axel_knutt wrote:drossall wrote:Brucey wrote:If your bike weighs ~10kg then it has to see an acceleration of ~10G for the load on the rim to exceed 100kg. 100kg is the approximate load in a single spoke, so the load on the rim in this case is not wildly dissimilar to that seen when a single spoke breaks. 10G is quite a lot; if sustained then most people black out, but it is not inconceivable that bumps in the line might generate loads of this kind despite the suspension in the carriage.
Really? Very small movements of course, but it's quite hard to see such forces being exerted and passengers not at least feeling ill.
I used Def Stan 07-55 Pt2 for vibration testing, the severity specified for equipment used in wheeled vehicles was 1.5g, (10Hz - 150Hz). For equipment used in tanks (which are subject to enormous amounts of vibration caused by track patter) the severity was still only 4g. I saw a helicopter life raft being tested at 6g, and the din was deafening, it was loud even in the next lab with the door shut.
I was thinking of a single impact such as a bad rail joint or points, coinciding with a wallow such that the suspension in the carriage was already nearly bottomed out. The result could be the bogie slamming into the bottom of the sprung part of the carriage giving a single hard impact (think running through a pothole in the car). Passengers are sat on their own suspension (seat springs plus gluteus maximus) so would not feel the full benefit in the same way.
My point was that such impacts are not inconceivable but they are not exactly likely either. There certainly shouldn't be continuous vibration of that type. If such impacts did occur, a single overload event might be enough to do whatever is going to be done to the bike.
If you bike weighs 20kg and is hung up by the front wheel, a 10G event could exceed the normal design loads on the fork.
If the bike is hung up by someone clumsy and the mountings are rigid enough, there could be an impact that is harsher than you might expect; just dropping the bike one inch onto the hook might exceed 10G depending on how stiff the parts are that take the impact.
Note also that there might be lateral accelerations; these are usually small in railway wagons but occasionally the buffers see a bigger load than normal and this may jolt the bikes too.
When bikes are hung up side by side, there is always a chance that the pedals will clash and the load of both bikes may be seen mostly on one hook.
Most of these issues could be sidestepped simply by making the hooks slightly springy rather than rigid in tension. I don't know that any are likely to be like that though.
cheers
