Ackermann Principle

[karman1970]

I'm a broke college kid searching for a job.  What do you think my credit looks like?    Besides, F1 and F3 aren't exactly the same thing (minor detail, but I'll take what I can get).  I was referring to my buddy's Formula Mazda and the few Formula Fords I've sat in.  From the drivers seat they always look to have a lot of toe-in.  I even measured the Mazda one day at different steer angles to prove myself wrong.  Not saying it didn't have reverse Ackerman, but I sure couldn't tell with a tape measure.

I've read about some road race cars using reverse Ackerman, but on a very limited basis.  In all honesty, I still can't really fathom why one would want such a thing.

[plkracer]

Here are my thoughts and opinions... This is based on a few hours of driving my car. It has so little ackerman that I doubt it can be counted as any. Based on the fact of how my heims are set up, you can't steer the inner tire more (through ackerman) without lessening the angle of attack of the outside tire. On a high speed corner, the inside front wheel will actually pick itself up, but exactly off the ground, but to the point where I doubt it is doing much. 90 percent is on the outside tire. If I had ackerman, the outside tire would not be steering as much, therefore I believe I would have some understeer. Seems awkward right? It depends on how much deflection you have. I will admit that the car has some understeer at slow speeds, but that isn't enough that a little gas cannot fix.

On my next car, I think I will set the heims up differently, and put ackerman into the design. Why?? Because it would help slow speed steering with the spool and with the different heim setup, I could get more angle out of the inside tire without screwing with the outside tire.

[Admin]

as light as the front end of my car is, even adding ackerman, the spool would still push the front end of the car at low speed  regardless...

[plkracer]

So you put ackerman into the design? Was this the rorty car?

[artie on edge]

I think a very valid point has been made here, its been made before but not hilighted. Ackermann is (on our vehicles anyway) relevant to slower speeds and not so much for the higher speeds because of the comments just made by Karman, if both front wheels ARENT sharing the steering load, ackermann doesnt count at all.

yep most of my cars have been known to pick up an inside wheel and the back is rarely tracking with the front wheels anyway (slideways!!), so do we only use it for parking and pitwork?

[Nutz4sand]

At high speed the outside tire IS doing most of the steering but the other tires IS going to come back down sometime and a smooth handling car will have both front tires driving in the same direction. If the tires are not pointed in the same direction as weight is reapplied to the inside tire the vehicle will be squirrely unless its under say ten MPH. If you are hauling butt from a left to a right turn its gonna be a handful and then some. Even leaving a turn to a straight-a-way is gonna fish for traction if the tires are not pointing the smae way.

I agree the picture of the F1 car is right after some damage. Show me ten cars BEFORE a race that do that.  Thats negative ackerman but I have never seen one THAT bad actually running a race. 


 

[Entropy]

In reading this thread I have a question or two.
Most of the discussion thus far is using pavement cars as examples, F1 etc, is that what ya'll run?
A few posts note that you are driving sideways in the corners so the principal does not apply. Are ya always sliding the slow way around the corner? Do you understand what happens, and you need at opposite lock?
Is no one running 4WD?
Is everyone running rigs that are so light in the front that correct steering geometry is not necessary? Or is it like Rock Crawlers where the complete suspension can be FU and it will still 'work'?
Anyone running 4WD?
Has anyone ever actually tested Ackerman on the same chassis, same trail/track, same day? Or are ya'll just talking out your arsses?

[Nutz4sand]

Well shed some light on us Entropy.

1st. Why people bring F1 cars with maybe 30mm of travel into a long travel forum is a mystery. I answered but would not have been the one to bring it up.

2nd. "Sliding the slow way?" Explain that please. The fast way around a corner on asphalt is the tail following the front but on dirt it is not. You will never get a rear to follow a front fast on loose terrain at any speed. So if you can please share with us.

3rd. Also explain what happens with the slide and the opposite lock thing. We are eager to learn if you can teach.

Rock crawlers and what we do are not even in the same basket IMO.  I guess a mini rock cramwer would be and some have tinkered with those but most are builiding go fast toys.

There have been a few 4x4's and if I was building a woods rig it would be 4x4 for the mud encounters and such but I am more of a sand person and have entertained the idea but see no NEED for it in the sand. 
 

4th. I beleive that lighter rigs literally need better geometry as they will be twitchier due to less weight on the tires.

[Entropy]

[Admin]

I got to say, I have never exited a corner sliding with the wheels still cocked all the way, I think the theory behind weighting the inside tire and getting an iratic reaction is bullshit myself, and your never going to load the inside tire right out of the corner, unless you are braking really really hard, I generally don't load my inside tire until i am a good distance away from the corner....

[Entropy]

[Admin]

Huh, deleted 3 replies were?

I have not, tested my car with and without ackerman, Livewire has on his car....His knowledge is hands on experience, and not speculation... IMO i do not believe inducing ackerman will make my car turn any better, rather it be at 60 or 6 mph...

[Entropy]

[Admin]

Im not certain, avg speed around the 9/10th was like 47 mph, 3 180 degree corners, 5 90 degree corners, and 6 jumps...

[artie on edge]

Hmmm... I am now wondering about the value of this thread. I started it beacause I had read a few comments which indicated Toe Out On Turns was a misunderstood phenomenon. The motivation was partly selfish as I am undecided as to whether it is required in racing off road terms.

I had hoped to promote discussion to help enlighten us all.

I think I might have help cloud such enlightnement. My apologies to all if this is the case. I included the pic of the F1 car to highlight the use of Rev Ack because someone challenged its useage, not to endorse its use on our style of vehicle or to compare a 3" travel vehicle with a 20" travel vehicle.

Entropy you asked the question about credentials, I dont expect you to take my word on anything which I post, I expect you to investigate for yourself after being alerted to issues by my posts, as with all who use this forum.

Im a little agrieved that you should ask for credentials (we didnt ask for yours) but am going to supply mine, this once only.

Automotive mechanical engineer (all my life, im now 46)

Owned a suspension, steering and brake workshop for most of my early life

Taught braking suspension steering practise and theory at university for 10 yrs to training engineers

Last 10 yrs as a financial investment adviser (Which has only taught me the folly of owning these cars..but who cars)

My racing history is by way of speedway sports sedans, go carting, formula 3000 (aussies version), off road (full sized) and now superlites (aussie class) Ive never been any good at any of these but have immensley enjoyed myself.

I am not now and never have been a Duner, so I do not understand the needs of this class of vehicle use, nor do I use the vehicle in any recreational way, apart from testing all my wheel time is under racing conditions.

Entropy, all posts on this site are opinions, if you wish to dismiss opinions, please do so, but please don tell us you are dismissing our point of view. Thats somewhat personal. And mate, I dont talk out my arse.