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 Post subject: Ackerman
PostPosted: Mon Nov 05, 2012 2:48 am 
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Proven Drifter
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Ok, doing some research to make some mad steering angle on the miata. ( Maaaad steering angle like you won't believe.... when I get wheels. )

But I am wondering how I should set up the ackerman on such a short/light car. The miata is set up factory with low ackerman.
I have seen drift cars with zero ackerman, positive and negative ackerman.

Theories please.

And if you don't know what ackerman is. easiest way to describe it is with this:
http://www.compgoparts.com/TechnicalRes ... eering.asp

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 Post subject: Re: Ackerman
PostPosted: Mon Nov 05, 2012 7:56 am 
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Proven Drifter
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You want zero Ackerman so your not scrubing speed immediately after initiation.

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 Post subject: Re: Ackerman
PostPosted: Mon Nov 05, 2012 4:33 pm 
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Proven Drifter
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akerman is kind of like the differential of steering geometry

when you turn, there's an instant center, a point you'll circle around if you hold the wheel

perfect akerman (1) makes both front wheels point toward the instant center
The car's width causes two different radii around the instant center, so the inside wheel is turned more

With drifting, when you're steering left, your instant center is actually on the right
this would mean that your inside wheel is now steering less than the outside wheel, giving your car some crazy toe out

My drunken theory says that you'd want negative akerman on a drift car, but since you're usually going for max angle, the steering input has no relation to the arc you're traveling, so you'd have to setup negative akerman based on avg angle and avg track speed... something like that

In practice, I'd say that 0 akerman is a good place to be. It's not perfect, even though 0 is a sexy number (don't judge me)
If you're going to drive it on the street any, I'd recommend against going negative, that's crazy.

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 Post subject: Re: Ackerman
PostPosted: Mon Nov 05, 2012 6:04 pm 
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Proven Drifter
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I was reading a bunch on drift works ( UK drifters mostly )

Stock setup ( some ackerman ) makes for a better driving feel.
Zero ackerman helps you hold speed mid drift, and is basically required for reverse entries.
Negative ackerman, Would feel terribly on the street.... but you could reverse entry and control it all day long.

I have 2 spare set of knuckles for the miata. I might redrill one normal/low ackerman. And one negative.

All I need now is a taper ream.

Also this is what negative ackerman looks like on the soarer, the s14 looks like it has a near 0 setup.
Image
Image

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 Post subject: Re: Ackerman
PostPosted: Tue Nov 06, 2012 4:58 am 
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Proven Drifter
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More info: Sorta more miata related.

Quote:
As for Ackermann, do you want positive Ackermann (inside wheel steers a greater angle than outside), or negative ackermann (outside wheel steers more than inside)?

If you want positive, it means that your tie rod bj's either must be closer to the centreline of the car for a rear steer, or further from the vehicle centreline for a front steer (i.e deeper inside the wheel). The below is the first case, i.e. rear steer, postive Ackermann. Given the space constraints we have inside our wheels, it can be more difficult to bury the tie rod bj further inside the wheel to achieve positive ackermann with a top steer, (i.e. forward mount)


I made a picture for this.
Image

Miata parts look like this, which would be a low ackerman, great for turn in. And the lower ackerman should help hold high speed drifts.
Image
Image

But... I might try zeroing it out.

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 Post subject: Re: Ackerman
PostPosted: Tue Nov 06, 2012 7:50 am 
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Proven Drifter
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Location: Okinawa, Japan / Bartlesville, OK
Mike Kojima likes a bit of ackerman for what it's worth. Dai's car runs 326 power knuckles I think. There seems to be two schools of thought. Some like the big angle and some like the steering feeling.

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 Post subject: Re: Ackerman
PostPosted: Tue Nov 06, 2012 8:05 am 
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Proven Drifter
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I think I am going to redrill the first set at stock miata low ackerman, and see how it works out.
Then I can do a zero, and negative set later.

Negative ackerman + big power would be a win drifting on a track I think.
Zero ackerman would be the middle ground, ok driving feel, not much tire wear from DD and less front tire wear drifting.
And stock would be the best DD for feel and less tire wheel on non opposite lock driving.

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 Post subject: Re: Ackerman
PostPosted: Tue Nov 06, 2012 8:24 am 
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Proven Drifter
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Greg's knuckles we were on at the event had a bit of ackerman in them but still gave a ton of angle. They were also pretty normal driving around town and the 3.5 hours to and front the event.

It's all opinions and drivers preference when you really start deciding what you like.

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 Post subject: Re: Ackerman
PostPosted: Tue Nov 06, 2012 10:40 am 
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Supreme Nut
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For what it's worth Danny George runs a zero ackerman setup on his miatas.


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 Post subject: Re: Ackerman
PostPosted: Tue Nov 06, 2012 6:32 pm 
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Here's a thought, having static toe in would create a negative Ackerman effect at some given drift angle...
I'll do some math to see if its practical when I'm not busy

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 Post subject: Re: Ackerman
PostPosted: Tue Nov 06, 2012 9:48 pm 
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Proven Drifter
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How often do will you really try to do backwards entries? i run zero ackerman to be able to maintain med-high speed entries, i remember initiating at 60 and being at 50 before the apex. I mean if you have two spares go for it, but the steering feel it gonna suck, and you can still do backwards entries on zero ackerman. Lets not make those too easy to do :mrgreen:

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 Post subject: Re: Ackerman
PostPosted: Tue Nov 06, 2012 11:10 pm 
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Proven Drifter
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And not to mention backward entries are terrible looking with the stupid stall and straightening that happens when getting back on the power.

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 Post subject: Re: Ackerman
PostPosted: Tue Nov 06, 2012 11:20 pm 
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Proven Drifter
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I am not a fan really of the normal reverse entries.

I am talking about spinning past 90degrees on a corner, and catching up with 90 degrees later. Super early entry.
Not I went backwards for a second, stalled lost the angle and back to drifting.

Reverse four wheel drift. Like this super sweet paint drawing i did in 30 seconds.
Image

Not this:


this:

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 Post subject: Re: Ackerman
PostPosted: Tue Nov 06, 2012 11:50 pm 
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Word! Vomited on the first one and watched the second one a few times.

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 Post subject: Re: Ackerman
PostPosted: Wed Nov 07, 2012 12:10 am 
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Proven Drifter
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2nd one is boss, but you definitely dont need neg. ackerman to do that, plus negitive ackerman will still scrub speed.If you enter early as they did in the video, youll be going like half speed by the time you get back on power. And with a turbo engine...laglaglaglaglag...second gear...boost :8

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 Post subject: Re: Ackerman
PostPosted: Wed Nov 07, 2012 1:27 am 
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Proven Drifter
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There are ways of dealing with lag..... my MS2 ecu doesn't support it.
But when I get a big turbo I may upgrade to MS3, and anti lag. :lol:

But zero offset seems to be the best off all words, daily, drifting, and tire wear.
Only down side is a little loss of feel on grip driving ( but who does that in a miata. :lol: )

Time to order a taper reamer. And maybe in stall my modded rack into the car, and see what negative offset I need.

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 Post subject: Re: Ackerman
PostPosted: Wed Nov 07, 2012 4:48 pm 
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Proven Drifter
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I think in you situation, I would drill, ream, repeat. Just moving the pickup in is going to add decent angle. It looks like almost zero ackerman from the factory, but that could be front steer fooling with my eye.

Then if you like what you got form the drill/ream setup cut the knuckle arms down and move the pick up points inline with the flca balljoint and have short arm, zero ackerman knuckles.

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 Post subject: Re: Ackerman
PostPosted: Wed Nov 07, 2012 4:57 pm 
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Proven Drifter
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I took a bunch of pictures, there is quite a bit of ackerman, maybe not 240 stock, but some.

I am going to need some wheels before I try anything though. Modded steering = tire rub on stock wheels/tires.
So, I need some massively low offset wheels, I might just order 2 soon.

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 Post subject: Re: Ackerman
PostPosted: Sun Dec 02, 2012 12:02 pm 
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Kansei Drifter
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Location: drifting in my mind or online. possibly in a car or on a bike. maybe in a train.
15x7 with 0 then 1.5 inch spacer.

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 Post subject: Re: Ackerman
PostPosted: Sun Dec 02, 2012 2:00 pm 
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I could just get way negative offset wheels to start with. Bigger lip that way, and cheaper with no spacer.

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 Post subject: Re: Ackerman
PostPosted: Sun Dec 02, 2012 4:36 pm 
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Kansei Drifter
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Location: drifting in my mind or online. possibly in a car or on a bike. maybe in a train.
Well I have some of those laying around here. just didn't know if 1.5 would be too much.

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