torsion bar spring rate ?

I want to fit torsion bars to the rear of my 32 Ford. The rear weight is 1485 lbs. What spring rate would I need to support this weight?

I know the arm length and bar dia. calculations, I need the total at the end of the bar.


Ago

 

150lb/in.

That will give you a resonant frequency of slightly over 1.4Hz.

This is assuming that the figure of 1485lbs is ready to roll, with fuel, a bit of luggage, a passenger, and yourself on board.

 

I would love to see the calculations needed for this.....seems there wasn't enough info in the request too.
Thanks, knowledge is king!

 

Thanks Ned, that is what I had in mind. Winters performance and Schroder website should help with calculations. Might have to go with Midget race car torsion bars.


Ago

 

You don't include the weight of the rear end,wheels,shocks,etc in the weight used for the calculations. All of that is resting on the ground. Your weight seems very high as is. I would assume about 700 lbs sprung weight. I run 80 lbs wheel rate on my roadster.

 

the size of the bar(length and diameter) depends on the length of the arm how close it's mounted to the wheel and how high it's mounted in the frame

 

That is very true. I'd forgotten about that.

If we thus subtract some for unsprung mass, and add some for passengers, fuel, etc., let's say the in-use sprung mass works out to 1200lbs.

The spring rate should be 120lb/in for a resonant frequency of 1.4Hz.

The formula is:

K = M x f² / 9.7969, where​

K = spring rate in lb/in
M = sprung mass in lbs
f = resonant frequency in Hz