WRC1

Hello from California. This being my first post I guess i should explain why im posting a question on a british forum. Well, in short, Americans are morons. The longer explanation is that while high performance subarus have been popular in Europe and Japan for well over 10 years now, the subaru craze has just hit america. So most people on the american forums have very little experience in what they are saying.

Anyway on to the question. Im getting new struts and springs for my classic impreza and wanted to get some recommendations before I buy. Im going with Koni Yellows and Ground-Controls (springs on adjustable spring perches). Im just not sure what spring rate i should go with. This car is going to be a daily but it will see A LOT of track time, i dont mind a harsh ride that much. I was thinking about 425 lb ft. in front and 500 lb. feet in rear.

Do any of you have experience with spring rates like these? any suggestions? comments?

Thanks
~Leor

Fat Boy

Nice first post, but don't fancy your chances when the States wakes up, but in the meantime, you could do worse than have a look at nasioc.com - a very good AMERICAN scooby site......

Anyway, I'm sure someone will answer your queries in more detail shortly on here although the front spring rates should be higher than the rear for starters (rear approx 80-90% of front rate as a rough guide so 425/350 say, but that will be very hard and probably underdamped). Other things to consider are introducing some more caster, reducing bumpsteer,a more aggressive negative camber stance, better bushes, a bigger rear anti roll bar, metal drop links.

Have a look at the subaru project articles on here for a lot of advice on setting up scoobies properly
http://www.whiteline.com.au/

WRC1

I post on nasioc regularly (well over 600 posts) and when i post a question like this i get responses like dont go over 300/300 youll break your back if you go higher.

In actuality you can go with almost any spring rate and not have harsh ride as long as the struts are valved accordingly.

The reason why im thinking 425/500 is to get rid of some of that subaru understeer by stiffening up the rear a bit more then the front.

I guess i should post the over few things ive done to the car.
I have a WRX 20mm rear sway bar (It came with a 13mm stock)
Azenis Sports
-1.5 camber in front
-2.0 in rear
O toe all around
3.5 degrees of caster in the front ( from what i understand it is non adjustable in the rear)

Im planning on doing drop links and bushings but those alone arent going to make up for the handling im looking for

~Leor

Fat Boy

Still back to front, I'm afraid - it should be more negative camber on the front than on the rear - it isn't a 911 - or it'll understeer/push more than normal.

Valving - yep right, but then if you or your local supplier have WRC level suspension knowledge or capabilities then i guess that you wouldn't be on here chasing early stage knowledge ( or running with back to front settings...).

It's your car, but IMHO I think that you're going far too stiff as well, unless it is an out and out competition car which you state it isn't as there is a law of diminishing returns - if you're just trying to stay in your seat over every expansion joint or pothole then you're not pressing on and so will be slower then a softer, better controlled car.

Anyway, Sti or whiteline adjustable rear bar anti roll (or swaybar) and solid rear droplinks, plus some rake (back higher than front) will all help front end bite, plus rear end action (oooeerr). Getting there on other mods. No back end caster isn't poss or required - toe in/out can be played with though - Again have a look at Whiteline's site as posted above - particularly it's extreme settings, and that's where you should be shooting imho.

WRC1

True.

Koni Yellows can hold 500 to 550 pound springs without a revalve easily. Plus I know a shop that builds SCCA (Sports Car Club of America) Pro Race Cars that revalve/rebuild Konis is i wanted to go higher. BTW, that shop thinks my set up suggetions "would be amazing on the track"

www.tripointengineering.com

I dont drive hard on the streets and the tracks are smooth enough to not worry about that.

Point taken.

On a side note my friend has a Acura (Honda) Integra GSR 170ish HP (Im not sure if the UK has these, its one step below the Type R) with yellow and 400/450 stock engine with only a cat back and we kill modded STis and EVOs at the track. That is why im considering going with this set up.

~Leor

Fat Boy

You're talking about WRC level tarmac spring rates. Great for a competition car but not for the road.

Shame the great suspension shop didn't point out the bollocks about running harder springs at the back - maybe they should stick to their speciality....

As for the rest of it you just lost me when you went all "fast and furious/ ricer" at the end. My humble p1 with very limited mods eats honda type Rs on or off track so I guess all the evos and stis being beaten by a car one step down from a type R are either being driven by crap drivers or maybe they're running back to front suspension set ups ?

Bye

WRC1

fast and furious??? Ya, paying for a track day and keeping it off the streets is really ricer of me. And BTW competition spring rates for road racing cars (non WRC) are usually in the 800-1000 range if not higher.

Can you please explain to me in technical terms why a stiffer rear spring rate is so bad, maybe im missing something?

DuncanG

WRC1, Fat Boy has given you a lot of good advice there, but a few points -

Our roads here are far too rough for anyone to run those spring rates daily, so you wont get the experience your looking for here. Plenty of folk on NASIOC are running very high rates and it seems to be becoming popular to run higher rates at the rear for Autocrossing, but not for circuit work.

Your friend with the Integra is using 400/450 lb/in (not lbft!) springs - I guess you want to go a step 'better' You can't compare Subaru and Honda spring rates - the Subaru uses strut suspension with a motion ratio (MR) very close to 1, while the Honda uses double wishbones at the rear with a much lower MR and either double wishbones or struts at the front. I don't know the MR of the Honda front struts; struts usually have a MR close to 1 but not always. Basically the MR is the leverage on the spring, a lower MR means a higher spring rate is required for the same effective wheel rate. {wheel rate = spring rate * (MR^2) }

For road and circuit where you want the car to be well balanced the spring rates (or more correct the wheel rates) should be roughly in proportion to the corresponding corner weight to get the front and rear sprung frequencies about equal or little higher at the rear. The impreza has a weight distribution of about 60:40 f:r and the MR at the back is a little lower than the front so you end up with the rear rates being around 80% of the fronts. Auto crossers use higher rear rates to de-stabilise the back end, but you dont want that in a road or track car (I hope).

I thought the Koni yellows were meant to be an upgrade for the standard struts using standard or mildly uprated springs. I'd be very surprised if they'd still work well for spring rates about double what they're intended for. So I think you should expect to have them revalved. Get a digressive response, if you can, so that they are stiff on turn-in but not too stiff when hitting a small bump.

You can go much stiffer on the antiroll (sway) bars. You started with a 13mm at the rear so what is the front? Uprate the front to 20 or 22 and the rear to the same or +2, depending what you can get for your model. If you started with a puny 13mm bar what model is it and what power are you running BTW?

Try 400f/350r springs as a starting point and don't worry that your Honda pal has bigger springs than you. If you still find those too soft after upgrading the damping and sway bars then its cheap and easy to change the coil-over springs.

WRC1

DuncanG,

Thanks for the great info, I understand it better now.

Just a couple things, the honda has double-wish bone in front and rear, which means his rear. Ill call him and find out the MR just out of curiosity.

My car came stock with a 19mm front and 13mm rear sway bar. I was planning on going with 24mm adj. rear and a 22mm front and new droplinks the same time i put on the new suspension.

My model car is a 2000 Impreza 2.5RS, it was sold in america to test the waters for the WRX and STi. It has 2.5L NA engine (165HP 166 lb tq). Sportier suspension then the regular imprezas and some random STi body work (Ver. 5 front end Ver. 3 rear end)



EDIT: My friend thinks his MR on his honda is .7. If that is true His wheel rate would be more then double mine with the same spring rate. Something has to be off with his calculations.

~Leor

DuncanG

Sorry I should have said

wheel rate = spring rate * (MR^2)

so your friends wheel rate is only half his spring rate, not double.

WRC1

I think you where right with wheel rate=spring rate/ MR^2. My friend and i looked into it further and found out that the MR is 1.5 front and 1.35 rear. Do you know exactly what MR is on a GC impreza?

~Leor

DuncanG

It seems that MR can be defined in either of 2 ways:
MR = spring motion / wheel motion, in which case MR will be less than 1
or
MR = wheel motion / spring motion, in which case MR will be greater than 1.

I think the first convention is the more common, but I'm sure that in all common suspensions the spring motion is less than the wheel motion so if it has been identified as being > 1 you can simply invert the number to use the alternative definition.

So the values of 1.5 front and 1.35 rear would translate to 0.67 front and 0.74 rear.

MR for Subaru struts is in the region of 0.95.

GFimpreza

Hey WRC1,

I do realize that a lot of guys on the US forums don't know jack, but there are plenty of knowledgeable people out there with setups like the one you are talking about.

A trip to the "Motorsports" forum on nasioc and the search button will yield a lot of info on koni suspension setups with high spring rates.

Good Luck.

-Lyle