torsion bar spring rates

[fabo]

Hi guys, would like to know if anyone knows the long 28 & 30mm torsion bar spring rates and rates for the std front bj beam leaf stack...its for the company who is custom making my shocks to suit my circuit/hillclimb beetle...I tried emailing swayaway but have not received anything back as yet..

Thanks
Fabo
Australia

[Marc]

There's a calculator at their website which should give you what you need for the rears. I don't know the rate of a stock front stack.
http://www.swayaway.com/calculators/swa ... .php#step9

[Steve Arndt]

I have never seen front spring rate of the leaf pack published. You may have to find "K" empirically.

[fabo]

All good guys,I have the rear numbers but still in search for the front..

Cheers

[Marc]

If you have Microsoft Excel 2000/03/07 you can get a 30-day trial download of mitCalc here: http://www.mitcalc.com/en/download.htm

Scroll to section 13 on this page for basic info on rectangular torsion springs: http://www.mitcalc.com/doc/springs/help/en/springs.htm

I'm unsure as to whether one can simply add the individual rates of stacked leaves or if there's more to it than that, but hopefully it's covered in the Help page of the program - there is this note in Sec 13: Tip: Detailed information on the calculation of torsion bar springs can be found in the theoretical section of help.

One thought I had was that one could possibly use the wheel rates (which take the control arm lengths into account) and the design front & rear axle loads to infer what the front spring rate would be, given the rate of the stock rear torsion bars. To the best of my knowledge all BJ front springs are the same (with the exception of those used on Thing/Trekker/181) even though there have been 3 different diameter - and/or length - rear bars from `66 to `78: 552x22mm, 552x21mm, and 676x22mm.
You'd also want to take into account the natural frequency of each end; typical passenger cars use a front frequency that's ~20% lower than the rear to inhibit oscillation, and odds are that VW engineers didn't break that rule...although they may have just designed by cut-and-try
http://www.optimumg.com/docs/Springs&Da ... _Tip_1.pdf
...probably quicker and more accurate to just figure it out experimentally as Steve suggests.

[Steve Arndt]

You could solve for K the spring rate constant with a pretty basic rig. Beam clamped securely with leaf springs and arms installed. Angle protractor. Floor jack. Scale to measure the force. Rotate through a variety of angles and measure force per degrees.

[fabo]

Thanks guys,i have the numbers im after..

[fusername]

wanna post em up here for the rest of us curious folks?