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


Reply
 
Thread Tools Search this Thread
Old 11th May 2006, 12:54   #31
BHPian
 
2fast4u's Avatar
 
Join Date: Mar 2005
Location: pune / Bahrain
Posts: 488
Thanked: 5 Times
Default

mr netarchie i think its better u use the owners manual. u may get too confused otherwise. engine braking, brake pads, friction, cutting gears its all just too much too soon.
2fast4u is offline   Reply With Quote
Old 11th May 2006, 21:31   #32
Team-BHP Support
 
Rehaan's Avatar
 
Join Date: Feb 2004
Location: Bombay
Posts: 22,364
Thanked: 22,568 Times
Default

Ok,

I'm going to try to clear things up here, and can pretty much guarantee that this IS the best method. (Ofcourse open to debate).

NEVER keep the clutch pressed or shift into neutral when braking UNTIL you have reached 10km/h or less. (just before the engine is about to start shuddering/knocking)

Netarchie,

First - let me negate your "saving fuel" arguement...
When you are in neutral or have the clutch pressed, the car has to keep fuel going to the engine in order to keep it running. This uses fuel, naturally.
When you are in gear, and you take your foot off the accelerator, modern cars (which are fuel injected and pretty intelligent) sense the decelerating load on the engine and CUTS ALL FUEL SUPPLY TO THE ENGINE. This uses virtually NO fuel. The only thing keeping the engine spinning is the rolling of the tires transfering power back up the drivetrain, keeping the engine spinning. And at the same time you are getting engine braking! Talk about a sweet deal.

Secondly - a small point to note about "shifting to neutral on the expressway".
When you drive at a high speed for a long time, a phenomenon called velocitizing occurs. It basically means you dont have a realistic feel of exactly how fast you are going, which means slowing down will be harder than you think, which means ANOTHER REASON TO USE ENGINE BRAKING. If you want to just roll to a hault over 1000mts, feel free to do so, but STAY IN GEAR, the higher the gear (eg. 3rd, 4th, 5th gear) will make your rate of deceleration slower, whereas a lower gear (2nd or 1st) will slow the car down more rapidly. Regardless of the gear you are in, if you are not pressing the accelerator, chances are that NO fuel will be being used.

Thirdly - Vivek, for tips on driving an automatic, check out this thread.

Fourthly, and finally - Why engine braking is better!
1. It saves your brakepads from overheating and causing VERY dangerous brake fade. (Believe me, your brakes just WONT work when they get hot!)
2. It will save fuel, as mentioned above.
3. It will give you better control when turning. (try this out by taking a corner at Xkm/h and in 2nd/3rd gear, and then try doing it at the same speed in neutral and see the comparative lack of control you feel.)
4. YOU WILL STOP FASTER using engine braking.
Vivek2kny, your point about the quantity of friction between the tyres and the road being the limiting factor (so what difference if it comes from the brakes or engine?) makes sense in theory, BUT it doesn't take in several other factors.
For eg. getting the maximum out of your brake pads is not easy. If graphed, there is a non-linear curve of the amount of braking you are getting for a constantly increasing brakepad pressure on the rotor. Several factors influence this curve, including temperature, type of brakepad, type of rotor, speed of rotation etc. Hence, getting it consistently perfect is nearly humanly impossible, so if you have engine braking on your side, its much easier to get the maximum deceleration.

Still not convinced? - Try this -
Find an empty peice of straight, clean surfaced road. Make sure noone is behind you, get upto about 60-70km/h and shift into neutral. At a predetermined marker on the road brake as best as you can. Make a note of when the car comes to a complete halt.
Now, do it again. Get upto the same speed, but stay in 2nd gear. Make sure theres no car behind you, and at the same marker brake as best as you can, KEEPING THE CAR IN 2nd gear, only to press the clutch just before your car comes to a hault. Take a note of where the car came to a stop.

I am pretty sure that you will find that your stopping distance was significantly shorted when you left the car in gear, as well as much more confidence inspiring!

Try it out and let me know.
If i havent explained anything clearly enough, please let me know.

cya
R

Last edited by Rehaan : 18th September 2011 at 14:56.
Rehaan is offline   (9) Thanks Reply With Quote
Old 11th May 2006, 21:59   #33
BHPian
 
Fiero's Avatar
 
Join Date: Mar 2006
Location: new delhi / pune
Posts: 293
Thanked: 0 Times
Default

rehaan ,this is what i understand from your post

suppose the force needed for minimum possible braking distance is Y

when you brake ... you don't know how much to press the brake to get retarding force equivalent to Y ... you the brake too hard ... you risk locking

let braking force be X and engne braking force be Z

X + Z in practical situations will be closer to Y ... thus less braking distance

but then what happens if X + Z is greater than Y ... skidding ???

and what about cars with ABS/EBD ... the effect of engine braking should technically(and even practically) be minimal , right ?? coz the car will apply force Y(or very close to it)

Last edited by Fiero : 11th May 2006 at 22:01.
Fiero is offline   Reply With Quote
Old 11th May 2006, 23:23   #34
BHPian
 
netarchie's Avatar
 
Join Date: Feb 2006
Location: Navi Mumbai
Posts: 397
Thanked: 8 Times
Thumbs up

Thanks, Rehan and others, i am convinced now 100% and find no significant advantage of this neutral method.
good that i posted this query or else i would have never known.
Maybe this habit creeped into me because i used to drive a diesel car till late
I had also read about this method somewhere in the internet, somehow cannot find the exact link now.
i also thought this was one way of avoiding the clutch plate wear and tear more than increasing the FE.In my indica it would not allow me to ride in a high gear with a low speed and low gears used to make lot of engine noise, so this was one way of shutting its mouth.
Just to quote an example with my Indica,
say iam driving at 70 odd Km/Hr and i am in 5th gear, i see a red light ahead, so i have to slow down now, if i remove my foot of the gas and apply brakes gently, sooner or later its going to knock. so to come to a lower speed i need to downshift to 2nd gear. which means pressing the clutch 3 times to match the correct revs in each gear 4,3,2. If i use the neutral method i have to press the clutch only twice. once during fift to neutral and again during neutral to 2nd or 1st depending on the speed. This was the logic.And this neutral thing is only possible whn the road ahead is free, withouse or less traffic, cant be done in a bumper to bumber traffic.
But now when i am using a petrol car, it exact opposite, i dont have downshift so often.So when i went for a drive to actually study my driving habbit i found that i dont neutral it so often as i usd to do it earlier.here for e.g. what i observed as to what exactly i did was when i was approacing a speedbreaker and i was abt at 50km/hr speed and in 5th gear,i slowed down gently till i aproached the breaker, i shifted to neutral when my front tyre just climbed the speed breaker, my speed would have been 10 km/hr that time, whn my rear wheel also passed the breaker i put it 2nd nd continued.

And abt driving downhill in neutral.
when i mentioned downhill in my earlier post, it was small slopes or inclines like maybe a flyover in mumbai and not the hilly (ghats) downhills. I know much abt engine braking and haVe used it quite efficiently in real downhills drives.
The whole logic of the neutral method was to avoid wear and tear of the clutch plate and the brake liner. FE was only the by-product of the method or a bonus as you may call it.
Since this does not hold true, best is to change my driving style.
by the way Fiero made an intersting comment and my car has ABS... :-)
netarchie is offline   Reply With Quote
Old 12th May 2006, 01:12   #35
BHPian
 
jango's Avatar
 
Join Date: Mar 2006
Location: New York & kotayam
Posts: 798
Thanked: 19 Times
Default

Never do that, alsways use engine braking , and drive like a professional
jango is offline   Reply With Quote
Old 12th May 2006, 17:32   #36
BHPian
 
Join Date: Apr 2006
Location: Bangalore
Posts: 66
Thanked: 0 Times
Default I agree

Quote:
Originally Posted by revharder
you are absolutely crazy!

you gets into neutral while coming downhill???
the best practice in downhills is to get into a gear which you would have used while climbing that uphill! just try to visualise on that!!

and regarding shifting 1000 meters before hitting that toll booth or speedbraker, don't do that coz if something gets in front of you out of blue, then you won't be having any engine-braking to assist you!

i guess the safest and most practical way to brake is to do it gently and when the car is about to give you jerk, shift down by pressing that clutch !!
I do agree completely with what revharder is trying to say.
Never go on neutral in the downhill and also when the engine is running and you want to slow down. Its always a best practise to shift the gears according to the speed of the of the engine in that way you are best utilising the fuel and you also have the better control over the enigine and the vehicle. Thank god you are not shutting off the engine and applying brakes to save fuel
*Happy driving*
RoaringEngine is offline   Reply With Quote
Old 12th May 2006, 20:51   #37
Senior - BHPian
 
vivekiny2k's Avatar
 
Join Date: Feb 2005
Location: cincinnati, jabalpur,chennai
Posts: 1,241
Thanked: 163 Times
Default

Quote:
Originally Posted by Rehaan
Ok,

I'm going to try to clear things up here, and can pretty much guarantee that this IS the best method. (Ofcourse open to debate).
R
thanks Rehan,
I agree, as i said, for the planned braking.

but still I can't convince myself to do a gear shift when i see an urgent need of braking, I guess my eyes will be clenched closed and full force on the brake

may be i will learn, or may be the airbags will take control.
vivekiny2k is offline   Reply With Quote
Old 13th May 2006, 04:09   #38
Team-BHP Support
 
Rehaan's Avatar
 
Join Date: Feb 2004
Location: Bombay
Posts: 22,364
Thanked: 22,568 Times
Default

Quote:
Originally Posted by Fiero
rehaan ,this is what i understand from your post

suppose the force needed for minimum possible braking distance is Y

when you brake ... you don't know how much to press the brake to get retarding force equivalent to Y ... you the brake too hard ... you risk locking

let braking force be X and engne braking force be Z

X + Z in practical situations will be closer to Y ... thus less braking distance

but then what happens if X + Z is greater than Y ... skidding ???

and what about cars with ABS/EBD ... the effect of engine braking should technically(and even practically) be minimal , right ?? coz the car will apply force Y(or very close to it)
Fiero,

I understand what you are trying to say in your example, however, my point is that "Y" is not a constant, it changes according to the current speed you are at, temperature and lots of other factors. Hence, having "Z" as a constant added to "X" gives you more flexibility to control "X".

Regarding ABS / EBD, keep in mind that they are not applying brake-force, but reducing/governing brake-force (atleast in the case of ABS, and probably EBD to the best of my knowledge? barring the new S class etc< is that even still called EBD?). Your question still is valid though, and i cannot give you a entirely knowledgable answer without going into details that i am not well versed in.
Given the fact that brakes are basically friction, you should do some research on friction and look at graphs to get an idea of what i am talking about. etc.
And hopefully somewhere in the midst of that physics talk and confusion you will feel that having engine braking will be better
Sorry i cannot verbalize my thoughts on this accurately. But as i said in my earlier post. TRY IT...and see the difference.

Quote:
but still I can't convince myself to do a gear shift when i see an urgent need of braking, I guess my eyes will be clenched closed and full force on the brake
Vivekiny2k, I agree with you there. Its almost impossible to downshift in a PANIC situation.
BUT, its still better if you are IN GEAR in this kind of situation than if you were in neutral / clutch depressed.

cya
R

Last edited by Rehaan : 13th May 2006 at 04:41.
Rehaan is offline   Reply With Quote
Old 13th May 2006, 13:14   #39
BANNED
 
revharder's Avatar
 
Join Date: Jan 2006
Location: New Delhi
Posts: 460
Thanked: 47 Times
Default

Quote:
Originally Posted by vivekiny2k
I guess my eyes will be clenched closed and full force on the brake
this strictly calls for a reality check!
i know old habits die hard, but you need to know the better technique to stop the car!

donot rely heavily on airbags, etc.
moreover, once you know how to stop well in time, might be there won't be any need for deployment of airbags!

Happy Learning,
Drive Safe!!
revharder is offline   Reply With Quote
Old 13th May 2006, 22:09   #40
BHPian
 
2fast4u's Avatar
 
Join Date: Mar 2005
Location: pune / Bahrain
Posts: 488
Thanked: 5 Times
Default

Quote:
Originally Posted by revharder
this strictly calls for a reality check!
i know old habits die hard, but you need to know the better technique to stop the car!

donot rely heavily on airbags, etc.
moreover, once you know how to stop well in time, might be there won't be any need for deployment of airbags!

Happy Learning,
Drive Safe!!
and i thought driving is second nature for all manual gearshift owners. i dont need ebds, abs and what not to keep in control of what im driving, just the simple brakes should make u know whats ur stopping distance be it any kind of surface (other than a oil / diesel slick surface). i feel this ebd abs etc is all to increase confidence of drivers driving and makes them lethargic by a few seconds in stepping on the pedal. most of cars involved in accidents in uae are all +2000 yr model cars. too fast too late crash.
PS : Automatic trannies may be the other cause.
2fast4u is offline   Reply With Quote
Old 13th May 2006, 22:33   #41
Senior - BHPian
 
vivekiny2k's Avatar
 
Join Date: Feb 2005
Location: cincinnati, jabalpur,chennai
Posts: 1,241
Thanked: 163 Times
Default

Quote:
Originally Posted by 2fast4u
and i thought driving is second nature for all manual gearshift owners. i dont need ebds, abs and what not to keep in control of what im driving, just the simple brakes should make u know whats ur stopping distance be it any kind of surface (other than a oil / diesel slick surface). i feel this ebd abs etc is all to increase confidence of drivers driving and makes them lethargic by a few seconds in stepping on the pedal. most of cars involved in accidents in uae are all +2000 yr model cars. too fast too late crash.
PS : Automatic trannies may be the other cause.
jumping to the conclusion?

ebd abs airbags and what not is not to keep the car in control, but to save ur life when u actually crash. and do i see 'this will not happen to me' syndrome?

lethargy is personal choice, but opting for these safety measures is a great favor one can do to his family. remember, it's not always ur mistake that can lead u into a crash.

for the crashes in uae, apart from the model year, try geting statistics on the drivers' profil, and car purchasing capacity, to make it a fair comparison. don't just blame the cars.

my earlier comment shud have been read with the smiley.
vivekiny2k is offline   Reply With Quote
Old 13th May 2006, 23:44   #42
Senior - BHPian
 
Shan2nu's Avatar
 
Join Date: Feb 2004
Location: Hubli - Karnata
Posts: 5,525
Thanked: 87 Times
Default

Quote:
ebd abs airbags and what not is not to keep the car in control, but to save ur life when u actually crash.
Actually, 2 off the 3 mentioned systems are there to help you control the car.

EBD and ABS serve no purpose in an event of a collision.

Then again, no matter how many safety features your car has, if you arn't alert, you will eventually hit something.

Shan2nu
Shan2nu is offline   Reply With Quote
Old 14th May 2006, 10:20   #43
Senior - BHPian
 
Gordon's Avatar
 
Join Date: Feb 2004
Location: Mumbai
Posts: 2,420
Thanked: 162 Times
Default

I never shift into neutral while coming to a halt, or for that matter press the clutch. If I'm doing 60kmph and I have to brake, I wouldn't press the clutch nor change the gear, till I brake to a proper speed and till I get the slightest hint that the car demands it (minor vibrations can be felt). If you still don't press the clutch after this, the car will jerk.

On the turn I'd brake till the turn and when I reach the turn, I'd engage clutch and change gear and turn.

If you press the clutch or enter neutral gear when you are on high speeds, its dangerous, since you're letting the car just flow without any control on it. You have no control on it. Its just moving freely. The only control you have is with the brakes.

Quote:
Originally Posted by khaadu75
NEVER GO DOWNHILL IN NEUTRAL
Yes, you go downhill in neutral and you're as good as committing suicide.
Gordon is offline   Reply With Quote
Old 14th May 2006, 10:41   #44
Senior - BHPian
 
vivekiny2k's Avatar
 
Join Date: Feb 2005
Location: cincinnati, jabalpur,chennai
Posts: 1,241
Thanked: 163 Times
Default

Quote:
Originally Posted by Shan2nu
EBD and ABS serve no purpose in an event of a collision.
not in collision, but in panicky braking.

ABS starts releasing and rebraking only when it senses that wheels are locking, right? and i have never pushed my car to that limit.

so it's useless for me (and @2fast4u) until i actually slam the brakes someday.
vivekiny2k is offline   Reply With Quote
Old 16th May 2006, 00:25   #45
Senior - BHPian
 
vivekiny2k's Avatar
 
Join Date: Feb 2005
Location: cincinnati, jabalpur,chennai
Posts: 1,241
Thanked: 163 Times
Default

tried this on my galant today.

instead of braking in 'D' at the signal, changed to lowest gear first. not much diference, car behaved slightly heavier, but kept rolling. I had taken my foot off the gas pedal.

then when i tried braking when close to the signal, whoa, that was much quicker than i expected. braking was much stronger.

what i think is when i took the foot off the gas pedal, nothing much happened. but when I put my foot on brake, the fuel supply was cut off.

Is it true? is there a connection between brake pedal and the car's computer that signals engine to cut off it's supply when braking?
vivekiny2k 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 08:41.

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