951 030 rear spring rate
11-17-2004, 10:58 PM
#6
Rennlist Junkie Forever
HMD
The difference you refer to only applies to, in a 951, a coil-over shock/spring setup on the rear of a 951. A torsion bar has no difference. A torsion bar produces what ever it produces to the rear wheel based on the diameter of the torsion bar.
In the case of a 1988 Turbo S, 1989, 1990, 1991 , 944 turbo, and all 968's, the rear torsion bar is 25.5mm which produces an effective wheel spring rate of approximately 175lbs.
When you're talking about a car that's had its torsion bars removed, then you're referring to a coil-over shock with a coil spring on it.
In this case, the difference between spring rate and effective wheel rate is just as it sounds. Spring rate is what the actual spring is rated at. Wheel rate, is the rate that is actually measurable at the wheel.
The reason the two differ is because of the geometry of the rear suspension. The rear shock mount, at the lower control arm, is not at the centerline of the axle. It's inboard, and toward the pivot point of the control arm, which is not at the axle centerline. Thus there is lack of mechanical leverage with respect to how the springs acts on the control arm.
Example: A car with no rear torsion bars, and a 350lbs rear coil over shock/spring, produces approximately 197lbs to the rear wheel (or 197lbs effective spring rate).
TonyG
The difference you refer to only applies to, in a 951, a coil-over shock/spring setup on the rear of a 951. A torsion bar has no difference. A torsion bar produces what ever it produces to the rear wheel based on the diameter of the torsion bar.
In the case of a 1988 Turbo S, 1989, 1990, 1991 , 944 turbo, and all 968's, the rear torsion bar is 25.5mm which produces an effective wheel spring rate of approximately 175lbs.
When you're talking about a car that's had its torsion bars removed, then you're referring to a coil-over shock with a coil spring on it.
In this case, the difference between spring rate and effective wheel rate is just as it sounds. Spring rate is what the actual spring is rated at. Wheel rate, is the rate that is actually measurable at the wheel.
The reason the two differ is because of the geometry of the rear suspension. The rear shock mount, at the lower control arm, is not at the centerline of the axle. It's inboard, and toward the pivot point of the control arm, which is not at the axle centerline. Thus there is lack of mechanical leverage with respect to how the springs acts on the control arm.
Example: A car with no rear torsion bars, and a 350lbs rear coil over shock/spring, produces approximately 197lbs to the rear wheel (or 197lbs effective spring rate).
TonyG
11-18-2004, 03:18 AM
#7
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TonyG,
Thanks for the explanation what I wanted to find out is the spring rate for this spring
951-333-531-31-504
As I have Eibach coils at the front and I think they are a bit more than 160lb (yet to find out their rate) I was wondering if I need to go stiffer spring on the rear coil over.
Thanks for the explanation what I wanted to find out is the spring rate for this spring
951-333-531-31-504
As I have Eibach coils at the front and I think they are a bit more than 160lb (yet to find out their rate) I was wondering if I need to go stiffer spring on the rear coil over.
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11-18-2004, 01:12 PM
#10
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hmd,
Maybe you could explain precisely what you're doing. Are you installing the 968 M030 helper coilover shocks? Do you have some other aftermarket coilovers installed on the rear? If not, all that your have back there to play with is a torsion bar which you would have to pull and replace with a larger diameter one to increase the rear wheel rate.
Maybe you could explain precisely what you're doing. Are you installing the 968 M030 helper coilover shocks? Do you have some other aftermarket coilovers installed on the rear? If not, all that your have back there to play with is a torsion bar which you would have to pull and replace with a larger diameter one to increase the rear wheel rate.
11-18-2004, 04:58 PM
#11
Nordschleife Master
Effective wheel rate up front is around 90% isn't it?
So stock the effective rates would be around 144# front and 175# rear.
The strange thing about it is that most poeple seem to recommend/run around 550# springs front and around 650# springs rear when going full coil over in a track car application.
That would equal effective rates of 495# front and 364# rear.
Seems to me that would understeer a lot!
So stock the effective rates would be around 144# front and 175# rear.
The strange thing about it is that most poeple seem to recommend/run around 550# springs front and around 650# springs rear when going full coil over in a track car application.
That would equal effective rates of 495# front and 364# rear.
Seems to me that would understeer a lot!
11-18-2004, 05:48 PM
#12
Former Vendor
Stock effective rates are ( 951 )
-> '88 Fr: 112 /Re: 126 = 1:1,125
'88 M030 & '89 Fr: 143 ( progressive )/ Re: 175 = 1:1,223
'90-> Fr: 143 /Re: 175 = 1:1,223
968 CS with M030 -option has rear effective rate of ~228 ( t-bar + helper ),but who could tell for sure which front spring does it use...? Because it seems that it's the same than the '90 front spring,143 ( 944 343 531 01 ). Then the ratio between front and rear effective ratios would be 1:1,594. But unmodified 951's tend to be a bit soft at the rear...?!
If this ratio, 1:1,22 ,is to be followed,550 fronts ( 495 eff. ) should have 1200 ( 670 eff.) coil-overs at rear....pretty steep,isn't it?
-> '88 Fr: 112 /Re: 126 = 1:1,125
'88 M030 & '89 Fr: 143 ( progressive )/ Re: 175 = 1:1,223
'90-> Fr: 143 /Re: 175 = 1:1,223
968 CS with M030 -option has rear effective rate of ~228 ( t-bar + helper ),but who could tell for sure which front spring does it use...? Because it seems that it's the same than the '90 front spring,143 ( 944 343 531 01 ). Then the ratio between front and rear effective ratios would be 1:1,594. But unmodified 951's tend to be a bit soft at the rear...?!
If this ratio, 1:1,22 ,is to be followed,550 fronts ( 495 eff. ) should have 1200 ( 670 eff.) coil-overs at rear....pretty steep,isn't it?
Last edited by pete95zhn; 11-18-2004 at 06:16 PM.
11-18-2004, 06:28 PM
#14
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Awesome. Thanks. Those are the 968 M030 rears so the answer is your rear effective (or wheel) rate is ~230 lbs.
Here's a link to a spring rate chart for 944 based chassis used by racers compiled by 'lister Dan. As you can see there's quite a bit of variance in the ratio of rates front to rear. Generally when you get up into really high rates for the fronts the rears don't need to get raised proportionally.
Dan's 944 Spring Rate Chart
Here's a link to a spring rate chart for 944 based chassis used by racers compiled by 'lister Dan. As you can see there's quite a bit of variance in the ratio of rates front to rear. Generally when you get up into really high rates for the fronts the rears don't need to get raised proportionally.
Dan's 944 Spring Rate Chart
