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> Does that really work? I mean, can you really just say "oh, this thing has
> 4 wheels, so each one only takes 1/4th of the load"?
Well from experience most cars are pretty equal for left/right weight
distribution, and as I said worst case is probably 70% on the front wheels.
So yes, probably 35% of the total weight is the maximum on any single wheel.
> Also, something like a Prius is 3042 Kg (unloaded). I'm presuming they
> make these ramps with a damned wide margin for safety.
Usually when you buy a pair of those ramps they will be marked as supporting
a certain load. 2 ton per pair of ramps is common. If you go over that
then obviously there is a large risk they will break.
> But can you really do that? Can you really just say "there's 4 columns, so
> divide the load by 4"? Wouldn't it depend on the angle of the force being
> applied?
Of course, I was simplifying to get a rough estimate. In reality you would
have to take the worst case loading condition, which is probably with the
tyre directly on top of a single column.
> And what about the horizontal elements? They need to not bend at the
> points where they're unsupported as well.
You would obviously check for this if you were designing it, but I assume
this wouldn't happen as a tyre usually spreads out the load across an area.
The loading would be concentrated at the tops of the support columns as
these won't budge.
> Looks thinner tham 5mm to me - but then again, it isn't cylindrical...
Yes, something like an I beam or a hollow cylinder is a more efficient use
of the metal.
> Just how strong is steel?
It varies from about 250 - 750 MPa. That's the stress you need to apply to
it before it starts to deform plastically. As an example, my steel ruler
has a cross section of 1mm x 25mm, you'd need to pull on it with between
6-18 kN of force, that's the weight of a car.
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