Pro and Anti Ackermann

[amaury_reno]

Hi guys, I notice that Formula 1 and single seater cars turns with MORE steering angle on the OUTSIDE wheel than the INSIDE.


Is this ANTI-ackermann or PRO-ackermann? Sorry if this sounds like a re-post but i just want a confirmation.

[McMrocks]

http://www.f1technical.net/forum/viewto ... f=6&t=8874



from Marcush. if this is anti-ackerman your picture probably shows pro-ackerman (if our eyes don't play tricks with us)

[Tim.Wright]

The first picture is anti ackerman. The second is pro ackerman.

There is loads of information on this if you both to look.

BTW, anti ackerman seems to be pretty common in F1 at Monaco. I don't know the particulars as to why, but its usually a tyre driven design choice.

[tim|away]

@amaury_reno
Your picture is almost certainly an optical disortion due to the lense and perspective.

A better basis might be something like the following photo. Note, this is a very rough sketch that you shouldn't take in any way scientifically, but it provides a slightly less distorted view.



Here is another one if you want to analyse it

[olefud]

The first picture is anti ackerman. The second is pro ackerman.

There is loads of information on this if you both to look.

BTW, anti ackerman seems to be pretty common in F1 at Monaco. I don't know the particulars as to why, but its usually a tyre driven design choice.

It’s just a theory, but I suspect that in the low speed longer Monaco corner(s), i.e. sans aero down force, the cars tend to wallow a bit in under steer. The problem appears to be in getting the car to rotate rather than lack of centripetal force. With fairly extreme anti Ackerman, the inner tire will drag a bit to create a force couple that helps rotation. This assumes that the outer tire pretty much defines the turning arc, but, with a low CoG, the weight transfer is a question.

As with Ackerman in general, they can get away with gobs at low speed, tight corners since steering inputs will be much less during high speed work.

[Luke]

The inside tyre is generally always carrying less vertical load. Generally speaking the less vertical load a tyre has, the lower the amount of slip angle it can sustain. Or more to the point the peak lateral load happens at a lower slip angle, hence the desire to run less steering angle on the inside compared to the outside tyre (anti ackermann)

[thisisatest]

the pic with the lines depicting ackerman, the right tire seems especially not-lined-up. i'd say it's a bit anti-ackerman.
which to me says theyre running quite a bit of anti-, as (as i understand it) f1 cars are typically set up with a good chunk of front wheel toe-out.
possibly they run the anti- just to get enough steering lock?

[Greg Locock]

My cow orker did a study on this at low speed and found that the optimum relative steer at full lock of the two front wheels for an SUV was less than 100% ackerman but more than 0%. Any divergence from that optimum meant that to some extent the wheels were fighting each other. It is very common to have to compromise this on production cars because the crude answer for a tight turning circle is to steer both wheels as much as you are allowed to by the sheet metal etc, never mind the niceties.

[autogyro]

Ehhh, the overhead shots don't show ackerman angle, they show the toe in/out at that particular steering position.

[Tim.Wright]

Ehhh, the overhead shots don't show ackerman angle, they show the toe in/out at that particular steering position.

This too.

Speaking of ackermann without speaking of the initial toe setting is only telling half of the story. Even a 100% anti-ackermann setup will be pro-ackermann in the on centre range if you have static toe-out.

[gixxer_drew]

the pic with the lines depicting ackerman, the right tire seems especially not-lined-up. i'd say it's a bit anti-ackerman.
which to me says theyre running quite a bit of anti-, as (as i understand it) f1 cars are typically set up with a good chunk of front wheel toe-out.
possibly they run the anti- just to get enough steering lock?

How much toe are you thinking is a "good chunk"? The numbers i saw was a few years back were pretty typical for any race car.

[thisisatest]

...good chunk, a good amount. i wasn't trying to imply that they would use more/less what other racecars used, just that a decent amount was used. some people may not be aware that the wheels dont start out pointing exactly straight...

[dynatune]

All these pictures are very interesting and show that there still seems to be more than 1 road to ancient Rome. Ackermann has had many variants in F1 and it seems to be a reoccurring item every 5 years or so. When I was involved in the design of F1 cars Monte Carlo / Monaco was the only circuit that was NOT running negative/anti-ackermann but extreme positive/pro-ackermann to the point of well beyond 100%. The reason behind this was given by the fact that the inside front tire in most of the corners was anyway "in the air" and cooled down. So we tried to make it run at the highest possible slip-angles whenever it was on the ground (during cornering) in order to heat the tire up. That did work well. I hope I did not gave away some secrets

Cheers,
Dynatune, http://www.dynatune-xl.com

[MatsNorway]

Necrotime...

So is this done due to the tyrewall flexing more on the outside tire so you simply compensate for that? Is that the meaning of Slip in this context?

I guess you would run less Anti the smaller the profile then.

[Greg Locock]

Hi Mats, I don't know what the physical cause is, but basically the graph of slip angle vs max Fy peak moves around as you change Fz, so for max latacc you need to know the Fz on each tire, and then work out the difference in slip angle you need, and then provide that via toe and ackerman.