Solving Torsion Spring Problem with 100 lb Force

[bpaliwal]

I am struggling through a problem in one of my designs and would appreciate some help.
Please refer to the image attached.

Problem Description:
S = Torsion spring
F = fixed point
T = tire

A tire is attached to a torsion spring through an arm as shown in the image. The torsion spring has one end connected to a fixed wall and the other connected to the arm S-T at point F.
How much spring rate (lbs-in/degree) should be there on the spring S, so that the tire T is subjected to a force of 100lbs in the downward direction before any deflection occurs in the spring?

Also, I forgot to mention in the image the angle of S-T with the horizontal is 33.127 degrees.

Any help would be appreciated.

 

[cjl]

If you want the tire to be able to be subject to 100lb of force before there is any deflection, you need the mechanism to be against an end stop and the spring subject to pretension. If you don't have an end stop and a pre-tensioned spring, there is no spring rate you can chose to achieve this - no matter what the rate is, you will always see some deflection at any force level.

 

[bpaliwal]

If you want the tire to be able to be subject to 100lb of force before there is any deflection, you need the mechanism to be against an end stop and the spring subject to pretension. If you don't have an end stop and a pre-tensioned spring, there is no spring rate you can chose to achieve this - no matter what the rate is, you will always see some deflection at any force level.

Thanks for the response.
I am working on the pretension design for the spring. All I am concerned about is how much spring rate do I need?
Considering everything is weightless, will it be just the 100lbs force multiplied by the horizontal distance between the tire and the spring center? Regards

 

[JBA]

For what you have shown you would be calculating the required torque of the spring. Once you have that value, then it is just a matter of going to catalogs to find an appropriate spring that will supply that torque.
Spring rate for an application is only a factor when there two required forces and required angle of rotation for the spring between those two forces.