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Old 01-16-2007, 06:23 PM
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calculating spring/torsion bar rates

am replacing the buggy spring front on my T with a torsion bar suspension. The front end weighs 1120 lbs.Will retain the straight axle. The bars will be longitudinal. The levers will be 14". How do I go about calculating the torsion bar rate.
Bars are 60$ apeice so don't want to do a try and fit.
Thanks for any and all help

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Old 01-17-2007, 02:55 PM
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http://www.proshocks.com/calcs/torsionrate.htm
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Old 01-18-2007, 07:24 AM
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Thanks, interesting site but still doesn't tell me what I need to know which is how do I determine what rate bars to buy to fill the parameters given.
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Old 01-18-2007, 09:09 AM
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Don't the race car places that sell those bars have specs on them??
Noticed you're talking about 14" levers...wouldn't that put the bars in the middle of the chassis running down through the oil pan?? What length spring are you replacing with the bars?
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Old 01-18-2007, 05:53 PM
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The equation would be:

rate = 1.14e6(D^4)/[L(A^2)]

where "D" is the bar diameter, "L" is the bar length, and "A" is the arm length. (All dimensions in inches.)

So, with the 14 inch arm, it becomes:

rate = 5816 D^4/L

If you wanted, say, a wheel rate of 150 pounds per inch, this could be a 38.5 inch long bar of 1 inch diameter.

(Edit: Just compared this with Johnsongrass1's calculator and got the same answer.)

The further outboard the reaction point at the end of the arm, the greater the roll stiffness.
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Old 01-18-2007, 06:40 PM
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Quote:
Originally Posted by pasadenahotrod
Don't the race car places that sell those bars have specs on them??
Noticed you're talking about 14" levers...wouldn't that put the bars in the middle of the chassis running down through the oil pan?? What length spring are you replacing with the bars?
Yes they do. I can get bars rated from 600 to 1500 in 25 increments but which one do I use? You also have to realise that I am a mathmatical moron. I bought math for dummies but couldn't figure out the page numbers.
With the 14 " levers, the bars will lay just inboard of the frame rails with the outer attaching point 3" inboard of the kingpin. I may shorten them just a bit to put the bars under the frame rail . The front of the rail is dropped (z'd) 6" so the bar support tube would go under the top part, through the Z and over the back portion of the rail.
The spring is a 26x 1 1/2 5 leaf. stiffer than a wedding dxxx.
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Old 01-19-2007, 01:13 AM
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First of all, I'd be willing to bet that spring you have there is a trailer spring, not a car spring. That's why it is so stiff, LOL.
You didn't mention what axle you have on your car so I will just say this. All of the spring-over axle set ups I've seen on old cars had the lever of the T-bar hooked up to the spring perches. Spring behind axle set ups I have seen converted or built with T-bars have them hooked to spring perches as well but to custom brackets welded to the axle.
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Old 01-19-2007, 06:14 AM
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Checked my coil over charts and they all seem to recommend something in the area of a 140lb spring when using coil overs on that weight car..I woudl imagine something of that rate would work using torsion bars..also if one is to make the length of the arm somewhat adjustable it may be possible to do some fine tuning..that is if you feel the need for that..

Also using some adjustable shocks can help tune the ride as a lot of those are tuned waay stiff..

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Old 01-21-2007, 02:31 PM
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Quote:
Originally Posted by 61bone
Yes they do. I can get bars rated from 600 to 1500 in 25 increments but which one do I use? You also have to realise that I am a mathmatical moron. I bought math for dummies but couldn't figure out the page numbers.
With the 14 " levers, the bars will lay just inboard of the frame rails with the outer attaching point 3" inboard of the kingpin. I may shorten them just a bit to put the bars under the frame rail . The front of the rail is dropped (z'd) 6" so the bar support tube would go under the top part, through the Z and over the back portion of the rail.
The spring is a 26x 1 1/2 5 leaf. stiffer than a wedding dxxx.
600 per inch........ not even close. And if you shorten the arm, the effective rate gets stiffer.....

Why don't you look into a Posies spring? Or just reduce the rate on the spring that you have?
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