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-   -   Strange loss of braking ability. What happened? (https://www.team-bhp.com/forum/technical-stuff/149153-strange-loss-braking-ability-what-happened-5.html)

Not necessarily, rather than "Speed Vs Gear", it has to be "Speed Vs Engine speed"
For example, the Honda City i-Vtec at 100 kmph in second gear is below its red line, so down shifting to 3rd from 5th at that spped is definitely not going to result in permanent failure of the engine / drivetrain components. But in cars with shorter gearing ( especially diesel cars ) this may not be possible, as at 100 kmph, the car would be above the rev limit in 3rd gear too (?!) thus leading to internal damage.

But engine braking, when done in the right way, along with pedal acctuated braking - is one of the safest ways of reducing speeds with shorter distance.

As Aroy posted it doing in an Alto, where the gearing is shorter, I think the engine will shoot up in the range and over-revving for these small engines, that too suddenly is not a thing to be taken kindly by the small engines. And even if the engine is capable of coping with it, there is a drivetrain that suffers. And last but not the least, sudden deceleration can cause your car to spin out of control as the wheels may lose traction with the road.

OT but using the same engine braking in two-stroke scooters/ engines is a blasphemy.

:eek: W h y? That is an empirical assumption. Nothing is going to happen, whether to the engine, gearbox or suspension - none of them is facing undue stresses in dropping 2 gears. In fact, engine braking is the preferred method for safe deceleration - even going down a slope.

- Engine speed will always be within limits (within a couple of seconds)
- Engine components are tested for much more than red-line speed, and one is unlikely to reach those speeds
- No injection is taking place, so temperatures are well within limits
- Suspension doesn't get a jerk at all: both the chassis and the body are at speed, and neither is decelerated unduly when using engine braking
- Why will the vehicle go out of control? All the wheels are rolling, no?
- There will be a lag before injection is resumed due to driver demand (if Acc pedal is pressed) - the ECU is still facing negative torque (engine RPM accelerating without injection), so it will overrule driver demand till conditions are right

Engine braking, by dropping 1 or 2 gears as the situation warrants, is part of training for professional drivers in most countries (in India one is trained only to point the vehicle in the desired direction).

Even at 100KMPH?

Never denied that engine braking is a bad technique and surely it is the best thing you can do while coming down a slope or ghat roads. My point is just that if you come down too many gears at once, you can lose traction with the road because the car's inertia will keep it pushing forward but the gear ratio might want to contain the speed. This differential can be dangerous, esp. with gravel on roads, or any such adverse conditions where road grip may be compromised. This situation is technically termed 'shift-locking'.

Also, I have seen people that they try to match the speed of the engine to the gear by revving it a bit while keeping the clutch depressed. Once, that has been achieved, then only they take off the A pedal input. That method damages clutch, needless to say.

Also, dropping to 3rd gear from 5th at a speed of 100KMPH is also dangerous because it *does not* light up your brake lights even at that massive deceleration and thus creating a huge probability that the rear traffic may rear-end you.

For me, if while doing high speeds, I need to reduce my speed immediately because of traffic, I will first use the brakes and then simultaneously downshift for engine braking to come into effect. If I have time, I will go for the release-re-apply method or pump the brakes. Another case, if I just feel that I am going a bit too fast, I will just take off my foot from the gas pedal for a while and let the engine braking do the trick for me.

I still believe that the gearbox (and a bit of clutch too) will suffer if one tends to use engine braking with inappropriate gears.:) A good driver will understand his car gearing ratios and choose the proper gear to use engine braking.:)

Just some brake dust which had settled between your brake pads and discs which got removed after u braked a little a little ahead. Nothing to worry. Drive on. Get the pads and discs sand papered only if the sssssssssss sound is coming while you brake or when you are driving.

Classic case of brakes getting overheated. Nothing to worry. Just let the brakes go for a bit and then re apply when you brake hard.

Dropping 2 gears at a time say in an Esteem say he is driving at 100 in 5th and wants to use engine braking and engages 3rd won't damage anything other than will put a tiny viny amount more load on the synchronizing rings. But the right way to use engine braking is

5th --> 120 kmph

Want engine braking

4th---> Downshift and let clutch go, car will slow down

Then downshift to 3rd and then let clutch go again, car will slow down further.

Downshifting 5th to 3rd is not going to harm anything in the current moment but yes the synchronizer in the 3rd gear will be under little more load and if you keep doing it for long long years, the chances of a synchronizer ring breaking are present too. At the end of the day, its a small thin metallic ring.

Downshift further if needed to slow down more.

The speed at which the downshiftwill change according to vehicle and engine characteristics.

For example, in a Swift Diesel if you downshift to 3rd at 120 kmph, firstly the gearbox will resist like its life depended on it and even if you do manage to shove it in and let the clutch go, you ll see the rpm around 5000+ which is almost near its redline and would not advice to reach there.

Secondly the synchronizers in a diesel are under way more load than in a petrol. Downshifting into improper gears can ruin the gearbox in no time.



:thumbs up:thumbs up

Please compute the numbers instead of wondering. With a diesel, one is likely to be at 1500-1700RPM in 5th. It will initially go up to 2300 if one switches to 3rd. I am sure you can dig up the corresponding numbers for petrol engined vehicles.

:Shockked: Why are we talking of rallying / drifting techniques when the discussion is on normal driving circumstances? In that technique, one would have already ridden the brakes till the car is at a handleable speed before shifting. That needs a LOT of practice, doesn't happen by itself, works ONLY on RWD vehicles (one generally uses handbrake in rallying on turns), and doesn't have top-of-mind recall in emergency situations. Simplify, @saket77-ji!

- In engine braking, the wheels are always rolling (despite the shift) and the vehicle won't skid. Isn't that the primary objective of ABS? Please refer to the ABS thread. The 'shift-lock' (shift gear to lock wheels) is to cause the rear to drift by locking wheels - drift won't happen if rear wheels don't lock

- You are assuming wheels lock when there is a large difference in (computed) engine speed. No, they don't

- The gear ratio doesn't contain speed. The energy of the moving vehicle is dissipated in the compression strokes of the rotating engine. And the engine is *always* rotating (in the context of this discussion). Are you assuming that the engine suddenly stops rotating on changing gears? Because, *only then* will the wheels lock

If there is a bad driver behind you, you are likely to get rear-ended even if you had a 5' flashing sign saying "Stop, for God's sake". You are, for whatever reason, assuming that when one goes from 5th gear to 3rd gear at 100kmph, the car will decelerate to 20kmph in 2 seconds. That is the least time taken for the other guy to realize, brake and slow down to avoid colliding with you. In reality it takes much longer to decelerate to 20-30kmph.

Please try it on an empty road yourself - that is all one can say.

You can't be doing that if you are at 100! One always does engine braking before applying brakes. That *reduces* the chances of a skid if one happens to slam brakes all of a sudden. Engine braking is more effective in reducing the vehicle speed, IF one has distance to do that. ABS is still the best in such situations. "Pumping" brakes cannot replicate that - it only reduces braking effectiveness without significantly reducing chances of skidding. Come on, you will never be fast enough to do it every 50ms.

A good driver will always
- know where to be on the road, and to keep (speed dependent) appropriate distance from the vehicle in front
- know not to disturb others on the road
- know how to concentrate and constantly project what *can* happen in front (and not suddenly notice traffic, especially at 100kmph)
- know not to rely on complex techniques, since K.I.S.S. is the best principle in any extenuating circumstance
- know to keep the speed as appropriate to road circumstances, and not do 100 if the road or traffic is not suitable to sustain it

Gearing and such technicalities are the last things on one's mind when in trouble. One always brakes instinctively - engine-braking is a technique to learn and memorize till it becomes 2nd nature. That is why it is taught everywhere.

A quick search in the official reviews of TBHP, most cars seem to clock 100KMPH mark at anything between 2-2.5K. So, surely shifting into 3rd gear from here is taking you considerably higher than 2300 RPM that you stated.

Not at all talking about drifting techniques. I probably used the wrong word - Lock. They don't lock. But sand and lose gravel may result in skid by losing the traction in case of sudden engine braking. Why would it be so difficult to be easy with the transmission and shift down one gear at a time when one is doing speeds as high as 100 KMPH and require engine braking, given that one has distance at his disposal.

Please see the previous point.

That is a bad point Anirudha. That point says that brake lamps are useless since if you have a bad driver in the following car, you will be rear ended anyway? Am I to think that then let us remove all the brake lamps because a bad driver will anyway rear end us and the good ones will anyway save us from the hit?

And 20 or 30 KMPH is not the point here. One can be rear ended even at 120 KMPH. It is your relative speed to the following car that matters. Even if I am using engine braking, I am in a habit to just give a deaf touch to the brake pedal so that the brake lamps come on, warning the following vehicles.

I am skipping the part in your post which talks about good drivers. If being good drivers were the only criteria, then the same good drivers would not have suffered because of mistake of morons on the road; multiple reports on our own threads.

+1. Agree with it completely. The natural instinct in emergencies is to use the brakes. Engine braking comes only if you have time or if it is a planned braking.

The stress is as much as you would get to 6K+ RPM, not much. The reason for going to 90 in second is the acceleration. When you overtake you do so in the least possible time especially on moderately crowded highways. The difference between 5 seconds and 20 while overtaking is the difference between being able to or not.

The gears are rated for the maximum torque the car is capable of delivering, and high RPM whether while accelerating or decelerating should not generate additional torque. Secondly at high RPM, you can only slow down and that too rapidly, so there is no danger there.

I have been doing this for more than fifteen years and there has been no effect on either the clutch or the gear box or the engine. In fact after a spirited drive, the engine smooths up and the FE increases.

That is not to say that you rip the car for ripping, these maneuvers are for cases which require them. Regularly going to 90 in second will affect the FE massively, but it is comforting to know that you have the power reserve when you need it.

We are discussing of engine braking for petrol engines or diesel?

Coming down 2 gears in a diesel car is NOT a good idea as 100 kmph @ 5th gear is at 2300 rpm so downshifting to 3rd gear would definitely redline the engine and decelerate too fast even to imagine by the guy behind.

I use engine braking + normal braking always but no jumping gears at any time.

Anurag.

I was discussing high revving engines where that is possible. Definitely normal diesel engines are out of this gambit.

In higher end cars like the Cruze or Mercs of Beemers yes, but in Swift Diesels and those range of cars, at 100, you are at 2300 rpm in 5th geer and most of them have 3rd gear maxed out at around 90 to 95 kmph and requires a customary 4th to break the 100 barrier. Shifting to 3rd at 100 in these vehicles is a definitely not a recommended practice unless you need extreme deceleration. If you continuously do end up shifting to 3rd at 100 in these cars, the synchronizer ring in the 3rd cog will be history in no time.


Agree, I never jump gears too, never ever. If required. I downshift a gear, release the clutch which slows down a car a bit then downshift again and release the clutch, but never go for 5th to 3rd or 4th to 2nd. If you try to do something like that, the way the transmission shifts you can realize, its not happy with what you are doing.

No point in being paranoid about sand and gravel. As long as one is not pulling a stunt, *and* the wheels are rolling, vehicle's inertia keeps it pointed straight. The moment the wheels lock - for whatever reason - one can expect a deviation.

And yes, the right method is shifting one notch down. But, even shifting 2 notches down is not going to cause a catastrophe. Won't cause gearbox failure, won't cause engine seizure, won't cause body to come off the chassis. Once one knows how to do engine braking, one actually does it 1 gear at a time.

The point was about showing consideration to the driver following you. You don't seem to be getting a measure of how fast or slow engine braking happens. Unless you go from 5th to 2nd or 1st (where probably the weakest links in the transmission chain will fail immediately due to rate of rise of loading), going down 1 or even 2 gears causes deceleration which is slower than using brakes. Slower, but surer - independent of brake condition or foot pressure on brake. Slower, but with far less chances of locking wheels.

If you are aware of the traffic (both in front and behind), and you are a decent driver, you will neither put yourself in harms way, nor be in a situation where others are disturbed. Engine braking situations at high speed occur on highways, and not within the city.

The point I was making was that if the vehicle following you has not left enough gap (yes, there are a *lot* of blessed people who ride tails at high speeds), it doesn't matter whether you have working stop lights or not. For anyone else who has left a decent distance to the vehicle in front, engine deceleration in the vehicle in front is not going to cause a panic situation - whether brake light comes on or not. That is called anticipation - the following vehicle will also drop down a gear to brake.

You are again speaking empirically. It doesn't matter at what speed you were, it is the difference in speed that governs the impact results. That is, the impact if you were at 0 and the vehicle behind was at 40, is going to be the same as when you were at 120 and the vehicle behind at 160.

Simple physics, sir. How long do you think it will take a vehicle the size of Swift to decelerate from 100 to 60 (differential of 40 over the guy following; engine-braking alone only)? 1 sec? 2 sec? 5 sec? 10 sec? Even assuming that the guy behind was not alert, how long will it take him to react?

No point griping about bad drivers. At the moment one reaches an alarming situation due to a mistake done by someone else, one is actually being a bad driver because one didn't anticipate the few possible things that the guy in front could do. Brake, go left, go right - all suddenly, right? Any other possibilities? Is that too much to anticipate?

Also, an 'accident' shouldn't be articulated as 'suffering' - even good drivers can be in situations where there is very little time or distance to manoeuver out of danger.

Probably you didn't understand the meaning of a technique 'becoming 2nd nature by training'. :) It will be a good experience for you to try getting a driving license in, say, Germany or Netherlands or Japan.

In India, to get a driving license one only needs to prove that a. can hold steering steady, b. doesn't jerk the vehicle when starting, and c. shows the correct hand signals!!! No one teaches you nor tests you for your knowledge of
- where to be on the road
- who has right of way at a crossing
- how to handle merging traffic
- how to overtake at speed
- how to space your vehicle from the one in front, ... the list is endless.
Apologies for an old man's rant. We are far away from the thread topic.

You simply cannot anticipate a lot of things that can happen. Few months ago, a car coming from opposite direction banged into the metal barricades kept on the road as a median. That entire barricade came hurling towards my car and hit the driver door with immense impact. I had posted about this on TBHP too. Could you have anticipated that? I could not, despite my good anticipatory skills.

May be I did not get the meaning of 2nd nature of driving but that does not take away the fact of driving more than 20 years on Indian roads with cars like Amby and Fiat 1100D, safely with no/ minor incidents and definitely never rear ended anyone or got rear ended too (if you don't count a tractor which rammed into my car while my car was parked) .
I don't know what it takes to get a licence in Germany or Netherlands or Japan, but if good driving is the criteria, then I will have no worries. :thumbs up

There is a lot of things which come as reflexes to me (or anyone) while driving which I cannot write about. Talk about second nature!

Wish to end this argument as it is not taking us anywhere.

Regards,
Saket

The points that I wrote in my previous post at the end. One gets an illustrated book to learn what one *must do* in various scenarios. One gets tested *and* certified by the Driving School instructor. Nothing is left to chance, intellect or innate physical abilities. The instructor stands to lose his livelihood if the person getting a license doesn't drive the same way everyone is supposed to. Not by 'reflexes' but by education and training. There is no alternative. If one gets into a culpable accident, they trace the instructor and put you back into a classroom!

:) '2nd nature' are things that get ingrained into the mind to give a deterministic response in a situation, like shot selection in cricket (reflexively one can only avoid a bouncer, but not play a shot). The difference between 'Reflexes' and '2nd nature' is the use of the conscious mind - not required with 'Reflexes'. 'Reflexes' dull with age, '2nd nature' doesn't! You must be a naturally safe / defensive good driver :thumbs up, but reflexes have nothing to do with it.

Agreed. Wrong term that I used, but I hope you will blame it on my vocabulary rather than...well...2nd nature of my driving!lol: