observer would likely not, or likely might not. see the countersteering effort at all, as it is only felt by the driver in the FFB response and the motion that initiates implementation takes about or less than 4/5ths of a second, (according to sources in above posts).

Traction increases due to throttle are anticipated on the front in direct coordination by simultaneous steering input to balance the car on an accelerating trajectory.

This is how with direct control all four tires can be placed and held in optimum slip.

Throwing a car into a semi-controlled full lock powerslide is not the same as placing and holding a car in optimum slip.

The preferred slip angles are zero, because it means the car is going straight and covering the most distance in least time.

During a turn within a corner, the preferred slip angles are the minimum that carry the car through on the maximum radius line.

Less than optimum slip is better if it means higher speed through a corner.
If you don't need to, don't go there.

The point of taking a car to optimum slip is not to reduce the time and distance within the turn. It is to have more speed at exit, and most importantly, to in-effect lengthen, most of the time, or sometimes shorten, the distance of the next straight.

By making the next straight longer, another second or so at higher top speed can be achieved, which is when the most time anywhere on track is saved, and distance covered, before slowing for the next turn.

That is one way a tenth is gained and over several laps can yield a challenge for position.

Engineers for tire manufacturers tell race engineers and drivers the loads required to put their tires in optimum slip.

It is the driver's responsibility to know how to do that and their job to get it done.

JMO

Questions and guesses
All caveats apply
Reserving the right to edit
Apologies if this does not translate well
Please ask if any confusion
Probably will appreciate any correction and discussion

Edited by John Woods, Mar 20 2021 - 08:47 AM.