On Wed, 02 May 2012 08:21:07 +0100, John Williamson wrote:

Lieutenant Scott wrote:
On Tue, 01 May 2012 18:41:22 +0100, John Williamson
wrote:

Lieutenant Scott wrote:
On Mon, 30 Apr 2012 23:45:59 +0100, Davey wrote:

On Mon, 30 Apr 2012 21:44:06 +0100
"Lieutenant Scott" wrote:



Remind me not to buy a car from you.

You seem to be under the mistaken idea that a car can't pull something
that hard. Think how tough a towbar and attachments has to be to pull a
caravan safely.

Not all that strong, as you're pulling a rolling load at either moderate
acceleration or at a steady speed. Back of envelope says a maximum of
half a ton total, summing the horizontal and vertical components.

What about when you put your foot to the floor while towing? You've
still got the full power of the engine pulling on the towbar. I suppose
I was adding momentum of the car too though, but then again there will
be some safety margins I can make use of.

Work out the torque at the driving wheels, which will let you work out
the acceleration, then compare that with the force required to
decelerate the mass of the car at about ten times that accleration. For
most cars, maximum acceleration is well under 1G, while the deceleration
when you're snatching a stump is at least 5G. The safety margins are on
the order of 100%, not 500%.

Well the tow bar is still on the car.

A steady pull of that magnitude is fine. Pulling out a tree stump is a
shock load which is well in excess of what the towbar and its fixings
are designed to take. I'll try it with a Land Rover with a good chassis,
but I'll use a kinetic energy recovery rope to do it. The clue here is
that you managed to snap a towrope and a chain, which says that the peak
loads were way above the design limits of the car and towbar.

No, it says they were above the design limits of the chain, which is a
lot thinner than the towbar and fixings.

Then you must be driving a tank. The towbars on most cars are fastened
to metal which is less than 1mm thick. Even my Land Rover has a chassis
which is less than 3mm thick at the point of attachment, and that's
reinforced for kinetic energy recovery, which is a posh name for doing
to bogged down vehicles what you were doing to trees.

I'm thinking of the steel tubes which run from the towbar itself to the chassis, they're pretty thick.

I can't believe those are fastened to metal 1mm thick, that would bend with the weight of the towbar, and definitely if you for example stood on the towbar, which simply doesn't happen.

Luckily, I live somewhere your car will never be sold.

Are you sure? I sold a Honda CRV to a guy in London.

Still safe. I left London a decade ago. London's also big enough that
you can always find a fool who'll buy anything you want to sell. ;-)

It had LPG conversion. Don't. Petrol engines were not designed to use LPG, and shouldn't be made to do so.

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