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Old 27th July 2007, 13:36   #1
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Question What is right mechanism to reduce speed?

I used to try out different options different times, wanted to kick off discussion on it.

Consider we are going in top gear and in speed which is not comfortable for next lower gear - say, my car has 5 gears, running in 4th gear is comfortable (RPM below 1500) not more than 50kmph, I am speeding at 70kmph in 5th gear.

Now either due to known stops (signal/speed breaker) or sudden obstacle I need to reduce the speed of car. There are few ways.
  1. To stop within short time, I apply break and keep reducing gears quickly.
  2. If I start reducing at considerable distance from stop, then I first stop acceleration, reduce gears one by one (RPM may be between 1500 to 3000 at each gear) and finally the speed is reduced/fully stopped (briefly applying break).
  3. Abrupt stop - no way else to just put down break to fully stop
#3 is anyway unexpected, so lets leave it for this discussion.

Lets take the goal is to get good FE (since this situation happens freq in city rides) as well as not driving in higher RPMs to keep engine's condition good (am I right?).

To meet this goal, what do you guys think is right way?

I follow #2 mainly and #1 as applicable.
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Old 27th July 2007, 13:44   #2
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If FE is your concern then you need to have good judgement when it comes to braking. If you know you have to brake, see if you can coast with your foot off the accelerator, thus reducing your speed. Rather, I have seen people accelerate all the way upto 2 feet from the vehicle in front and then apply brakes. If you let go of the A pedal you might not have to brake in the end at times.

If emergency braking is required then there is nothing like engine braking on our cars. With a steady and light foot on the B pedal go through the gears keeping in mind that you don't "over rev" in that particular gear you are going down to. It is not necessary to go through each gear. Suppose you are doing speeds of 120 in 5th gear and you need to brake quick just downshift to 3rd directly and brake lightly. Going into 2nd from 5th might be harmful to the engine as you might tend to over rev the engine in 2nd.

Also to find out which gear it is safe to shift down to, it would help if you knew where your limiter kicks in (at what revs and what speed in each gear).

Last edited by mclaren1885 : 27th July 2007 at 13:46.
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Old 27th July 2007, 13:44   #3
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I guess engine breaking ceratinly helps.

I used to comit the folly of clutching and breaking at the same time.

Was corrcetd by an expert on the subject. hence for me its simultaneous down shifts and gentle breaking while driving a manual.

I guess with the Auto box you dont really have a choice but to let go of the throtle pedal and plunge the break lever, and hold on to dear life unless offcourse you have ABS.
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Old 27th July 2007, 14:02   #4
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The most seamless method would be gradual braking towards a known obstacle like a speed breaker.

For maximum deceleration when drastic/unexpected obstacles come up esp at high speeds, engine braking + regular foot braking helps. Dont even consider using the handbrake in such a circumstance!
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Old 27th July 2007, 14:14   #5
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Like Mahesh mentioned gradual braking is the way during city drives.Pretty easy I must say.

Quote:
Dont even consider using the handbrake in such a circumstance!
Easy and a quicker way of learning to drift .
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Old 27th July 2007, 14:33   #6
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I assume by saying 'engine breaking' you all mean downshifting gears.

As I understand from replies, engine breaking with slight B pedal should make it easier for known obstacles - so that engine is not over rev'd in any gear as well as breaking is not applied abruptly, achieving FE & good engine life.

BTW during abrupt stop, do we get to downshift gear? I could only focus on B pedal?
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Old 27th July 2007, 20:41   #7
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Quote:
Originally Posted by sathya_nars View Post
BTW during abrupt stop, do we get to downshift gear? I could only focus on B pedal?
What you are doing is absolutely right. When attempting an abrupt stop, disregard downshifting and focus on the brake pedal and of course the steering so that you are prepared to counteract a skid, just in case.
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Old 27th July 2007, 20:58   #8
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suppose i judge that i need to be in 2nd gear to pass the obstacle and i am in 5th gear.. can i brake till speed is suitable for 2nd gear and downshift to 2nd from 5th? this is what i do.. or do i have to go 5-4-3-2 instead of 5-2. in fact my downshifts are always direct to the desired gear in the city but upshifts are always gradual.
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Old 27th July 2007, 21:13   #9
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Quote:
Originally Posted by rr_zen View Post
What you are doing is absolutely right. When attempting an abrupt stop, disregard downshifting and focus on the brake pedal and of course the steering so that you are prepared to counteract a skid, just in case.
Infact, what you guys are suggesting here is absolutely wrong. In case of abrupt stops its MANDATORY to downshift on FWD cars. This is to have a balanced weight distribution. As opposed to having the rear end light and thus prone to stepping out by only using the brakes. It could prove fatal were the tires to lock up.
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Old 27th July 2007, 21:48   #10
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Quote:
Originally Posted by mclaren1885 View Post
In case of abrupt stops its MANDATORY to downshift on FWD cars. This is to have a balanced weight distribution. As opposed to having the rear end light and thus prone to stepping out by only using the brakes. It could prove fatal were the tires to lock up.
When we say 'abrupt', the scenario that is being referred to normally is one where the driver has hardly anytime to bring the vehicle to a halt, due to less time on hand to react. Given this scenario, downshifting from 5th to 4th, 4th to 3rd...and finally 2nd to 1st is virtually impossible.

Downshifting for sure is the best and safe way to bring the vehicle to a stop but not in a scenario that is referred as ‘abrupt’. The success of engine braking is directly proportional to the time that the driver has on hand, to react to the situation.
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Old 27th July 2007, 22:00   #11
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Quote:
Originally Posted by rr_zen View Post
When we say 'abrupt', the scenario that is being referred to normally is one where the driver has hardly anytime to bring the vehicle to a halt, due to less time on hand to react. Given this scenario, downshifting from 5th to 4th, 4th to 3rd...and finally 2nd to 1st is virtually impossible.

Downshifting for sure is the best and safe way to bring the vehicle to a stop but not in a scenario that is referred as ‘abrupt’. The success of engine braking is directly proportional to the time that the driver has on hand, to react to the situation.
Read Mclarens first post, he clearly mentions that going down all the gears 1 by 1 is not needed. Abrupt stops would actually need downshifting to a lower gear (3rd or 2nd or even 1st) as the case may be (Depending on initial speed). Its not difficult. It becomes natural reaction with practising downshifting as per Mclaren during regular stops.


stimulus

- right leg -brake
- left leg - dis-engage-engage
-left hand - guide to the "to" gear

Right leg -left leg - left hand - works simultaneously

Last edited by 1100D : 27th July 2007 at 22:07.
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Old 27th July 2007, 22:03   #12
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Quote:
Originally Posted by mclaren1885 View Post
In case of abrupt stops its MANDATORY to downshift on FWD cars. This is to have a balanced weight distribution. As opposed to having the rear end light and thus prone to stepping out by only using the brakes.
Quote:
Originally Posted by rr_zen View Post
When we say 'abrupt', the scenario that is being referred to normally is one where the driver has hardly anytime to bring the vehicle to a halt, due to less time on hand to react. Given this scenario, downshifting from 5th to 4th, 4th to 3rd...and finally 2nd to 1st is virtually impossible.

Downshifting for sure is the best and safe way to bring the vehicle to a stop but not in a scenario that is referred as Ďabruptí. The success of engine braking is directly proportional to the time that the driver has on hand, to react to the situation.
IMHO, Both of you guys are right. In an emergency, there is very little time to react, all you have to do is slam the brakes & hold on to the steering & try to control the car if you have enough time, then slot it into 1st gear straightaway, there is no point in doing anything else.
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Old 27th July 2007, 22:37   #13
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Quote:
Originally Posted by rr_zen View Post
When we say 'abrupt', the scenario that is being referred to normally is one where the driver has hardly anytime to bring the vehicle to a halt, due to less time on hand to react. Given this scenario, downshifting from 5th to 4th, 4th to 3rd...and finally 2nd to 1st is virtually impossible.

Downshifting for sure is the best and safe way to bring the vehicle to a stop but not in a scenario that is referred as ‘abrupt’. The success of engine braking is directly proportional to the time that the driver has on hand, to react to the situation.
Only braking is no doubt better for fuel efficiency but in case of life threatening situations in FWD cars one has to dowshift and downshift hard (not gradual).. suppose someone is almost heading for a head on collision and there is no escape route then I think he/she should forget about the car, slam the brakes, slot to 1st gear (no heel toe in this situation) and pray....
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Old 27th July 2007, 23:58   #14
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Quote:
Originally Posted by rr_zen View Post
When we say 'abrupt', the scenario that is being referred to normally is one where the driver has hardly anytime to bring the vehicle to a halt, due to less time on hand to react. Given this scenario, downshifting from 5th to 4th, 4th to 3rd...and finally 2nd to 1st is virtually impossible.

Downshifting for sure is the best and safe way to bring the vehicle to a stop but not in a scenario that is referred as Ďabruptí. The success of engine braking is directly proportional to the time that the driver has on hand, to react to the situation.
rr_zen, as pointed out by 1100d it is not necessary to shift down in a sequence. By this I mean you don't have to go from 5th - 4th - 3rd - 2nd to stop your car. For eg, say you are at 120kmph in 5th gear. You see something abruptly and decide to stop. What you ought to do is know a few things. Like what speed does your car hit at redline in second gear. What could your rpm's be in case you downshift a couple of gears at one go.

Say if I am doing 180 in a baleno there is no chance of me being able to shift into 2nd from 5th. Since the engine will be over revving and could be fatal to the engine. Instead what I would do is shift into 4th, braking at the same time and shift immediately into 2nd. If I am doing 120 in 5th gear it goes without saying that one can easily shift to 2nd as baleno redlines in 2nd at 100. So if you are judiciously using the brakes and downshifting in this manner it IS the quickest and safest way to stop a car.


Point in case, suppose I am at 120 and need to stop abruptly using the brakes as you pointed out, what could happen is.

1. Locking up of brakes, thus eliminating steering manouvarability and also increasing your braking distance.

2. Transfer of weight from rear end to front end by braking thus the rear end of the car is prone to step out causing massive oversteer which could prove to be fatal once again. Most often the reason why you see cars loosing control on hard braking

To avoid this, were you to use engine braking the weight transfer will move towards the rear keeping the car in a more stable condition, prevent tire locking and enable you to maybe steer away from danger. Also the fact that now that you are in the right gear you could use the power on tap and accelerate away from the obstacle. By staying in 5th gear to duck either sides of the obstacle will be impossible.

As 1100d has pointed out its an instantaneous reaction once you understand how it works.

On seeing the obstacle, brake lightly with right foot. Go on the clutch with your left foot, use left hand to downshift into a suitable gear while maintaining steering position with the right hand. Continue to brake with your right foot GRADUALLY and not abruptly how ever panic stricken the situation maybe. Keep calm and remember the basics. Half the accidents in India are caused due to people not following this simple technique.
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Old 28th July 2007, 00:09   #15
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Taking what Mclaren may have missed out (but would have definitely going at the back of his mind) is, with the cars available in our market, braking HARD from triple digits speeds is not about stand on the brakes hardest and pray to God that it stops. The surface contaminants, the slopes or even condition of your tyres could then mean you would be loosing out of control. From those speeds, its a measured process. Unless one is prepared or able to do that, it is not advisable to go to those speeds and keep there continously.

Brake modulation is a "Must", (unless you have ABS)
Engine braking is a Must from those speeds and for lower speeds its recommended.
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