Spring rates on 30mm torsion bars
#3
Rennlist Member
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?
#5
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
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
#7
Rennlist Member
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#8
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.
#9
Rennlist Member
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.
#10
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.
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.
#12
Burning Brakes
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
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
#13
Rennlist Member
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.
#14
Rennlist Member
#15
Rennlist Member
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.
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.