308 Spring rates - Ferrari Life
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post #1 of 44 Old 03-20-2012, 11:00 PM Thread Starter
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308 Spring rates

I've been reading all the shock/spring thread on this forum and " the other forum " . As I have the back suspension apart to replace all the bushings . So while I'm in there I might as well look at shocks/springs .
Options are
Rebuild the Koni's with threaded outer for ride height adjustment . This seems quite expensive once you have added the rebuild , new bushings and threaded sleeves and nuts . the Koni's are not really easily adjusted for dampning/rebound . But are the closest to stock , if that matters
QA1 from a cost perspective are brilliant and they seem to work well for a lot of people
Ohlins STJ ( as mk e ) at $600 per shock expensive
Ohlins TXX36/40 the ultimate shock . Not sure if they could be made to fit ??? They come on quite a few superbikes . I was wondering if these could be used as they can be had at a similar price to the STJ off eBay . Possibly the valving would need changing , luckly they are fully rebuildable .
Adapt another make of coil overs to fit ( I've found a set of Penske's although they are a bit short )

So here's my real question . With all the talk about spring rate .
The stock Koni's on a 308GTB are 200 pounds all round ( that's the springs on them ).
For QA1 anything from 250 to 400
m ke 450 front 400 rear ( IIRC )
BUT what about the preload we put on the spring ? On the Koni rear shock the spring is preloaded by +/- 100mm ???? what does that do to the spring rate ?????
In a QA1 situation the ride height can be dropped . As you lower the spring seat to drop the car you are reducing the preload and as such reducing the the spring rate ( am I understanding this correctly ?? ) So yes you start with a higher poundage spring , but you don't preload it as much .
Has anyone measured the actual spring rate of an assembled Koni shock ?
In m ke's case everyone is supprised at his hard spring rates , but we don't know how much preload he is running ?

Last edited by duck.co.za; 03-22-2012 at 06:15 AM.
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post #2 of 44 Old 03-21-2012, 04:19 AM
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Great questions. I actually have this project next on the list. Looking forward to following this!
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post #3 of 44 Old 03-21-2012, 04:33 AM
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I’m running about +1/4 of preload in the front and -1/4(meaning the spring flops around at full extension) in the rear

The spring rate doesn’t change with pre-load. If you want the car to settle say 4” and you have a 200 lb/in spring with a 1000 lb corner weight (assuming the ratio is 1:1) then 1000/200 = 5”, but you only wanted 4 so you need 5-4 = 1” preload to set the car where you wanted.

As a general rule you want the softest springs that will keep the suspension from bottoming out so sports cars that are meant to go fast have stiffer springs with less preload and luxury cars have softer springs with more preload.

In a 308, the f/r weight spilt is about 35/65 but the spring motion ratios are also different leading to the front wanting about 50 bl/in more spring rate than the rear.
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post #4 of 44 Old 03-21-2012, 11:18 AM Thread Starter
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So you are saying the GTB spring is 200 pounds per inch . We preload it by 4inches and to make it move another 1 inch from this preload will only take 200 pounds ?
So then why preload it ?
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post #5 of 44 Old 03-21-2012, 11:56 AM
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Quote:
Originally Posted by duck.co.za View Post
So you are saying the GTB spring is 200 pounds per inch . We preload it by 4inches and to make it move another 1 inch from this preload will only take 200 pounds ?
So then why preload it ?
no, no. If you pre-load it by 4" then you have 200*4 = 800 lbs then to make it move an additional inch you need an ADDITIONAL 200 lb so 800+200 = 1000lb total

if the rate is 200/in then:
1" = 200
2" = 400
3" = 600
4" = 800
5" = 1000

It doesn't make any difference to the spring what portion is from preload, the spring only cares how far it's moved.

The suspension designer cares though. If you need 1000 total and the car has 6" total suspension travel and you want the suspension to be in the midpoint normally or 3" of travel.....then you get 600 lb from the 3" of sage but you still need 400lbs more to hold the car up and you get that 400lbs from preload.
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post #6 of 44 Old 03-21-2012, 04:28 PM
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no, no. If you pre-load it by 4"...
I'm continually in awe. Jeez. You really do need to start your own replica/hot rod company.
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post #7 of 44 Old 03-21-2012, 05:09 PM
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I'm continually in awe. Jeez. You really do need to start your own replica/hot rod company.
I actually paid attention in HS physics

I heard something the other day that stuck with me:

"The older I get the more I know that what I know is mostly what I don't know"

I "knew" so much more when I was younger..........
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post #8 of 44 Old 03-21-2012, 09:46 PM Thread Starter
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Ok so the 800 pounds is holding the car up and we still have 200 pound spring rate to move it another inch ?
So with a 800 pound spring we would run no preload , but it would take another 800 pounds to move an inch ?

So with a softer spring we run more preload , just to hold the car up and get a softer spring rate

Thanks
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post #9 of 44 Old 03-22-2012, 04:36 AM
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Dave, whatever you're doing I will follow suit and do as well. So keep us posted. This is great info.
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post #10 of 44 Old 03-22-2012, 06:25 AM Thread Starter
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When you search the stuff is out there !!! I been searching instead of doing my job
and found a couple of sets of Penske's ? all different options , but I think all can be made to work .
The Penske's seem easier to find than the Ohlins . I'll keep you posted
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post #11 of 44 Old 03-22-2012, 08:38 AM
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Quote:
Originally Posted by duck.co.za View Post
When you search the stuff is out there !!! I been searching instead of doing my job
and found a couple of sets of Penske's ? all different options , but I think all can be made to work .
The Penske's seem easier to find than the Ohlins . I'll keep you posted
Some how I just knew there was no frikin way you'd buy NEW shocks

I was looking at Penske's as an option when I bought mine....I can't recall what pushed me to Ohlins??...probably just that I'd used them on my race bikes and was happy so I stuck with them.

I have the external rebound adjuster too. It was optional when I bought mine, not sure if it's standard now or not.
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post #12 of 44 Old 03-22-2012, 11:13 AM
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QA-1's with 350# front and 300# rear will be better than you need unless you track your car and have a very tuned in sense on suspension settings. I have them on my 308 and I have 1000s of miles of testing in everything from Trans Am cars to Indy Lights. Work great, a TON better than stock, and cheap as hell..
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post #13 of 44 Old 03-22-2012, 11:33 AM Thread Starter
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QA-1's with 350# front and 300# rear will be better than you need unless you track your car and have a very tuned in sense on suspension settings. I have them on my 308 and I have 1000s of miles of testing in everything from Trans Am cars to Indy Lights. Work great, a TON better than stock, and cheap as hell..
That's in the back of my mind . I'm curios to see what's out there and for how much ?
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post #14 of 44 Old 03-22-2012, 11:56 AM Thread Starter
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Missed out on a set of Ohlins TT44 with remote canister. Look at all the option/variants . Long bottom eye/mount could be useful at the back

Found a set of steel Leda's at a reasonable price

Then the black set of Penske's . The top mounts need to be changed , not sure if this is possible ?

Then the silver Penske's which are very short , although the seller is addament his shock guy can make them work ?

I'll keep looking
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post #15 of 44 Old 03-22-2012, 12:06 PM
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Quote:
Originally Posted by spang308 View Post
QA-1's with 350# front and 300# rear will be better than you need unless you track your car and have a very tuned in sense on suspension settings.
What's all this talk about girly springs?


With a 350/300 spring setup you'll want pretty heavy antisway bars....like 1 to 1 1/8 in front and maybe 7/8 - 1 in back yes?
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post #16 of 44 Old 03-27-2012, 11:33 AM Thread Starter
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Found a set of Penske 7500 single adjusters , they have a 6" stroke , which makes them good for the back and a little long for the front ? As mk e pointed out , they could have a spacer fitted inside the shock to reduce the extended ( full droop ) length

Then I've found a set of Penske 8100 double adjustable with remote canisters for almost the same money ?

Is it worth going with the extra complexity of double adjusters ???

Also interesting is the shock end eye is longer then a QA1 possibly negating the need for a custom eye .

These shocks are secondhand , but if you add up the QA!'s , Verells very neat eye extenders and his bush kit they are very similarly priced

Thoughts ?
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post #17 of 44 Old 03-27-2012, 10:47 PM Thread Starter
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The set of Penske 8100 remote canisters I found at a good price are way to short
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post #18 of 44 Old 03-28-2012, 01:44 AM
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Originally Posted by duck.co.za View Post
The set of Penske 8100 remote canisters I found at a good price are way to short
If the stroke is long enough you can just extend the lower eye.

double adjusters are better, 4 (high/low speed c/r) are better yet......but do you need any of that? Probably not. At the track C & R adjusters are probably required but on the street.....I don't know. I have just R adjusters and I really only mess with them when I'm autocrossing and even then not always because I'm there to have fun more than make everything perfect. I think the main advantage on a street car is being able to do some fine tuning at install time without needing to take the shocks out and have the shop change stuff inside.
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post #19 of 44 Old 03-28-2012, 02:47 AM Thread Starter
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[QUOTE=mk e;186541]If the stroke is long enough you can just extend the lower eye./QUOTE]

I've looked at that ? they are only 10" long , so going to require the eye extended by 7" at the back ?

Think it's a better plan to take 6"strokes and put a spacer in them to to reduce the extended length by an inch for the front ?

Ok so single adjusters are most probably more sensible
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post #20 of 44 Old 03-28-2012, 02:50 AM Thread Starter
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Now how does the valving work ?
Can you tell the shock guys I'm using a 400 pound spring and the static corner weight is 450 Kg . And they valve them accordingly ?
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