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


Reply
 
Thread Tools Search this Thread
Old 25th April 2009, 02:17   #16
BHPian
 
alexnazim's Avatar
 
Join Date: Dec 2005
Location: New Delhi
Posts: 90
Thanked: 0 Times
Default

Quote:
Originally Posted by equinox22 View Post
It is correct that ABS reduces braking efficiency on loose surfaces or snow. This does not mean loss of direction control but the stopping distance. I have experienced this first hand on the Civic v/s the Focus. The wheels do not lock and hence the car does not stop but keeps rolling slightly.
Well, I actually it would be much safer cause every time your car skids the distance covered to stop is longer than had it stopped normally.
alexnazim is offline   Reply With Quote
Old 25th April 2009, 18:03   #17
BHPian
 
equinox22's Avatar
 
Join Date: Mar 2009
Location: Chicago/Pune
Posts: 163
Thanked: 3 Times
Default

Quote:
Well, I actually it would be much safer cause every time your car skids the distance covered to stop is longer than had it stopped normally.
Not when you are in snow. It's better if the wheels lock so they dig in through the powdery layer of snow and reach the hard tarmac below. In normal road conditions it is certainly better to have ABS. But when all four wheels are on snow it is not so. Even the vehicle manual says so.

Quoting from the Civic Si manual:
A vehicle with ABS may require a longer distance to stop on loose or uneven surfaces, such as gravel or snow, than a vehicle without antilock brakes.
equinox22 is offline   Reply With Quote
Old 26th May 2009, 23:20   #18
BHPian
 
neel385's Avatar
 
Join Date: Nov 2007
Location: Kharagpur
Posts: 530
Thanked: 401 Times
Default

Quote:
Originally Posted by equinox22 View Post
Quoting from the Civic Si manual:
A vehicle with ABS may require a longer distance to stop on loose or uneven surfaces, such as gravel or snow, than a vehicle without antilock brakes.
Well, if the manual says so there must be some truth in it, but going by the basic understanding of braking and friction per se', it really does not make sense.

The braking efficiency will be maximum at a certain slip ratio between the wheel and the surface, and, if the tyre starts skidding, the slip ratio reduces to 0 and thus brakeing efficiency is adversely affected. So really cannot understand hoe a non ABS brakeing system will be more efficient than an ABS system, irrespective of the type of surface
neel385 is offline   Reply With Quote
Old 27th May 2009, 01:24   #19
Team-BHP Support
 
Zappo's Avatar
 
Join Date: Oct 2005
Location: Hyderabad
Posts: 5,653
Thanked: 2,013 Times
Default

If you look at the way a typical ABS system works it may explain why the Civic manual says so. ABS basically uses the sensors on the 4 rotating wheels to detect the comparative turning rate (how fast or slow the wheel is rotating). When it detects a sizeable difference between the speed of one tyre from the rest it immediately reduces the brake force on that wheel (by releasing the hydraulic pressure) and brings it back to the same speed. This operation may repeat several times to get the desired effect (and thus the pulsating feeling of the pedals in ABS cars, particularly if you drive without a footwear).

In doing the above the ABS unit (the ECU) also ensures that the car does not go into a skid because of the locked wheels. Now in a loose gravel, snow etc kind of situation where the friction offered by the surface to the rubber is significantly different from the standard surface (the reference point for most of these lookup tables must be based on the tar or concrete roads I would assume) one may find that though the car wheels are not exactly locking in and thus the car does not skid the car also does not stop as quickly either.

On the other hand, a non ABS car on such surfaces will have its wheels locked and may start fishtailing but still it will probably stop much quicker as the wheels would have completely locked (in emergency braking). Remember the manual says that the braking distance for an ABS car will be more on such surfaces in comparison to a non-ABS car but it does not say that in doing so the non-ABS car will not do any theatrics. It may stop but you may find yourself facing the way you came (particularly on loose sheet ice, snow etc). And in extreme cases where you are driving a non-ABS barge (say a tall SUV kind of vehicle) you may even have a scope of the fishtailing vehicle topling over sideways during the skid.

Last edited by Zappo : 27th May 2009 at 01:31.
Zappo is offline   Reply With Quote
Old 1st June 2009, 19:12   #20
BHPian
 
equinox22's Avatar
 
Join Date: Mar 2009
Location: Chicago/Pune
Posts: 163
Thanked: 3 Times
Default

Zappo has summed it up well. I meant only the braking distance and not overall control of the car. I used to have a non-ABS Ford Focus. On snow even braking from 20 mph I have had the car slide and turn before it came to a stop. With the Civic, the car usually does not go out of control but I can feel the ABS working while the car keeps moving forward.
equinox22 is offline   Reply With Quote
Old 1st June 2009, 20:57   #21
BHPian
 
neel385's Avatar
 
Join Date: Nov 2007
Location: Kharagpur
Posts: 530
Thanked: 401 Times
Default

Quote:
Originally Posted by Zappo View Post
In doing the above the ABS unit (the ECU) also ensures that the car does not go into a skid because of the locked wheels. Now in a loose gravel, snow etc kind of situation where the friction offered by the surface to the rubber is significantly different from the standard surface (the reference point for most of these lookup tables must be based on the tar or concrete roads I would assume) one may find that though the car wheels are not exactly locking in and thus the car does not skid the car also does not stop as quickly either.

On the other hand, a non ABS car on such surfaces will have its wheels locked and may start fishtailing but still it will probably stop much quicker as the wheels would have completely locked (in emergency braking). Remember the manual says that the braking distance for an ABS car will be more on such surfaces in comparison to a non-ABS car but it does not say that in doing so the non-ABS car will not do any theatrics. It may stop but you may find yourself facing the way you came (particularly on loose sheet ice, snow etc). And in extreme cases where you are driving a non-ABS barge (say a tall SUV kind of vehicle) you may even have a scope of the fishtailing vehicle topling over sideways during the skid.
There is no reference point for ABS systems. Like you pointed out earlier, ABS ECUs just keep a check on the differential speed of all the wheels and when one wheel's speed is significantly out, it cuts in and un-brakes the wheel. Another point that is often overlooked is that, once this un-braked wheel spins up again,and it's speed is again greater than the other wheels, ABS again kicks in and brakes this wheel. That's why the pumping sensation.

A non ABS car doesn't stop because the tyres are locked in. It is important to understand that a skidding vehicle will always have a greater stop distance compared to a correctly braked vehicle.

An explanation to this is that, in a non ABS system, the tyres, because of getting jammed, dig into the underlying soft surface (dirt/gravel/snow) and hence the stop distance is lesser. ABS prevents this from occurring since the tyres never lock up. Some ABS calibrations reduce this problem by slowing the cycling time, thus letting the wheels repeatedly briefly lock and unlock. Some vehicle manufacturer provides an "off-road" button to turn ABS function off. The primary benefit of ABS on such surfaces is to increase the ability of the driver to maintain control of the car rather than go into a skid — though loss of control remains more likely on soft surfaces like gravel or slippery surfaces like snow or ice. On a very slippery surface such as sheet ice or gravel, it is possible to lock multiple wheels at once, and this can defeat ABS (which relies on comparing all four wheels, and detecting individual wheels skidding). Availability of ABS relieves most drivers from learning threshold braking.

( wikipedia + allied info)

Last edited by neel385 : 1st June 2009 at 20:59. Reason: placed reply in quote
neel385 is offline   Reply With Quote
Old 2nd June 2009, 00:28   #22
BHPian
 
TRAUMASURG's Avatar
 
Join Date: Apr 2009
Location: CANTON,NEW YORK
Posts: 79
Thanked: 5 Times
Default

Quote:
Originally Posted by ImmortalZ View Post
That is one of the disadvantages with ABS. On loose surfaces like sand and slippery surfaces like ice, ABS will cause reduced braking efficiency because in those conditions, you want the wheel to lock up to get some sort of friction.
That what exactly you do not want to do.If you lock the wheel you are in for a slide and you might find yourself in front if an on coming truck or something worse.ABS will let you maintain steering control.Remember abs will increase braking distance because it will pump your brake many times in a second ,so that you dont lock your wheels thus increase your braking distance.It is one of the requirements for new car sold today in US,along with ABS there is ESR/ESP/ASR/PASM and brake assits are all latest techs to keep you safe., addition there is blind spot assist,accident presafe,etc all availble in the cars They all help in keeping us safe.But remember laws of physics.SLOW DOWN, BE SAFE,STAY AWAKE..Speed kills
TRAUMASURG is offline   Reply With Quote
Old 8th June 2009, 13:29   #23
Senior - BHPian
 
ImmortalZ's Avatar
 
Join Date: Jan 2008
Location: Trivandrum
Posts: 2,133
Thanked: 139 Times
Default

Yes, I want to keep my steering while going off a cliff.

On a more serious note, speed doesn't kill. It's the suddenly stopping part that does you in.
ImmortalZ is offline   Reply With Quote
Old 8th June 2009, 13:53   #24
BHPian
 
mustang89's Avatar
 
Join Date: Feb 2009
Location: new delhi
Posts: 348
Thanked: 0 Times
Default

guys isn't this thread losing its direction?the topic reads as ABS types and generations but what we have been discussing is ABS vs NON ABS on snow/loose gravel.although this information has definitely added to our knowledge but still it isn't serving the purpose the thread was meant to serve.
mods please check.
mustang89 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
Flaws in Maruti Swift (all generations) theMAG Technical Stuff 75 18th February 2016 15:01
Honda CRV - generations (in India) johy The Indian Car Scene 15 2nd April 2014 14:17
Generations of Alto Technocrat The Indian Car Scene 5 17th November 2004 20:46
Photo : All 4 generations of the M5 GTO The International Automotive Scene 9 15th September 2004 18:38


All times are GMT +5.5. The time now is 04:33.

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