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Location:
Finland
Registered:
June 2002
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removing Ackerman Steering
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Sat, 31 August 2002 00:07
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I haven't read a thing on reducing/removing Ackerman Steering phenomena on any internatiional web forum.
I do however know some gravel rallying racers here in Finland have paid attention to this and changed steering geometry to get rid of Ackerman geometry. This makes car to behave more predictably while sliding.
Is fooling around with this acknowledged widely ?
-A.
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I supported Toymods
Location:
Adelaide
Registered:
May 2002
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Re: removing Ackerman Steering
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Sun, 01 September 2002 05:54
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Ackermann is built into cars to make them easy to drive on the road. Hence, to have non would have many a mum complaining.
I think being a road orientated car forum there is not too much discussed on here. Maybe on rally forum's but not much here. I doubt if I wasn't involved in building a race car at uni I would know what you'r talking about and how to get rid of it.
I can see the point tho, you want to be able to control the steering whilst rallying and not thave the thing trying to correct itself. Insead of fighting the steering, it would do what you want.
Surely there would be as many problems as finding zero ackermann and mounting it as the gains would allow.
Jaz
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I supported Toymods
Location:
Perth
Registered:
May 2002
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Re: removing Ackerman Steering
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Sun, 01 September 2002 06:33
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Is that the self-centering effect you are talking about?
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Location:
Brisbane / Gold Coast
Registered:
May 2002
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I supported Toymods
Location:
Adelaide
Registered:
May 2002
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Re: removing Ackerman Steering
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Sun, 01 September 2002 13:06
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It is at this point that I suggest to everybody to read all of Carrol Smith's books:
TUNE TO WIN
PREPARE TO WIN
ENGINEER TO WIN
and there are more.
http://www.carrollsmith.com
He gives HIS thoughts on everything, puts down big companies, calls people idiots (or atleast infers). Its great. All the while still being a books full of great racing technical information.
Wanna build a race car: read Carrol Smith.
We did, We are. look here
Jaz
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Location:
Finland
Registered:
June 2002
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Re: removing Ackerman Steering
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Sun, 01 September 2002 16:06
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Ackerman steering means that inside tyre will get turned in more than the wheel on the outside. See more at: http://www.auto-ware.com/setup/ack_rac.htm
The main reason why this is a handicap in gravel rallying is this.
As the car is sliding sideways at great speed, both of the front wheels do not point directly down the road. Since only one wheel is pointing where driver wants car to go, the other wheel is scrubbing the road, thus slowing the car down.
I do know a way how some cars have this Ackerman removed but it would not work for me since I have to keep my ride street legal. One other method involves heating up steering arm with a torch and bending it a little bit. This would not be apparent to a naked eye at roadworthy (MOT) test, but I cannot help thinking this would weaken the cast iron molecyle structure, hence better keep torch well away fron steering arms.
- - -
Thumbs up for this site !
I posted this thread also at American club4AG.com but it didn't generate any (meaningful) response, and only 30 views. This site however generated some buzz around this steering geometry topic. Thank you for your input.
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I supported Toymods
Location:
Adelaide
Registered:
May 2002
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Re: removing Ackerman Steering
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Sun, 01 September 2002 16:20
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I havn't read that site (it's late), but is the alteration worth the effort?
Maybe you should pick up some spares, alter them, put them on and have some test sessions. I reckon it would be hard to notice the difference on gravel surfaces. On tarmac, it may be more noticable.
What car are you rallying?
Jaz
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Location:
Finland
Registered:
June 2002
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Re: removing Ackerman Steering
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Mon, 02 September 2002 13:07
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Not rallying in a true sense of the word. Competing is just too costly business for me.
I'm ever so slowly building up an rwd Starlet that is more suited to gravel rather than paved streets.
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Location:
Tasmania
Registered:
May 2002
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Re: removing Ackerman Steering
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Mon, 02 September 2002 14:51
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This is all most interesting to me. I am one of those few crazy people that has actualy cut and welded my steering knuckles experimenting with things like this, and driven it on the road for about 2 years. Don't tell anyone.
The last time I did this my aim was to quicken the steering (by making the arms shorter), and also add more ackerman. I wanted to get the "correct" ackerman angles, as the standard car was not perfectly correct in toeout on turns. (This also changed bump steer, but never mind that). For a track/road car, like a F1 or something, having correct ackerman should improve grip as the wheels are pointing the dirrection they should be with minimal slip. On a production road car, the ackermann effect is reduced to keep the turning circle small. When I changed this to have thereticaly corrrect ackermann angles, I lost some lock-to-lock movement, and the turning circle became larger. This is the main thing that is not good for a rally car. I would spin out in some turns because I ran out of lock!
I am cutting my knucles again soon, and will take out all the ackermann angles (and keeping them short for quick steering), but I may gain some bump steer but don't worry about that.
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Location:
Finland
Registered:
June 2002
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Location:
Tasmania
Registered:
May 2002
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Re: removing Ackerman Steering
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Tue, 03 September 2002 01:40
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I can't agree with that last bit sorry. The steering rods should be paralel to the control arms, and of equal length. The angle does not matter so much, as long as they are parallel. Moving the rack up or down will create nasty bump steer, asuming the steering was a ok setup from the factory. If you want to change the angle of the control arms and steering arsm after lowering, you need roll center blocks under the strut. This is about roll center though, not bump steer. With my KE30, the steering arms are actualy a little longer than the control arms, which creates some nagatibe bump steer (understeer). I want to get rid of this and make them all the same length if I can, at the same time as having no ackerman effect (for smallest turning circle and oposite lock on corners).
Please, pass on any other Finnish rally tricks you know of.
Also, at the Carrol Smith website, I can not purchase any books because they don't give an address or tell the currency of the prices.
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Location:
Madrid - Spain
Registered:
August 2002
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Re: removing Ackerman Steering
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Tue, 03 September 2002 03:49
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This all sounds interesting. From what I have read, the biggest debate over Ackerman in industry and racing is that the ackerman angle changes depending on the slip angle of the front tyres.
Even on shopping trolley type cars, full ackerman is generally regarded as being too much. I think that zero ackerman isn't advisable for a rally car because you will be losing too much grip on your inside wheel, reducing the responsiveness of the car, but thats just my 2cents worth.
I found a great automotive book shop while living in Perth. http://www.pitstop.net.au/ these guys stock the Carrol Smith and mail order anywhere in australia within a couple of days. Prices are very reasonable too.
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Location:
Tasmania
Registered:
May 2002
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Re: removing Ackerman Steering
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Tue, 03 September 2002 05:10
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Well, I am going to give it a go, zero ackerman, this weekend.
I surgest this may be a good move for sealed road drifting as well, as the max steering angles should be increased for more oposite lock to avoid spining out. I will see.
On sealed roads, the outside wheel does the most. I think the car is likely to go where the outside wheel is pointed. Often race cars get the inside wheel off the ground and it doesn't seem to upset them. Maybe in refined types of racing like open wheelers ackerman plays a part. I suspect that the steering angles used at speed are not big enough for ackerman angles to play a big part.
And for rally, where half the time you are steering in the oposite direction to where the car is turning, I don't think ackerman angles are relvent any more. Its probably more important to have maximun steering lock to lock.
This is so fun. I will let you know how it goes.
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Location:
Madrid - Spain
Registered:
August 2002
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Re: removing Ackerman Steering
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Tue, 03 September 2002 06:06
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My only concern with zero ackerman for rally is it may reduce the the initial turn in response of the car, but give it a go and let us know the pro's and con's of zero ackerman
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Location:
Tasmania
Registered:
May 2002
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Re: removing Ackerman Steering
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Tue, 03 September 2002 13:06
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OK I will do that, but in earlier days, I had Technical Lego cars that had zero ackerman, and I'm 99% sure initial turn in would not be changed. I would think front grip through a long hard corner would be more of an issue. The angle difference is so small.
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Location:
Tasmania
Registered:
May 2002
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Re: removing Ackerman Steering
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Sun, 08 September 2002 17:17
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Previosly, I had modifyed my steering knuckles for true ackerman, and I also
shortened them for quicker steering. This worked good, but the minimum
turning circle was a bit large. Performance was good.
OK, I cut my knuckles again and welded them up for parallel steering, no
ackerman! Since this is a road going old corolla, not a fully adjustable
race car, some aspects are a bit crude. I worked out the bump steer as much
as I could,but its not perfect. The only testing I have done is on wet
roads with poor tyres, and some gravel rally work.
To my surprise, the steering is alot slower, lighter, and more turns lock to
lock. Now about 3-1/4 turns from 2-5/8 turns before, and this is with the
same length knuckles! How does that work you say? Play with a model and
you will see.
Due to the outside wheel getting more turn, I can now do u-turns in no space
at all. Great!
Performance: The steering is too slow for me. This is not due to poor grip,
just the slower geometry. Road holding is still there I think. Maybe it
does understeer a bit more, but I had poor conditions. The steering feels
more constant ratio. With ackerman, it seams to quicken up at either
extream.
Conclusion: If you are designing a car, no ackerman is ok I guess. Bear in
mind a quicker steering box or rack will be needed than if you where to have
ackerman angles (or shorter knuckles). Wether ackerman angles improve grip
or not I'm not sure, there are lots of other things effected that are more
important to me.
Increasing the ackerman angles to true ackerman or beyond will quicken the
effective steering ratio, but increase your minimum turning circle.
Decreasing ackerman angles to near zero or negative, will slowen the
effective steering ratio, but decrease the minimum turning circle.
Note: When changing the angle of the steering knuckle for different ackerman
effects, you will end up adjusting the steering tie-rod to suit, which
effects bump steer.
I am going to change it again, back close to factory specs. I will have
less ackerman than factory, but not zero. This is mainly for turning circle
issues. Also, I will keep the knuckles short for quick steering, and to
counter the slow effect of reducing the ackerman angle.
OK, so zero ackerman may be great for rally, but you need much shorter knuckles and/or quicker steering rack/box to suit.
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Location:
Finland
Registered:
June 2002
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Location:
Tasmania
Registered:
May 2002
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Re: removing Ackerman Steering
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Mon, 09 September 2002 17:45
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Ok. Lets try the proper spelling "ackermann" and you get quite a bit of info. The very best quote on the internet is this:
"Ackermann Steering
Every area of human interest has its dark corners guarding arcane information, useful to very few but implying vast knowledge when dredged up and injected into a dull conversation. Airplane design, for example, has the infamous Reynolds Number, just the thing to spring on an instructor during a flight review who thinks he/she's got you on the run."
"In automobiles, the trivia winner simply has to be Ackermann steering. The mere mention of it in a room of would-be racers makes the conversational volume level plummet. To prepare you for such a day, here's a tantalizing set of online conversations that came through the Internet's 240 Z car list. You don't have to understand it. Just memorize a few lines, toss them in at the next meeting and watch the fun."
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Location:
Tasmania
Registered:
May 2002
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Re: removing Ackerman Steering
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Mon, 09 September 2002 17:57
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I found a Excell program that I downloaded and am playing with. You get to type in all the specs of your car, and it gives a graph of wheel angle difference with rack movement. It also gives a graph of what the graph should look like for optimal handling, acording to the programer. I think it is quite good, because it takes into acount wheel slip angles (front and back) and placement of the rake behind the wheel center distance.
There are so many angles all working at once in steering it is mind boggleing. Very few people would have a full grasp of everything that happens. After a sleepless night and experimentation with both 100% and 0% ackermann, I am going to go back to almost factory spec ackermann angles, or a bit less. It depends mostly on front wheel slip, but it seams about 50% ackermann is good on a road car. Even if the knuckles are parallel, this can also be achieved by mounting the rack further back (as it often already is on many cars). I am not changing the ackermann simply for the ackernamm effect, but for the side effects these things have. Because I need quick steering, and I need good handling at low speeds, and I need strait line stability, and I need to do tight u-turns.
Most webpages that mention this miss out on alot, but some are good. Most are theory, because sadly few have actualy experimented.
Let me know if anyone has questions.
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Location:
Terrigal
Registered:
May 2002
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Re: removing Ackerman Steering
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Mon, 17 November 2003 00:48
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Wanted to dig up this old thread as i'm currently convering my RA28 to rack 'n pinion and with this comes all the fun and games of designing ackermann and bump steer etc.
The positioning of rack in relation to the angle the steering arms will be with the end of the steering knuckles/tie rod ends. How much does this effect ackermann?
See pic below. The rack sits behind the outer tie rod ends.
Is that going to give negative ackermann.. More turn on the outside wheel than the inside?
Thanks
Joel
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Location:
Madrid - Spain
Registered:
August 2002
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Re: removing Ackerman Steering
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Mon, 17 November 2003 02:28
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It won't give you negative but it will slightly increase the ackerman steering. Not by a lot though.
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Location:
Terrigal
Registered:
May 2002
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Re: removing Ackerman Steering
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Mon, 17 November 2003 03:25
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Wouldn't it be a slight decrease? eg. more neutral or moving towards the outside wheel turning more?
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Location:
Northwestern Sydney
Registered:
August 2002
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Re: removing Ackerman Steering
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Mon, 17 November 2003 03:49
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I've been following the Rack and pinion steering conversion as I'm planning trying it myself, I've now read this thread and my brain hurts 
Me thinks more looking into how steering works in the first place
might be a good place to start. I'd like to say somthing constructive but all I can say is "nice pic of a pile of steel"
I think the outside wheel would turn more but I'd need to sketch somthing up and play with it on cad to prove it
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Location:
Terrigal
Registered:
May 2002
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Re: removing Ackerman Steering
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Mon, 17 November 2003 04:03
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Mmm yeah headaches.. Would be good to move the rack forward but that isn't very easy with the xmember in the way.
I think will bolt it up and get some of those turntable/plate things to measure toe with and just turn the wheels and see the angle differences between the inside and outside.
Been doing some reading.. Seems a lot of race cars want the outside wheel to turn more as in high speed cornering you have more weight on the outside wheel and very little on the inside.
But i'd imagine this would have negative effects to everyday driving.
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Location:
Madrid - Spain
Registered:
August 2002
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Re: removing Ackerman Steering
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Mon, 17 November 2003 04:03
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The outside wheel will turn more but the inside wheel will turn in more than the outside wheel, hence increasing the ackerman effect. It is caused by the angle of the tie rod compared to the arc of the steering arm. I am sure you can appreciate that when you are pulling almost parallel to an arc (almost radially) then for a small imput movement, there will be a large output. When pulling from parallel to the ark tangent, the movement is roughly equal.
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Location:
Northwestern Sydney
Registered:
August 2002
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Re: removing Ackerman Steering
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Mon, 17 November 2003 04:06
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| TurboRA28 wrote on Mon, 17 November 2003 15:03 |
Mmm yeah headaches.. Would be good to move the rack forward but that isn't very easy with the xmember in the way.
I think will bolt it up and get some of those turntable/plate things to measure toe with and just turn the wheels and see the angle differences between the inside and outside.
Been doing some reading.. Seems a lot of race cars want the outside wheel to turn more as in high speed cornering you have more weight on the outside wheel and very little on the inside.
But i'd imagine this would have negative effects to everyday driving.
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that would have alot to do with the camber that race cars use also negative effect on a road car.
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Location:
Terrigal
Registered:
May 2002
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Re: removing Ackerman Steering
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Mon, 17 November 2003 04:10
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Anthony do you think it would be beneficial to try and get the rack closer to the xmember to have the steering arms straighter?
I am thinking if the bracket design is changed and go over the top of the xmember i can get the rack another 20mm or so closer.
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Location:
Northwestern Sydney
Registered:
August 2002
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Re: removing Ackerman Steering
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Mon, 17 November 2003 04:13
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| gold28 wrote on Mon, 17 November 2003 15:03 |
The outside wheel will turn more but the inside wheel will turn in more than the outside wheel, hence increasing the ackerman effect. It is caused by the angle of the tie rod compared to the arc of the steering arm. I am sure you can appreciate that when you are pulling almost parallel to an arc (almost radially) then for a small imput movement, there will be a large output. When pulling from parallel to the ark tangent, the movement is roughly equal.
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That makes sense, I've never looked into it in depth but if if is any assistance I'll draw somthing up to give some sort of idea of where the rack shoud be located in relation to the ball joint to achieve what you want.
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Location:
Madrid - Spain
Registered:
August 2002
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Re: removing Ackerman Steering
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Mon, 17 November 2003 04:34
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I would be more worried about the height of the rack than the fore-aft location. Ackerman is one of thoes things that is both good and bad depending on what you are using the car for. whereas bump steer is definitly something to be avoided
Noone really uses %100 ackerman and this is easily seen in any car park with painted or polished cement. If the cars had %100 ackerman then the tyres shouldn't squeel going around the corners. There has been a lot of people using zero ackerman on both road cars and rally cars. In my opinion (which isn't really worth much anyway) ackerman is overrated when it comes to performance driving, because as soon as one tyre starts to generate a slip angle then everything changes. The outside tyre will start to slip more than the inside one, effectively increasing the ackerman angle. In this case, I would probably recommend reducing the ackerman but you can't do that with the rack location. Only changing the steering arms will reduce it.
The most important thing for you Joel is to minimise the bump steer and try and get the rack as close as possible to where the original was. And do the bump steer before you put the RCA's in. otherwise they will stuff up all your hard work.
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Location:
Terrigal
Registered:
May 2002
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Re: removing Ackerman Steering
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Mon, 17 November 2003 04:45
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Yeah, will keep my inital efforts in eliminating bump steer.
But wouldn't I want the RCA's in first, as if I get it at the correct height for zero bump (or close to), then put the RCA's in, the angle of the control arms will change and introduce bump steer again?
I'm happy its all starting to take shape anyway.. Been big learning experience! Even if the first attempt isn't perfect, it can always be improved on.
Probably should be having this discussion in the other r&p thread going at the moment.
Lambolica - if its not too much trouble i'll take you up on that offer to draw it up.. More info the better I think.
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Location:
Madrid - Spain
Registered:
August 2002
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Re: removing Ackerman Steering
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Mon, 17 November 2003 04:50
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| gold28 wrote on Mon, 17 November 2003 15:34 |
And do the bump steer before you put the RCA's in. otherwise they will stuff up all your hard work.
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What I meant to say was "and do the RCA's before you do the bump steer, otherwise they will stuff up all your hard work"
Sorry about the bum steer  
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Location:
Northwestern Sydney
Registered:
August 2002
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Re: removing Ackerman Steering
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Mon, 17 November 2003 05:02
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| Quote: |
Lambolica - if its not too much trouble i'll take you up on that offer to draw it up.. More info the better I think.
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When you get this sorted I'll be stealing the setup for mine (the idea not the setup) If I help it makes it feel more like borrowing than stealing 
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Location:
Terrigal
Registered:
May 2002
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Re: removing Ackerman Steering
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Mon, 17 November 2003 05:35
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Haha thats cool I want to supply all info and findings and eventually results.
Will continue to post in the other thread going about it. When finished if the result is any good i'll write a tech article 
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: removing Ackerman Steering
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Mon, 17 November 2003 06:10
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| Jonny2TG wrote on Tue, 10 September 2002 03:45 |
Ok. Lets try the proper spelling "ackermann" and you get quite a bit of info. The very best quote on the internet is this:
"Ackermann Steering
Every area of human interest has its dark corners guarding arcane information, useful to very few but implying vast knowledge when dredged up and injected into a dull conversation. Airplane design, for example, has the infamous Reynolds Number, just the thing to spring on an instructor during a flight review who thinks he/she's got you on the run."
"In automobiles, the trivia winner simply has to be Ackermann steering. The mere mention of it in a room of would-be racers makes the conversational volume level plummet. To prepare you for such a day, here's a tantalizing set of online conversations that came through the Internet's 240 Z car list. You don't have to understand it. Just memorize a few lines, toss them in at the next meeting and watch the fun."
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LOL, i remember reading this with much mrth many moons ago,.. where is it from??
as far as ackermann goes.....
it's used because inside and outside tyre have a different radius (form the point that the car is turning around) and so need to be at different angles to follow this line.
on road cars where you actually use full lock, ackermann is good as you don't scrob the tyres at full lock, and will generally reduce tyre wear.. the proviso of this is that you are not actually sliding the tyres at all.... soon as you do, true ackermann is out the window..
what it comes down to is the % of slip that a tyre needs for it to have maximum grip. road tyres are like 10% slip or more, whereas race slicks are only a few percent slip. (this is all on tarmac) you need to design the steering geometry with a few things in mind....
1) how much will the wheels be realistically turned when cornering hard (and design for that).
2) the weight transfer from inside to ouside wheel, or basically the difference in the wheels contact patch load.
3) how much grip will that load impart
4) how much slip gives best traction
5) what angles the tyres need to be (ie ackermann or not) to impart this amount of slip.
race guys often don't take ackermann into consideration because of a few things.
1) there is so much weight transfer the inside wheel is doing virtually nothing, although the angle will affect going turing in, and powering out of corners.
2) the amount of steering input used in tarmac race cars is much smaller than if you are doing a three point turn so you are taking about two tenths of sfa when it comes to altering the steerign angles....
if you really want to get serious about it. find a corner on a track, or skid pan etc etc, that you cna take at a good speed, and has about the most steering input you would want at speed.
take note of the steering wheel position. adjust toe-in and toe-out and keep going round the corner... this way you can measure the wheel angles that work best, and then alter the ackermann angles so you get the right angles at the right time....
it will be different for every car, and every suspension setup., due to spring and shock rates, body roll, and every angle in the suspension..... but it makes for funny drunken discussion with car buddies  and lots of impromptu diagrams made of snakes and pretzel sticks and such......
Cya, Stewart
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Location:
Northwestern Sydney
Registered:
August 2002
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Re: removing Ackerman Steering
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Mon, 17 November 2003 06:16
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Bags driving your car on the skid pan whilst you take photos of the car and taking notes 
Wow this sounds like fun now!!
/end sarcasim
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Location:
Victoria
Registered:
May 2002
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Re: removing Ackerman Steering
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Mon, 17 November 2003 08:32
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i dont know what the problem is
rack and pinion steering was just soo easy with lego 
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Location:
Terrigal
Registered:
May 2002
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Location:
Tasmania
Registered:
May 2002
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Re: removing Ackerman Steering
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Tue, 18 November 2003 07:33
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Having the rack behind the steering knuckle ends like you have in the picture, will give more of a ackermann effect. That is, inside wheel turns more than the outside wheel, like normal. Try and replicate the original steering geometry of your original car, (RA28?) and keep the steering arms sort of inline with the steering knuckle ends. If you have to mount the rack further back behind the crossmember which gives a slight angle in the steering arms, then that is ok to a cirtain extent. Achermann does not effect the performance of steering that much, but changing it will effectively change you lock to lock steering ability (it gets complicated to understand how). If you mount the steering rack too far back (lots of achermann) the steering wheel will tend to lock in place when reversing on full lock. (Yes I have done this, tryed many setups).
As I have said, the MOST important thing in all this is bump steer. Many cars new and old have some bump steer designed into them, but it is negative bump steer if you can understand that, which actualy makes the car understeer a bit, makes it more stable. If you have posative bump steer (hard to explain), that is very dangerouse and the car tends to oversteer. But still, what we want is zero bump steer.
To get this ***IMPORTANT INFO, LOOK HERE***
Make it so the steering arms and the lower control arms are both parallel and the same length **** This is measured from the pivot points of course.
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