Ackerman vs Anti-Ackerman front geometery

[rthy]

this is a thread to discuss the modifiecation of the original ackerman angle that is stock to Toyotas,


heres a pic shamelessly stolen from seamus


http://img227.imageshack.us/img227/9088/heyman2cc7.jpg

http://img151.imageshack.us/img151/6467/heyman1ge0.jpg


these arms have been shortened and straightened out so there is nill ackerman compensation.

What do people think?

[Delazy]

they are actually seamus's pics sam....not dongaz

keen to see results from them tho.....been considering buying some of the heyman or kuroi modified knuckles for awhile now......these might be a better option :D

[Rollabender]

I'm not a fan of cutting and shutting steering arms, but that's just me. I'd have some milled up.

Eliminating the ackermans angle is fine for a track only car, but you wouldn't want it for a street car.

Good luck doing a u turn if you do!

[ae86hachiroku]

Just to help out, these are the arms from HEY-MAN products.

[attachment=29507:stuff_268.jpg]

Will be using it on my own car.

[slydar]

anyone who has done it says its awesome.

brett (srtoy) purple jdm garage hachi has done it.

shane bingham has that set up in his old white car (i would be surprised if he didnt take the arms to japan with him and theyre in the silver car)

LOTS of top d1 cars ect have custom knuckle arms for this reason as well as bump steer/roll centre correction (you see it alot in option mags).

[pope]

Most of what i've read suggests that Ackerman is good for low speed stuff and for higher speed it doesnt matter so much.

I have no doubt that Toyota would have designed the Ackerman angle that we have for town based speed and corners, to aid in drivability and tire wear.

Most of the stuff i've read suggests that the load on the inside tyre is generally very low in circuit cornering so stressing too much about Ackerman while interesting may not be very noticable.

Having said all that i've not got any experience with modifying Ackerman angles so i may be completely wrong.

[slydar]

cutting and welding is a bit scary.. but if you had them "milled" youd wanna make them thick/ fancy material. stock theyre forged. but i do agree, strength is an issue. in fact its the only issue stoping me from doing the mod.

[Rollabender]

<div class='quotetop'>QUOTE (slydar @ Aug 9 2008, 01:52 PM) <{POST_SNAPBACK}> (index.php?act=findpost&pid=573339)</div>
cutting and welding is a bit scary.. but if you had them "milled" youd wanna make them thick/ fancy material. stock theyre forged. but i do agree, strength is an issue. in fact its the only issue stoping me from doing the mod.[/b]

Pluuuuuuuuuuuuuuuuuuuus one.

[70XIN]

I can't comment on the ackermans thing, because i have very very little knowledge of it (and not afraid at all to admit it), i simply went by the recommendations of some who have been mentioned/posted in this thread :)

On the comment of strength and such, i'm 50-50 about it. Sure, cutting and welding is never as strong as a single piece, but *i* made sure i V'd the metal, and made multiple passes with as much penetration as possible... plus, if you see how narrow a standard non-PS arm gets towards the tie-rod end of it .. it makes me a lot less nervous about running these arms.

But i'm not ruling it out, the thought of them breaking always lingers in my mind.

I guess you could always heat-treat/cryo/etc the arms afterwards too, if you're that worried



I guess the strength/awesomeness of them is something that will best be tested. :sweat:

[Jonny Rochester]

Sam, do you realise what a large and dark topic you have opened?

With the knuckles pictured (zero ackemann = parallel steering, shorter length), I predict the following:
- similar but different feel
- not good or bad, just a bit different
- more linear steering ratio
- more turns lock to lock, but more effective steering angle (outside wheel can turn sharper)
- smaller turning circle (will be able to U-turn in the street without handbrake)

[Patto]

i would prefer ackerman myself

never done it on a car but when i ran my go kart with zero ackerman it was no where near as quick (laptimes) as when it had "factory" ackerman..

[RobertoX]

<div class='quotetop'>QUOTE </div>
more turns lock to lock, but more effective steering angle (outside wheel can turn sharper)[/b]

I reckon same turns lock to lock.... the steering rack hasn't changed. You will get a greater amount of angle of steer at the limits of lock though. This is independent of what knuckles you use.



I'm not sure about the anti ackerman geometry.
I did some testing of a race car with ackerman geometry and anti ackerman geometry steering arms. Hands down the ackerman was better but it really depends on the application.
It's all about the slip angles of the tyre at load, with anti ackerman you end up running a lower slip angle on the inside wheel which may or may not be better depending on the load on the tyre and the characteristics of the tyre itself. The lateral force produced by the tyre drops of after a certain slip angle, if you exceed this slip angle you are not using the tyres to their full effect.

With ackerman geometry you also get a yaw moment from the inside tyre "dragging" which helps the car to turn in.

Personally, I wouldn't use cut and welded forged parts in my car unless done by an incredibly good acredited welder. And I would probably want the welds tested (ultrasonic or something)

[Jonny Rochester]

more linear steering ratio
Normaly, even if the rack/pinion ratio is linear, the resultant steering ratio is variable. The steering gets quicker as you get to the end of the lock. Once you start turning, the inside wheel steers very quickly. With parallel steering this is slowed down alot. The result is more turns lock to lock, but this gives better control. If the knuckles are also shorter than normal, the resultant ratio may feel about the same, but more linear. Meaning, same amount of steering input steers the wheels the same amount.

more steering angle
Normaly, your maximum steering angle is limited by the angle of the inside wheel. With small modifications, you can get the inside wheel to about 45 degrees. But at this time, the outside wheel is not turned as hard. In theory, with parallel steering you could get both inside and outside wheel turned at 45 degrees. And as the angle of the outside wheel mostly dictates your minimum turning circle, with parallel steering you maybe able to do a U turn in a small street. In practice, you may be limited by rack travell, knuckle touching the lower arm, or the tyre hitting something.

A setup I would surgest
Welded knuckles with no ackemann, same length as "PS" knuckles. Plus a quick rack, to quicken the steering again since the parallel knuckles slow it down.

a standard AE86
does not have "full ackermann" that I know of. I think it is about half ackermann effect. If you run theoretical ackermann angles, the inside wheel turns too sharply, hits the lock stop when the outside wheel has not turned enough. The result is you have to do 3 point turns alot. For the sake of parking (and drifting) factory cars come with about 1/2 effect ackermann. (A guess, I havn't measured many).

[_matt]

in a wrap up, overkill for street cars which most cars on this site are (including mine ofcourse) which in itself has overkill suspension/steering mods, that it doesnt necessarily need, but gives u the piece of mind that u can pretty much do anything on the track/street with ur oh so powerfull 16v/20v max 100kw motor :rolleyes:

[RobertoX]

Jonny, you said "more turns lock to lock". This is the number of turns of the steering wheel when you have the steering at full lock one side and go to full lock on the other. This will not change when you change the knuckles over (well not unless the old knuckles were stopping the steering from getting to full lock somehow).

This will only change when you change the rack, (eg adding "lock spacers" makes more turns lock to lock)

[Medicine_Man]

Random Image I had related to said topic.. (Found it somewhere ages ago)..

[Jonny Rochester]

<div class='quotetop'>QUOTE (RobertoX @ Aug 9 2008, 05:13 PM) <{POST_SNAPBACK}> (index.php?act=findpost&pid=573412)</div>
Jonny, you said "more turns lock to lock". This is the number of turns of the steering wheel when you have the steering at full lock one side and go to full lock on the other. This will not change when you change the knuckles over (well not unless the old knuckles were stopping the steering from getting to full lock somehow).

This will only change when you change the rack, (eg adding "lock spacers" makes more turns lock to lock)[/b]


I sympathise with your understanding Roberto. I once thought the same. It takes a while to get a grip of this in your head.

When you go from ackermann to parallel knuckles (and retain the same knuckle length), you do gain more turns of the steering wheel from lock to lock (if the steering angle is not limited by rack movement, but limited to wheel angle).

It is one of those funny mystical illusions that is very difficult to understand. I can prove it with geometry, and I have tested it on a actual car. It gets very 3 dimensional to describe, so I will let you all think about it. :rolleyes:

[greeneyes]

The problem with non-ackerman steering arms is that both front wheels point in the same direction in a turn. Turn 30degrees and both point that 30degrees.

This means they will describe the same diameter turning circle, but of course on a car the inside wheel must drive around a smaller circle than the outside one.

We did the same when rallying, cut & welded the arms, but on gravel the lack of ackerman steering was not important and we really wanted the higher ratio.

[RobertoX]

But on the standard car it is limited by rack travel, is it not?

If not limited by rack travel, then of course by letting the rack travel further, the steering wheel will will go through more revolutions.

On the standard set-up, I understood that the limit of steering wheel travel was defined by the limit of rack travel. The 'lock spacers' that people use wouldn't work otherwise.


Think about it this way, if you disconnect all of the suspension from the cross member so that nothing is attached to the steering rack then go and turn the steering wheel you will have the same amount of turns lock to lock. It is simply a function of the effective length of the rack gear and the rack to pinoion ratio.

[kaibeecee]

I wouldn't run the items pictured on the street.

S13 is a different story though, as there's a little bit more surface area to play with on the arms

[Konakid]

Driving without any Ackerman effect would be similar in feel to having a locker in a fwd car wouldn't it? Out side wheel would get scrubbed to shit when turning, would go through tyres so fast.

[MSF Racing]

can you just bore and sleeve for the ball joint then use the original ones reversed

[86adz]

whats the ackerman effect like when s13 conversion is done? is it more or less than using 86 suspension sorry to open another can of worms in this thread..

[Jonny Rochester]

<div class='quotetop'>QUOTE (RobertoX @ Aug 9 2008, 07:33 PM) <{POST_SNAPBACK}> (index.php?act=findpost&pid=573474)</div>
But on the standard car it is limited by rack travel, is it not?

If not limited by rack travel, then of course by letting the rack travel further, the steering wheel will will go through more revolutions.

On the standard set-up, I understood that the limit of steering wheel travel was defined by the limit of rack travel. The 'lock spacers' that people use wouldn't work otherwise.


Think about it this way, if you disconnect all of the suspension from the cross member so that nothing is attached to the steering rack then go and turn the steering wheel you will have the same amount of turns lock to lock. It is simply a function of the effective length of the rack gear and the rack to pinoion ratio.[/b]


You are right. But when you change from ackermann to parallel, the inside wheel will not be turned as far when at full lock. But the outside wheel will be turned further. The inside wheel will still have a bit of room left. To take advantage of this you add a spacer or something to get the same steering angle of the inside wheel that you had before. The result is you need to turn the wheel more times to achive the same steering angle of the inside wheel.

I did my testing on a older car with worm and ball steering which was not travel limited.

[Dongaz]

I realise that making them shorter will have the advantages of it being more direct in the steering and you won't have to turn the wheel as much for the same angle. If you like the style where both wheels are at the same angle rather than having the inner wheel turn further to get more angle then these would be for you. Its really what style you prefer driving. I would have thought that having ackerman incorporated in the knuckles would help get the angle when drifting...but then again its what the driver wants.
Oh and as Jonny said before the linear and variable steering rack would also change the situation aswell. Standard rack is variable while the quaife quick rack is linear from what I remember.
Each to there own.

[Simon-AE86]

having never driven/drifted a car with no ackerman's i have no idea what it would feel like, Can someone enlighten me what you could expect to notice straight away?

[rthy]

I think I can answer that one, ok I admit it wasnt on a car by my first recumbent trike had no acherman compensation for the front wheels, when trying to go around a corner the inside would try and drag/bounce outwards and the outside would be constantly drag. It would promote understeer for me and was quite unpleasant to err.. ride with. It was almost like having a locked diff for the front wheels.

[Jonny Rochester]

Both the standard and quaife racks are linear in ratio. My variable ratio comment is in regard to the effective wheel angle vs steering wheel input. Because the tie rods move in an arc, not just left and right, so funny strange geometry happens.

[rthy]

hey I was thinking every single person on here has pretty much talked about adjusting acherman angles for grip but I think it may help people steer better when drifting, although very ironic me being a non drifter here goes:

The princible of the acherman angle is such that the outside wheel is angled to turn a larger radius, however when drifting and using opersite lock the wheels are angled different from each other but the road is going underneath them straight. Hard to explain but relative to the front wheels while countersteering the wheels are not doing any turning and are facing in the direction the car is going, however because of the acherman effect one wheel will not be facing the right way.

Have I lost it or am I onto something here?

[mikewestphoto]

That's the way I think of it and with more lock you get more dynamic toe out added to the static toe you already have which I guess would be undesirable.

[slydar]

<div class='quotetop'>QUOTE (Sam_Q @ Aug 19 2008, 09:20 PM) <{POST_SNAPBACK}> (index.php?act=findpost&pid=577468)</div>
hey I was thinking every single person on here has pretty much talked about adjusting acherman angles for grip but I think it may help people steer better when drifting, although very ironic me being a non drifter here goes:

The princible of the acherman angle is such that the outside wheel is angled to turn a larger radius, however when drifting and using opersite lock the wheels are angled different from each other but the road is going underneath them straight. Hard to explain but relative to the front wheels while countersteering the wheels are not doing any turning and are facing in the direction the car is going, however because of the acherman effect one wheel will not be facing the right way.

Have I lost it or am I onto something here?[/b]

yeah sam probably. its for drift cars only really. well i would have assumed theyre the only ones who'd benefit.

[rthy]

yeah I know its for drift only but I would of thought someone would of thought of this point earlier seeing that theres more drift vs grip guys on here

no idea if there would a real world difference though, for me this is one of those things I just let be