So I’m digging around looking up F1 suspension info and find “Anti-Ackerman” steering.

Wha? Who? Cool!!

http://www.smithees-racetech.com.au/ackerman.html
…used to change the dynamic toe setting, by increasing front wheel toe out as the car is turned into the corner.

All kinds of other interesting concepts in there too: “pneumatic trail”, “self aligning torque”, “bump steer”, “caster trail”…!

I assume F1 cars use some Anti-Ackerman %. My question is this: do F1 cars use variable Ackerman % through the turning radius, or maybe even dynamic throughout a race (or just a static linear % setting)?

It also seems like you would want to have Ackerman% variable based on speed as well (not just steering wheel angle), and tire temp, as well as road conditions, in order to optimize and attenuate car balance dynamically through the turn. But that would be “active steering”, and I imagine – like “active suspension”, probably banned. True?

Certainly KEY for mechanical grip calculations – certainly KEY for getting heat into the tires and tire management – certainly KEY relative to straight line speed. Thus, I assume an Ackerman range is a suspension design/build principle vs. a driver preference (e.g. Fernando’s quick turn in, more toe, since relatively more outside pneumatic trail compared to teammate). Maybe not. Maybe both.

Then I found this nostalgic 07 entry, from our very own.
http://www.speedtv.com/forums/viewthread/137115/P0/

More key info here: http://www.muller.net/mullermachine/docs/ackerman.html


So what do you think:
1.) is Anti-Ackerman used in F1?
2.) is it inherent in chassis design or adjustable as part of track setup? (or both)
3.) is it variable through the turning radius or a straight linear % setting/linkage?
4.) is it adjustable throughout the race? (e.g. get heat into new tires)

I'm guessing that there is not much use for anti-Ackerman in F1; the inside front wheel on slow corners is VERY lightly loaded, making Ackerman almost a moot point, and in high speed corners even though the steering angle is much less, I think you would want some Ackerman so the tires would track true with minimal steering induced slip angle.

I'll be interested in seeing what some of our other posters have to say.

ipso - 20 October 2009 03:39 PM

So I’m digging around looking up F1 suspension info and find “Anti-Ackerman” steering.

Wha? Who? Cool!!

http://www.smithees-racetech.com.au/ackerman.html
…used to change the dynamic toe setting, by increasing front wheel toe out as the car is turned into the corner.

All kinds of other interesting concepts in there too: “pneumatic trail”, “self aligning torque”, “bump steer”, “caster trail”…!

I assume F1 cars use some Anti-Ackerman %. My question is this: do F1 cars use variable Ackerman % through the turning radius, or maybe even dynamic throughout a race (or just a static linear % setting)?

It also seems like you would want to have Ackerman% variable based on speed as well (not just steering wheel angle), and tire temp, as well as road conditions, in order to optimize and attenuate car balance dynamically through the turn. But that would be “active steering”, and I imagine – like “active suspension”, probably banned. True?

Certainly KEY for mechanical grip calculations – certainly KEY for getting heat into the tires and tire management – certainly KEY relative to straight line speed. Thus, I assume an Ackerman range is a suspension design/build principle vs. a driver preference (e.g. Fernando’s quick turn in, more toe, since relatively more outside pneumatic trail compared to teammate). Maybe not. Maybe both.

Then I found this nostalgic 07 entry, from our very own.
http://www.speedtv.com/forums/viewthread/137115/P0/

More key info here: http://www.muller.net/mullermachine/docs/ackerman.html

So what do you think:
1.) is Anti-Ackerman used in F1?

Not used on any race car that I know of...

2.) is it inherent in chassis design or adjustable as part of track setup? (or both)

Most of what's being discussed here, would require some form of steering rack design (different than a rack and pinion). The spindles however could be designed to accept alternate locations and setting for multiple settings of ackerman through tie rod locations on the outer wheel.

3.) is it variable through the turning radius or a straight linear % setting/linkage?

The system used in the drawing isn't a rack and pinion, but according to the geometry of the drawing it would be variable according to turning angle..more steering, more ackerman added.
Most ackerman settings in racing are either causing toe out with more steering (mostly used), 0 ackerman or toe in with increasing steering angle. The last one is rarely used...

4.) is it adjustable throughout the race? (e.g. get heat into new tires)

Mechanically not possible in the drawings...

wilmywood8455 - 20 October 2009 07:01 PM

I'm guessing that there is not much use for anti-Ackerman in F1; the inside front wheel on slow corners is VERY lightly loaded, making Ackerman almost a moot point, and in high speed corners even though the steering angle is much less, I think you would want some Ackerman so the tires would track true with minimal steering induced slip angle.

I'll be interested in seeing what some of our other posters have to say.

I assume some anti-Ackerman in F1 for quicker turn-in. (And assuming F1 tires are <= the 2% slip mentioned for Indy tires – and because the suspension is so stiff – and because F1 front ends are so light in low speed/tight corners – so relatively less roll, less tire slip (and likewise less pneumatic trail), so overall less disparity between the two front wheels – hence less likely “need” for pro-Ackerman [dynamic toe in].)

That was the logic anyway. I have no idea if that floats.

So it seems to me that other than go-carts & F1 (and possibly autocrossing) I suspect “pro-Ackerman” is the call, where you have more disparity on the outer wheel tweaking more slip from the tire. (Total swag.)

Interestingly, in the non high performance domain, I should think anti-Ackerman is more stable – and thus probably more appropriate for non-sporty road cars – just like road cars have a bit of understeer dialed in for safety. I guess 100% Ackerman (or neutral – neither anti/pro) would be best for the original example given – that of a car rolling slowly over British high society gravel driveways – making as little noise/disturbance as possible (like Kwai Chang leaving no marks walking across rice paper.)

And since I’m not a math guy – what % of pro-Ackerman approaches parallel steering? (Or is that a trick question?)

So I have like four thoughts going on at once – and they are all probably exactly wrong.

What I do know is that driving my old M3 hard through a turn makes “turn feel” smother. Like using a very sharp knife on a piece of steak (vs. a dull one) – you can feel less resistance. I suspect a bit if pro-Ackerman is at play in that car.

Vs. a Porsche 911, where the light darty front end suggests anti-Ackerman would be best (like an F1 car).

speedsense - 21 October 2009 01:29 AM

1.) is Anti-Ackerman used in F1?

Not used on any race car that I know of...

2.) is it inherent in chassis design or adjustable as part of track setup? (or both)

Most of what's being discussed here, would require some form of steering rack design (different than a rack and pinion). The spindles however could be designed to accept alternate locations and setting for multiple settings of ackerman through tie rod locations on the outer wheel.

3.) is it variable through the turning radius or a straight linear % setting/linkage?

The system used in the drawing isn't a rack and pinion, but according to the geometry of the drawing it would be variable according to turning angle..more steering, more ackerman added.
Most ackerman settings in racing are either causing toe out with more steering (mostly used), 0 ackerman or toe in with increasing steering angle. The last one is rarely used...

4.) is it adjustable throughout the race? (e.g. get heat into new tires)

Mechanically not possible in the drawings...

Are the cars you know of F1 cars? (Apologies if I should know that already, based on your post history.)

Check this find out (all chuffed with myself!) regarding variable ratio rack and pinion drives in F1 steering systems!
http://www.zakgear.com/Rack.html

The lower drawing in the OP is of a go-cart, so just for demonstration purposes showing clearly different angles through turn radius and the rod mechanism on how it’s achieved through different leverages.

…

This guy’s post helps me quite a bit.

http://forums.bimmerforums.com/forum/showthread.php?p=12057071#post12057071
“Parallel steer is NOT 100% ackermann.
…
For the case where only the front axle steers, you basically assume that both of the rear tires are traveling with zero slip angle. Which, incidentally, includes the implicit assumption of zero toe angle. This constrains the body slip angle (i.e., the slip angle at the center of gravity) and the slip angles at the body points above each of the front contact patches. The optimized case (100% ackermann) is when you set your steering angle at each front wheel equal to the slip angle of the body at the point above the contact patch (so the tire slip angle equals zero). The kinematics of the steering system don't make this possible throughout the steering range, so you have to do some engineering and decide which way you want your error to occur, at each point throughout the steering travel.”

And this.

http://www.eng-tips.com/viewthread.cfm?qid=188073&page=2
And Ackermann isn't all there is to it. Cornering at any sort of speed begets roll, which typically involves caster and camber gain, both of which affect toe, which then throws any static determination of "perfect" 100% Ackermann correction out the window anyway.

I'd take Greg's point #1 as meaning that for the general car buyer you shouldn't make the car too responsive on turn-in, as it may get ahead of some drivers' skill or (temporary) attention levels for the prevailing conditions. Whether co-incidentally or not, less than 100% also gives the driver who's operating up nearer the limits a little cushion by providing slightly more total grip on the end that steers. Overall, a pretty good trade for losing a little of the very low speed behavior.”

ipso - 21 October 2009 03:58 PM

speedsense - 21 October 2009 01:29 AM

1.) is Anti-Ackerman used in F1?

Not used on any race car that I know of...

2.) is it inherent in chassis design or adjustable as part of track setup? (or both)

Most of what's being discussed here, would require some form of steering rack design (different than a rack and pinion). The spindles however could be designed to accept alternate locations and setting for multiple settings of ackerman through tie rod locations on the outer wheel.

3.) is it variable through the turning radius or a straight linear % setting/linkage?

The system used in the drawing isn't a rack and pinion, but according to the geometry of the drawing it would be variable according to turning angle..more steering, more ackerman added.
Most ackerman settings in racing are either causing toe out with more steering (mostly used), 0 ackerman or toe in with increasing steering angle. The last one is rarely used...

4.) is it adjustable throughout the race? (e.g. get heat into new tires)

Mechanically not possible in the drawings...

Are the cars you know of F1 cars? (Apologies if I should know that already, based on your post history.)

Check this find out (all chuffed with myself!) regarding variable ratio rack and pinion drives in F1 steering systems!
http://www.zakgear.com/Rack.html

The lower drawing in the OP is of a go-cart, so just for demonstration purposes showing clearly different angles through turn radius and the rod mechanism on how it’s achieved through different leverages.

…

This guy’s post helps me quite a bit.

http://forums.bimmerforums.com/forum/showthread.php?p=12057071#post12057071
“Parallel steer is NOT 100% ackermann.
…
For the case where only the front axle steers, you basically assume that both of the rear tires are traveling with zero slip angle. Which, incidentally, includes the implicit assumption of zero toe angle. This constrains the body slip angle (i.e., the slip angle at the center of gravity) and the slip angles at the body points above each of the front contact patches. The optimized case (100% ackermann) is when you set your steering angle at each front wheel equal to the slip angle of the body at the point above the contact patch (so the tire slip angle equals zero). The kinematics of the steering system don't make this possible throughout the steering range, so you have to do some engineering and decide which way you want your error to occur, at each point throughout the steering travel.”

And this.

http://www.eng-tips.com/viewthread.cfm?qid=188073&page=2
And Ackermann isn't all there is to it. Cornering at any sort of speed begets roll, which typically involves caster and camber gain, both of which affect toe, which then throws any static determination of "perfect" 100% Ackermann correction out the window anyway.

I'd take Greg's point #1 as meaning that for the general car buyer you shouldn't make the car too responsive on turn-in, as it may get ahead of some drivers' skill or (temporary) attention levels for the prevailing conditions. Whether co-incidentally or not, less than 100% also gives the driver who's operating up nearer the limits a little cushion by providing slightly more total grip on the end that steers. Overall, a pretty good trade for losing a little of the very low speed behavior.”

No F1 car experience except with historic F1 cars. Worked with just about every thing else underneath though....

The variable rack is a quite interesting piece, and would likely replace power steering on an F1 car. Rack pinion ratios are changed quite frequently especially if the car races on both ovals and road courses. On road courses you may insert different rack and pinion ratios like on differences between a slow cornering speed courses like a street vs a generally high speed cornering course.
Though this isn't effecting the ackerman, only the speed of the steering wheel input. Where the "effect" is to either slow the steering (ovals, high speed courses) or speed it up (slow cornering speeds).
Ackerman is more of a "tuning tool" on a street vehicle where you aren't generating high tire slip angles like you will on a racing tire.
Many more things are involved, including ackerman, to achieve a good turn in response and well beyond street car technology at work. Especially when the suspension can altered through it's geometry to achieve a result. Ackerman is a concern, but much further down the list of things that are done for reasons of a good turn in car and one that remains good to the apex.....