I talked to my friend Chris (pismoboy from ttora), who used to design tbars for a major nissan aftermarket company, and he says the tbars are in the linear elastic region throughout their travel. Cranking the tbars does not exert any more torque on them at ride height. If the truck is raised 2 inches, then, yes in the last 2 inches of compression, there will be more torque on them.

BTW guys, I'm at work right now so it's kinda hard to reply to everything, but I'll do my best. Hopefully frank can help out when he has time, too.

There are a lot of misused terms out there. This is explaining the phenomenon, not discounting it. No offense to Frankenyota but you are actually propagating a more myths.

Preload adjustment in the motorcycle world needs to be understood correctly so you don't missapply it here. You increase the ride height in anticipation of a heavier rider. The rider is the extra pre-load, the motorcycle does not gain weight. We call it a preload adjustment because we are compensating for the anticipated weight but it is important to distinguish between a larger person on a motorcycle and a truck that has not gained any weight and therefore preload.

A bit about spring rates. There is no such thing as a "soft zone".(this is a myth) Torsion bars are linear springs as are coil springs. (I'll post a graph when I get home.) Progressive rate springs are different in their geometry and I'll talk about it in a minute. The spring rate of the metal does NOT change at ALL.. EVER... unless plastic deformation occurs or you re-heat treat the metal. (plastic deformation does occur over a long period of time assuming you don't exceed the yield strength of the metal) it is a fixed property of the metal. To change this, you need to basically bend the spring (strain hardening) or heat treat it to obtain different characteristics. The spring simply responds to force but does not in itself change.

Now progressive springs us different geometries as I said. For example, you can have a cone shaped coil spring. Here, as you compressed each coil it only moves to the point you are resting on the coil below. If you make the coils thicker, the spring rate effectively gets higher. I say effectively because the mechanical properties of the metal are the same, we just changed the geometry. (again it's the root cause behind the perception thing)

You might *percieve* a difference in ride quality and that perception is correct, it's the root cause of the phenomenon that is being adressed here.

Frank.

Maybe I'm not familiar with that particular motorcycle design, but from where is the extra force to compress the spring coming? Isn't the spacer an offset? In the end, if you want that spring to compress more you need to push it harder.

Frank.

All springs HAVE to operate in their elastic region or they are no longer springs.(springs have to return to their original shape or they are just bent pieces of metal) If it was out of that region, every time your flexed it, you'd bend it, and you'd lose ride height. You'd have to adjust it after every bump <img src="/forums/images/graemlins/lol.gif" alt="" /> and it will fail in short order.

You are aboslutely correct regarding the torque in that last 2".

Frank.

On a motorcycle, are you always riding around with the travel fully extended (other than when you hit bumps)? If so, then yes the coils are being squeezed together. If not, then it's the same thing as the rear coil suspension you described.

Yes, you are right Frank, I got myself confused in the rush to reply.

Technically, stress relaxation is a logorithmic function of time. So, stress relaxation occurs the most at the beginning and tapers off. The amount of relaxation is dependant on the stress and the temperature. I did some stress relaxation tests here at work last year where we were trying to find the relaxation charactistics of some super alloys that we make.

AHHHHHHHHHH just not worry about it,cut it off and throw a straight axle under it.then ya wont need to worry about your stiff lifted ride by cranking up the bars <img src="/forums/images/graemlins/lol.gif" alt="" />

Cool. That makes a ton of sense now that I think about it. My guitar strings behave just as you described. My brain fart.

Did you guys find that over long periods after the initial stretch it stopped or did it decay at a more constant rate? I only ask because my truck being old needed a front end boost when I got it. It is possible it was adjusted to be where it was but I'm not sure. The bolts didn't look like they had ever been touched.

Also, did you find anything on say a spring that was operated within one range and then much later operated in a more extreme range? Basically I'm fishing for info on our t-bars as we expand the travel windows of our trucks years after they were made.

Frank.

Actually, I'm doing just that.... <img src="/forums/images/graemlins/notooth.gif" alt="" />