Classic impreza suspension advice
 

Good afternoon all,

I will start with a brief outline of the situation: I have a 98 type R which has usual breathing mods + remap, so the power is fine. I recently fitted a swirl pot setup to eliminate fuel surge under cornering (which I was experiencing, on the road). All great. I used the car for commuting as I like to drive a "real" car at all times, as well as evening / weekend spirited driving. Will likely do 1-2 track days per year, but the overall aim is for the 99% of the time I drive on the British back roads.

The car is on non adjustable coilovers with 20mm rear ARB with straight steel drop links, rubber bushed. Front ARB appears to be 19.4mm (possibly means its 20, just where i measured it?) also with straight steel drop links, rubber bushed.

Next on the to-do list is sort out the sus. As it stands, the car doesn't appear to roll much under hard cornering; the only problem i seem to get is initial understeer. In the wet, the back slips out nicely, but in the dry, front end seems to lack in grip.

So I will definitely be upgrading the rear ARB. I have read many threads on this and the general idea is 22mm if you aren't smooth, 24mm if you are. I am not, so I would guess 22mm is what I would need. But as I am coming from 20mm as it is, opposed to some people who jump from 18mm to 20mm, should I perhaps fit 24mm as its the understeer I want to eliminate?

Also, when I fit the larger ARB, should I get alloy drop links, despite having straight steel ones as it is? They are rubber bushed... would poly bushes offer much improvement here at all, or shall i stick with what I have? Do poly bushes exist for standard drop links or does everyone just replace the whole lot? They are in fine condition, not deteriorating at all...

So onto the front. If I am advised to go for 24mm rear, clearly I will need 22mm front. Not a problem. Please advise! I have read about people fitting 22mm all round. This a good idea? I would also like to fit an ALK to give me some more front end grip. Should I do this if I am to leave the front std 20mm ARB, or only if i fit 22mm? If i fit the 22mm front, will the effect of the ALK be reduced because of this?

I will also be fitting subframe locking bolts. Cheap and easy.

Once all of this is done, I will take it for 4 wheel alignment. I want 1 degree -ve camber all round, will I require camber bolts for this or can this be achieved with what the car has as standard.

If anyone can offer any advice on these topics or anything I have missed (this is my first 4WD car) so no doubt there will be plenty.

Thanks

No need with subframe locking bolts at the rear, the STi rear subframe is solid mounted already as I understand it.

Definately get the ALK, sounds like that should be your first mod, once you have that determine what your car is doing and progress in steps, rear ARB first, I suspect you won't want a front.

Dial in about -1.5 camber at the front, get rear camber bolts (about £25) if you want to adjust the rear, adjust the rear to get the characteristics you want, I am running mine at 0 to promote some movement at the rear to reduce understeer, the more rear camber (-ve) you have the more you head back to understeer!

Simon

OK no subframe locking bolts then. Shame they are the cheapest part I no longer need!

I'll def get an ALK for now then and set the camber. I assume this can be done without bolts for the front then? What will the car be set to from factory (or parhaps a better question, what will a 12 year old impreza be running at, typically)

May as well do rear ARB too but leave the front for now. back to the old 22 vs 24 debate. From what I have read 22 would be more suitable, but it hardly seems like much of an upgrade coming from 20...

Thanks

Hi James , there are 2 mods out of all other mods which stand out for me
1st caster , 5.5 deg positive caster
2nd v70a soft tyres , will do 2 to 3 k on the road they are fantastic in the wet or dry i with a gain of for what i do 2 secs a mile , only thing with the v70a is they throw stones up under your arches sounds worse than it is.Rgds Shonner

The how are you achieving the 5.5+ caster? I currently have proxies... they seem brilliant so probably wont deviate far from them. If I do go for different tyres, I will get ever so slightly stickier rubbers.

Thanks

follow link for info on caster, https://www.scoobynet.com/suspension...-any-good.html

what proxies are you running ?

I can't remember exactly, i THINK T1R, but not 100% sure

What i found was how ever much i spent on the chassis the car still didn't turn in as i wanted i tried many list 1a tyres , once i put kumho's on it transformed the car , suspension started to work and all other mods .
good luck shonner

A 22mm rear bar is 33% stiffer than a 20mm, 24mm is 73% stiffer, I'd go with 22mm for now!

The Impreza has front camber bolt as standard, should get to nearly -2degrees, any more and you need an aftermarket camber bolt in the other hole.

Simon

You should consider caster adjustable top mounts. You'll get alot more than with the ALK and for a similar price. Added some to mine recently, running about 5 degrees and the cars become far more rewarding to drive. Increased dynamic camber and more feedback at the wheel. Best way to minimise the dead feeling of four driven wheels!

Sounds like you're on the standard ARBs. Best bet start with a 22mm rear adjustable. If its not stiff enough you'll have no trouble selling it on. It sounds counter intuitive, but ARBs actually reduce grip across an axle (by increasing weight transfer). Think of them as a handling mod to make small balance changes.

So why do so many people fit the ALK if the same and more can be achieved by the top mounts? Surely the poly bush a la ALK isn't that much of a benefit? Thinking about it, should the ALK even be fitted if retaining the rubber bush the other side of the wishbone?

To quote whiteline,
This kit changes your front suspension geometry by lowering the pickup point for the lower control arm. The result is a decrease in the built-in anti-dive/anti-lift geometry effect, meaning your front-end will stick more in both acceleration and braking modes.

The mechanics are a little tough to explain, but in short the front wheels will droop a little more on acceleration (making the front end stick more), and the nose of the car will dive a little more under braking (again making the front end stick more). This makes your Subaru more neutral and less prone to wash out the front end under hard cornering when braking or accelerating.

Polyurethane bushings help to firm up steering response in the front end. If the standard poly bushings might be a little too firm for you, choose the "Comfort" kit, which uses slightly softer bushings to reduce vibration and harshness.

alk is just 1 item on a very big shopping list to get you car's handling as near perfect as you can .

There is a downside to top mounts - you loose the nice soft rubber mounting and gain more noise/harshness. TBH on a Classic its not that noticable over all the other rattles and IMHO the trade off is more than worth it.

ALK is good for 0.5 degree, top mounts about 3 degrees. Every little helps...

22mm rear ARB otherwise you'll get snap oversteer on your car (a car that is fairly light)
You dont need Castor adjustable top mounts - this is total overkill. I have spent about £100k on my car and Castor adjustable mounts are not part of this and wont be part of any future spend
Personally I wouldnt bother with ALK though I have one on my 99sti. A good 4 wheel set up will sort out the understeer anyway with the Camber and castor adjustment
You dont need camber bolts on what your looking for
I have -2 all round on my car and -1.75 on my GTR35...
-1 sounds like factory standard and is not enough negative camber. If your not tracking I'd suggest you set for -1.5 (1 degree 30 mins).. you might have an issue getting to -1.5 without rear camber bolts but best to try and see first
Tyres wont be particularly relevant unless your tracking and your not... you wont notice much on road driving

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