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New Spring Setup - ERS etc HELP!

1019 Views 10 Replies 5 Participants Last post by  8valvegrowl, 
golfitup
I have the autocross car, and here is what I currently have:
- front and rear Koni springs
- rear Koni adjustable shocks
- front KYB shocks (terrible)

I am planning to move to the following:
- rear 350 lb/in Eibach ERS ???? length
- front 450 lb/in QA1 or similar tapered (but linear) spring ???? length
- front and rear Koni adjustable shocks

I am moving to running 215/45-16 tires on a 16x7 inch rim. Currently the car has terrible body roll (evident by my spring/shock setup). It also sits very high and I want to get the CG down.

My problem is trying to calculate what length of springs to get for the front and rear? I remember seeing a flush rear with an 8 inch ERS spring, BUT that was with 19 inch wheels. Would it be okay to run a 7 inch ERS with my /21545-16 tires? What length for the front spring? 10 inches? How much would it drop?

How do I calculate all this? I think I can take the corner weights of the car, along with the lb/in of the springs on the rear or front and see how much the spring would compress from its standard length . . . Possible?

Can anyone please point me in the right direction? I don't have any stock numbers to compare to (stock heights, etc) so its hard to calculate what a difference would be.

Thanks.
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8valvegrowl
I would NOT go with a shorter spring. The problem is preload. You need to have enough spring length to prevent the spring from falling out when the rear axle is unloaded.

Go with the 8" spring in the rear, you can always change the length later by trimming a dead coil.

As for the front. I would measure the front spring length compressed, uncompressed but in the strut, and then free. You can look up the stock spring rates via search function here on the forum, then using 1/2kx^2 you can figure out most of what you need for the fronts.

Where have you found tapered springs that match the dimensions of the Saab strut?
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saabkid37
8valvegrowl said:
I would NOT go with a shorter spring. The problem is preload. You need to have enough spring length to prevent the spring from falling out when the rear axle is unloaded.

Go with the 8" spring in the rear, you can always change the length later by trimming a dead coil.
Click to expand...
im pretty sure a 7 would not fall out. and i thought a linear spring didnt have dead coils?
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golfitup
8valvegrowl said:
I would NOT go with a shorter spring. The problem is preload. You need to have enough spring length to prevent the spring from falling out when the rear axle is unloaded.

Go with the 8" spring in the rear, you can always change the length later by trimming a dead coil.

As for the front. I would measure the front spring length compressed, uncompressed but in the strut, and then free. You can look up the stock spring rates via search function here on the forum, then using 1/2kx^2 you can figure out most of what you need for the fronts.
Click to expand...
Yeah I need to do the math and see where everything will sit. Ive been looing for the stock specs and I have not found much luck yet on here.

8valvegrowl said:
Where have you found tapered springs that match the dimensions of the Saab strut?
Click to expand...
QA1 is gonna make me custom springs to the specs I need. I just have to figure out the height and width at both ends to fit the stock housing.

I want a lower drop than the Koni's give, but being a much stiffer spring, it will have to be lower.
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dave del
i have 400lb race springs in the rear that i'm pretty sure are 6" tall.....they dont fall out
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golfitup
dave del said:
i have 400lb race springs in the rear that i'm pretty sure are 6" tall.....they dont fall out
Click to expand...
ERS? Can you give some more info please? Pictures?

You are the one with the front coilovers? Im thinking you may not have 400 lb in the rear that WAY stiff for dd
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G
The brand of the spring doesn't matter. Just dictates what color it will be.

You need to find/ rent/borrow a set of corner weight scales. Start with that data. Then you need to know linkage rates for the springs. Knowing stock coil rates is important too. Known ballast VS Sag can help with that. Given sag on a certain weight along with the linkage rates and starting weight of the car can calculate almost everything you need to know. Excel will be your friend here. Once you have that you can start with a baseline setup and go from there. Also know you need the dampers to match the springs. After swapping each end about 6 times at least you will have a decent starting point to take it to the track for some development work and have a range to try with somewhat predictable results.

If you get it right the car will just work. I love the setup in my Viggen right now. Took me 3 hours to get to the neighborhood grocery store sunday. :) by way of Arkansas backroads and plenty of turbo boost!

215s really? 225-235s will fit and put more rubber on the road with the right wheel offset.
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golfitup
GenuineSaab said:
The brand of the spring doesn't matter. Just dictates what color it will be.

You need to find/ rent/borrow a set of corner weight scales. Start with that data. Then you need to know linkage rates for the springs. Knowing stock coil rates is important too. Known ballast VS Sag can help with that. Given sag on a certain weight along with the linkage rates and starting weight of the car can calculate almost everything you need to know. Excel will be your friend here. Once you have that you can start with a baseline setup and go from there. Also know you need the dampers to match the springs. After swapping each end about 6 times at least you will have a decent starting point to take it to the track for some development work and have a range to try with somewhat predictable results.

If you get it right the car will just work. I love the setup in my Viggen right now. Took me 3 hours to get to the neighborhood grocery store sunday. :) by way of Arkansas backroads and plenty of turbo boost!

215s really? 225-235s will fit and put more rubber on the road with the right wheel offset.
Click to expand...
Thanks for that Nick. I am working on it slowly lol.

With a 16 inch wheel, a 215 is the widest width that also has a 45 sidewall height.

If I could afford some 17 inch wheels, then sure 225-235 would be better, but I do not like the height and acceleration of the 225/50-16 tire. When I had race tires on the car, I was running 245/45/16 all around. My car got insane grip then, im just in a street tire class now on a limited student budget :)

Got any spring specs Nick? Any Koni Sport specs? Thats what I have on the car now.
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G
Oh and you need letters like these:
I Could get aways with it since there are not a lot of Saabs competing around here.


Once you know the weight as run then you can start to figure out the suspension frequencies you need. The rates come after that.
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dave del
golfitup said:
ERS? Can you give some more info please? Pictures?

You are the one with the front coilovers? Im thinking you may not have 400 lb in the rear that WAY stiff for dd
Click to expand...
They're cosmo racing springs and yes I do have nick's coilovers up front. 400 in the rear is not too stiff because the wheels are not seeing that 400lbs with the springs being underneath the body in the mid part of the axle beam.
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8valvegrowl
saabkid37 said:
im pretty sure a 7 would not fall out. and i thought a linear spring didnt have dead coils?
Click to expand...
They won't be dead, you are correct. Depending on the spring rate, a shorter one could fall out.

Anyway, taking lots of measurements will be your friend here. Corner scales are a must.
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