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Discussion Starter · #1 · (Edited)
I just came across this interesting thread on ScoobyNet UK:

http://www.scoobynet.co.uk/bbs/thread.asp?ThreadID=131392

Pages 2 and 3 have some very interesting comments from Whiteline - including the fact that installing the kit actually results in more lift and that they will change the misleading name to something more appropriate.

Chris

edit: fixed link
 

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Discussion Starter · #2 · (Edited)
We got into a deep discussion about this on another forum. Thought I'd share the results.

What the ALK does is eliminate (mostly anyway) the built in anti-dive/anti-lift geometry of the suspension. This allows all the weight to go onto the springs, so that they are more heavily loaded and can do there job better over bumps, undulations, etc. It also adds caster that has been talked about in other threads.

Here's Whiteline's explanation:

http://www.whiteline.com.au/docs/articles/Effect_of_WL_ALK_a.pdf

Below is a chicken-scratch, oversimplified, exaggerated diagram I drew to illustrate the effect caster has on lift and dive. Including an Inverted strut (don't know why, that's just how I did it! Makes no difference)

Fig. A. Shows the case of negative caster. The bottom of the strut is behind the top. The force of braking makes the car body want to move forward relative to the wheel - the wheel is slowing and is coupled to the body via the strut. With negative caster the body wants to slide up the "ramp" created by the angled strut. Note that this upward force would be counterbalanced by the associated weight transfer toward the front. But in an extreme case like this, the front end could actually rise under braking. This eliminates the action of the spring and strut so that they can't follow the road surface well.

Fig. B shows the case of positive caster, as is present in the stock suspension and to a greater degree with the ALK. In this case, the body will slide down the "ramp", loading the spring and strut.

Note that both of these cases are exaggerated - the actual angle is in the 1 - 3 deg range, not 15 or 20 like the drawing!

The stock angle is positive, but barely, and becomes less so as the rear bushing flexes under load, so that the actual effect is a slight tendency to move up the "ramp", offsetting some, but not all, of the downward force due to weight transfer.

The ALK makes the effect about neutral - the front dives according to the amount of weight transfer to the front, uninfluenced by the geometry of the suspension.

edit: disclaimer: this illustration does not illustrate exactly what is going on but rather, I believe, is a simpler way for the layman to get his head around what is going on with the ALK (see below).
 

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Discussion Starter · #3 ·
It took me a couple of days to figure out how the ALK resulted in more front end lift AND more front end grip. The reason is that the stock anti-lift geometry holds the front end down by adding a percentage of the unsprung weight up front (like 30% IIRC according to Whiteline) to the sprung weight. In other words, it's keeping the front end down by decreasing pressure on the front tires. Less pressure = less grip.

Chris
 

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hmm, maybe I need to more carefully re-read your posts and those made by whiteline on scoobynet, but my interpretation of what they said is that the caster is not the main improvement from the ALK while you are saying it is. I thought that a stock WRX runs about 3.5 degrees static caster and the ALK only increases this by about .5 degrees which is nice but doesn't seem to provide the "softening" of the front suspension that Whiteline mentions. It seems that that Whiteline is claiming that it is the other geometry changes that provide the greater benefits seen by the ALK.
 

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Discussion Starter · #5 · (Edited)
Wow - somebody who actually understood all that stuff first time out! ;)

You're right, it's not just the change in caster that is going on. The key word in the description with illustration above is "oversimplified". What it's actually doing is changing the angle of the lower control arm to affect the same "ramp" effect. Thinking about the caster was how I originally got my mind around the problem and it's easy to illustrate. Those illustrations on ScoobyNet UK seemed to confuse as many people as they helped, and the Whiteline drawings are definitely confusing. But you're right, that drawing could use a disclaimer.

I'd welcome a better illustration of the effects of changing the control arm angle - I can see it in my mind but I don't know that I can draw it in a manner that makes sense.

I believe that you could get the same effect with caster - or at least a good portion of it - but you'd need a lot more that .5 deg like you say. The ALK is a pretty sophisticated bit of chassis engineering in a simple little package.

Chris
 

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"understood all that stuff first time out" might be a bit of an overstatement as I had to read your post and the stuff at scoobynet a few times before I could really visualize everything. I think I'm going to have to spend some more time thinking about it and looking at the suspension geometry before I really understand it as much as I'd like. I must say that it was a nice break from the satellite System Definition Manual I was reading. Kinda nice to think about something a little more tangible than the lower levels of a protocol stack.

Unfortunately, it does make me want to buy and install an anti lift kit just so I can see first hand the changes it makes to how everything bolts together. Unfortunate because buying involves money :D

And thanks for the PMs.
 

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Discussion Starter · #7 · (Edited)
Actually, the part itself is super simple. If you crawl under the car right behind the front wheels you can see the rear transverse link bushing/mount, at the rear of the control arm (transverse link in ScoobySpeak). It's a fairly large, kinda snail shaped piece of aluminum with a rubber bushing in the middle. It's right above and slightly in front of the back end of the bolt-on subframe. Now just imagine that peice being spaced straight down from the body by 20mm. There you have it - ALK. The ALK has an offset bushing for the angle change, but otherwise that's it. Not that they employ a spacer - the spacing is cast in to the aluminum mount. They also space out the subframe so they can clear the "taller" (lower?) piece.

It's cheap too! ;) :D

In red in this diagram:
 

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An interesting side note is that the RA spec C utilizes a very similar transverse link that also increase positive caster by about .5 degrees. They don't use any busings for the subframe and the subframe is disgarded. Not a big deal as most RA's are destined for rally cars and they need to lose the weight, in addition they seam weld the chassis- making a subframe obsolete.

The new US STi also has an additional .5 degree of caster, so it is a good bet it is utilzing this same setup. I'm curious if it will have a subframe (designed to fit) or be w/o one. I for one would not want to get rid of mine (unless I was drag racer looking to shed lbs or a rally car driver seam welding) as it adds a significant amount of rigidity.

I understand the positive effect of ading caster, I still don't have a grasp on how it helps beyond that.

Big Sky
 
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