What spring rate with GC coilovers/Koni Yellows?

[bvass]

I plan to autocross and road race the car BUT I sill want a somewhat decent ride on the street. I have the Tanabe GF210 and they seem a little soft especially in the back. Weight distribution for my car is 2012lbs front and 1302lbs rear (Yes I know she is heavy). I have Koni Yellows shocks and the RM sway bars. What spring rates should I order the Ground Controls with?

 

[Dallas J]

Ive been extremely happy (and quick) with 2.0Hz front and 2.1Hz rear basic natural frequencies. But Im also on 275 V710s. If youre running DOT slicks then I would go with something in that range.

If youre on street tires I would drop down to 1.7-1.8 front and 1.8-1.9 rear.

Using motion ratios of 0.76/0.91 front/rear, the spring rates come to 706lb/in front and 350 lb/in rear rates. The equation is N.F. = 3.13 * Sqrt(( M.R.^2 * Spring Rate) / (Corner Weight)).

 

[bvass]

I would be running on street tires (Dunlop Star Specs). Wouldn't 700lbs in the front be too stiff for a daily driver?

 

[Poloturbo]

For the best "confort" on the street as not that harsh and quite a bit more handling for road course I've got 450 front, 350 rear. If you can use Hypercoils springs.
It is in fact A LOT more stiff than stock but the better for track use.

Search on the subject a bit it'S been beaten to death

 

[Dallas J]

450 just isnt enough front spring for the 350 rear spring. We just have too much front weight and a crappy M.R. Of course Im sure youll argue, but A) Ive tried it along with any combination you can make with 300, 350, 450, 550, and 700lb/in springs, B) The math is sound, and C) ask anyone who's been successful racing 2gs, more front spring = more grip when you're out of the range.

I would suggest 600/300 for street tires and a street car.

I use my 700/350 setup on the street and dont have much problem with the koni rebound turned down, but it isnt a cream puff by any means. Im actually gonna switch to an EvoIX and Ill run something good for the summer season and just switch to a regular lowering spring on stock struts for the winter. From what Ive seen, the biggest loss in comfort and largest increase in noise comes from loosing the isolators when going with a coilover.

 

[bvass]

For the best "confort" on the street as not that harsh and quite a bit more handling for road course I've got 450 front, 350 rear. If you can use Hypercoils springs.
It is in fact A LOT more stiff than stock but the better for track use.

Search on the subject a bit it'S been beaten to death

I have searched a lot and every thread I looked at had a different view on it. I have read at least 50 threads both here and on the Link forums. Even in this 1 thread I have 2 people telling me completely different things - one says 700lbs on the front the other 450lbs, this is a huge difference.

Can I use the Hypercoils with GC coilovers? Where would be a good place to buy them?

 

[Dallas J]

Yeah, you can use the 2.5" hyperco springs in 7" or 8".

I like to buy my stuff from dudiak racing (Dudiak Racing Products, Lead the Pack on the Track)

 

[bvass]

450 just isnt enough front spring for the 350 rear spring. We just have too much front weight and a crappy M.R. Of course Im sure youll argue, but A) Ive tried it along with any combination you can make with 300, 350, 450, 550, and 700lb/in springs, B) The math is sound, and C) ask anyone who's been successful racing 2gs, more front spring = more grip when you're out of the range.

I would suggest 600/300 for street tires and a street car.

I use my 700/350 setup on the street and dont have much problem with the koni rebound turned down, but it isnt a cream puff by any means. Im actually gonna switch to an EvoIX and Ill run something good for the summer season and just switch to a regular lowering spring on stock struts for the winter. From what Ive seen, the biggest loss in comfort and largest increase in noise comes from loosing the isolators when going with a coilover.

Thanks for the info. I am definitely leaning towards stiffer springs in the front, I am afraid 600lbs might be a little too stiff for the street.

 

[everbruin]

600/400 koni on my 2g w/ dunlop z1* 255/17, streetable but bad in bumpy san fran.
in back 300 is too soft, you'd need a high ride.

 

[Scott McIntyre]

I've run 500/400, 750/400, and 900/400 on both the street & track, on street tires & r-compounds.

The front didn't begin to feel stiff until 900. At 900, it feels more evenly matched with the 400 rears. I find it perfectly comfortable on the street, but probably more spring than you'd need running on street tires.

I'd suggest going with Dallas' rates of 700/350.

 

[laser92DSM]

Hey not trying to thread jack but what spring rates could I run. I have Fuzion Zri tires on Oz Supperleggeras 225/45/17. Not my choice of tires but they came with the rims and they are brand new. Im going to daily drive them but with a little autocross on the side.

Also this is on my 93 Talon AWD.

 

[Dallas J]

I have no clue about 1g setup, the motion ratios, or the weight distribution so I couldnt really make much of a guess.

With the 700/350s when I hit a speed bump the rear feels stiffer than the front. You cant just look at the spring rate by itself since its part of a system, to compare stiffness you need to look at the whole picture.

 

[bvass]

Well I have decided to go with 500/250 rates initially and see how they feel. I have the RMDSM sway bars and the car is already decently responsive with 330/175 springs so I figured they just may be stiff enough for the occasional track day. If they are still soft I will go to either 600/300 or 700/350 Hyperco springs depending on how the car feels. Thank you everyone for the great info!

 

[Dallas J]

I think thats a good choice, and you can always go stiffer for the summer and softer for the winter when youre not racing as much.

Once you get that done, you can start looking into more camber! Either mod your stock upper arms or find a set of SPC uppers.

 

[laser92DSM]

Yea thats what i was thinking i have been trying to see if any body can help me i have been searching but no luck. Thanks Anyway

 

[bvass]

I think thats a good choice, and you can always go stiffer for the summer and softer for the winter when youre not racing as much.

Once you get that done, you can start looking into more camber! Either mod your stock upper arms or find a set of SPC uppers.

I think once I install the coilovers if the balance is good I will concentrate on getting used to the car, improving my driving skills and getting consistent lap times and after about a year or so I will see where I want to go with the set up. Camber correction will be on the top of my list along with some full coilovers like the JICs.

 

[Poloturbo]

I think it's a good choice also. I find that with 600 or more spring the stock (as not revalved) konis are at there limit.
I'm using 450/250 right now because of more street use this year and with more than 10 track days it wasn't bad.

 

[Dallas J]

I think theirs several of us using OTS koni's with 700-800lb/in springs in the front per DG' results on the shock dyno. I pull mine off often for various reasons, and they've been handling the 700's for about 2.5 years now without any signs of leaking or lack of force.

Although, I think Im gonna swap back to the stock suspension for the winter not cause of the stiffness but because the noise sucks. Without the isolator pads and using spherical bearing upper mounts all the road and exhaust noise just pushes into the car.

 

[Scott McIntyre]

For winter, I had always swapped in 500 front springs, and swapped out the spherical bearing plates for the stock upper shock mounts (to save the bearings from winter salt / sand / snow).

 

[krusty_9]

On my 1g, I went with 450 front, and 350 rear. The rears felt much stiffer than the fronts, and after running that setup for the past year, I'm going to up the fronts to 600 and see how it feels after the first event.

 

[daren_p]

Kinda late on this one but I run a 500lb front spring & 350lb in the rear. If I go to a track, its only been to the 1/4, so I based my descision on mainly daily driver but wanted it to handle descently when pushed & would be an alright setup if I do ever descide to take corners at the track.

I would probably agree with the others in that a 600lb front spring probably won't feel super stiff. The 500's in my front do seem a good amount softer then the 350's in the rear. I don't mind the 500's in the front at all for the daily driver but sometimes find the 350's in the rear abit on the firm side. If I was doing it again, I'd probably go 300 in the rear but its not big enough of an issue, for me to swap the springs I already have. The 350's in the rear do really help with squat, or should I say lack of on those nice launches though.

On smooth roads, their not an issue but I'm sure like most, not all your roads are "ideal".

 

[ACM]

My experience with Koni/GC is that Konis have too much compression damping and not enough rebound damping to go past 550 in the front and 300-350 in the rear. This may be due to the side loads imparted by GC upper mounts I was running, or it may be simply as stated, I'm not sure, but I do know that Konis cease to function effectively above those rates when used with GC upper mounts. Konis get really funky in the last half turn of adjustment, that may play a significant role in this.

Moving to Shocktek Bilsteins on the same GC upper mounts was a dramatic improvement over Konis at the same spring rates, and then from GC upper mounts to pillow-balls was another significant improvement.

And then the spring rates just escalated wildly

Damping is _so_ much more complex and sophisticated than we realise as drivers, it makes at least as much difference in our times as a switch from all-season street rubber to race tyres. But there's no way you can know this until you make that transition.

So if you're running SCCA Solo II in ESP - please do me a favour, stick to your Konis ;-)

Charles

 

[Dallas J]

Its too bad we just dont have any real options for DSMs. It seems like either you had to be around and ready to buy about 3 years before I got into it, or already know a lot about dampers to custom make your own set up.

Id really love to get my hands on either the penske's or shocktek's I know are floating around but all the new development is pretty much gone to the evo's.

 

[ACM]

The Penskes are available to order From Ankeny Racing at any time. Guy will build them to order, just call him up. Guy has the valving sorted for autocross and road course use.

I would not recommend picking up a set of used Shockteks as they are difficult to revalve/rebuild, and many of the parts were custom made. I still have my old Shockteks , along with the engineering drawings to recreate those custom parts - trouble is that getting just a couple of shafts made and plated costs several hundred dollars. Early Shockteks used 4130 for the shafts, whereas later ones used a much weaker metal - 1018 or 1020 - and bend; you'd need to replace them with something like 4130 or 4340, have them plated at TechMetals - who have minimum batch/quantity requirements - and you'd be all set. Except that you could have bought a set of Konis for that much...And I still managed to bend one of those front shafts :-( The shafts are custom, the adjusters are custom, the adjuster bodies are custom - even the damper bodies were custom modified from other Bilstein applications ! You can do it, but at the end of the day you will have spent more than the cost of low end Penskes, which would still work better.

Ohlins is a more practical route. Ohlins are fitted to high end production cars that see all kinds of conditions, and survive happily on dirt bikes for years, so their year-round suitability has already been confirmed. Single/double/triples should be possible for a lot less, but the valving expertise isn't there. When I looked at this option it came in around $3-4k for triples, it turns out that ITR bottom mounts are near identical to the front of a 2G, and these are OTS parts for Ohlins - rears are more complicated though, as nothing in the range uses a pin mount the size of the 2G rear; that would require custom machined Ohlins mount, or custom pin mounts to replace the OEM pins. Not too bad if you make a few dozen sets, but making just one pair...It is practical though, provided you don't mind developing the damping rates yourself; you'll be revalving every weekend for a couple of months before you get there, so you'll need easy access to a clean room, high quality, consistent shock fluid, plus a Nitrogen charging setup. The cost of having a shop do this for you would be prohibitive, so you'd have to do it yourself. Start out with Shocktek's valving specs and work from there. It's definitely an option, and if I had the time/money I'd take it on in a heartbeat. But of course I don't have either, not with the racecar downstairs sucking all my resources already. I've already researched the Ohlins route in some detail, I would love to build a set for my street 2G.

Charles

 

[Dallas J]

Thats good info about ankeny racing. I didnt know their was anyone still making the penske's fit dsm's with our odd front and rear mounting. And thanks for the info on the shocktec's. All the stuff Ive read said they were amazing, but sounds like that comes at a price. OTS equipment is always preferable (IMO) to obscure and long lead time custom pieces especially in a wearable item.

[off topic]
Ive kinda had some dilusions of grandeur about making my own shock dyno and building a Bilstein or Ohlin setup. At the end of the day I would probably spend more than getting triple adjustable Penske's, not sure if the outcome would be better/worse/equal but I would learn a ton.

I think I still have to decide if Im going to stay with the DSM which will pretty much require a new car sans the sunroof or jump ship to an Evo or Z06. Im too far to realistically get to nationals, but want to stay regionally fastest (NW) and maybe move into the PAX class which SM really doesnt work in.

[/off topic]