Front suspension

Post by **Alec** » Mon Dec 10, 2007 1:49 pm

Hello all,

can any one tell me what the front spring rate is for a 1968 Morris Minor?
I realise that it is easy to give spring rate as lbs per inch for coil springs, but torsion bars?

Alec

Post by **jonathon** » Mon Dec 10, 2007 2:02 pm

New around 220lbs. the measuring spec is the same for all springs, inc the torsion bars as basically they are rotational springs.

Post by **Alec** » Mon Dec 10, 2007 5:24 pm

Hello Jonathon,

I don't know how to relate to that figure. My point about coil springs is that they can be compressed by one inch and the required force measured. Obviously the leverage of the suspension arms then determines the true rate.
Now with a torsion bar there must be some form of torque figure rather than direct measurement. Does the figure you quote mean that a load of 220lbs directly over the wheel drops the body by 1".

Alec

Post by **jonathon** » Mon Dec 10, 2007 6:42 pm

Honest answer Alec is, don't know re torsion bar testing. Just know the spring rate from dealings with Chris Street when I was his agent. Tend not to involve ourselves with them nowadays, apart from removal or setting up.

Post by **IslipMinor** » Mon Dec 10, 2007 7:13 pm

The rate of 200 lbf/in would seem about right for the 'wheel' rate, i.e. for each 200 lb loaded onto the wheel the body will drop by 1".

This would be the equivalent of having 400 lbf/in springs mounted halfway along the lower wishbone.

Post by **bmcecosse** » Mon Dec 10, 2007 7:19 pm

Try it out - get two people each weighing 200 lbs and get them to sit on the front wings (one on each) - if the car drops 1" (I bet it drops more!) then that rate will be right. Coil springs are just torsion bars that have been wound into a - well -coil shape!

Post by **Alec** » Mon Dec 10, 2007 8:23 pm

Hello Richard,

400lb\inch is a very high rate for a light car, my Triumph 2000 has 195 lb\inch as standard. As it is a Macpherson strut then there is little leverage as the spring is near the end of the track control arm but even so.

BMCE, I agree, I think (if I knew anyone as heavy as that) I'm sure that it would droop a lot more. I do understand that a coil spring twists the rod as a torsion bar does. But the rating is far more difficult to quantify.

Alec

Post by **Nadir** » Mon Dec 10, 2007 8:27 pm

Why? Surely as easy to measure using, say, a spring scale as a coil spring? What am I missing here?

Post by **bmcecosse** » Mon Dec 10, 2007 8:41 pm

Nothing - we just need to know the leverage on the spring. Torsion bar would probably need to be rated in lbs/degree rotation.
But what matters is the 'wheel rate' as seen on the car. So - weight on car and measure deflection - it's easy!