calculating torsion - EDIT Got a bar and basic calcs now

[KiwiBacon]

why do you ask by the way?

I can then give you an idea of how much roll stiffness you've got and how that compares with what you're planning to add.

[rockcrawler31]

why do you ask by the way?

I can then give you an idea of how much roll stiffness you've got and how that compares with what you're planning to add.

Ahh okay

I'll try and get a hold of Shane and find out the exact rates and also get some dimensions and placement of the coils.

On another subject - I spoke to performance metals today trying to get dimensions of materials for the links to the axle tubes. I reckon my links will be about 250mm absolutely max total length including the length of the heims. I'm looking at using either an M12 or a 5/8th Heim in standard carbon steel body as the load ratings for these are over 13.4Kn dynamic and 17.5Kn Static in the smaller M12 size.

I got the impression from the steel salesman that the weak link will not be the heims but the tube that i make the links from. I was thinking of using 19mm OD and 4.7mm wall ChroMo tube. Do you think that will be strong enough in the compressive mode over a length of say 200mm?

Also how much harder is it to tap ChroMo compared to normal mild using normal tap sets? am i just going to snap the tap?

[KiwiBacon]

why do you ask by the way?

I can then give you an idea of how much roll stiffness you've got and how that compares with what you're planning to add.

Ahh okay

I'll try and get a hold of Shane and find out the exact rates and also get some dimensions and placement of the coils.

On another subject - I spoke to performance metals today trying to get dimensions of materials for the links to the axle tubes. I reckon my links will be about 250mm absolutely max total length including the length of the heims. I'm looking at using either an M12 or a 5/8th Heim in standard carbon steel body as the load ratings for these are over 13.4Kn dynamic and 17.5Kn Static in the smaller M12 size.

I got the impression from the steel salesman that the weak link will not be the heims but the tube that i make the links from. I was thinking of using 19mm OD and 4.7mm wall ChroMo tube. Do you think that will be strong enough in the compressive mode over a length of say 200mm?

Also how much harder is it to tap ChroMo compared to normal mild using normal tap sets? am i just going to snap the tap?

I can't imagine a 19mm pushrod that's 200mm long being the weak link in a swaybar setup.
I've never done tried to tap chromoly, but plenty of stainless which is probably worse. The temper of chromoly can vary a lot. Drill the holes 0.1 or so mm bigger than the tap chart suggests and use a good lube with a sharp tap. You can get blue taps for really hard metals but I don't think you'll need them.

[sierrajim]

All this mathematical tech makes my head hurt.

I had been told in the past that front torsion bars (Pathfinder I think) work in the rear of a GQ, so maybe in your's??

[rockcrawler31]

All this mathematical tech makes my head hurt.

I had been told in the past that front torsion bars (Pathfinder I think) work in the rear of a GQ, so maybe in your's??

I know what you mean but i've made enough expensive mistakes in the past using trial and wastage method so i'd like to do this correctly the first time if i can

[pinkfloyddsotm]

Christ i don't know. I'd have to contact Shane from suspension stuff who sold them to me.

The rears are 5" single rate heavy duty coils for an 80 series. I could go and measure the wire size to get a bit of an idea.

The front are 5" flexi coils

Dobinsons all round, and probably too heavy a rate really, i originally had 5" flexi coils on the rear but they didn't provide nearly enough body roll control on cross slopes so i went heavier single rate coils. The problem was that on the flat the ride was compromised and hard as buggery as a result - Way more than enough to hold up the weight of the car on the flat but nowhere near enough (due to inboarding) to stiffen the rear on any kind of side slopes or articulation.

I'm hoping that with the sway bar i can run longer - lower rate coils all round so the rear stops dislocating and banging every time they do that, and so that the front is free to compress and flex instead of being the main roll stiffness for the truck

why do you ask by the way?

to figure out your spring rate ,its this equasion;

(spring tensile modulus)* (wire dia in inches)^4 / 8 * ( # of active coils)* (coil spring overall dia in inches) ^3

11,250,000psi is the springs torsional modulus but this could be different on whatever material your spring is made from, but using that comes pretty damn close your spring rate .

number of active coils is the number of coils able to compress ,or the total # of coils minus the top and bottom since their unable to compress, also if the 2nd coil from the top is tightly wound to the first coil i just made that half as you see in my equasion.

so..

11,250000 * (0.2) ^4 / 8 * (7.5) * (5.5) ^ 3 = 280. 07578
and my coil spring rate is actually 285lbs/in so you can see its pretty close.

im no expert but i did alot of studying of the coilover bible about a month ago

[pyrohamish]

Cr-Mo failing under compression is 51.6kN (any length)
under buckling 966kN (200mm long) buckling will occur at any more than 670mm

using E=210GPa
sigma=410Mpa

for tube size given

[MART]

I used a sprint car torsion bar . 300 lbs for my zuk , they where hollow with splined ends and had about 14 to 16 inch arms , they also had less rated bars , they flex very easy under load and kept it very stable on and off road , Cheers Paul.

[98lux]

http://www.pirate4x4.com/forum/showthread.php?t=885246