Kippax

i noticed the anti-lift kit claims to relocate the position of the rear pickup point. this is impossible in the x-y plane ( without twisting bushes) as the front pick up point is fixed. am i missing something?

stu.

dowser

Don't know, but it improves steering feel on turn-in no end

Richard

AJbaseBloke

And the steering rack mounts help quite a lot too - everything gets better, feel and response wise

Then you'll need a front lower arm stiffener to get the ultimate feel and rigidity...and the mods go on...and on...and on...

SimonH

I asked this on another thread last night but no-one's answered yet: is it worth taking the ALK off my MY00 and putting it on the P1 I'm getting?
Cheers

johnfelstead

the main job of the ALK is to increase static caster and reduce the inbuilt anti dive geometries. As standard the Impreza has a better front setup for under heavy braking than acceleration, it has a tendency to squat at the rear and lift the front end under power, inducing power on understeer. The ALK does exactly what it says on the tin, it helps prevent front end lift, thus reducing the amount of power on understeer.

Kippax

AJbaseBloke - where do you get the uprated steering rack mounts and front lower arm stiffeners from?

dowser

Simon - yes, it is

Richard

DuncanG

John, have you measured any change in anti-squat behavior or does it just feel better?

It seems to me that by lowering the rear mount you will increase dive & squat (in theory), and will have virtually no effect on castor for the small amount of lowering involved. Has anyone measured a castor change?

I'd suggest that the active ingredient in the ALK is the stiffer bush and that the small change in geometry is insignificant and further-more if you want to reduce dive/lift then the rear mount should be raised (not lowered) relative to front mount.

Please note I havn't tried the ALK myself but I would like to understand it better before I shell-out my hard-earned dosh. It smells of snake-oil to me.

Andy.F

Duncan

You are correct

The main benefit is from the stiffer bush reducing castor change under braking/power. There is also a slight increase in castor due to the strut bottom being pushed forward slightly. This can improve 'feel' with the standard over assisted steering.

Contrary to popular belief the 'anti lift kit' does not actually reduce lift !!! In fact if you work out the geometry (and I have) it actually increases the lift/dive moment arm (CG height/Instantaneous pitch centre) under acceleration or braking conditions.



I think not John but then we never agree, do we


[Edited by Andy.F - 9/15/2002 12:59:16 PM]

Kippax

agree. the effects of the ALK must be due to stiffer bushes, not the negligible change in castor and as previously discussed, you CAN'T move the a-frame further forward.

AJbaseBloke

Stu,

The steering rack bushes are by Whiteline, too.

Well, I won't get between 2 denizens of the board, but the ALK certainly seems to help the nose stay in in all conditions - and it certainly feels like some dynamic caster has been introduced by the way things load up (or the reverse in some situations). Eitherway, having had both the std and comfort versions, I can say that I am very happy with the ALK (esp. now that I can hear myself in the car ).

Should note that I have lower arm stiffeners, tower bar, swaybars, end links, and Eibachs (over the std Bilsteins) - that all keeps things pretty true through the corners these days

Oh, and just quietly, Subaru seems to agree that some more caster would be good - the next Impreza seems to be getting some of the geometry tweaks from the Spec C

Cheers

Andy.F

Additional castor only helps if you have insufficient camber for maximum grip from the outer front tyre. Typically, road cars have 0.5 to 1.5 degrees negative camber, this less less than required for max lateral G but helps keep tyre wear uniform across the tread.
Track cars will run closer to 3 degrees neg camber to improve G. Adding castor to a track car may induce excessive dynamic camber in the turns and actually reduce front end grip.

DuncanG

Does anti-dive mean pro-lift?

<<Whiteline website says --
Anti-dive geometry slows down the weight shift to the front wheels which results in a gentle tightening of the cornering line with throttle lift-off, the standard panic reaction. However, one of the costs for this design compromise is front lift under acceleration as anti-dive will generally mean pro-lift.
>>

Surely this is just plain wrong; dive and lift are two sides of the same coin - if you make the suspension more prone to dive during braking by lowering the rear mount (which is their intention) then surely you must increase lift when the forces are reversed under acceleration!? (waiting to be shot-down )

Well looking into it more closely I now think that the change in Height of the rear mount could be a red herring. I hadn't realised originally that the ALK actually moves the mount further outboard.

Moving the mount outboard will increase castor (by rotating the ball-joint forward) and reduce lift/dive (ignoring effect of height change) by reducing the trail angle (or increasing the lead angle?) of the track-control arm. Think of it as a semi-trailing or semi-leading arm.

So does it work by design or by accident?

Kippax

the front pickup is fixed so its extending the shocker slightly, not increasing castor much. you'd have to rotate the a-frame downwards at least 15degrees to achieve 0.5degrees extra castor.

Pavlo

You can have both anti dive and anti lift at the same end, but I don't know how you would do it with Macphearson strut suspension without drawing it out.

Thing to remember is the 2 are not just opposite.

When braking, the upright transmits the force from the caliper to the wishbone, and you have the additional force from the wheel.

When accerating you just have the tractive force in opposite sense to braking, but no opposite to the caliper forces.

Also the rake of the car will be different in each case, as will the CofG, further complicating things.

Paper model with drawing pins can work wonders.

paul

MorayMackenzie

I fitted the anti lift kit to my previous wrx, and it didn't make any noticible difference. I haven't bothered repeating the experiment on the sti.

Andy.F

Eh ? I thought it was called an 'anti lift kit' ? but it is 'pro-lift Sounds like they didn't know what the hell it would do so they covered their **** by claiming both

To 'slow down' weight transfer to the front then you need to reduce anti dive. Just like you increase squat (dive at the rear) to slow down the weight transfer to the tyres to avoid shock loading them on a drag car.

The increased castor by moving the rear pivot outwards is what people are feeling IMHO as better turn in.

Lowering the rear pickup will NOT improve anti dive or anti lift, it will however promote both lift and dive.

Pavlo

Hmm, lowering rear pick up would indeed increase dive.

[laymans terms]
The idea is if you look at the side of the car, and you angle the wishbones towards the centre of gravity, the forward force under braking wouldn't do anything other than put a side load on the wishbones. This is 100% anti dive if you do it at the front, and 100% anti squat if done at the rear.

In practice it makes it a bitch to drive, as you have no give under braking, so you can bounce off the tyres, skate all over the road and end up in the gravel. But you can run less than 100% anti-thingy, and compromise.

Increasing the castor will do all sorts of things, increase neg-camber on turn-in, increase the inside wheel "jacking" on turn in, and increase weight transfer off the inside rear wheel as a result.
[/laymans terms]

Can't see the logic in the "anti-lift" bit, but stiffer bushes on the mounts is nice, and increased jacking will promote better initial turn-in, so you might feel the car is a little more twitchy, with heavier steering.

Upon further thought, I think I would rather spend the money a powerflex bushes on the wishbones.

Paul


[Edited by Pavlo - 9/16/2002 9:47:18 PM]

scoobeee

So who's right then ? Does it reduce front lift or increase it ?

Pavlo

dunno, to be honest, you would normally stop the front rising by holding the back in place.

If anything I would guess it increases lift if it lowers the rear wishbone mount.

wheel pulling forwards, chassis pulling backwards (momentum) if you tilt the wishbone back, you would expect the wheel and hub attached to it to pull it forward, and therefor down, promoting lift.

Paul

Andy.F

Hehe, agree with Pavlo......... I win

[Edited by Andy.F - 9/17/2002 11:23:30 PM]

Mike Tuckwood

OK, this is one for the experts.

The simple facts are that it works, trying to pick away at the threads of such a complex subject is all well and good, but you will find very few people who have used ALK's that dislike what they do.

They do measurably change static castor, they do reduce weight transfer by reducing lift under power. Moray can't drive for toffee so his opinion is discounted.

I have an article at work which covers it in a more practical way, if anyone wants one mail me direct. I'm sure some will continue to pick at it but the simple facts are, just as John Felstead says, that it does exactly what it says on the tin.

Mike
Scooby Mania

Pavlo

It may do a lot of things, but what it won't do it reduce lift at the front in a straight line.

And until someone can show me a log with rideheight Vs accel with and without the kit, I wont be changiny my mind.

However, the effects of more static caster are not to be underestimated, and I can well imagine it reduces power understeer with some lock on the steering wheel, and increases bite on turn in.

paul

[Edited by Pavlo - 9/18/2002 9:52:22 AM]

Andy.F

Mike

Even self acclaimed 'experts' can't change the laws of physics.

Suspension dynamics is not a simple topic however a reduction in pitch centre height whilst maintaining the CofG will result in increased lift under power.

Please supply some 'facts' to back up your claims

dowser

Guys, go post your question at http://www.mrtrally.com.au/forums/forum.asp?FORUM_ID=19
and get an answer from Whiteline themselves

Richard

Andy.F

I tried that the last time I asked the question....... it all went quiet !! Even Claudius backed out

OK I'll try again, although I don't really expect the supplier to admit in public that an anti lift kit....doesn't !! If only they'd called it a 'castor change kit' or 'turn in kit' There appears to be little doubt that it improves the standard cars turn in ability and feel

[Edited by Andy.F - 9/18/2002 12:06:31 PM]

Kippax

red = standard, green = ALK, blue = the other way

isn't the worst place for the coloured dot (rear mount) right on top of the pitch centre?

assuming the pitch centre is not lower than the rear mount to start with, wouldn't moving the rear mount down reduce lift?

[Edited by Kippax - 9/18/2002 3:11:04 PM]

Wurzel

iTrader: (1)

Am I the only one that hasn't understood a word on this thread even when one of you said <Laymans Terms>

bottom line is it worth fitting or not to a MY00 with KW Coilovers metal drop links, whiteline front and rear sway bars, 17" wheels and blue paint??????

Pavlo

Nice picture!

Assuming the right of the picture is the front of the car, and the "dot" mounting points are pivots for non traling arm suspension, so wheel moves up and down in a straight line, and not pivoting around the points.

From what has been said the ALK puts the rear wishbone mount in the green position, instead of the red postion of stock.

The arrows at the bottom of the wheels are pointing the wrong way in terms of tractive effort. There will also be a force acting at the CofG (big blackdot?) towards the left of the picture equal to:
unspring mass*rate of acceleration.

It's quite plain to me, that if the ALK increases caster, lift will be increased.

Paul

Andy.F

Kippax

As Paul states, turn the tractive force arrow around, then consider that every action has an equal and opposite reaction.

The strut is going to extend more with increased Castor.

Also when the wheel pulls forward on the lower mount point, the higher this point is, the more it pulls the body down(anti-lift)

The AL kit lowers this point, hence increases lift.