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Old 1st August 2006, 22:15   #1
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Default Stability: A height to width issue

Friends:

I had some thoughts about dynamic stability of various cars that we usually consider.

First, most cars have similar density: mass per unit volume (integrated over the entire volume).
This is dictated by the gauge of sheet metal, glass, upholstery and contribution of heavy metal: engine, gearbox and axles.

Then suspension-type has an impact on stability,
however this impact is small compared to that of the stance of the car:
its aspect-ratio of height to width!

This becomes a strong figure of merit, while considering its on-road agility,
its susceptibility to being blown off-track in a crosswind,
as also its liability to topple during ferocious cornering.

That said, here are the height-to-width aspect ratios of some known models.
A caveat: Misled by marketing hype, some of these hard numbers may shock some of us.



Hope Maruti's new Zen won't disappoint by defecting to the tall-boy brigade!

Ram

Last edited by Ram : 1st August 2006 at 22:18.
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Old 1st August 2006, 22:39   #2
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Looks like this is relatively new list coz last time I had seen the Indian car list I saw some merc model on the top followed by OHC...and the rest.

Last edited by Rtech : 2nd August 2006 at 23:02.
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Old 2nd August 2006, 00:19   #3
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HHmm .. Pretty weird .. Just off driving a ford ikon D a few minutes back and it certainly did seem to be heeding to the chubby character wonder how it got up in the squat categ ??

Having owned a zen prior to the baleno , pretty shocked to see the zen being rated under chubby .. It does feel certainly as low if not lower than the baleno .. That said my observations neednt necessarily be wrt to the height to width ratio but the seating position in general i suppose ..

Also having driven most of the cars under the squat categ pretty extensively , must say that i have experienced levitation only on my baleno or is that i havent pushed the other vehicles that hard ??
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Old 2nd August 2006, 01:20   #4
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See, track to height ratio is just a dimensional indication of it's proportion and does not necessarily equate to better/worse handling.

Whats important here is center of gravity. A tall car, designed to hold 70% of it's weight low down, will handle better than a sporty looking car, which is top heavy.

This is a good read, but not something i'd take seriously. If all these cars were to be tested, they wouldn't end up in the same order, as far as handling and stability goes.

Shan2nu
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Old 2nd August 2006, 02:52   #5
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Well after the Ford Explorer rollover saga, the US-DOT is using this ratio as a rough measurement of roll-stability. Dont remember what the cut off is.

First vehicle to fail it in India will be the Gypsy.
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Old 2nd August 2006, 03:25   #6
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No, I think it will be the omni. Top gear hamster rolled UK version of omni while trying to do a scandanavian flick(why would he do that in a RWD is anybody's guess) while trying to outrun the Stig.
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Old 2nd August 2006, 04:11   #7
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Track to height ratio and centre of gravity are the fundamental requisite for a great handler...having said that, there are loads of other factors that either enhance or diminish a cars handling...namely wheelbase, weight distribution, suspension system, tyre angle selection etc

So, as Shan2nu mentioned "dimensional indication of it's proportion does not necessarily equate to better/worse handling".
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Old 2nd August 2006, 06:31   #8
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Quote:
Originally Posted by The Wolf
Looks like this is relatively new list coz last time I had seen the Indian car list I saw some merc model on the top followed by OHC...and the rest.
The Old Honda City has the exact same length, width, height and wheelbase as the Maruti Baleno. It's almost as if both cars were made to meet the same spec.
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Old 2nd August 2006, 08:02   #9
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Quote:
Originally Posted by Shan2nu
See, track to height ratio is just a dimensional indication of it's proportion and does not necessarily equate to better/worse handling.
You may be right if the roof and top half of the tall car is not made of steel and glass but of styrofoam (thermocole) instead. But which one is?

Quote:
Originally Posted by Shan2nu
Whats important here is center of gravity. A tall car, designed to hold 70% of it's weight low down, will handle better than a sporty looking car, which is top heavy.
Didn't I anticipate that this perspective would be proposed? Of course, that is why it was important to clarify:
"most cars have similar mass per unit volume (integrated over the entire volume). Most if not all cars are made of nearly identical gauge of sheet metal, identical density of glass, upholstery and contribution of heavy metal: engine, gearbox and axles."

As far as I know, no vehicle with heavy-metal on its roof to make it top heavy, would be called "sporty looking". A crane or earthmover, maybe! Not a passenger car.

Most tallboys are meant to be used as kei-jido-shas and rick-shas, convenience vehicles to fetch the grocery in bumper-to-bumper downtown areas.

Are they top scorers in wind-tunnel aerodynamics?
No sir, on the contrary, they have slab sides that catch the wind like a sailboat.
And their fuel-economy motivated light weight plays the devil on the highway.
A strong gust of crosswind or overtaking Volvo coach, rocks and nudges them off course.

The only modicum of respectability comes quite misleadingly, from their purchase price-point in our country.

On the other hand, it is the squat low-slung cars that inspire confidence at speeds above 75 km/hr.

Quote:
Originally Posted by Shan2nu
If all these cars were to be tested, they wouldn't end up in the same order, as far as handling and stability goes.
Show me one tallboy that would test better than the rare squat low-slung car.
I will show you scores of squat low-slung cars that would worst the tallboy.

We don't have any regulatory body with the backbone to test all our Far East tall boys and outlaw the sale of those that fail. And won't there be pressure to skew or hush-up results to protect the vendors' investments?

At this time, the (success/failure) performance of our cars in mature developed world markets can be one good metric to help us identify the jewels from the lemons in our midst.
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Old 2nd August 2006, 10:36   #10
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Handling isn't about track to height ratio. This is just a fraction of what contributes to it.

The Innova for example is a taller car but still handles well bcos of it's relatively stiffer suspension. Planning on getting it for the next track day, lets see how it does there.

If we go by your list, the Mitsubishi Lancer should be one of the worst handling car in it's class bcoz it comes below the OHC, Baleno and Ford Ikon but handling tests by Overdrive have shown diff results.

The Octavia does better than the Baleno in cornering speeds but your list says something else.

Touring cars usually corner at 1.7 Gs where as a low slung Mclaren F1 or Ferrari Enzo will give out at 1.00-1.20 Gs.

Making a car as low, wide and long as a an F1 car wont make it corner at 3Gs. It has to be designed like an F1 car in every aspect.

I ain't sayng this doesn't help but you can't completely rely on it. It may or maynot work.

Shan2nu

Last edited by Shan2nu : 2nd August 2006 at 10:37.
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Old 2nd August 2006, 10:38   #11
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Quote:
Show me one tallboy that would test better than the rare squat low-slung car
The Ford S-Max? Its a MPV and on hard cornering it doesnot roll over.
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Old 2nd August 2006, 12:12   #12
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Quote:
Originally Posted by Mp421b
The Ford S-Max? Its a MPV and on hard cornering it doesnot roll over.
So, because it didn't roll over like its other MPV brethren, does it become a expressway cruiser like the Lancers, Accords, Camrys and Octavias?
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Old 2nd August 2006, 12:19   #13
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Quote:
We don't have any regulatory body with the backbone to test all our Far East tall boys and outlaw the sale of those that fail. And won't there be pressure to skew or hush-up results to protect the vendors' investments?
All these tall boys have been on sale in other developed markets for years now. Surely they have been tested and approved by competent authorities over there?
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Old 2nd August 2006, 12:49   #14
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Quote:
Originally Posted by Rtech
All these tall boys have been on sale in other developed markets for years now. Surely they have been tested and approved by competent authorities over there?
That hits the nail on the head. Exactly what I had in mind too. To allege that tall boys like Santro are unsafe at speeds in excess of 75 kmph is simply not credible. Maybe Ram was referring to *cornering* at speeds in excess of 75 kmph? Even then my own experience with the Santro firmly refutes that contention.

It is true that tall boys may require more steering inputs to keep them on course when they are at high speeds (130+ kmph?) say, in strong cross winds. But then they are also highly responsive to steering inputs precisely because they are small and light -- so it just boils down to getting used to the feel of these tall boys. Of course it is nobody's case that tall boys are safer than sedans. But to go to the other extreme and allege that they have to be taken off the roads will not cut any ice with millions of users both in India and abroad -- not to mention top car companies like Hyundai and Suzuki. At the very least Ram has to back up his allegations with hard statistics showing that tall boys are too unsafe to be driven on Indian highways.

And I don't think that the Santro, at least, is as top-heavy as some SUV's like Scorpio. I think these SUV's probably have much higher ground clearance and so the resulting higher CG makes them more prone to rolling over, as compared to Santro, even if Ram's stated criterion of height to width ratio is satisfactory (I don't know if it is).
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Old 2nd August 2006, 13:20   #15
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Good work Ram!!!

Lets not take it as a Bible. This is definitely a good reference for a rookie.

As many pointed out here, there are exceptions, but that doesn't demerit the list.

I have one disagreement-The Lancer. Lancer is much wider than Ikon and has almost the same hight. The how came it falls below Ikon?

Last edited by WhiteKnight : 2nd August 2006 at 13:25.
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