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Old 14th February 2011, 11:18   #46
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Default Re: Emergency manouveur in my i20 diesel. Need to understand what happened

Thank you khoj and ph03n!x. Yeah, that torque over steer was that I was referring to.

For sagarpadaki and ph03n!x, it is a lesson well learnt, without much of damage. For us it is free education.
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Old 14th February 2011, 12:36   #47
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Default Re: Emergency manouveur in my i20 diesel. Need to understand what happened

Quote:
Originally Posted by khoj View Post
In a curve down shifting is the way to go when you feel the car beginning to go away from the intended trajectory. Braking in the middle of the curve is almost always disasterous. One should be done with all the brake inputs before one enters the curve. Once in, the Centripetal force that holds it in the curve does not like being disturbed. Downshifting is the way to go whether you need to slowdown or need to increase the speed to hold the trajectory of travel in curves that become tighter as you go further in to them.


@sagarpadaki

What happened in your case is that after the first input to the left the car's mass also followed to go left and when you fed in the second input it took time for the mass of the car to change its direction of travel from left to right. This made the car trip on itself as while the front wheels were pointing due right the car's mass was still travelling left. This made the car trip on itself and you felt that in the form of a lift of the rear tire (should have been the left rear). As you straightened up the mass had shifted due right and with the decrease in speed as the tires became stationary the mass read momentum continued to the right and that turned the car. Do let me know your final stationary position, as in facing away from the central median or towards it. Per my understanding it should be the latter.

The i20s long wheel base and the low C.O.G. saved the day for you as did the ABS and the braking components which in an ABS variant for a given car are far superior compared even to those in non ABS versions of the same model.

ESC would have helped here in avoiding this gap between the steering input and the mass(momentum) following. EBD would have helped definitely as it would have transferred more brake power to your two left wheels which were on the road and thereby had more friction/traction to work with. This would have given you a shorter straight line distance to halt than what an ABS only equipped vehicle would take.
i20 has ABS+EBD combo for the top end ASTA model(which we have).Even i am wondering why the EBD didnt work or maybe i didnt notice it.Yea the lower GC was also one of the factor.Had it been a sumo or scorpio it would have rolled over.

Yes,at one instant i was facing at the median and heading into it.Dont know if it as my final position or not.But i made rapid corrections once again to get back into proper direction.


Quote:
Originally Posted by ph03n!x View Post
Like Khoj said, cutting down a gear (or two in my case) helped me reduce speeds and gain traction. It is probably the braking on the sandy banks of the road (combined with my foolishness of attempting the curve in 5th @ 70 KMPH) that set me off course - the car refusing to turn while am in the curve. And the Getz has this torque over-steer that would have kicked in when I cut gears down, making me go towards the median.

I also recently learned that the usual nitrogen pump that I fill my tires is not calibrated, and fills about 3 PSI higher - combine that with the almost worn out S.Drive (~37k KM), and its recipe for disaster!
phoenix wont the down shifting cause wheel-spin to occur especially in the high torque engines like ours?
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Old 14th February 2011, 14:06   #48
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Default Re: Emergency manouveur in my i20 diesel. Need to understand what happened

EBD just applies more force to the wheels(s) that are not locking, i.e. when ABS is acting, EBD allows higher pressure to build up at the brake modulator, increasing braking effectiveness - as long as those wheels are not locking up. Since EBD does not give a direct feedback to the foot, it is rather difficult to figure out whether it is acting or not.

Also, EBD expects the driver to slam down on the brake pedal to be effective. Testing on dry tarmac, one can make out from braking distance, differentiating between gradual hard press of the brake and slamming. If wheel lock occurs on any wheel, it will allow ABS to take precedence.

Quote:
Originally Posted by ph03n!x View Post
... the car refusing to turn while am in the curve. And the Getz has this torque over-steer ...
Isn't that under-steer?

Last edited by DerAlte : 14th February 2011 at 14:10.
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Old 14th February 2011, 15:52   #49
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Default Re: Emergency manouveur in my i20 diesel. Need to understand what happened

First of all, On highways , stick to the middle lane , neither the farthest one away from the central divider, nor the one beside the center divider.Its one those points clearly mentioned in the Book you get for procuring driving Licence.

Consider this incident one had years ago:--One had a freak incident ,in which an attempt was made from my side to bring the non-turbo indica--which one was driving 80+ kmph-- under control so that it wouldnt accidently hit traffic on the right side.Mind you, One was on the left extremety, driving over sand mixed with whats used in construction material and the right side of mine was a well laid 3 lane road with traffic moving on it slowly, which i choose to evade simply because my car was overheating--Radiator Fan not working-- one was in a hurry to reach city and avoid a breakdown in the outskirts--between the city and highway .What one didnt realise while driving on the sand mixed surface was that it had bumps and craters very well concealed by the sand mix , it was only when one drove over one--without realizing its presence-- that the car jumped in the air for a second and reached ground .Brake pedal was pressed so as to stop the car yet it was jutting into the right side traffic. In order to avoid hitting the right side traffic, one intentionally excercised a maneouvre , which forced the car to left side followed by a 360 spin over the sand mix surface, blew a whole lot of dust and startled those car drivers on the right side. The end result: one avoided the car going to right side and jutting into the right side traffic. The car stopped on the left most extremety 1 meter away from a ditch, and engine still running.My instincts and a foreboding of something like this was about to happen saved me that day.


One lesson --and I may be a bit incorrect in what i am about to state, but whatever stated is purely based on a lesson learnt --was, ABS or No ABS, coupled with EBD, on gravel or sand none will enable to bring the car to a complete stop simply by pressing the brake pedal alone.
Try engine braking, out-steer or out-manueovre that may help. Why I imagine this?

Simply , consider a car without all the ABS and EBD etc and it being driven over gravel or sand surface lets say 80+kmph. Pump barkes on this car, front wheels would lock. The Front tyres would then try to sift through the sand or gravel mix to reach the hard surface beneath and then the actual process of slowing down may begin. All along , the car would still be moving ahead and would take some time and distance to come to a complete stop.

And in an ABS fitted car driven over the same surface--here is what I imagine and leave others here to correct me, if one is incorrect. The wheels wouldnt lock, the tyres as far as i imagine would glide over the surface let alone sifting or digging into the gravel or sand surface to reach the hard surface. One really don't believe this car would stop simply by pressing the brake pedal.

I think, the moment to took the left flick you brought all 4 wheels on the road surface which is quite fortunate and even though later a right one made you loose control of car, the important thing was that atleast all 4 wheels were on road-- not like before when two were in gravel or sand--and with your instincts and car safety systems to prevented injury to others and yourself.
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Old 14th February 2011, 17:06   #50
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Default Re: Emergency manouveur in my i20 diesel. Need to understand what happened

Quote:
Originally Posted by sagarpadaki View Post
phoenix wont the down shifting cause wheel-spin to occur especially in the high torque engines like ours?
Not sure about stock wheels, but I have some nice grip from my 195/55 R15 Yoko S.Drives
Quote:
Originally Posted by DerAlte View Post
Isn't that under-steer?
I went through both - the under-steer where the car refused to turn while I am about 40% into the curve, and then the over-steer when I braked a bit and cut gears - almost getting me hit the median face-on!
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Old 15th February 2011, 15:49   #51
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Default Re: Emergency manouveur in my i20 diesel. Need to understand what happened

Quote:
Originally Posted by ritedhawan View Post
Simply , consider a car without all the ABS and EBD etc and it being driven over gravel or sand surface lets say 80+kmph. Pump barkes on this car, front wheels would lock. The Front tyres would then try to sift through the sand or gravel mix to reach the hard surface beneath and then the actual process of slowing down may begin. All along , the car would still be moving ahead and would take some time and distance to come to a complete stop.

And in an ABS fitted car driven over the same surface--here is what I imagine and leave others here to correct me, if one is incorrect. The wheels wouldnt lock, the tyres as far as i imagine would glide over the surface let alone sifting or digging into the gravel or sand surface to reach the hard surface. One really don't believe this car would stop simply by pressing the brake pedal.
Completely agree with you. That's the reason why people who go off roading desire to have some kinda switch to turn ABS off. In sand, slush, snow non-ABS vehicles will stop quicker.

Quote:
Originally Posted by ritedhawan View Post
Consider this incident one had years ago...
Had a slightly similar horrifying experience while driving down to Bikaner last year. I was taking a long & gentle right hand curve, doing around 120, when this moron on a bike decided to cross the road left to right. He was some distance away so I slowed down a tad knowing he had enough time to cross. Then what happens, his bike stalls and he runs away throwing it on the road. I had to make a quick left-right flick on the steering which made the left tyres go onto sand. Needless to say, after the right flick of the steering I was doing a Scandinavian flick at a high speed. After three attempts of opposite locking, left lock, right lock and again left lock, I knew I wasn't being able to get the car straight. Thank God this was in Rajasthan where there's ample deep sand on shoulders and throwing my car into that saved the day. After some moments of being in a Merrie-go-round, we came to a standstill. Before I can collect my wit and reach the fallen bike, the moron had managed to ride off like the devil himself was after him (I was shouting the most appropriate expletives running towards the bike).

EDIT:

Quote:
Originally Posted by ph03n!x View Post
I went through both - the under-steer where the car refused to turn while I am about 40% into the curve, and then the over-steer when I braked a bit and cut gears - almost getting me hit the median face-on!
Yipes! That must have been mighty scary. One of the reasons why I have to reign in my desire to enter kinda tight corners at high speeds.

Last edited by lordofgondor : 15th February 2011 at 16:13.
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Old 16th February 2011, 22:04   #52
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Default Re: Emergency manouveur in my i20 diesel. Need to understand what happened

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Originally Posted by kalpeshc View Post
Wouldn't EBD help in this case? I was under the impression that EBD was precisely for this.
Nope, EBD wouldn't make any difference because you don't even need to touch the brakes to make the car slide in the given situation. A twist on the steering is enough.

What would help in this case : ESP Electronic Stability Program. Nothing else. And who better than good ol' Tiff to demonstrate.

Watch, especially from the 6th minute onward:



Of course, we have our own video too:



And a report (Mercedes Safety Tech Demo - At the Mumbai Airstrip) on Merc's demo of electronic safety aids.

ESP & ABS will be standard equipment on all Indian cars one day; I'm just wondering how many more people have to die before the government makes it mandatory.
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Old 19th February 2011, 15:47   #53
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Default Re: Emergency manouveur in my i20 diesel. Need to understand what happened

^^ What brilliant videos GTO! Thanks for sharing. This surely clears any confusion on the car skidding and the importance of ESP and ABS.

I also wish that Govt makes it mandatory for all cars to have Airbags, ABS and ESP. Heck, reduce your custom/excise duties and other non-sense taxes and pass on the benefit to the customers.
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Old 21st February 2011, 22:51   #54
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Default Re: Emergency manouveur in my i20 diesel. Need to understand what happened

Quote:
Originally Posted by sagarpadaki View Post
i20 has ABS+EBD combo for the top end ASTA model(which we have).Even i am wondering why the EBD didnt work or maybe i didnt notice it.Yea the lower GC was also one of the factor.Had it been a sumo or scorpio it would have rolled over.

Yes,at one instant i was facing at the median and heading into it.Dont know if it as my final position or not.But i made rapid corrections once again to get back into proper direction.




phoenix wont the down shifting cause wheel-spin to occur especially in the high torque engines like ours?
Hi
If the mods in heaven spare this reply, good. If not, today will be my last set of posts.

Generally, what we do when we drive is to keep an eye in front and rear and plot the movements of all objects on the road we are sharing. The educated guesswork that can be due to luck or experience can be enhanced as detailed below, since 99.9% of cars in India, don't have ESP, yet.

What happened was not a tank slapper(used with reference to bike shimmy), but rather what could happen to every car in certain situations, that does an unintentional unexpected accident avoidance exercise.

A similar thing happened to an acquaintance with the same car, who had moved to lower aspect wider tyres from the same brand. He saw a dog in front of him while driving at 100 kmph, braked, lost the driving line by 1 foot, steered to get back, but over steered, lost control, veered and hit a lamp post. Airbag did not function as the pole did not give enough deceleration like a wall would. Car was a write off, replaced the car and put some other brand tyres. Most tyres, even some OE ones are not the best handling ones, as in India non-safety priorities are too many.

The friction circle is an example - tyres can either brake, accelerate or corner 100%, not even two at the same time.(search internet for 'friction circle'). In your case and the above case, braking and giving multiple steering inputs at the same time, combined with an average handling car, resulted in loss of control.

The New Zealand Motorcycle safety Foundation reports 1.8 seconds before an incident as the available reaction time. So being alert is key. They advise selecting one of the 5 best actions you can do without thinking, so like chess moves in your head, we better know our situation scenarios in advance. If you choose wisely, your chances are better.

1) The steering is not infallible, and can only guide the car in normal situations. Good steering is heavier to steer than normal, with good road feedback, but no one wants a sore arm after a long drive. Thats why most good cars have tight steering, to avoid too much input.

2) Drive smoothly, as planned driving is safest. So braking, acceleration and cruising are all completed in advance - in the head. Your driving line is a key to survive - some internet search will help. Search for 'driving line'.

3) Practice and experience helps - especially driving alone on an isolated road. Dusty but smooth roads are ideal for trials at lower speeds without damaging your car or tyres,and yet get the same rear swingout. Learn the limits of your car and your driving skills and stick to it.

4) Brake in a straight line always, even with ABS and EBD. When you cannot avoid hitting the object in front, release the brake and steer your way out after decelerating to the minimum speed possible. ABS and EBD will work on a curvy road but efficacy is less in panic situations. No doubt it saved your lives here.

5) Brake steadily but gently; panic braking makes things worse, especially in a corner with cars that are not famous for handling ability.

6) Always select a car from safety first point of view, and take better handling cars. If the car is not the best for handling, learn to manage it's limitations.

7) Keep a distance of 100 meters from the car in front, unless you are overtaking. Overtake without hesitation when it is all clear, stay behind till it is OK.

You are one of those who got away. Congrats and be alert always. Wearing seat belts, is a great way to live longer.

Johnn
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Old 11th November 2011, 08:43   #55
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Default Re: Emergency manouveur in my i20 diesel. Need to understand what happened

Scary experience!

My learnings:
1. ABS and EBD are only effective on paved surfaces, when the tyre has some grip on the road surfaces.
2. Weight shifts when we flick the steering, causing car to change the line.
3. This effect is even more pronounced under braking, as the front wheels act as pivots.
4. The rear tyres try to grip the surface, but the sideward motion along the wheel axis) tends to "trip" the car - this is more so when the CG of the car is above the center of the wheel. If the CG of the car is below the wheel axis, the car simply skids...

My question:
1. Is it going to be unsafe if we have more load in the boot?
2. Whats the role of suspension in this? will a softer suspension absorb the weight shift (slight body roll)? or will the stiffer suspension set up be better to force the wheel to skid sideways but not allowing the car to trip and roll over?
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