>> 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.

Hmm, interesting. I wouldn't have expected that to work.

> Usually when you buy a pair of those ramps they will be marked as 
> supporting a certain load.

Sure. I just meant that they probably design them to easily support more 
weight than any common car that somebody might try to put on them.

> 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.

Isn't the worst-case when you drive the car onto the ramp and the 
suspension jiggles it up and down over one support 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 to me like the tire would usually sit between the two horizontal 
struts. One is directly over an upright, but the other is on the middle 
of the beam. (Obviously that isn't a problem or they'd have added 
another upright...)

>> 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.

A few of those struts seem to be angled. But most of them are just flat.

>> Just how strong is steel?
> 
> 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.

Jesus, that's strong! o_O

So... what the hell is the thickness of a tin can then? Those seem to 
deform pretty easily.

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