Go Back   Team-BHP > Under the Hood > Technical Stuff


Reply
 
Thread Tools Search this Thread
Old 19th September 2011, 17:47   #316
Team-BHP Support
 
noopster's Avatar
 
Join Date: Feb 2010
Location: Pune
Posts: 8,665
Thanked: 9,197 Times
Default Re: Driver ignorant of how ABS works; Turns Chevy Captiva upside down

Wow- 14 pages just to end in us concluding that humans are morons

Seriously though- have learned more about safe braking through this thread (ABS or non-) than anything I have ever read before in my nearly 20 years of driving.
noopster is offline   Reply With Quote
Old 19th September 2011, 17:57   #317
Senior - BHPian
 
Join Date: Apr 2008
Location: Dombivli
Posts: 2,627
Thanked: 1,191 Times
Default Re: Driver ignorant of how ABS works; Turns Chevy Captiva upside down

Or what happens in case of a non-ABS car when the driver slammed on the brakes, the wheels locked, the driver tries to steer the car around the obstacle and so turns the steering towards left, and suddenly the wheels find traction?
honeybee is offline   Reply With Quote
Old 19th September 2011, 18:09   #318
Team-BHP Support
 
suhaas307's Avatar
 
Join Date: Aug 2009
Location: Bangalore
Posts: 8,055
Thanked: 6,602 Times
Default Re: Driver ignorant of how ABS works; Turns Chevy Captiva upside down

Quote:
Originally Posted by honeybee View Post
Or what happens in case of a non-ABS car when the driver slammed on the brakes, the wheels locked, the driver tries to steer the car around the obstacle and so turns the steering towards left, and suddenly the wheels find traction?
I suppose the car would already be spiraling out of control by then. At the time when the driver slams the brakes and swerves to the left, assuming that there isn't much traction and the brakes have locked up, the car would be headed straight for its obstacle at an angle, as if drifting/sliding towards it. The driver would be a goner. And if it is taller car, like a Santro, it might even flip, due to its small wheel diameter, slim tyres, narrow track, and tall body. A car which is lower to the ground and with a wider foot-print may not flip and just slide

Even if the car finds traction in the last second, the momentum would be good enough for the car to slam into the obstacle. It's very hard to regain control of the vehicle once the brakes have locked up and the car is on an unstoppable slide. Perhaps if the obstacle has moved or isn't there anymore (even if it is present), one can try and regain control of the car by pumping the brakes and feeding the throttle as well as the steering-wheel with minimal inputs, assuming that the car has regained some traction.

Last edited by suhaas307 : 19th September 2011 at 18:13.
suhaas307 is offline   Reply With Quote
Old 19th September 2011, 18:34   #319
Senior - BHPian
 
Join Date: Apr 2008
Location: Dombivli
Posts: 2,627
Thanked: 1,191 Times
Default Re: Driver ignorant of how ABS works; Turns Chevy Captiva upside down

If while sliding the tyres suddenly found traction, wouldn't the car stop going in the existing direction and change directions?

Let's say the driver is at around 120kmph. He sees an obstacle up ahead, say about 50 metres, and slams onto the brakes, at the same time trying to steer left. Now, the wheels lock up just as they are changing directions and so the car starts skidding towards the obstacle, not head-on, but say at a small angle such that if the slide continued, the RHS headlight/skirting would hit the obstacle first.

After the car slides a few metres, the tyres suddenly find traction. They are already turning away left from the car's slide path. If they find traction the car would stop its onward slide and turn in the direction the tyres are facing?
honeybee is offline   Reply With Quote
Old 19th September 2011, 18:43   #320
Team-BHP Support
 
suhaas307's Avatar
 
Join Date: Aug 2009
Location: Bangalore
Posts: 8,055
Thanked: 6,602 Times
Default Re: Driver ignorant of how ABS works; Turns Chevy Captiva upside down

Quote:
Originally Posted by honeybee View Post
If while sliding the tyres suddenly found traction, wouldn't the car stop going in the existing direction and change directions?

Let's say the driver is at around 120kmph. He sees an obstacle up ahead, say about 50 metres, and slams onto the brakes, at the same time trying to steer left. Now, the wheels lock up just as they are changing directions and so the car starts skidding towards the obstacle, not head-on, but say at a small angle such that if the slide continued, the RHS headlight/skirting would hit the obstacle first.

After the car slides a few metres, the tyres suddenly find traction. They are already turning away left from the car's slide path. If they find traction the car would stop its onward slide and turn in the direction the tyres are facing?
When the car is on its slide 20 meters away from the obstacle, and it finds traction, the car would turn in the direction that the wheels are pointed at. Remember, the rear wheels just follow the car, and it's the front wheels that do the turning and put the power down, (in a FWD car). Mid slide, the driver would instinctively dial in a degree of opposite lock to counter the slide, so the wheels would be facing forward or even a little to the right.

When the car regains traction, it is advised that little steering inputs towards the correct direction of driving would be required if you want the car to fall back in line. One should not throttle excessively either, as the car would be doing a much lower speed. Instead, hold the steering tight and depress the clutch once the car begins to fall out of the power-band and when you feel the engine rocking. Of course, you shouldn't worry about all this, and instead concentrate on keeping the car on the road and pump the brakes in order to regain the car's braking ability completely.
suhaas307 is offline   Reply With Quote
Old 19th September 2011, 21:12   #321
Distinguished - BHPian
 
supremeBaleno's Avatar
 
Join Date: Dec 2005
Location: Weekdays@Chennai, Weekends@Kerala
Posts: 5,164
Thanked: 1,638 Times
Default Re: Driver ignorant of how ABS works; Turns Chevy Captiva upside down

Some years ago, there was a similar related discussion about situations involving frantic emergency braking, with some mentioning about how they would downshift gears (needs more time than hitting the clutch discussed here) before hitting the brakes. Well, if you have the time to think of downshifting gears and actually do it, that situation is nowhere near to what can be called emergency braking.

Regarding whether it is good to hit the clutch and brakes simultaneously, IMO the way to do it is to hit the brakes and later depress the clutch only on possibility of stalling. But this depends on how we drive and where we are driving. If we are on the highway at high speeds, our left foot would be either on the dead-pedal or away from C-pedal - so chances are we hit the brakes first. In the city with traffic, it might be hovering over the C-pedal or even riding it like some do (knowingly or otherwise) - in which case, we could hit both B and C pedals simultaneously.

Quote:
Originally Posted by honeybee
So is it a better strategy to brake and swerve, or to just brake or to just swerve? If we could plan it and practise it, we could actually put it to good use during an emergency.
Emergency situations do not give much time to think/plan and to add confusion, each case is different from the other. Add to this the fact that each of us could make a different decision, given the same situation.

Funny that I saw this thread today, because yesterday I faced a similar situation. I was on the NH47 driving towards Alappuzha in our Swift-ZXi (has ABS). I am doing something like ~30kmph after crossing a 2-lane bridge following an auto in front of me that was going very slowly, yet not giving way. I have my son with me and I am in no hurry, but there is a Sumo behind me getting very impatient and honking. The auto guy suddenly moves to the left extreme of the road (maybe assuming that I am honking), which I take to be giving me way to overtake him and so I attempt to pass him - but for reasons best known to him (maybe he was irritated by the honking), when the front of my car is almost in line with the auto's rear, he swerves back onto the road. Something that I did not expect him to do. Also note that on his giving way, I had stepped on the gas to complete the overtaking manouvre. No thinking, nothing. I stood on the brakes and also swerved the car to the right (oncoming traffic lane - since NH47 here is a piddly 2-lane road) to avoid hitting him. I hear (or I think I did) some sound which I think is maybe I hit the rear corner of the auto and I am sweating and angry. I dont remember, but since the car did not stall, I should have hit the clutch - cant remember whether it was along with the brakes or after braking - most probably former. Also, I "think" ABS could have kicked in, though I dont remember pulsating brake pedal. Luckily the Sumo did not rear-end me. The auto guy drives off as if nothing happened. I try to calm myself down and parked off the shoulder and inspect the front left of the car expecting a dented bumper atleast - not a scratch.

So, I avoided an accident by swerving away. But I was just lucky that there was no oncoming traffic, else I would have been badly hit. And ofcourse in that situation, there was no option to swerve to the left.
supremeBaleno is offline   Reply With Quote
Old 19th September 2011, 21:17   #322
BHPian
 
noidea's Avatar
 
Join Date: Apr 2010
Location: Kolkata
Posts: 143
Thanked: 75 Times
Default Re: Driver ignorant of how ABS works; Turns Chevy Captiva upside down

Driver error, no doubt, but the first experience with ABS is a little unnerving to say the least. The first time it happened with me it scared the dickens out of me.
Funny but I never let my driver drive above 100 though I allow myself to cross that limit very often.
noidea is offline   Reply With Quote
Old 20th September 2011, 00:01   #323
Team-BHP Support
 
Samurai's Avatar
 
Join Date: Jan 2005
Location: B'lore-Manipal
Posts: 22,385
Thanked: 14,314 Times
Default Re: Driver ignorant of how ABS works; Turns Chevy Captiva upside down

Fortunately, I bought my first ABS equipped car right before winter, got to experience the ABS working in 10mph itself thanks to snow.
Samurai is offline   Reply With Quote
Old 27th January 2012, 15:12   #324
Senior - BHPian
 
VeluM's Avatar
 
Join Date: Jul 2008
Location: Bangalore
Posts: 1,298
Thanked: 665 Times
Default Re: Driver ignorant of how ABS works; Turns Chevy Captiva upside down

Quote:
Originally Posted by Samurai View Post
There are ECUs that send more fuel to the engine when brake is jammed and accelerator pedal is left untouched?
Sorry about this, but I finally have a source and from a TBHP review, no less:

Quote:
Originally Posted by Rehaan View Post
Just like the Micra it will lug at 40 km/h, 4th gear @ 1200 rpm Ė this is probably made possible by the ECUís anti-stall feature which opens up the throttle slightly (youíll feel a bit of acceleration once the revs drop closer to 1000 rpm).
VeluM is offline   Reply With Quote
Old 29th January 2012, 00:00   #325
Team-BHP Support
 
Samurai's Avatar
 
Join Date: Jan 2005
Location: B'lore-Manipal
Posts: 22,385
Thanked: 14,314 Times
Default Re: Driver ignorant of how ABS works; Turns Chevy Captiva upside down

Quote:
Originally Posted by VeluM View Post
Sorry about this, but I finally have a source and from a TBHP review, no less:
Please highlight where Rehaan mentions the jammed brakes.
Samurai is offline   Reply With Quote
Old 29th January 2012, 00:18   #326
Senior - BHPian
 
VeluM's Avatar
 
Join Date: Jul 2008
Location: Bangalore
Posts: 1,298
Thanked: 665 Times
Default Re: Driver ignorant of how ABS works; Turns Chevy Captiva upside down

Quote:
Originally Posted by Samurai View Post
Please highlight where Rehaan mentions the jammed brakes.
Just supporting info for my previously disregarded point that the ECU does increase RPM when sensing a potential stall. Please highlight where the brakes come into the picture QED, and finis.
VeluM is offline   Reply With Quote
Old 12th March 2012, 18:17   #327
BHPian
 
vivek_vt's Avatar
 
Join Date: Jul 2006
Location: Hyderabad
Posts: 62
Thanked: 32 Times
Default Re: Shifting to Neutral or Pressing the Clutch when Braking - Is this right?

Quote:
Originally Posted by GTO View Post
I reiterate, only an IDIOT will shift into neutral when coasting. Here's an older post:

According to Toyota, shifting to neutral doesn't save any fuel. Most modern cars come with a fuel-cutoff system. Thus, stay in gear so you save fuel & get free engine braking.



C&D linky

And here's another confirmation:
What if I do not want to brake? I will give an example. The bike I drive, Bajaj Avenger has a very wierd gear ratio. The engine is very noisy at speeds of 100 and fifth gear. If I stop the accelerator the bike reaches a speed of 60 in a matter of seconds. Although this is very good in terms of safety, but what If I want to cruise for a km before a stop. Is depressing the clutch right in such an instance.

Also I have a habit of depressing clutch while driving car. Again for the same reason. Don't want to decelerate too quickly. As in, I do not need the engine braking to take effect (And I think I had this in my mind that I get better fuel efficiency from this stupid habit). However the deceleration is very slow compared to bike. So I will change my habit and strictly use clutch for changing gears only.(Esp since most of my driving happens in himachal) I always wanted to clear this doubt with an expert, and somehow landed up here finally.
vivek_vt is offline   Reply With Quote
Old 12th March 2012, 19:22   #328
BHPian
 
rangakishen's Avatar
 
Join Date: Sep 2011
Location: Gothenburg
Posts: 200
Thanked: 87 Times
Default Re: Shifting to Neutral or Pressing the Clutch when Braking - Is this right?

Quote:
Originally Posted by vivek_vt View Post
What if I do not want to brake? I will give an example. The bike I drive, Bajaj Avenger has a very wierd gear ratio. The engine is very noisy at speeds of 100 and fifth gear. If I stop the accelerator the bike reaches a speed of 60 in a matter of seconds. Although this is very good in terms of safety, but what If I want to cruise for a km before a stop. Is depressing the clutch right in such an instance.

Also I have a habit of depressing clutch while driving car. Again for the same reason. Don't want to decelerate too quickly. As in, I do not need the engine braking to take effect (And I think I had this in my mind that I get better fuel efficiency from this stupid habit). However the deceleration is very slow compared to bike. So I will change my habit and strictly use clutch for changing gears only.(Esp since most of my driving happens in himachal) I always wanted to clear this doubt with an expert, and somehow landed up here finally.
First of all, in car you will hardly experience such engine braking as you have mentioned for your avenger. Put it in 5th or 6th at 100 kmph and the car will happily go along, may be slowing down to 80 kmph over a period of time.

Quote:
Originally Posted by bblost View Post
I use the Clutch when changing gears. Period. The clutch is not meant for deceleration. Maybe for a timed heavy acceleration. But in day to day driving, its has no role in slowing down.
About your bike: As mention above, the clutch is primarily meant to be used ONLY for smooth delivery of power without damaging the relatively moving parts. I.E> Only for moving from stand still, changing gears, heavy accelerations etc.,

I do not know the solution to the problem. But disengaging the clutch and traveling large distances and at such speeds is certainly not advisable. This will result in wear and tear of clutch plate. In a bike you should invariable keep the clutch engaged and throttle at suitable position if you wish to cruise at 100 kmph. I say "in a bike" because shifting to neutral in NOT an option at all since its a sequential gearbox.

My .02$!!

Last edited by rangakishen : 12th March 2012 at 19:30.
rangakishen is offline   Reply With Quote
Old 12th March 2012, 19:26   #329
Senior - BHPian
 
m_upreti's Avatar
 
Join Date: Feb 2008
Location: Navi Mumbai
Posts: 1,571
Thanked: 305 Times
Default Re: Shifting to Neutral or Pressing the Clutch when Braking - Is this right?

Quote:
Originally Posted by the_maassk View Post
I can confirm this is true. I have an Aveo U-VA with a ScanGauge II installed. If I take my foot off the A pedal, the fuel to the engine is cut-off (ScanGauge shows 0.0 LHK (liters per hundred kilometers) and the Fuel Loop is open.
Is this in neutral or in gear.

In my Scorpio even I lift my foot off the A pedal, and the vehicle is in geat (say 1st) it continues moving without stalling which shows that the fuel is being fed to the engine ( I have however not tested the distance it would move in this condition, but it does manage to climb a 25 degree ramp without any issues).
m_upreti is offline   Reply With Quote
Old 12th March 2012, 20:48   #330
BHPian
 
Born2Slow's Avatar
 
Join Date: May 2007
Location: Bnagalore/Cochin
Posts: 86
Thanked: 42 Times
Default Re: Shifting to Neutral or Pressing the Clutch when Braking - Is this right?

All of the modern vehicles cut fuel on the overrun in gear, the fuel is introduced back as the rpm drops and at a value little higher than normal idle rpm to prevent jerking. So it is more economical to be in gear as the engine breaking is not very pronounced in cars.

As for bikes without electronics if you want max mileage then accelerating to a moderate speed (say 70) and then pull in your clutch and as the speed drops release the clutch and again accelerate (repeat the process). Very inconvenient but on long empty stretch of roads will give you more mileage than riding at a steady speed. Your clutch should be fine , not the best way to ride a bike though.
Born2Slow is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Palio 1.2 nv - Pressing the clutch pedal while starting the car kapilsharma80 Technical Stuff 24 18th February 2013 22:12
Xing: High rev when pressing the clutch during gear change raghu Technical Stuff 11 11th October 2009 07:06
cheen-cheen-cheen noise when pressing accelerator vebmetal Technical Stuff 15 27th August 2008 13:33
Which is the right Sequence Clutch-Brake Or Brake-Clutch ankura12 Technical Stuff 2 9th July 2007 10:02


All times are GMT +5.5. The time now is 05:35.

Copyright ©2000 - 2017, Team-BHP.com
Proudly powered by E2E Networks