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Old 10th July 2013, 16:22   #1
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Default Evasive manoeuvres & Rollovers?

Suddenly people who bought or are going to buy their first compact SUVs seem a worried lot. After that Ford Ecosport toppling incident the people who were brashly boasting that they drive their SUVs at 140-160 kph have disappeared into the woodwork. It is a good thing that this incident received the publicity it has got. There is a lesson for all of us on how to drive a SUV, especially those of us who have upgraded from a hatch or small sedan.

However, is there a way to calculate at what horizontal tilt and speed a SUV will topple over?

If we can work that out for our cars, we would drive safe and also enjoy driving? Let's hope there is simple answer
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Old 10th July 2013, 16:53   #2
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Default re: Evasive manoeuvres & Rollovers?

Sir,
It is not the horizontal tilt of the road which leads to a car toppling over. A combination of high speeds and a sudden pull of the steering can cause any vehicle to topple over. More so if the road is not even or has some obstruction which causes one set of wheels to lift off the road.

SUVs are more likely to topple under these conditions because of the raised center of gravity when compared to lower slung cars.

EDIT:
That said, there is a tilt test usually used to test the stability of double decker buses, in the UK.
Wiki link: http://en.wikipedia.org/wiki/Tilt_te...le_safety_test)

Last edited by EagleEye : 10th July 2013 at 16:57.
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Old 10th July 2013, 17:19   #3
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Default re: Evasive manoeuvres & Rollovers?

Quote:
Originally Posted by EagleEye View Post
Sir,
It is not the horizontal tilt of the road which leads to a car toppling over.
Wiki link: http://en.wikipedia.org/wiki/Tilt_te...le_safety_test)
Thanks EagleEye, I am well aware that it has nothing to do with the tilt of the road. However, my question was about how to calculate the maximum tilt that an SUV will take before actually toppling sideways.

SUVs have a high center of gravity and are generally heavier than a sedan of equal length and proportion. It means that unlike the sedan, with its lower clearance helping it grip the road better, the SUV will have all its weight thrown to the tyres on the outside of the curve.. Obviously this combination of height and weight can topple the car over in high speed cornering.

I want to know if there is SIMPLE way to calculate this 'tipping angle' for a SUV so we can be better drivers.

Just came across this link on 'Rollover' in Wikipedia

Last edited by woodcrawler : 10th July 2013 at 17:30. Reason: Adding a link
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Old 10th July 2013, 17:46   #4
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Default re: Evasive manoeuvres & Rollovers?

Quote:
Originally Posted by woodcrawler View Post
Thanks EagleEye, I am well aware that it has nothing to do with the tilt of the road. However, my question was about how to calculate the maximum tilt that an SUV will take before actually toppling sideways.

SUVs have a high center of gravity and are generally heavier than a sedan of equal length and proportion. It means that unlike the sedan, with its lower clearance helping it grip the road better, the SUV will have all its weight thrown to the tyres on the outside of the curve.. Obviously this combination of height and weight can topple the car over in high speed cornering.

I want to know if there is SIMPLE way to calculate this 'tipping angle' for a SUV so we can be better drivers.

Just came across this link on 'Rollover' in Wikipedia
First of all, there is no easy way to calculate the tipping angle of you car as such. It would depend on your car's weight distribution, speed, road curvature, road banking angle if any and coefficient of friction between the car's tyres and the road. A free body diagram of the centrifugal forces, gravitational force and frictional force will give you the answers you want. Simply speaking, the sum of moments due to "centrifugal force and frictional force" should be less that the sum of moments due to the "gravitational force and normal force on the outside tires".

But this for a layman will be full of assumptions.

Secondly, this knowledge in no way will contribute to driving "safely". It might only increase your knowledge. It will not help in any practical situation except may be off roading.

When it comes to high speed driving, tilt angle, critical speed etc etc., will not matter. Driver being capable of giving the right steering correction (only in the final moments) matters most.

EDIT: Just to understand dynamics.
Evasive manoeuvres & Rollovers?-vahicle.jpg

Last edited by rangakishen : 10th July 2013 at 18:04.
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Old 10th July 2013, 18:04   #5
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Default re: Evasive manoeuvres & Rollovers?

so, the way you do this is this:

- Take the car to an open ground
- Get the jack, preferably two. Ideally, this should be from a lorry
- Keep jacking it up until the car tips over

Say "oops" and draw a line from the top of the jack to the inside edge of the tires. The angle that it forms with the ground is the tip over angle.

Wasnt meaning to be facetious but there is no way to actually measure this. The only advice is to be sensible on the road. Just because a car can do 150kph does not mean you should. Even hard braking (for that somnambulist cyclist or that dog chasing a bitch), under the right circumstances can tip you over. A friend of mine rolled his Santro because he had to get off the road in a hurry to avoid an oncoming lorry. The shoulder was about 4 inches lower & at his speed he just rolled.

So, be sensible.

Last edited by Technocrat : 11th July 2013 at 01:34. Reason: We do not allow any mention of Alcohol, next time you would be infracted. Thanks
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Old 10th July 2013, 18:44   #6
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Default re: Evasive manoeuvres & Rollovers?

@Woodcrawler - I am assuming that you are asking this only for academic interest and in actual driving scenarios it would not really help in any way.

If it could have been measured accurately i guess SUV manufacturers would have started advertising the product as having the highest topple angle just as they give the water wading capability in the list of features.
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Old 10th July 2013, 21:03   #7
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Default re: Evasive manoeuvres & Rollovers?

Quote:
Originally Posted by rangakishen View Post
First of all, there is no easy way to calculate the tipping angle of you car as such.....
But this for a layman will be full of assumptions.

Secondly, this knowledge in no way will contribute to driving "safely". It might only increase your knowledge. It will not help in any practical situation except may be off roading.

When it comes to high speed driving, tilt angle, critical speed etc etc., will not matter. Driver being capable of giving the right steering correction (only in the final moments) matters most.

EDIT: Just to understand dynamics.
Attachment 1108746
Quote:
Originally Posted by amitwlele View Post
@Woodcrawler - I am assuming that you are asking this only for academic interest and in actual driving scenarios it would not really help in any way.
@ Rangakishen: I asked this question here because I own a Renault Duster and I got it because I could do a little 'safe' off-roading. I had a Fiat Punto and my trips to wild places were curtailed by my car's inability to take on the rough roads. There are a couple of groups in FB that have the Duster owners / fans discussing issues. I have seen there a few members boasting about the speeds at which they drove their Dusters (triple digit speeds )

When a thread was posted about the Ecosport toppling on a test drive I was concerned. Personally, I don't do anything more than a 100kph even on highways and take my corners in lower gears. However, I realized that there are people who have graduated from a small sedan or hatch into this 'compact SUV' segment because they are affordable, and use these cars very rashly.

@amitwlele: The whole intention, therefore, was to see if we can have some way to calculate the maximum speed the driver should use to tackle hard corners, instead of just throwing the car, themselves and other road users in danger.

After a little searching I did come up withthis site on School Physics

It gives a formula which will give the maximum speed at which a curve can be taken without toppling over.(I only wish there was a simpler formula though). If every driver who feels the adrenaline rush now & then can work out the speed for the vehicles they drive I guess we'll have safer roads

Last edited by Technocrat : 11th July 2013 at 01:13. Reason: Removed hish speeds, also avoid highlighting selctive parts of text in Bold. Thanks
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Old 10th July 2013, 21:21   #8
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Default re: Evasive manoeuvres & Rollovers?

^^^
Oversimplistic to the point of being useless.
What would happen if one were driving on say an ice lake (using normal tyres)?

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Old 10th July 2013, 21:45   #9
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Default re: Evasive manoeuvres & Rollovers?

Quote:
Originally Posted by Sutripta View Post
^^^
Oversimplistic to the point of being useless.
What would happen if one were driving on say an ice lake (using normal tyres)?
Perhaps, but that is because it is not so 'simple'. It is impossible to get the radius of every curve on the highway or the actual height of the center of gravity of the vehicle. However, if we can plug in approximate values we could throw up some numbers that we could use to make our driving habits more safer.

As for icy lakes, I'm not sure that was mentioned in the discussion or did I miss it? In any case I don't think anyone would attempt driving on one at 140 kmph
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Old 10th July 2013, 21:50   #10
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Default re: Evasive manoeuvres & Rollovers?

Quote:
Originally Posted by woodcrawler View Post
As for icy lakes, I'm not sure that was mentioned in the discussion or did I miss it? In any case I don't think anyone would attempt driving on one at 140 kmph
Hi,
Think over it!

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Old 10th July 2013, 22:25   #11
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Default re: Evasive manoeuvres & Rollovers?

I still dont get how will it help ? Should a driver get down, make his measurements, calculate the safe speed, and drive below that speed ?
Quote:
Originally Posted by woodcrawler View Post
@amitwlele: The whole intention, therefore, was to see if we can have some way to calculate the maximum speed the driver should use to tackle hard corners, instead of just throwing the car, themselves and other road users in danger.
A simpler way than all that research & calculations is to check the owner's manual - Many (if not all) mention the safe (max) speed at which to take corners. A sensible approach will be to go slower in case of adverse conditions.
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Old 10th July 2013, 23:24   #12
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Post re: Evasive manoeuvres & Rollovers?

There is a big problem with the word SUV - Sport Utility Vehicle.

The word SUV is/was coined and used mainly in USA then it was used by car manufacturers worldwide.

Let us analyse this word a little closely.

What does the word sport in SUV stand for?

Which sport are we talking about?

There are only two sports I know which involves cars.

1. Car racing

2. Offroading

Now you all of you would agree with me that UVs which are being promoted as SUVs are actually hazardous for both these purposes.

Cars like Duster (without 4x4) and EcoSport are actually worse at both situations.

People who drive their UVs like Ferraris thinking that they are good at racing have obviously misunderstood and being fooled by these marketing professionals, and some of them may in fact lose their lives.

People who take their SUVs (without a proper 4x4) to destinations which require a proper 4x4 system are also fools who have not understood the limitation of their SUV or whatever these contraptions should be ideally called.

Sorry for a long rant.

My 2 cents.

Thanks.
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Old 11th July 2013, 00:47   #13
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Default re: Evasive manoeuvres & Rollovers?

Well, I wouldn't know how to calculate it but I surely would guess that Duster is least likely to topple because of a very wide footprint and a low height. Infact, this combination of high GC yet low height is what also reduces oscillations and makes it comfortable and also less prone to toppling. I would imagine its chances are even lower than some hatches like Ritz, Wagon R, Estillo, etc. Ecosport on the other hand is taller and has less wide foot print so clearly looks to be more prone.
In reality, once you get used to your baby, by natural instinct you start knowing the precise speed down to the decimal to deaccelerate to while cornering on any surface, except say ice or oil slick that you may not be used to driving on.
I being used to a Honda City & Baleno (later sticks to the road like a lizard to a wall) was driving a friend's Safari Dicor once (for the 1st time) from Del to Udaipur. At one instance while at 110 kmph, the road took a natural gentle curve but the car "felt like" rolling over (not actually) and I had to slow down immediately. Again tact is required in such situations because sudden slowing will surely cause a roll over. Fortunately road was empty so I let the car stray across lanes to turn even more gently than the angle of the bend besides using engine braking.
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Old 11th July 2013, 03:19   #14
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Default re: Evasive manoeuvres & Rollovers?

Quote:
Originally Posted by woodcrawler View Post
However, is there a way to calculate at what horizontal tilt and speed a SUV will topple over?
American car magazines like Motor Trend, Road & Track, etc., used to test a car's "Lateral Acceleration", and the figures were calculated in "g" values. Generally a car with a higher "g" value could corner better, and hence offered better stability through turns. A high C of G vehicle like an SUV usually returned low "g" values.

Indian magazines don't do such useful testing unfortunately. But if you understand the principle, and get an open road which can be used as a skidpad, one can test for oneself their car's limit's.

Try this for starters:

http://www.mrwaynesclass.com/circula...orner/home.htm

Cheers.
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Old 11th July 2013, 03:35   #15
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Default re: Evasive manoeuvres & Rollovers?

I think the moose test is more appropriate to this situation.

moose test or elk testis performed to determine how well a certain vehicle evades a suddenly appearing obstacle

http://en.wikipedia.org/wiki/Moose_test

See one of the many videos here (A duster is shown towards the end)

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