Mid-door Vans

All vehicles (and airplanes) need to twist and give a bit. A rigid frame that has no give at all may crack at the seams. A friend of mine spent most of last year on the road in Oz doing every outback track he could find. Before he left he made a large strong roof-rack for his LC, guess where he now has structural cracks in his 4wd? The roof-rack was so rigid the vehicle could not 'ripple' over the roof so the top of the vehicle pillars took all the twisting load and now need remedial welding.

I go along with Notso above - it's up to the designer. I love wondering around a campground looking at all the different designs of trailers and vans, thinking if I like the design and guessing if they have a weakness then talking to the owners about any problems that they have had. You soon learn what works and what doesn't.

Good post Kiwi Kia - I hadn't thought of that in regard to a roof rack but I can see exactly what you mean - thanks.

Mike Harding

Hi Mike, If you have ever seen a video clip of vehicle crash testing and if the film is slowed down you can see large ripples run across the roof and back again like ripples on a pond. After the dust settles the roofline may show no permanant damage which is amazing after seeing how large the ripples were that ran back & forwards across during the crash. When flying watch how much the wings twist and bend, the normal flex at the wingtip on a B-52 is 27 feet! Flexing and bending (within design limits) is good - rigid snaps.

I have a patricular interest in what you are saying kiwi and the whole topic is quite amazing. Just to add a bit, most metals can go through elastic distortion or bending and will spring back to its original shape. If you stay within the lower elastic region you can bend the metal theoretically an infinate amount of times with no fatigue. I would say in a car crash the metal is close to the area where the metal becomes plastic but as you say, there is no real damage so perhaps not. Anyway the wings of the plane will be able to repeat this movement forever. I was once in a russian building in moscow 512m high. The top of the building which was around 20m higher than where I was moves 12m in wind!!!! and get this, the foundations were only 2m deep!!!!!!!!!! amazing.