TB diameter = what effective spring rate?

[Compulsive]

In trying to sort out my new set up I have been searching for a torsion bar to spring rate chart but I haven't found one

There was one link that showed what the effective spring rate at the wheel would be but this doesn't help to compare the TBs to linear rate springs. In case I am not making sense, what I want to know is if a 23mm front bar would be effectively the same as running 250lb or 350lb or 500lb or whatever front springs on a coil over set up.

Can anyone tell me what effective spring rates these hollow bars would have on a 930?

23mm
24mm
31mm
33mm

[emcon5]

more t/bar stuff - anyone got experience/comments on 21/31 combo?

Are lightening the 911 and torsen bar size/rigidity related?

Need Advice - 23mm Front T bars ...

Tom

[Bill Verburg]

you can't just compare spring rates between a coil over and t-bar setup. Because the Geometry is different a 250lb/in t-bar and 250 lb/in coil over won't have the same wheel rate.

You really want to know wheel rates to make valid comparisons between the 2 types of setup

[cstreit]

Bill, presumably that's because the t-bar is acting farther forward on the swing-arm (acting as a lever arm?). Is there anyone with enough math in their head to figure out an approximation?

[Dave at Pelican Parts]

Effective wheel rate goes up with the fourth power of the TB diameter, and goes down with the distance between the TB center and the wheel.

For a coil-spring, the effective wheel rate is the spring rate multiplied by the distance from the suspension pivot point and the spring mount, divided by the length from the pivot to the wheel.

A gross oversimplification, I'm afraid, but it does give you some idea...

--DD

[Bill Verburg]

Originally Posted by Dave at Pelican Parts

Effective wheel rate goes up with the fourth power of the TB diameter, and goes down with the distance between the TB center and the wheel.

For a coil-spring, the effective wheel rate is the spring rate multiplied by the distance from the suspension pivot point and the spring mount, divided by the length from the pivot to the wheel.

A gross oversimplification, I'm afraid, but it does give you some idea...

--DD

You are confusing wheel rate w/ spring rate
Effective spring rate goes up with the fourth power of the TB diameter

Effective wheel rate goes down with the distance between the TB center and the wheel.


The length of the lever arms and the angles of the lever arms(aka geometry) and friction/stiction modify the effect of the spring be it a t-bar or coil

[Dave at Pelican Parts]

If the effective spring rate goes up, so does the effective wheel rate.

As I said, it was a massive oversimplification...

--DD

[911st]

Rear (Size -- lbs/inch):
24.1 122
25 140
26 165
27 191
28 221
29 254
30 294
31 332
33 427

Front: This is for a Carrera, a wide body is less do the the increased length from the a arm pivot to the center of tread :
18.8 110
21 173
22 210
23 250

Please verify.

[RaceProEngineer]

Originally Posted by Bill Verburg

The length of the lever arms and the angles of the lever arms(aka geometry) and friction/stiction modify the effect of the spring be it a t-bar or coil

That is why in the real world (and referring to Chris' call for trig), we use MOTION RATIO to determine wheel rate. (How many degrees [converted to inches] must the T-bar rotate when the attached wheel moves UP exactly 1 inch?) There can be so many variables, each individual car needs its own reckoning.

Ed

[JohnJL]

911st, are those hollow or solid bar approximations? I'm looking for what my 31 hollow rears and 23 hollows might be in springrate as I'm considering a coilover conversion.

thanks

[911st]

Those are for Solid Bars.

Most the hollow bars are marked in there solid bar equivalents. Thus a 30mm hollow bar is usually not 30mm but a bit more.

I do not expect there is a hollow Porsche 911 torsion bar that actually measures at 30mm but I could be wrong.