lee101315

Does anyone know the what 30 mm torsion bars equate to in stiffness?

Van

About 329 lbs/inch wheel rate (assuming solid bars).

333pg333

Van, I don't think that is the wheel rate, I think that's the spring rate itself. I think you would divide that by about .65 to get the actual rate at the wheels, no?

Van

Patrick, that would be for calculating from a rear coil over - not a rear torsion bar.

Bri Bro

I used the numbers from Sway-A-Way, I was told they supply most of the torsion bars to other vendors.

Approximate Wheel Rates
Diameter / 924 & 944 LB/IN

22 mm 98.03
23 mm 117.11
24 mm 138.84
25 mm 163.47
26 mm 191.24
27 mm 222.4
28 mm 257.22
29 mm 295.98
30 mm 338.97
31 mm 386.47

http://www.swayaway.com/TechRoom_VWguides.php

CPR

FYI...I have a set of 28mm and a set of 30mm going for sale soon.

Sory for the hi jack

333pg333

Isn't a spring a spring?

Bri Bro

The coil overs attach to the arm some distance back from the wheel hub which reduces the force of the spring. The torsion bar doesn't have this problem. The end of the TB attaches to the spring plate at a right angle to the hub, no force reduction.

333pg333

That's a good explanation thanks Brian. However, then when calculating the wheel rate at the rear with a combination of t/b and coils, it is usually something around .65% yet that doesn't seem to allow for a vast range of possibilities. In other words you could have 30mm t/b and 100lb springs vs 20mm t/b and 800lb springs. So I assume that I'm missing something here. The average wheel rate at the rears on track cars tends to be 250-300lb/in from what I can gather.

Bri Bro

For coil over:
wheel rate = (spring rate) * (motion ratio)^2= (spring rate) * (0.65)^2= (spring rate) * 0.42
For Torsion bars, use the table from Sway-A-Away.

For a combination, you add the TB to the coil over. The problem is that you have to soften the TB for coil overs above around 100 lbs. Now your point comes into play, what is the rear wheel rate? I guess you just need to measure it and add or subtract coil over spring rates to get to where you what to be. This is why I would not run TB with coil overs.

2bridges

Hey Lee - 30mm will match nice with a 425# front spring if that is what you are asking

superloaf

so dumb question here but what is the equation for front spring rate to wheel rate? or is none needed & they are the same? and even dumber question; is the macpherson strut equation the same for mac struts from different cars?

Van

The motion ratio is about 91% - which makes the wheel rate 0.828x the spring rate.

The are not the same - they would only be the same if: a) the strut was perpendicular to the wheel axle; and b) if the strut was connected at the center line of the wheel. Those conditions would require the strut to go through the wheel.

Yes - the equation is the same. But the values will be different.

Van

Which will give you a front wheel rate of about 352 lbs/inch - a good match for a rear of 329.

Van

329 + 40 = 369 lbs/inch

65 + 317 = 382 lbs/inch

As Brian said, you're going to have to do some adjusting and re-indexing to make it work. That's why most people do a straight coilover.