[RdRacer301]

Originally Posted by homer09

no i wouldnt agree with this. the ALK kit bypasses the anti-lift effects subaru designed into the suspension.

the end result of the alk is a SOFTER front suspension (without changing the springs). this means that it grips better over bumpy roads. the front wheels will remain in better contact with the ground. if you increase the front grip, you improve turn in and increase over steer. the downside is you will have MORE nose dive and lift with with the ALK, but this was measured by WL to be less than an 1" on the softer wrx springs. (should be even less on sti springs).

the other result is the added castor, its advantages explained above.

I haven't given this enough thought nor do I have enough knowledge to have thought that far, but doesn't added castor tend to keep the car from nose-diving?

[Digitalfiend]

Well it seems the dynamic camber question has already been addressed (came here to post.) Nice info Homer and very nicely explained. Something that I don't think was mentioned was that more caster allows you to run less static camber, which in turn can improve straightline braking while still reaping the benefits of negative camber in the turns. Unfortunately, I don't know the proportion of caster to camber ratio (if there even is a general formula/rule or is car specific).

[homer09]

Originally Posted by RdRacer301

I haven't given this enough thought nor do I have enough knowledge to have thought that far, but doesn't added castor tend to keep the car from nose-diving?

yes it does! and that is why you can eliminate the anti-dive geometry of the impreza suspension without getting too much added dive.

as for a dynamic camber formula. i calculated it roughly the other day (very roughly) and about half a turn of the steering wheel will increase 1 degree of negative camber. (just to give you an idea).

[RdRacer301]

Originally Posted by homer09

yes it does! and that is why you can eliminate the anti-dive geometry of the impreza suspension without getting too much added dive.

as for a dynamic camber formula. i calculated it roughly the other day (very roughly) and about half a turn of the steering wheel will increase 1 degree of negative camber. (just to give you an idea).

Indeed. Just trying to clear things up as you said ALK "bypasses" the anti-lift effects Subaru designed into the suspension. I would argue that it increases the anti-lift effect....

As for the dynamic formula, obviously amount of castor you have would effect the amount of dynamic camber as you have explained. Thus, it is highly recommened that to get a true static camber reading, you want to have that particular wheel at zero toe.

[Pearson II]

Toe has no affect on camber.
As far as the half a turn gives you a degree of negitive camber...what amount of caster do you have?

[RdRacer301]

Originally Posted by Pearson II

Toe has no affect on camber.
As far as the half a turn gives you a degree of negitive camber...what amount of caster do you have?

Toe does have an affect on camber reading. Next time you have a car on the rack, move the front toe few mm each way, you'll see anywhere upto 0.5* change in camber. That's enough for me to have the toe @ zero on the corner I'm adjusting the camber. Then after camber is set, I'd finetune the toes.

As for castor, last time I checked (2month ago), I was at 4.5-4.6*, IIRC.

[Turninconcepts.com]

We have a local with an 07 going in for an alignment soon. I'll ask him for the caster numbers to get an idea where he is.

The 05+ could not get as much camber from just the stock bolts as the 04 could. The reason is because of the spacing between the bolts for the strut to knuckle attachment. The distance between centers on the 05+ was increased.

The ALK will increase lift and dive to allow the tire to better follow the road thus improving grip by keeping the tire from "skipping" over the surface. The characteristic comes from the housing, and how it moves the rear of the LCA downward thus changing the forward roll center.

The caster portion of the ALK comes from the eccentric bushing installed in it. it pushes the rear of the LCA ourward thus pushing the ball joint attachment point forward. In other words it moves the back our on an arc with the center of the radius being the front bushing on the LCA. because the rear moves out on that arc, and the LCA is rigid the ball joint end moves forward along an arc. remember the centerpoint for the radius is the front bushing on the LCA.

What the increased caster will give you is better stability in a straight line, improvement of the dynamic camber curve as you compress the suspension (but not super huge amounts - nhluhr calculated it), and a more quick "natural return to center" when coming out of a turn.

Now, given this one would think that this would be the holy grail, and you want as much caster as you can get. Well, it's good to a point. Once you hit that point the handling degrades due to funky stuff going on with weight jacking. The point on the impreza is about 7*. Do not exceed that.

I hope this clears up some questions.

[Turninconcepts.com]

Originally Posted by Pearson II

Toe has no affect on camber.

There is an affect on toe when you adjust camber. This is due to the location of the where the tie rod attaches to the knuckle. IF the tie rod attached perfectly centerline with the lower strut bolt on the knuckle there would be no affect, but that is not the case. Now in order for that to happen then the stock steering rack would have to be shimmed downward so far that it would start to affect ground clearance. Remember, everything is a tradeoff.

You cannot just go out to your garage and slam the camber without affecting toe.


Do some reading on Ackerman, and reverse ackerman for some more info.

Additionally, do not rule out bumpsteer. On our cars with a stock setup it's not that bad (on the RSX it's pretty sucky). Once you start to drop the car you start changing some angles and the bump steer gets worse. Now, the good springs have a small drop so most (MOST) folks don't really notice it, but if you start to slam the car then you can really notice it.

[RdRacer301]

Originally Posted by Turninconcepts.com

We have a local with an 07 going in for an alignment soon. I'll ask him for the caster numbers to get an idea where he is.

The 05+ could not get as much camber from just the stock bolts as the 04 could. The reason is because of the spacing between the bolts for the strut to knuckle attachment. The distance between centers on the 05+ was increased.

The ALK will increase lift and dive to allow the tire to better follow the road thus improving grip by keeping the tire from "skipping" over the surface. The characteristic comes from the housing, and how it moves the rear of the LCA downward thus changing the forward roll center.

The caster portion of the ALK comes from the eccentric bushing installed in it. it pushes the rear of the LCA ourward thus pushing the ball joint attachment point forward. In other words it moves the back our on an arc with the center of the radius being the front bushing on the LCA. because the rear moves out on that arc, and the LCA is rigid the ball joint end moves forward along an arc. remember the centerpoint for the radius is the front bushing on the LCA.

What the increased caster will give you is better stability in a straight line, improvement of the dynamic camber curve as you compress the suspension (but not super huge amounts - nhluhr calculated it), and a more quick "natural return to center" when coming out of a turn.

Now, given this one would think that this would be the holy grail, and you want as much caster as you can get. Well, it's good to a point. Once you hit that point the handling degrades due to funky stuff going on with weight jacking. The point on the impreza is about 7*. Do not exceed that.

I hope this clears up some questions.

I guess I was gravely mis-informed. I always thought the main purpose/intent of ALK was to increase castor by appox. 1* and allows the front suspension geometry (now that the front wheel sits slightly forward in relation to strut top, think of frontwheel of a chopper for an extreme case of visual) resist dive effect when you lift... I knew about "return to center" effect of increased castor, but I was not aware of all the changes in "dynamic" geometry of the frontend. I'm gonna have to read your post a few more times to digest all of it.

Learn something new everyday. Thanks, TiC.

[Pearson II]

TIC...you missunderstood what I wrote. I stated toe has no affect on camber not that camber has no affect on toe. Camber def affects toe. That is why the last thing you adjust when doing an alignment is toe.
Could you please explain what bump steer is and how it applies to cars. Thanks

[Turninconcepts.com]

Originally Posted by RdRacer301

I guess I was gravely mis-informed. I always thought the main purpose/intent of ALK was to increase castor by appox. 1* and allows the front suspension geometry (now that the front wheel sits slightly forward in relation to strut top, think of frontwheel of a chopper for an extreme case of visual) resist dive effect when you lift... I knew about "return to center" effect of increased castor, but I was not aware of all the changes in "dynamic" geometry of the frontend. I'm gonna have to read your post a few more times to digest all of it.

Learn something new everyday. Thanks, TiC.

The difference is in the housing - if you got the KCA375 which is the bushing without the housing you press that in to get .5* more caster. Sure you could clock it to get some of the drop of the rear of the LCA, we'll leave that confusing mess out for now.

The housing of the ALK is what does the drop to change the lower end of the LCA.

There's a really nice FAQ on nasioc, or read the description on our site. I borrowed it from nhluhr (with his permission) as it's the most easy to understand description of what the part does.

[Turninconcepts.com]

Originally Posted by Pearson II

TIC...you missunderstood what I wrote. I stated toe has no affect on camber not that camber has no affect on toe. Camber def affects toe. That is why the last thing you adjust when doing an alignment is toe.
Could you please explain what bump steer is and how it applies to cars. Thanks

Ah, I understand now where you're coming from. Sorry about that.

Bump steer is very simply steering by hitting a bump. As one side hits a bump the suspension compresses and changes the toe angle making that side steer.

If you do it on the unloaded side then it's not so bad, but if you do it on the loaded side in a turn then it can point the car where you are not telling it to go.

Bumpsteer can be corrected with a proper relationship of angles between the LCA and the tie rod. Start changing angles of things so that they are not close, and bumpsteer gets worse.

[Pearson II]

Thanks for all the help guys!

[Turninconcepts.com]

hey guys, I had another though on caster on the 07, and clearing this up for sure.

Measure the wheelbase. If it's 99.4" then it's the WRX spec. If it's 100.0" then it's the Spec C, and earlier USDM STi spec.

[Pearson II]

I'll try to do that today.