I noticed Spohn has a new design out for their wonderbar.

http://www.spohn.net/shop/1982-1992-...djustable.html

Has anyone used this yet?

I'm wondering if adjustable version is really worth the extra money as most of us are sporting the OEM or aftermarket ones.

 

No ... IMHO not worth it

 

I dunno....I just don't like the sound of pre-loading my subframes. Seems to me it could induce stress cracks over time.

 

Actually depending where the cracks are, preloading the rails can help keep tension off certain areas preventing crack growth. It all depends where the rails normally crack.

Good example of this concept would be pre-stressed concrete.

http://en.wikipedia.org/wiki/Prestressed_concrete

 

The tensile strength of concrete and mild steel are different I'd think...
I was referring to putting this on an intact car with no cracks in the frame.

But- I imagine if this were used on a car with existing issues, and then the cracks properly welded, it may do more good than any possible harm by preventing stress.

 

Sure the tensile strength is different, but that doesn't invalidate the concept.

Really what is important is crack growth and the fracture toughness of the material.

Fracture toughness of concrete is really awful when compared to any metal. We can learn a lot from the concrete guys as they are very creative with managing crack growth; they have to be.

A crack will only readily grow under tension. So if you pre-stress the material with enough compressive stress, then the operating tensile stress will merely reduce the pre-stress and prevent the part from going into tension.

Now my car does not have the frame rail cracking. But if usual location of cracking is in an area that would see tension or compression from pre-loading the adjustable wonderbar, then you could use that to your advantage.

Example. Lets say for a moment that the cracking normally occurs on the inside of the frame rails. You could adjust the wonderbar to shorter than normal will which would induce a compressive stress on the inside of the frame rails and would help keep the cracks closed. Of course that would make the situation worse on the outside of the frame rails. It is a balancing act.