Can someone tell me what are the primary factors informing a vehicle's stability?
I am told that the Daihatsu Zebra Pick-up (aka Hi-Jet) is unstable:
(photo) tinyurl.com/ya2h2ze
whereas the Mitsubishi Colt L300 is not:
www.ktb.co.id/product_detail.php?kid=8&pid=43
What factors inform this? Engine location? Front or rear-wheel drive? Vehicle width/height/length? Wheel size? Wheelbase length? Wheel position? Roll bars?
I'm considering the Daihatsu Granmax (aka Hi-jet) the replacement of the Zebra
www.daihatsu.com/catalogue/granmax/html/pickup/
The front wheels have been moved forward, the vehicle is 28 cm longer, 11 cm wider, and 7 cm heigher. The wheelbase is also 57cm longer.
Could someone explain to me why the old Hi-jet (Zebra) is unstable, and whether the new one is likely to be?
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The first thing to look at is the ratio of the height of the centre of gravity to the track width.
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And how would you find the height of the centre of gravity?
Track width I've got as 1.345m front, 1.33m rear for the Daihatsu Zebra (not stable), 1.44/1.38m for the Mitsubishi Colt L300 (stable), and 1.46/1.44m for the Daihatsu Gran Max (unknown stability).
Vehicle heights are:
Zebra 1.825m
L300 1.845m
Gran Max 1.85m
Vehicle length:
Zebra 3.915m
L300 4.17m
Gran Max 4.195m
Load deck length:
Zebra: 2.35m
L300: 2.425m
Gran Max: 2.35m
Vehicle length MINUS load deck length. (approximate cab length)
Zebra 1.56m
L300 1.745m
Gran Max 1.845m
The vehicle when loaded would be stacked with heavy loudspeakers, generators, lighting equipment, etc.
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Hmm, never mind, I googled:
"The center of gravity height is calculated by weighing the car when level and then raising the car at least 10 inches at the rear and weighing the front again"
neat bit of physics
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The roll centre is key, the point about which the vehicle rolls, that is all to do with suspension design and configuration.
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Hence ordinary cars are inherently more stable than 4x4s
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I checked the suspension as well:
Zebra
Front: MacPherson Strut with Double Acting Telescopic Shock Absorber
Rear: Rigid Axle with Semi- Eliptic Leaf Spring & Double Acting Telescopic Shock Absorber
Colt 300
Front: Double wishbone, coil spring
Rear: Semi elliptic leaf spring
Hi-Max
Front: Macpherson struts with coil springs
Rear: Leaf springs
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The roll centre is key the point about which the vehicle rolls that is all to do with suspension design and configuration.
chedder, I would argue that roll centre is not that relevant to roll over, indeed it is possible to have the roll centre above the C of G. Mind you, if you did that you would have some pretty horrible side effects.
What matters is the hight of C of G above the ground and the track, assuming the C of G to be on the cenre line of the car, and the lateral accleration you can generate although you could complicate it with aerodynamic aids.
The lateral accelertion will be limit will be set by how well the tyres stick to the road unless of course you have tried to pass that limit and you hit a kerb going sideways. Then the question is will the car roll first or tear the supension off first.
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chedder I would argue that roll centre is not that relevant to roll over indeed it is possible to have the roll centre above the C of G. Mind you if you did that you would have some pretty horrible side effects. What matters is the hight of C of G above the ground and the track assuming the C of G to be on the cenre line of the car and>>
As NC indicated static roll centre tells you nothing, its like treating the car as a solid cuboid on a flat surface, how the roll centre moves as the car moves on its suspension is important however.
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"The center of gravity height is calculated by weighing the car when level and then raising the car at least 10 inches at the rear and weighing the front again"
So assuming that gives a different weight, then what do you do?
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This will keep you quiet for a couple of minutes! And it will do the calculation for you.
www.longacreracing.com/articles/art.asp?ARTID=22
And a comprehensive explanation.
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This will keep you quiet for a couple of minutes!
thanks :-)
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Then we spoil it all and put a human being in the drivers seat.
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>>So assuming that gives a different weight, then what do you do?
Oh, it definitely does give a different weight.
I pity anyone choosing to weigh in their gold jewellry in our local shopping centre - the sharp traders have set up their stand and their weighing scales on on a slope, and thus are under estimating the weight of anything offered to them.
I've not read the web site, but the method can't vary much - I use a very similar method to find the centre of gravity of instruments. Moment of inertia determination is a bit more tricky!
Roll centre - particularly for vehicles with double wishbone suspension moves all over the place, and its static value doesn't help much as soon as the vehicle begins to roll. Other suspensions, leaf springs, for example have a much more stable, and usefully high roll centre. For a tall vehicle, a leaf sprung live axle makes a lot of engineering sense.
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Roll centre - particularly for vehicles with double wishbone suspension moves all over the place and its static value doesn't help much as soon as the vehicle begins to roll.>>
The way the roll centre moves as the vehicle moves on its suspension has to be accounted for.
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Yes, the fairly obtuse point I was making is that determining the height of the c of g is quite a task - determining the height of the roll centre and how the roll centre moves is way beyond the capabilities of all but a very small number of facilities in the UK, i.e., academically correct, but not of any practical use.
I've had a quick read of the web site, and there's one change I would make. In order to get the most accurate value, assuming the track width is less than the wheelbase, and the wheels aren't too wide, it's probably better to do the measurement side to side rather than front to rear - for a given height change, you'll get a larger angle, and a larger change in weight.
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"I pity anyone choosing to weigh in their gold jewellry in our local shopping centre - the sharp traders have set up their stand and their weighing scales on on a slope, and thus are under estimating the weight of anything offered to them."
The trading standards 'weights and measures' inspector would be interested in that one. Don't scales for trade have to be fitted with a spirit level and levelled before use?
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who in their right mind would take gold to a street urchin
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I saw one of these 'send us your gold' companies advertised on daytime TV. Checked their website and the prices they were offering were about half the true value.
Shocking - that people are stupid to fall for it.
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