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Spring rate/ length 
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On the Road

Joined: Sat Sep 29, 2007 3:45 pm
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Location: SL2 4JW
GTM: Libra
Post Spring rate/ length
Any Libra owners know the length and poundage of their springs :?:

I'm currantly running with 450lb/8in on the rear, 250lb/8in front.

I've tried 450lb/12in and 300lb/12in on the rear, but at £50 a go to experiment, it could get very expensive.

Gtmdriver, I seem to remember you worked out your own spring rates :?:

Could your formula be appilied to the Libra :?:

Bob S.

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Bob S.
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Mon May 19, 2008 1:13 pm
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Post Re: Spring rate/ length
Yes. It can be applied to any car, but you need a lot of information up front. Things like total weight, weight distribution, sprung and unsprung weight and so on.

If you want to go that way I'll give you a full list of the data you need and how to get it then what to do with it when you've got it?????

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Mon May 19, 2008 4:28 pm
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Post Re: Spring rate/ length
Sounds like a lot of fun/work.

I know total weight/distribution but not sprung/unsprung weight.
I had the car corner weighted last year at Andy Robinson Racing [nice chap].
He suggested to go from 450lb/12in to 450lb/8in but I'm still thinking it's not right?

I could phone GTM to find out what their supplying at the moment, but all the cars that I know all have different springs.

I don't want to cause you a lot of work for nothing John.

Bob.

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Tue May 20, 2008 8:37 am
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Post Re: Spring rate/ length
It's not a problem.

The best thing would be if you can get the information from other users but if all else fails and you need to start from scratch then let me know and I'll pass on what I can.

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Tue May 20, 2008 11:49 am
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Post Re: Spring rate/ length
This table is the one I produced to calculate my spring rates and length. It shows the data you need to collect or calculate along the way. The actual formulae I used came from Alan Staniforths 'Race And Rally Car Source Book'.

Image

Basically you need to know the sprung and unsprung weights at each corner. You need to know the ratio of wheel movement to spring movement (lever ratio) and you need an idea of the wheel frequencies you want to end up with. You can then do hard sums to work out the spring rates.

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Tue May 20, 2008 5:35 pm
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Post Re: Spring rate/ length
How many Libra owners here then :?:

Have I got to join TeamGTM to get an answer :?:

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Tue May 27, 2008 10:25 pm
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Post Re: Spring rate/ length
Hi Bob,
At least you Libra owners get a section :shock: , What about us poor spyder owners :cry:
Juls


Wed May 28, 2008 1:09 pm
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Post Re: Spring rate/ length
Juls wrote:
Hi Bob,
At least you Libra owners get a section :shock: , What about us poor spyder owners :cry:
Juls


FIXED :wink: a small over sight during the setup

what are you wanting to achieve bob, a smoother ride, better handling, or just a little tweak?

WEST

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Wed May 28, 2008 2:30 pm
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Post Re: Spring rate/ length
I would like a better ride and better handling :?:

I have managed to get hold of GTM,
They happen to be experimenting at Bruntingthorpe this week, and are down to 275lb on the rear. Said they would let me know what they come up with at the end of next week.

Bob S.

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Sat May 31, 2008 8:37 pm
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Post Re: Spring rate/ length
GTM also said that RDM used a formula to come up with 450lb rear/ 250lb front.

I'm just fed up with the back bouncing around.

Bob S.

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Sat May 31, 2008 8:44 pm
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Post Re: Spring rate/ length
bob snooks (835) wrote:
... 'm just fed up with the back bouncing around.
Bob S.


Just a thought if it's bouncing, have you looked at your damper settings?
There's a lot of interaction between spring rate and damper setting to get a good ride.


Sat May 31, 2008 8:51 pm
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Post Re: Spring rate/ length
When I first fitted new shocks/springs [450lb/12in] I tried every notch, the softer it was the more it bounce'd. So set it at 11 clicks [out of 13]. When I put on the 450lb/8in I came down to 8 clicks.
The fact that I have never been able to get the ride height correct [ie to high] tells me it's over sprung.
Last week I borrowed Phil Cope's shocks/springs, and the ride was far far better.
He's got 300lb/10in springs on the rear.

I've sent my shocks back to Protech to have them checked while I've got Phil's.

Bob S

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Mon Jun 02, 2008 6:53 pm
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Post Re: Spring rate/ length
There's a tendency to overspring 'sports' cars in the belief that the will handle better. On the road that doesn't hold true as the car just won't ride the bumps. What you really need is springs soft enough to absorb the bumps and keep the wheels on the road with dampers firm enough to prevent the springs from oscillating uncontrollably. That's why the Staniforth formulae take account of the wheel frequency. That gives an indication of the overall ride characteristics of the car.

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Mon Jun 02, 2008 7:05 pm
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Post Re: Spring rate/ length
It would be interesting then to compere the Staniforth formula against what GTM come up with :?:
What do I need to dismantle to find out the unsprung weight :?:

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Tue Jun 03, 2008 2:52 pm
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Post Re: Spring rate/ length
The unsprung weight at one corner is basically everything that goes up and down when you hit a bump..............

wheel and tyre
wheel nuts/bolts
hub or drive flange and hub carrier or swivel hub

.........and half the weight of things that are fastened to the chassis at one end...........

top and bottom wishbones or trailing arms
spring and damper
driveshaft

Basically everything to the left of the red line (if it was a Mini).

Image

I think that's it. Can anyone else add to this list?

I'll make a full list of the data needed and I'll bring my calculator to Newark if you can get the data before then.

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Last edited by gtmdriver on Tue Jun 03, 2008 4:49 pm, edited 1 time in total.

Tue Jun 03, 2008 3:17 pm
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