[stretch]

An update: I swapped out my progressive 315lb/in springs for 350lb/in linear springs. Now the front feels much, much better. I've yet to call Mark about this but plan to today- wanted to test things first!

I've gone over Eibach's spring catalog quite extensively and have some recommendations based on my own measurements. My spring recommendations are:

The Daily Driver:
280lb/in 9" long Swift springs front, 224lb/in 9" long Swift springs rear (these springs are available separately from Turn-in Concepts. Ground Control's 9" springs are progressive and 8" springs are too short at these rates. Avoid them both.
Your spring frequencies will be 1.67hz front, 1.81hz rear @ 3500lb wet weight.

The Weekender:
375lb/in 8" length front, 300lb/in 8" long rear (but equivalent Swift spring preferred in rear to gain 0.2" of stroke)
Your spring frequencies will be 1.97hz front, 2.13hz rear @3400lb race weight

The Tracker:
500lb/in 8" length front, 400lb/in 8" length rear
Your spring frequencies will be 2.27hz front, 2.46hz rear @3400lb race weight

I believe these are the required rates and lengths to prevent coil bind at typical ride heights. The spring frequencies are also fairly good. But please, measure for yourself to confirm this.

If you are using Ground Control's camber/caster plates, you will have even more bump travel and may have to limit how high you set your ride height. The combination has an insane amount of bump travel and very few spring combinations can take advantage of it all. In that case, you'll have to consider what ride height you want and choose 8" or 9" springs depending on your goals.

Eibach's spring catalog:
http://eibach.com/cgi-bin/htmlos.exe...88473100032549

Swift's spring catalog:
http://www.swiftsprings.com/file/Swi...Racingmain.pdf

Use my calculator to figure out how much of the spring's stroke is used to reach your ride height, then subtract that from the spring's total stroke to see how much bump travel you'll have:
Weight transfer, spring frequency, damper, body roll calculator... and more!

[Rootus]

Maybe you should go into business . Just like RCE does with the Tarmac 2's, you could take GC components and rework something to your specifications and call it the "Stretch DD/Weekender/Track Coilover".

[Tim Flat4]

For the road going weekend warrior would you recommend a spring rate in between DD and Weekender? Something like a 9" 350/275 rate?

This is kind of OT but I'm curious where one car shed 100 pounds between DD and Weekender. The spare and jack aren't that heavy and the rear seats weigh nothing.

[RainMaker]

Originally Posted by Tim Flat4

For the road going weekend warrior would you recommend a spring rate in between DD and Weekender? Something like a 9" 350/275 rate?

This is kind of OT but I'm curious where one car shed 100 pounds between DD and Weekender. The spare and jack aren't that heavy and the rear seats weigh nothing.

You throw the kids out of the car prior to tracking it. 1 65lb boy, 1 35lb girl.



If the answer is "My wife weighs 100lbs more than the typical track instructor."........ Yikes?

[Tim Flat4]

Hahaha! Neither apply to me (no kids, single and happy )

[lackskill]

Originally Posted by Tim Flat4

For the road going weekend warrior would you recommend a spring rate in between DD and Weekender? Something like a 9" 350/275 rate?

This is kind of OT but I'm curious where one car shed 100 pounds between DD and Weekender. The spare and jack aren't that heavy and the rear seats weigh nothing.

100lbs of sprung weight =/= 100lbs of spring rate. I think he was just recommending a higher spring rate exclusive of sprung weight.

[stretch]

Originally Posted by Tim Flat4

For the road going weekend warrior would you recommend a spring rate in between DD and Weekender? Something like a 9" 350/275 rate?

This is kind of OT but I'm curious where one car shed 100 pounds between DD and Weekender. The spare and jack aren't that heavy and the rear seats weigh nothing.

Well, Subaru lists an STI as around 3300lbs, so I figure 3500lbs with driver and groceries.

However, most corner-weighed STI's I've seen have come out around 3400lbs with driver. Whatever those track guys are doing seems to shed 100lbs.

In any event, adding/subtracting 100lbs has a small impact on the calculated spring frequencies.

[lackskill]

Originally Posted by lackskill

100lbs of sprung weight =/= 100lbs of spring rate. I think he was just recommending a higher spring rate exclusive of sprung weight.

Reading comprehension > me.

There are several other places you can shed weight.

Both bumper beams.
Front U-brace
lighter wheel/tire combo.
Coilovers
aluminum/CF decklid
spoiler
seats

[stretch]

Talked with Mark. He's going to allow me to exchange the springs "so long as he can still sell them", which shouldn't be a problem. That makes me happy.

He is also snail-mailing me a print-out of a shock dyno for the Koni SA struts. He's actually taking a set off the shelf now to redyno, which is great and why I'd only talk with Mark when dealing with Ground Control! He mentioned the bump valving being more linear compared to normal Koni's.

[4banger]

Originally Posted by stretch

He is also snail-mailing me a print-out of a shock dyno for the Koni SA struts. He's actually taking a set off the shelf now to redyno, which is great and why I'd only talk with Mark when dealing with Ground Control! He mentioned the bump valving being more linear compared to normal Koni's.

I can't wait to geek out on those graphs!

[StiLimited]

Thank you for this info. It really helps me. Any updates?

Originally Posted by stretch

My spring recommendations are:

The Daily Driver:
280lb/in 9" long Swift springs front, 224lb/in 9" long Swift springs rear (these springs are available separately from Turn-in Concepts. Ground Control's 9" springs are progressive and 8" springs are too short at these rates. Avoid them both.
Your spring frequencies will be 1.67hz front, 1.81hz rear @ 3500lb wet weight.

The Weekender:
375lb/in 8" length front, 300lb/in 8" long rear (but equivalent Swift spring preferred in rear to gain 0.2" of stroke)
Your spring frequencies will be 1.97hz front, 2.13hz rear @3400lb race weight

The Tracker:
500lb/in 8" length front, 400lb/in 8" length rear
Your spring frequencies will be 2.27hz front, 2.46hz rear @3400lb race weight

Eibach's spring catalog:
http://eibach.com/cgi-bin/htmlos.exe...88473100032549

Swift's spring catalog:
http://www.swiftsprings.com/file/Swi...Racingmain.pdf

Use my calculator to figure out how much of the spring's stroke is used to reach your ride height, then subtract that from the spring's total stroke to see how much bump travel you'll have:
Weight transfer, spring frequency, damper, body roll calculator... and more!

[kwan_1104]

are the recommanded rates for the stock struts or for the koni struts??

[stretch]

Originally Posted by kwan_1104

are the recommanded rates for the stock struts or for the koni struts??

275lb-in front, 225lb/in rear. You'll be a little underdamped, but not horribly so.

I'd highly recommend you get Ground Control's camber/caster plates to add bump travel to the stock struts. That's really the more important upgrade, much more important than the springs.

[kwan_1104]

i m on 04 sti strut, upgrading to the GD coilover conversion, sticking to stock struts for now, also getting the camber plates, but dun know what springs to get. would 375 front 300 rear be too much? whats the optimum? I am a weekender...
please help me out.....

[stretch]

Sorry, that 275/225 recommendation was for the stock struts.

I've run 350lb/in on the stock front struts and that was definately much too high.