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What Spring Rates to run?

27K views 108 replies 19 participants last post by  manny z 
#1 ·
I am installing a Mopar stage 3r suspension, currently has 517 lbs in front and 402 lbs in rear.

Rate Height
517 lbs - 6.69 inch
459 lbs - 6.69 inch
402 lbs - 7.87 inch

These are the specs I saw online for the Mopar offering. I was shooting for a combined front + rear = 1400 lbs or so, current setup would be 517 + 402 = 919 lbs which seems too soft for road course work to me. Advice?

Also some people have suggested installing the higher rate springs on the rear. I know most high-perf rwd cars rear spring rate is about double the front.

Any aftermarket springs recommended for these coilovers? If so I would consider running 450 lbs in front and 950 lbs in rear.

Thanks for your help,
David

Mods on car: Mopar stage 3 turbo, BFMIC, open exhaust, CAI, MM, Rage-tek bushings, planning on running 245/40R17 Dunlop Direzza tires
 
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#2 ·
I am by no means an expert but here are my thoughts -

1) As a general rule, a stiffer rear setup will help the car rotate more (oversteer)

2) You didn't mention sway bars...you should take those into account when determining stiffness of setup

3) A 950lb spring will probably be too stiff and a 450lb/950lb combination will probably not produce good results (back end will be loose). Did you mean 650lb?

4) Sometimes need to take into account the valving on the coilovers to make sure going to a much stiffer spring won't do more harm than good. Not sure if this is true with the Stage 3r's but on other coilovers have heard of this being an issue.

I currently run BC Inverted Coilovers with a 6k/8k (336/448) setup and Mopar Sways. The car is currently well balanced but not stiff enough. I am looking for a new setup and planning to run 8k/10k.
 
#3 · (Edited)
Currently running stock ACR sway bars, was considering stiffening the rear and possibly removing front swaybar. Corner exit traction is a big problem right now. I was curious also about what setups the World Challenge cars run.
After rethinking the spring rates some more I think combined 1150 lbs sounds better. So maybe 500 lbs front / 650 lbs rear?

I am using some ratios versus other track ready cars to arrive at these spring rates and no real world experience with SRT-4's
 
#5 ·
What is the I.D. dimension for the Mopar Stage 3R springs?
http://www.srtforums.com/forums/f221/stage-3r-coilover-info-sticky-319480/
This thread indicated 60mm or 2.36 inch, looking at the Ground Control website for springs they offer 2.25 inch and 2.5 inch I.D. springs, which is the correct sizing?

Also for ride height, are most people measuring from wheel center to fender? My car is currently 14-7/8" front and 14-5/8" rear. I was looking to setup car somewhere between 13-1/2" to 14".

-David
 
#7 ·
we run 850 front and 1100 rear this was the combo recommend to me by Rick Snyder from what he ran is his world challenge car I know there are guys running stiffer and we do change it up a bit from track to track
the problem you will find is your 60mm springs you already have the stiffest spring you can get in that size and as well the valving in your S3 struts will not handle a stiffer spring I dont know much about the BC's so I dont know if they are a better choice a cheep alternative would be Koni inserts
Hope this helps
Steve
 
#12 · (Edited)
Those are some stiff spring rates...what are you running for sway bars?

I run the BC Inverts and they come with 6k/4k (336/224) setup when purchased (if you don't request stiffer springs). Even if you do request stiffer springs, they don't change the valving.

My understanding from talking to BC and Ksport is that the recommendation is you don't go more than 2k higher if you want to match the valving. I have already ignored that and run 6k/8k and it seems fine but thinking of going to a stiffer spring and not sure if the rears will handle it.
 
#8 ·
H&R spring appears to offer 60mm race springs in 160mm and 180mm length, my 517 lb KW spring is 170mm length. I am not opposed to selling all my KW springs and installing H&R or Eibach springs, I am just not sure what spring length to buy. A few people have told me that S3r coilovers setup the car too low.
 
#15 ·
I am thinking the S3r's must be valved to handle 517 lbs springs, so running 650 lbs springs in the rear shouldn't be too much of a strech hopefully. I am thinking of running the following based on input from above:

Front - 517 lbs -170 mm - stock KW springs
Rear - 686 lbs - 180 mm - H&R springs #RF180120

-David
 
#16 ·
David,

How do you like the spring setup you have now (517/402lb)? Are you running at Gainesville Raceway road course mostly?

I'm running the Mopar Stage 3 coilovers (not the 3R's) with the springs that came with them (325/175lb I believe). I'm thinking about going stiffer myself but am curious how the car handles with the stiffer rear springs. Do you get a lot of rotation and snap/lift oversteer with this setup?

-Patrick
 
#17 ·
I have run Gainesville, Starke, and Roebling Road. I have not installed the stage 3r yet, currently I am running on ACR tokico's. I definately get lift throttle oversteer, but at Gainesville that is nice because it is such a tight course. With the stage 3 turbo now I am having real problems with over driving the suspension. I have ordered O.Z. racing wheels and Dunlop Direzza tires to install with this mopar 3r suspension.

-David
 
#20 ·
Why would you install koni inserts in stage 3r's =]
The stage 3 and 3r valving is the same for rebound dampening ( 20%under to 50% over the stage 2's IIRC ) the 3r adds compression dampening adjustability .. which of course is infinitely different than the static valving of the S3.

The world challenge cars run a no front bar and a front-heavier-than-rear spring set up to make sure that the bar would never lighten the inside tire on exit. The front heavier than rear spring setup was used to compensate for the lowering of roll resitance in the front, since the front bar was deleted. And on that note, the rear has an adjustable rear bar that is rather stiff.

Spring rates are useless to compare due to the differences in the geometry etc. But the key is to hit the track and decide where you are losing time. Once you have that you can decide how you want to balance the car.
In my stock srt-4 I delete the front bar and run s3r's with 700's and 350's
I run a modified acr setup in my s3 car again a front bar delete and I'm now running a custom progressive rate in the front which ends up being around 475 or so.

Of course there is no comparison to the WC car (I mean come on, its a full on race car... no shit.) But the stock engined car with the 3rs and 700f and 350r is best on a short technical smooth course. And the more compliant (S3 engined ACR suspended) car is FAR better on longer, rougher surfaced or rhythm tracks.

David
 
#22 ·
Well from what I can glean from the rules and the forums, on the currently built cars there is really no effective rule change. Except for new restrictors to modify output and some non-performance changes.

The new suspension rules mostly affect cars built 'new' for 09 season. From what I've heard.
David
 
#36 ·
wait til you get the BBK on there and get the suspension dialed in better....your wife is gonna LOOOOOOVE you :rofl::thumbsup:
 
#29 ·
Nice but I think probably you could lower it a bit more...
One more thing I used to have 600/600 f/b spring rates and that was very comfortable to drive on the streets still...now with the 850/1000....that;'s a different story, you better get ready for some ass kicking on our lovely freeways...lol
Make sure to have your car properly corner balanced...
 
#31 · (Edited)
I was wondering what ride height to shoot for. Here is a summary of what I have:

Stock 05 ACR
Front(14-7/8")-----Rear(14-5/8")-----Rake(1/4" neg)
3R - stop rings
Front(13-1/4")----Rear(13")----Rake(1/4" neg)
3R - adjusted
Front(13-3/8")----Rear(13-1/2")----Rake(1/8" pos)

The adjusted config is after 4 turns on the rear and 2 turns on the front up. Also these adjustments gave the car 1/8" rake. I wonder why the stock ACR suspension had 1/4" negative rake and the stop ring setting gave the car 1/4" negative rake as well? Should I have kept the negative rake in the car?
 
#30 ·
I raised it 4 turns off the rear stop rings and 2 turns off the front stop rings, trying to restore some rake to the car. Maybe when I corner balance the car I should work my way down towards stop rings from here. The alignment and tires really seem to help as well. This is also the 1st time I have used HOM and these tires are hooking well. The suspension is not too harsh considering my compression and rebound setting are aggressive.
 
#32 ·
adjust to stock height ( MFG recommended height ) and work from there. You lose camber faster and faster as the ride height is dropped. So you will lose the advantage of the engineering of the pickup points as you drop further and further. The car will end up being alot different to drive ( remember what I told you about compliance and that 'edge'. We want a nice rounded 'edge' (sic. forgiveness) but get the best stick outta the car. ) Well as you drop the car onto the floor you get a bunch of different things happening that were not 'intended' due to geometry changes. Agreed, you do gain the advantage of the lower roll center (CG) but the things that happen to the static geometry .. well its almost not worth it (IMHO). It all comes down to carrying and maintaining energy into a corner then being able to get back to gas before everyone else.

anyways there is a fine line someplace in there on ride height ... its lower than stock but WAY WAY above the stop rings.
If you truly want to get the most of the car leave it at stock height and drive the car on the track a few times adjusting damper levels. get a set of ragetek solid LCA bushings. Go out and play again. Get her all dialed in again (for the types of tracks you run) then start to drop and see what happens. I'm betting you will be back at nearer stock height than stop ring height in no time.

D
 
#33 ·
quick note: the WC cars have custom dropped spindles and re engineered pickup points... and yet we have problems dropping the car below 3.5 inches AGC. My WC TC car has issues spitting out the drive shafts if you try to lower it too far. (doesn't it, B Smith'es. =] )

D
 
#34 ·
I have 3 degrees neg camber up front and 1.8 neg in rear, using the slotted strut mounts and camber plates up front. In fact, I had to dial some camber out upfront. I also have the Rage-tek LCA bushing on and 4 rear adjustable SPC control arms. Car feels great. But I set the damper aggressive so the street ride is rough. I was concerned the stage 3R would be underdamped and so far that has not proven to be the case, I am actually considering backing off a click or so on my compression damping.
As for ride height, I was basing my setup off other successfully raced SRT-4's(non-WC) and I cannot remember any that were stock ride height. I want this car to compete favorably with C6 Z06's and Viper's. (non ACR's or Comp Coupes) I am going to Sebring for Winterfest in 2 weeks and should get a better idea how I like the car on a fast bumpy track, this will also be a good chance to see if I have narrowed the window of forgiveness too much.
 
#35 ·
Decided to raise the front of the car to 13-3/4" and keep rear at 13-1/2", which returns the original 1/4" of neg rake and gives the front some more suspension travel before hitting bump stops. Rear appears to have plenty of travel left.
 
#43 ·
Actually Sebring is the worst track ever to test your suspension on. The WC teams have to run HUGE HUGE spring rates to flatten the cars so for us it's bumpy as hell and turns 1 and 17 just SUCK. Your car with the softer springs will be ok but will roll like a bitch in the tight stuff and be generally pushy. Getting stick on exit is important.. if you get over aggro the front end will wash and poof will go all the momentum you were saving. There is the shiny smooth braking area into the hairpin that's an absolute bitch to find your marks in. Be conservative there till you have your braking point dialed in otherwise you will be mowing alligators. If you are over sprung at sebring don't sweat it you will likely be ok at the tracks closer to you =] however I still think you are still using a front swaybar so you might be able to save some momentum through the corner (less roll but a bit more push).. and FAR less bite on exit.

David J
 
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