[Diy_efi] Hydrogen Powered Vehicle - SUV safer?

[Bevan Weiss]

This is the point that I'm worried about.
New Zealand is starting to get more SUV's on the roads too, all of them
decidely clean (ie no rectreational 4wd'ing).

They just aren't designed for round town driving.  If you've ever been
4wd'ing you know that the suspension is very 'bouncy'.  It's loose for a
reason, to allow all four wheels to support the vehicle when one of them is
at a much higher altidude than the other four, ie on uneven ground.  With a
normal car with low suspension travel and tight springs that wheel would
force another wheel off the ground.

Now the problem...
This loose suspension also means that SUV's aren't designed for sharp
corners, because of the large transferance of weight to a loosely sprung
wheel, this causes a diving of the chassis at that wheel and a larger
overturning moment.

Compounded with the fact that SUV's are naturally heavier, this means that
they are much easier to roll over than a normal street car.  People don't
seem to realise this and drive them just like normal cars.  Perhaps even
taking more dangerous risks than they normally would, simply because they're
up higher and feel safer.


Now, when they do get involved in an accident, they weigh more than most
cars out there, so more of their energy will be transferred to the other
car.  Momentum must be conserved.  If the SUV is twice as heavy as the other
car and both are going the same speed, then total momentum before (speed*2 -
speed*1) must be equal to afterwards (speed'*3).  This results in the final
speed being speed' = (speed*2 - speed*1)/3 = speed/3.
The SUV has lost 2/3 of it's speed.  Ie if it was going 60km/h, it's now
going 20km/h... A reduction of 40km/h.  Not very pleasant, but quite
survivable.
The other car is now going... 2/3*speed (so 40km/h) but it's doing that in
the reverse direction.
Ie it's had to change it's speed by 100km/h.  How many people do you think
survive driving into brick walls going 100km/h?  After all it's the same
100km/h deceleration required...

It's quite unfair for an SUV driver to place other drivers at increased risk
just because it makes them feel safer.

That's just with plain solid body dynamics.  It gets even worse for the
other car if you take into account deformable body dynamics and the varying
chassis heights of the vehicles.  The SUV will roll forwards crushing down
onto the front of the car whilst the rest of the SUV propels it up and over
the car.  This results in the whole front of the car being crushed down and
back.  It normally traps the drivers legs under the dash and/or crushes the
roof (just behind A pillar) into the front seat passengers heads.

What were the positives again??


Bevan



> i think that people buy SUV's because they can, and because 
> for them bigger is better. last time i was in US i have seen 
> a pickup in the deck of which i could have easily u-turned my 
> european hatchback. 
> unfortunalty the SUVmania happened in europe too, and even 
> Porsche now builts a SUV. enough said. It is common to see 
> skinny little guys using 2000kg of metal to carry around 
> their 50kg boney asses. 
> typical scenario in some european cities is to buy a SUV to 
> the wife so she can go shopping or collect the kids from 
> school. all the offroad these vehicles get is the occasional 
> curb-climbing. 
> 
> i think that in the majority of cases, the SUV is the 
> pinnacle of stupidity, an object without real purpose, apart 
> the vanity of the owner rant over :-)
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