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Old 06-23-2010, 01:27 PM   #170
Josh69's Avatar
Joined: Dec 2007
Location: Euroland
Oddometer: 593
First off, since you were talking about hitting metal bridge beams and I was talking about hitting a pole - if you hit a hard object like these head-on, then the crash is probably not survivable.

Look at it this way: people in cars wrap themselves around poles or trees and with a metre of crumple zone in front of them plus airbags and they still get killed. 20 millimetres of foam padding, no matter how good it is, in a motorcycle jacket is not going to save you.

I'm also going to stop referring to 'energy' and refer to force. Energy absorption is hard to measure which is why the Euro test standard measures force transferred.

The Motoport Quad Armor from what I've read is about 20mm thick.
Case 1: 20mm thick steel plate. It is essentially completely rigid. Whatever you hit it with gets transferred direct to the other side.

Case 2: 20mm thick quilt full of duck feathers. Really soft and comfortable. However even minor impacts fully compress the feathers so it is ineffective as armor.

Case 3: 20mm Motoport armor or EU spec armor. Relatively stiff; takes a lot of force to fully compress it. This is the happy medium which reduces the force transmitted from one side of the motorcycle jacket to your body on the other side.

Wayne or whoever wrote the Motoport website does not appear to understand the physics of impacts. It does however look like Motoport have looked at a very large number of real crashes and even if they don't have much of an idea technically, they have seen what works and what doesnt.

Originally Posted by poonbean
That is quite helpful - you bring some clarity to Wayne's world. I'm just on my second set of CP clothing and really like it, but never quite bought into all of Wayne's descriptions. As a different kind of engineer and geologist, his descriptions did not make complete sense to me either.

Anyways - I do have a question from your discussion:

You initially say that "Steel is very stiff. If you want to transfer energy, using a lump of rigid steel to do it is a good way."

I think your comments on Wayne mix up the perspective. In this case, the test is using the moving steel to transfer kinetic energy to the armor to see how much energy is absorbed. However, when I'm moving and my kinetic energy hits sufficiently thick steel (a bridge girder comes to mind), instruments on the steel are unlikely to measure much, if any, transfer of my kinetic energy. What little kinetic energy that is absorbed occurs by subtle flexing, friction, heat, deformation, or if it is perfectly rigid, it is transfered to and absorbed by the ground at its attachments. The rest of the energy is, unfortunately, absorbed by the "weaker" item that hit it - the bike, me, and the quad4 armor. Obviously, the less energy the body is asked to absorb the better. If I were to hit a girder, clearly not enough of that energy from that impact would be abosrbed or transfered out of the impact by the girder and I and my quad4 armor would have to absorb the rest. Just like a hammer hitting the girder - the hammer bounces back and absorbs (along with the arm that swung it) much of the kinetic energy in that impact, and just a little kinetic energy is absorbed by the girder in heat or transfered to the ground.

Your steel statement seems to contradict your comment further down that says "The forces in a bad bike crash are so large that the armor needs to be reasonably stiff - or not feel soft to the touch - to absorb the impact."

So, which is it - does steel transfer or absorb?

It does seem to me that armor needs to find that balance between soft/flexible to absorb as much energy as possible while remaining somewhat stiff for durability and strong enough to spread (transfer) what it can't absorb over aa wide an area on the body as possible. All, of course, without sacrifcing comfort and good looks.
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