School me on truck frames- do they twist?

Yes, frames tist and flex. More than you think.

 

On a road building job pulling a bellydump in rough service I saw mine twist so much the bang board behind the sleeper dented the side air wing on the sleeper, not much but the bang board is about 4inches away.

 

......don't you mean "bases before I bite"?

 

Are they designed to twist that much there? Here I know some people here have the opposite problem; too stiff! That causes handling and stability issues over rough terrain, some wheels are lifted off the ground.

 

I believe frames flex depending on how rugged built. If they couldnt flex, they would break? How much flex, i have no idea? Any one else here will be able to tell you more...

 

Yes they are designed to twist like that, unless the frame has been painted somewhere on it there are warning stickers against drilling and welding on the frame as it is spring
steel. I have seen a lot of hack jobs on fixing them or changing the lengths of them, there are right ways and wrong ways for that. To stiff is of course a problem as well, just as you have spoke about handling problems. Breaking from being to rigid is another result, the world is an imperfect place to drive vehicles so they have to give and flex. There is a limit however, I pull a flatbed most of the time and the dynamics of a flatbed are completely different than a van. The only thing to keep the trailer from folding over on itself is the deck, if the deck screws come loose or break off over time then the deck is loose and the frame then over will over flex. You will know that there is a problem when welds holding cross members and suspension mounts start breaking and you spend most weekends under there welding it back together. As far as wheels lifting off the ground, suspension travel can come into play there also. If you are running spring ride equipment the springs may not have enough give either, air ride equipment can do the same thing but generally speaking air will have more give. Exception; there is a suspension on pulling units here made by Chalmers that is designed for extreme service and it acts like the old walking beam suspension but it is set up much better and has a bit better ride. Hope some of this helps.
J-J

 

No problems with cracking just stability when empty especially!