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Old 11th July 2013, 19:43   #46
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Default re: Evasive manoeuvres & Rollovers?

As a somewhat well-informed car owner / driver with 20 odd years of experience, my position on car safety is : the more there is, the better it is.

I just googled : measure of propensity to roll over

The first link belongs to NHTSA = http://www.nhtsa.gov/Research/Vehicl...ver+Propensity

A research paper dated Aug 2004 on the website is available at the following link "A Demonstration of the Dynamic Tests Developed for NHTSA’s NCAP Rollover Rating System - Phase VIII of NHTSA’s Light Vehicle RolloverResearch Program "

The Executive Summary (starts Page 14 of 120 of the pdf) is in fairly easy to understand language / terminology, how testing is done and what the conclusions are.

Page 55 of 120 of the pdf mentions that they measure the propensity to roll over, as the speed attained to safely go through a defined test course (double lane change), without incurring wheel lift of more than 2 inches.

One can also view what Consumer Reports has to say on this subject at http://www.consumerreports.org/cro/2...-101/index.htm ... the relevant section is reproduced below in toto ...

The National Highway Traffic Safety Administration (NHTSA) conducts on-road dynamic rollover tests on most new SUVs, pickups, and minivans. The tests score rollover propensity in part by putting vehicles through a handling maneuver called a fishhook, a quick left-right turn, at increasing speeds from 35 to 50 mph. This simulates a driver overcorrecting the vehicle's steering, something that can happen in an emergency.

If the vehicle lifts two wheels off the ground it's considered a "tip-up" and testing stops. If the vehicle slides out or gets through the test without incident at 50 mph, it passes.

Before 2004, NHTSA rated rollover propensity with a static (non-moving) measurement of a vehicle's shape and weight distribution. Called the Static Stability Factor (SSF), it's derived from a formula that compares a vehicle's track width with its center of gravity height. But starting with 2004 models, NHTSA added the dynamic (vehicle in motion) test, and the agency now uses those results to augment its rollover ratings.

NHTSA has compiled rollover ratings for scores of vehicles, including separate ratings for two- and four-wheel drive versions of SUVs. So far, no car or minivan has tipped up. In fact, NHTSA conducts on-road rollover testing on only two sedans per year and assigns star ratings to cars based on their SSF alone, as it did with 2003 and earlier models.

The scores. NHTSA combines the SSF and dynamic test to assign a rollover-resistance score of one to five stars. Five stars represents rollover likelihood in a single-vehicle crash at 10 percent or less; one star predicts a rollover likelihood of 40 percent or more. The SSFs underlying the star ratings vary from about 1.0 to 1.5. (The higher that number, the better.) SUVs usually measure out at 1.0 to 1.3, and cars normally fall in the range of 1.3 to 1.5.

"Our analysis indicates that the two tests together correlate with what we expect in the real world about 90 percent of the time," says NHTSA spokesman Rae Tyson.

What the results mean. Many SUVs have tipped up in NHTSA's testing—understandable since the dynamic test is designed to provoke a tip-up if a steering maneuver alone can produce one. What is surprising is that a tip-up doesn't affect the star rating much. That's because the government's rollover ratings give much more weight to the static measurement than to the on-road test. NHTSA's rationale for this is that the dynamic test looks for an untripped rollover tendency, which NHTSA believes are rare in real life.

"We take the position that if a vehicle can tip up in a steering maneuver, without impacting anything else first, then that's a good reason to look for a less tip-prone alternative," says David Champion, director of auto testing for Consumer Reports.

"Even supposing that the ratings are good at predicting rollover propensity, you really need to go beyond the stars," says Champion. "There's a big range between the best and worst within each star category. CU will not recommend any vehicle that tips onto two wheels in this test."

NHTSA's rollover ratings can be found at www.safercar.gov. For specific information about a vehicle's star rating, click on "Search 5-Star Safety Ratings," then select the vehicle class, such as SUV, then its year, then the make and model. Scroll down to the heading Rollover, and a chart there will tell you whether the vehicle tipped (under Dynamic Test Result), and also its likelihood of rollover expressed as an exact percentage rather than a star.

You can also see lists of all tested vehicles within a class (passenger car, SUV, etc.) starting with the www.safercar.gov home page, clicking on "Search 5-Star Safety Ratings" then selecting just the class, or class and model year.
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Old 11th July 2013, 20:02   #47
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Default re: Evasive manoeuvres & Rollovers?

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Originally Posted by phamilyman View Post
GThang,

It is a natural progression for the thread.


Please do share the 'high school basic physics' that would be less interesting but more accurate in its calculation - its an open thread, we can change the course as long as we can answer the basic question with the best information possible.
Progression means moving forward, right? Or is any direction considered progression?

Please refer post #14.

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Originally Posted by Samurai View Post
I just used a wrong word, I only meant dangerous testing. I deeply apologize of the wrong usage, I am no automotive professional to have known better.
Destructive testing is not limited to automotives, and is usually done in all kinds of manufacturing. Probably not so much in IT/software.

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Originally Posted by DerAlte View Post
Print Media pays its' reviewers for writing, which is their actual profession, not driving.
Interesting. So, a Road test Editor is nothing more than an editor? Wonder what Clarkson would have to say about that.
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Originally Posted by DerAlte View Post
There are very few 'print media' in the world (2-3) whose writers have the ability to drive to conduct tests the proper way. Done the proper way, the testing is done by engineers who have been trained in all aspects of driving including safety, and they are not 'professional drivers' by any flight of imagination.
Car and Driver, Motor Trend, Road & Track, Top Gear, and even some smaller publications give out lateral acceleration figures in their road test. Obviously you have not fully understood the skidpad test if you feel it requires highly trained engineers to do a basic arithmetic calculation.
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Originally Posted by DerAlte View Post
It is difficult to understand why, after admitting that your point is OT, you are persisting in trying to make your p-o-v understood with the same flawed methodology you are accusing others of.
Please clarify what you mean by flawed methodology I used? It is difficult for me to understand as well.

Cheers.
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Old 11th July 2013, 21:20   #48
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Default re: Evasive manoeuvres & Rollovers?

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I just used a wrong word, I only meant dangerous testing. I deeply apologize of the wrong usage, I am no automotive professional to have known better.
The used word "destructive" has caused all this debate. Although the term as such is incorrect, the intention is well understood and correct. We all know you are not an Automotive / Mechanical guy, so that slip of tongue is understandable. Good that you accepted it too !

Coming back to topic, lots of things being told about lateral acceleration, what is lateral acceleration used for, how do we decipher useful information from these values ? Only numbers won't make much sense.

BTW, talking about professional vs non professional testing, do you guys know who does the emission cycle (e.g. FTP75, NEDC/EUDC, BS-IV) tests at the certification centers? In most cases, ordinary drivers, with no formal education, not even enthusiasts. But they know emission cycle testing, and know it very well.

Spike
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Old 11th July 2013, 21:29   #49
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This thread is becoming a bit ridiculous. Refer to the thread starters question. Would first time suv buyers benefit from such an argument or from practical advice on how to modify one's driving style when moving to a suv?
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Old 12th July 2013, 04:27   #50
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Default re: Evasive manoeuvres & Rollovers?

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Originally Posted by gthang View Post
Progression means moving forward, right? Or is any direction considered progression?

Please refer post #14.
Well you may disagree, but initially I was more in favor of the elk test / safercar.gov stats - I quite like the rollover %, but your answer pointed me to something much more fun:
http://bradthx.blogspot.com/2011/02/...ion-meter.html
http://makezine.com/2008/04/28/how-t...your-own-gfor/
or even the apps such as :
https://play.google.com/store/apps/d...=search_result
and yes - thanks for the disagreement. Helped

Quote:
Originally Posted by SPIKE ARRESTOR View Post
The used word "destructive" has caused all this debate. Although the term as such is incorrect, the intention is well understood and correct.
+1

@Nilanjan: Point - but I think the key takeaway for me is being able to reference stuff like the rollover %, as well as the possibility using apps that convert our real life intuitive experience into usable g-numbers. You can then calibrate your experience by looking at the g-readings during a drive with what you were able to observe as a driver, and develop either a greater confidence on your vehicle's abilities (push it to the limits!), or back off Though of course in real life, with so many hazards on Indian roads - in the end one would keep the vehicle within a very safe range, not push it constantly to the limits.

Last edited by phamilyman : 12th July 2013 at 04:29.
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Old 12th July 2013, 08:04   #51
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Default re: Evasive manoeuvres & Rollovers?

I don't see where this point of "Many Indian users buy SUVs for the wrong reasons" is coming from. Whatever their reasons, they are selecting a product, and if they are satisfied with the product then that should be it.

Like the mythical Punjab Dhaba owners using washing machines for lassi making, it is none of our business.

I am interested in the technical parameters (especially having experienced a topple once - although aided by a truck pushing me over).

Regarding Sutripta's question about frozen lake, I understand he is referring to the lower coefficient of friction. But the broader question is would the topple angle be different for all kinds of surfaces? Mud / slush / sand / gravel / grass?

And suppose we compute the maximum permissible lateral acceleration on our vehicles -- would undulations on the road or small stones throw all calculations out of the window?

Last edited by chinkara : 12th July 2013 at 08:11.
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Old 12th July 2013, 08:10   #52
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Originally Posted by nilanjanray View Post
This thread is becoming a bit ridiculous. Refer to the thread starters question. Would first time suv buyers benefit from such an argument or from practical advice on how to modify one's driving style when moving to a suv?
What a nice eye-opener post just when things were getting cloudy with smoke and volcanic ash!
I totally agree.
Most users of different types of vehicles really do not stop to think before mashing their clod-hopping number tens on the accelerator pedal.
I think that a sound set of tips from experts on how to handle different situations in an SUV or car, would be far more valuable to the users of this forum rather than these involved, esoteric debates which sometimes look like they are beginning to verge on the wannabe quasi-erudite and totally impractical side.
Nilanjan, you might want to lead off with some tips, to which the many experienced SUV users out there can add!

Last edited by shankar.balan : 12th July 2013 at 08:19.
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Old 12th July 2013, 08:44   #53
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Default re: Evasive manoeuvres & Rollovers?

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Originally Posted by phamilyman View Post
Well you may disagree, but initially I was more in favor of the elk test / safercar.gov stats - I quite like the rollover %, but your answer pointed me to something much more fun:


You can then calibrate your experience by looking at the g-readings during a drive with what you were able to observe as a driver, and develop either a greater confidence on your vehicle's abilities (push it to the limits!), or back off Though of course in real life, with so many hazards on Indian roads - in the end one would keep the vehicle within a very safe range, not push it constantly to the limits.
Glad you are making progress

Any time you turn your steering wheel, i.e., go from straight line motion to circular motion, lateral acceleration contributes to a very important dynamic force.

Knowing your car's "g" limit and, yeah, being able to monitor it real time are great driving aids. You can run your own "Stability Control" algorithm in your head.

Some have said that more importantly than all calculations is a cool head to drive safe. But knowing the basic physics, and having an informed cool head helps even more.

Apologies if the thread seems ridiculous without youtube videos, but guess getting back to basics was not the reason you were browsing the Technical Stuff section of Team Bhp for.

Cheers.
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Old 12th July 2013, 10:40   #54
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Default re: Evasive manoeuvres & Rollovers?

I drive through a rather infamous Shiradi ghat every two weeks, sometimes more. In addition to the ghat, there are lots of twisting roads. Roughly, I drive about 350kms of twisty roads (Manipal-Sakleshpur) every month at the minimum, in a SUV. I also drive Jeeps with very questionable handling on the same roads. I do this in both dry season and very wet season. Therefore I have a layman's idea about how SUVs behave in quick turns or evasive maneuvers.

The Jeep experience is very useful because it makes you learn very quickly about SUVs and quick turns. My former CJ340 with rear CFLs had very soft suspension, even a regular twisty road at 40kmph would result in massive body roll.

Those of us who don't have the understanding of mechanical engineering, don't have the advantage of calculating all the dynamic forces at play. If we start worrying angles and g forces, we are really fooling ourselves. We can only observe behavior, and make use of it, and adapt to it. Therefore, I suggest practice, practice, practice... on twisty roads. You will soon know how fast you can turn at every kind of angles, in your SUV.
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Old 12th July 2013, 11:00   #55
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I drive through a rather infamous Shiradi ghat every two weeks, sometimes more. In addition to the ghat, there are lots of twisting roads. Roughly, I drive about 350kms of twisty roads (Manipal-Sakleshpur) every month at the minimum, in a SUV. I also drive Jeeps with very questionable handling on the same roads. I do this in both dry season and very wet season. Therefore I have a layman's idea about how SUVs behave in quick turns or evasive maneuvers.

The Jeep experience is very useful because it makes you learn very quickly about SUVs and quick turns. My former CJ340 with rear CFLs had very soft suspension, even a regular twisty road at 40kmph would result in massive body roll.

Those of us who don't have the understanding of mechanical engineering, don't have the advantage of calculating all the dynamic forces at play. If we start worrying angles and g forces, we are really fooling ourselves. We can only observe behavior, and make use of it, and adapt to it. Therefore, I suggest practice, practice, practice... on twisty roads. You will soon know how fast you can turn at every kind of angles, in your SUV.
I learned to drive a long while ago on an old CJ 500 jeep (amongst other vehicles like the Amby, a Massey Ferguson Tractor etc), in the Nilgiri hills.
That vehicle had a steering of jelly and a suspension of lead coupled with a gearshift of wool and brakes of cement.
If you turned the wheel, it would ponder a bit and then take about a week to fully understand, translate and execute the command. Same with the braking system. The value of engine braking, thus, was a hard lesson learned.

I also learned hence, a long long time ago, that ultimately one is not invincible when encased in bits of metal and plastic with not much other than some air-filled rubbery bits separating one from the hard ground.
With respect to all here, I would only venture to say that these SUV's and other vehicles will serve you well provided you know their limitations and treat them with care and respect while driving them accordingly as well.
One is not God and nor is one invincible...even the Great Achilles had his Heel...

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Old 12th July 2013, 11:33   #56
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Default re: Evasive manoeuvres & Rollovers?

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Originally Posted by Sutripta View Post
Hi,
Think over it!

Regards
Sutripta
Hope the weight of the car does not crack the ice on the lake...
But I did find this small article to give some pointers as to the max speed of a bobsled when it skids on the ice.

I remember having read that somewhere that the skid speed < rollover speed and both these speed limits don't depend on the mass.
Source: Mathworks.in
Quote:
Computing the Maximum Safe Velocity of a Bobsled on an Elevated Curve

Given an icy curve of radius R with elevation angle , we can compute the maximum safe (i.e., with no lateral skidding) velocity v of a bobsled entering this curve via .
In this demo, for purposes of simplicity we assume that there is no friction between the sled and the ice, and that the curve is banked at an angle of 30 degrees.

The figure above is a visual demonstration of forces acting on the bobsled as it enters an elevated curve of radius R. N is the normal force acting on the bobsled, is the gravitational force acting on the bobsled and is the reactive centrifugal force. For the bobsled to remain safely in the track while inside the curve, the reactive centrifugal force has to be equal to or less than the centripetal force exerted on the bobsled by the road.
The author has assumed no friction on an icy surface - this is a close approximation as friction is reduced due to a thin layer of water that forms owing to pressure on the ice surface.

However in case of extreme cold the coefficient of friction between tyre and ice can actually help.


For an understanding of possible coefficients of friction on ice, here's some information - this varies widely

Source: Hypertextbook.com
Quote:
Coefficients of Friction for Ice
Name:  coefficient of friction.png
Views: 796
Size:  44.3 KB

The average of the above coefficient of friction values gives us an experimental value of µk = 0.0168"
Finally here is a paper describing the physics of rollovers.
rollovers.pdf
Source : Physics of Automobile Rollovers, L. David Roper (http://arts.bev.net/roperldavid), roperld@vt.edu

Last edited by joybhowmik : 12th July 2013 at 11:40. Reason: Sentence construction corrected.
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Old 12th July 2013, 11:47   #57
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Frankly IMO there can be no theoretical explanation to this.

Potholes and bumps come in different shapes and sizes ! So one has to really sit with a calculator to determine the speed of approach and the other variables.
It all depends on how comfortable the Driver is at any given speed coupled with the drivers understanding of the limitations of the vehicle.

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Old 12th July 2013, 11:48   #58
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Here's another interesting read to calculate roll over angles:

http://www.jeepaholics.com/tech/cog/#_Toc535118719
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Old 12th July 2013, 12:16   #59
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Originally Posted by gthang View Post

Probably not so much in IT/software.
Destructive testing is used extensively in IT/Software too. Critical applications are put through destructive testing to establish reliability levels as are software products sold at a global level.

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Originally Posted by gthang View Post

Wonder what Clarkson would have to say about that.
When it comes to serious testing, Top Gear employs a professional driver going by the euphemism of Stig whose identity has been intentionally masked so that he does not take over part glory from Clarkson & Co.

Neither Clarkson nor his teammates undertake serious track testing of cars – this is left to the Stig. Clarkson does not portray himself to be a professional driver by any stretch of imagination either. He is a professional TV/ Print Media journalist whose gift of the gab works a lot more for him than his driving skills do.

Tiff Needell of Fifth Gear, on the other hand, is a TV / Print Media journalist who is also professional race / rally / Le Mans driver. Tiff was earlier with Top Gear.
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Old 12th July 2013, 13:12   #60
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Default re: Evasive manoeuvres & Rollovers?

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Originally Posted by NMS View Post
Frankly IMO there can be no theoretical explanation to this.

Potholes and bumps come in different shapes and sizes ! So one has to really sit with a calculator to determine the speed of approach and the other variables.
It all depends on how comfortable the Driver is at any given speed coupled with the drivers understanding of the limitations of the vehicle.
Well, theoretical explanation will be there. But what matters to SUV newbies is practical stuff.

There will be very very few who will be do justice to the numbers or mental calculations required. But since so many folks are buying SUVs, a scalable, easy to grasp approach is needed. An ordinary soldier doesn't need to understand the theories behind how a rifle fires, how much exact theoretical pressure to put on the trigger (unless he is creating a booby trap with that rifle using a string, say), detailed calculations regarding wind deflection etc. He just needs to grasp the basics and improve with practice. On the other hand a sniper has to do a deep dive.

All this technical discussion IMO is good for those snipers, not for the ordinary junta. Since this is a technical forum, perhaps it makes sense to split this thread into a technical discussion (where theory and calculations come into play) and a broader more practical thread. Or, if there is a way for the technical aspects to be distilled into simple easy to understand guidelines, then that would also be helpful.

Last edited by nilanjanray : 12th July 2013 at 13:17.
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