Downshifting in road cars

[N4D13]

Hi everyone! I got my driver's licence just a couple of years ago and I still have a beginner's doubt. It's about downshifting to reduce speed, e.g., when coming out of a highway. To which point is it beneficial or harmful to reduce speed downshifting rather than actually braking the car? Would it be advisable -or not- to, for instance, switch to 3rd gear when I'm doing 70 km/h to make the car go more slowly?

Hey, please don't be too harsh if it's a silly question or anything - I'm just 20 and it goes without saying that I don't have the experience, not any less the racing background, of some of the members in this forum! :p

[henners88]

I don't know if this is the done thing but I tend to pull my car into neutral and coast when I'm approaching a junction to save a bit of fuel. I'll get the car down to the suitable speed and select the correct gear. I do this on hills too but always keep my hand on the gear stick in case I need to use the gearbox to slow down. I've been driving for 14 years so perhaps I have too many bad habits I don't know. :)

[Mintexmemory]

When I took my test (1971) disc brakes were still a relatively de luxe item so drivers were taught to decrease speed by engine braking so as not to put too much strain on the drum brakes. Like Henners, over the years my driving style has changed so that I will coast in neutral as much as possible when slowing down scrubbing off excess speed by the occasional dab of the brakes. I never use engine braking unless driving down steep gradients in the mountains.

[Koz]

I don't know if this is the done thing but I tend to pull my car into neutral and coast when I'm approaching a junction to save a bit of fuel. I'll get the car down to the suitable speed and select the correct gear. I do this on hills too but always keep my hand on the gear stick in case I need to use the gearbox to slow down. I've been driving for 14 years so perhaps I have too many bad habits I don't know. :)

Freewheeling is stupid and dangerous.
In neutral you have no control. Keeping your hand on the stick means nothing, you will also have to rev match and think - that's the split second that kills you or someone else.

What happens if your engine stalls?

While in neutral you WILL waste more fuel, because the injector will be feeding fuel to the engine to keep it alive. Coasting downhill in gear, the injectors will pretty much stop pumping fuel to your engine.

The less time spent in neutral the better.

[Koz]

Hi everyone! I got my driver's licence just a couple of years ago and I still have a beginner's doubt. It's about downshifting to reduce speed, e.g., when coming out of a highway. To which point is it beneficial or harmful to reduce speed downshifting rather than actually braking the car? Would it be advisable -or not- to, for instance, switch to 3rd gear when I'm doing 70 km/h to make the car go more slowly?

Hey, please don't be too harsh if it's a silly question or anything - I'm just 20 and it goes without saying that I don't have the experience, not any less the racing background, of some of the members in this forum! :p

Beneficial or harmful... The idea is to always be in the correct gear for the correct speed.
Use your transmission (drop through the gears) in conjunction with the brakes to slow it down.
You should go downhill on a gear that will maintain the speed you want rather than final gear, because your speed will only keep increasing.

Popping into 3rd gear from 5th doing 140 isn't generally a good idea for the livelyhood of your motor, but it's not a big deal as long as your shift properly.

[A FONDO]

Engine brake for cars is pointless, it makes sence only for loaded trucks/buses. Early downshifting, especially with a gearbox without synchronizers can only bring you trouble. A friend of mine got his camshaft broken thanks to it. (his car was Opel though :D )

[Starter]

Engine brake for cars is pointless, it makes sence only for loaded trucks/buses. Early downshifting, especially with a gearbox without synchronizers can only bring you trouble. A friend of mine got his camshaft broken thanks to it. (his car was Opel though :D )
That wasn't the downshifting which broke the engine unless he went into too low a gear and over reved it.

[Starter]

The answer to your question is that it's your choice what to do. It is true that you have slightly better control of your car if it's in gear. Downshifting will save a little brake wear so long as you rev match, otherwise you'll substitute clutch wear for brake wear. I suggest you learn to heel & toe. The benefits are better car control, it sounds cooler, and you can impress the heck out of your friends with your skill.

[schmenke]

I always downshift (even in the wife's 6-sp auto minivan) to save brake wear. Like mentioned, as long as you watch your revs there is no danger to the engine.

[schmenke]

Engine brake for cars is pointless, it makes sence only for loaded trucks/buses. Early downshifting, especially with a gearbox without synchronizers ...

What modern car these days does not have a syncronized gearbox? :s

[Mark]

As long as you aren't bouncing it off the rev limiter then it's fine to use engine braking in this way.

I often do put it into 3rd coming off a motorway to slow down experience will tell you when to do that.

[SGWilko]

I don't know if this is the done thing but I tend to pull my car into neutral and coast when I'm approaching a junction to save a bit of fuel. I'll get the car down to the suitable speed and select the correct gear. I do this on hills too but always keep my hand on the gear stick in case I need to use the gearbox to slow down. I've been driving for 14 years so perhaps I have too many bad habits I don't know. :)

Modern cars will actually cut off the flow of fuel to the cylinders on engine braking, so you are likely using more fuel by coasting.

[Bagwan]

The use of engine braking is a wise one for a couple of reasons .
As has been mentioned already , it can save fuel .
More importantly , it saves brakes , and this is the most important thing in a crisis . Losing a clutch will only keep you stationary , and not make you dead .
Losing brakes can kill you .

But , there is one mitigating factor to engine braking that everyone using it must be aware .
When doing so , you do not display brake lights to those behind , and therefore can be at risk of being struck from behind by drivers not warned of your slowing speed .

So , if you choose to use engine braking , watch your mirrors , and dab those brakes a little so those others will get a clue .

[Bagwan]

Sorry Sorry double double post post .

[Zico]

In addition to Bagwans comments... The main reason to change down through the gears and use engine braking is to improve braking efficiency and performance. When freewheeling in neutral your 2 front wheels are braked independently of each other, an individual wheel can lock, ABS will be activated and stopping distances increased. When using engine braking the wheels are coupled to each other through the driveshafts, differential and gearbox while the torque and inertia from the engine and flywheel also greatly reduces the chance of a wheel lock up.

I reckon I could probably improve my stopping distances by around 20-30% by changing down through the gears vs freewheeling and just slamming on the brakes so it's definately a good habit to get from the off.

[Bagwan]

Is that actually true , Zico , as the diff on most vehicles doesn't lock , so would the engine braking be onto both wheels ?
Without a diff lock vehicles will spin the tire with the least grip , but does this work the same in reverse ?

[donKey jote]

When freewheeling in neutral your 2 front wheels are braked independently of each other, an individual wheel can lock, ABS will be activated and stopping distances increased. When using engine braking the wheels are coupled to each other through the driveshafts, differential and gearbox while the torque and inertia from the engine and flywheel also greatly reduces the chance of a wheel lock up.

Is that why you don't have a RWD vehicle, where the front wheel are always freewheeling then ? :andrea:

Not quite sure I understood that... an individual wheel can lock whether it's freewheeling or not :confused:

Anyway, the stopping distance would increase due to the locking of the wheel and not due to ABS :)

[A FONDO]

In addition to Bagwans comments... The main reason to change down through the gears and use engine braking is to improve braking efficiency and performance. When freewheeling in neutral your 2 front wheels are braked independently of each other, an individual wheel can lock, ABS will be activated and stopping distances increased. When using engine braking the wheels are coupled to each other through the driveshafts, differential and gearbox while the torque and inertia from the engine and flywheel also greatly reduces the chance of a wheel lock up.

I reckon I could probably improve my stopping distances by around 20-30% by changing down through the gears vs freewheeling and just slamming on the brakes so it's definately a good habit to get from the off.

Of course one should downshift the gears while braking! The initial dilemma was, should one use more aggressive downshifting in order to reduce or even avoid usage of the brakes.

[Zico]

Is that actually true , Zico , as the diff on most vehicles doesn't lock , so would the engine braking be onto both wheels ?
Without a diff lock vehicles will spin the tire with the least grip , but does this work the same in reverse ?


Yes, I suppose you are correct.... with fwd cars you have an open diff, or usually a 1 way diff (for acceleration only) in LSD equipped cars so its more to do with the weight/inertia from the engine braking reducing the chance of wheel lock up than a coupling linking each wheel. Engine braking certainly improves braking performance though.


Is that why you don't have a RWD vehicle, where the front wheel are always freewheeling then ? :andrea:

In theory fwd vehicles should be able to stop faster than a similar weight/spec rwd vehicle due to engine braking imo, no?


Not quite sure I understood that... an individual wheel can lock whether it's freewheeling or not :confused:

True, but see my comments above... less likely due to engine braking?


Anyway, the stopping distance would increase due to the locking of the wheel and not due to ABS :)

Yes and no. What I'm trying to say is.... If you can brake hard using as much of the available grip as possible without activating ABS you can usually stop quicker than with ABS activated as its only braking the wheel around half the time.

[Zico]

Of course one should downshift the gears while braking! The initial dilemma was, should one use more aggressive downshifting in order to reduce or even avoid usage of the brakes.


My apologies, my eyesight clearly isn't what it used to be. :/

[donKey jote]

In theory fwd vehicles should be able to stop faster than a similar weight/spec rwd vehicle due to engine braking imo, no?

True, but see my comments above... less likely due to engine braking?

not sure it's that relevant... your engine brake force is minute compared to the brake force. On normal tarmac at least.



Yes and no. What I'm trying to say is.... If you can brake hard using as much of the available grip as possible without activating ABS you can usually stop quicker than with ABS activated as its only braking the wheel around half the time.
Yes and no. If you can brake hard using as much of the available grip as possible without activating ABS you can usually stop quicker than with ABS activated (yes, although out of the reach of most normal drivers) because ABS only activates when you're past the optimum brake force. Apply too much force, and ABS will usually* stop quicker than with otherwise locked wheels, despite braking a few tenths less of the time.

*exceptions being for example deformable surfaces with older ABS algorithms

[Zico]

not sure it's that relevant... your engine brake force is minute compared to the brake force. On normal tarmac at least.

Agreed but it's the inertia behind the flywheel and rotating masses in the engine help stop the wheels from locking up and allows you to brake harder and stop quicker = relevant.



Yes and no. If you can brake hard using as much of the available grip as possible without activating ABS you can usually stop quicker than with ABS activated (yes, although out of the reach of most normal drivers) because ABS only activates when you're past the optimum brake force. Apply too much force, and ABS will usually* stop quicker than with otherwise locked wheels, despite braking a few tenths less of the time.

*exceptions being for example deformable surfaces with older ABS algorithms

Agreed.

[henners88]

Apologies for coasting in neutral.

[Gregor-y]

*exceptions being for example deformable surfaces with older ABS algorithms
Also known as my 2005 Subaru, whenever I'm not expecting it.

After 135,000 miles of downshifting the clutch is fine but the brakes were replaced around 100,000 miles.

[donKey jote]

Agreed but it's the inertia behind the flywheel and rotating masses in the engine help stop the wheels from locking up and allows you to brake harder and stop quicker = relevant.

What I mean is these forces are negligible ("not relevant") compared to those from the brakes, at least on normal surfaces with half decent grip.

What's important is that if you keep your wheels at the optimum slip, you stop quicker. This is what is relevant, not how hard you brake or whether it's using engine braking, ABS, you're own foot control system, or any combination of the three.

[Zico]

What I mean is these forces are negligible ("not relevant") compared to those from the brakes, at least on normal surfaces with half decent grip.

What's important is that if you keep your wheels at the optimum slip, you stop quicker. This is what is relevant, not how hard you brake or whether it's using engine braking, ABS, you're own foot control system, or any combination of the three.

Ahh. I thought we were discussing rwd vs fwd but no worries, I don't wish to debate the finer points and I think we understand each other. One thing is certainly true... ABS systems have come along way compared to the older systems that I'm more accustomed to than with the latest 4 channel systems. Apologies for beng way off topic from the threads original question... I think Gregor-ys comment covers it well from my POV though.

[TheFamousEccles]

Talk of downshifting to save brake wear is erroneous IMO - brake pads are made to wear out and as a consequence need to be checked regularly and replaced as necessary. Most automatic cars rely on braking to slow them as a vast majority of drivers are not trained to sufficient levels to consider using the autoshift in a manual mode, and of those who drive a manual car many in my experience have not been trained to "heel and toe" - a contentious thing on the road I think. Heel and toe is used by truck and other heavy vehicle drivers that don't have preselectors, but your average sedan driver on the road would likely increase their braking distance if they tried to do this.

Not that it shouldn't be taught however, anything that slows the car down more rapidly without causing brake lock-up is a good thing, but it is best on a track as you are all heading in the same direction, and corners/obstacles are generally known and skill levels are generally higher.

Take a defensive driving/advanced driving course - money very well spent and a heap of fun too. :up:

[Donney]

I always combine both things to have a better control of the car and so far so good.

[steveaki13]

I don't know if this is the done thing but I tend to pull my car into neutral and coast when I'm approaching a junction to save a bit of fuel. I'll get the car down to the suitable speed and select the correct gear. I do this on hills too but always keep my hand on the gear stick in case I need to use the gearbox to slow down. I've been driving for 14 years so perhaps I have too many bad habits I don't know. :)

I have done that in the past as well.


Apologies for coasting in neutral.

I too now owe that apology.

As it is I tend to just brake evenly while slowing down, rather than leaving it too late thus braking heavily.

I have also though downshifted at times on step hills etc.

I will have to try some of these tips to see how it feels.

The trouble in knowing little about workings of cars is that I too didn't realise that you waste fuel coasting.

[wedge]

Doesn't really matter, its whatever you feel comfortable with.

I used to stick it in neutral but now I leave it gear because of the sense of security of being in control and the need to make progress when appropriate.


Not that it shouldn't be taught however, anything that slows the car down more rapidly without causing brake lock-up is a good thing, but it is best on a track as you are all heading in the same direction, and corners/obstacles are generally known and skill levels are generally higher.

Harsh braking increases MPG because it is wasted energy hence KERS in F1 and so forth. So here's a fuel saving tip: when appropriate increase your braking distance/slowing down process by being smooth on the brakes (Jeez, I sound like JYS! and I hate is "smooth" diatribe). However if you don't use your car a lot then you need harder braking to rid the rust in the brakes.

[airshifter]

I tend to downshift, but at lower revs than I would upshift at. That allows the car to provide some engine braking and keeps you in a proper gear should you need to accelerate again. You don't have to bang downshifts at the redline or use heel and toe methods when dealing with normal traffic.

Most modern cars do in fact use a method of deceleration fuel cutoff, even some of the new automatics do it. At any time you are off the gas pedal even larger cars will show instantaneous fuel economy in the 3 digit range. In manual shift cars the MPG return is infinite during the time fuel is cut off, so if you can just get off the gas pedal a couple seconds sooner when approaching a light or stop it should have effect on your fuel consumption.

[Tazio]

Don't waste brake pad, and rotor millimeters by not using at least a little of your engines compression to brake by downshifting. Use your brakes in concert with your engine braking, and you will optimize brake, clutch, and transmission wear rates as long as you are not like a total dork and can't downshift smoothly. You can also save wear on these components by parking your rig, and not using it at all. :dork:

[ioan]

IMO the only time downshifting makes sense is on slippery roads, for the rest brakes are the best solution.

PS: Do the brake lights light up when you use downshifting to slow down?

[donKey jote]

PS: Do the brake lights light up when you use downshifting to slow down?
only if you're also on the brakes at the same time :p

[Starter]

IMO the only time downshifting makes sense is on slippery roads, for the rest brakes are the best solution.

PS: Do the brake lights light up when you use downshifting to slow down?
They do if you heel & toe.

[FormerFF]

No need to downshift while slowing. What I do is to simply let off the throttle and use what compression braking is available. When the engine speed is down around 1200-1400 rpm, I kick it into neutral and coast the last few mph. Brake pads are cheap, clutches are not. However, if you're on a steep mountain downgrade that's twisty, you may very well want to use a lower gear to get more compression braking, it's a little easier on the wheel brakes. For medium and heavy trucks in mountainous areas, it's a necessity, but unless you're driving a car made before about 1960, it's not required, as all recent cars have adequate wheel brakes.

I was recently in Arizona and was driving a Toyota Venza, which is something of a Camry wagon. We drove down a number of extended 6-8% grades, and barely had to touch the wheel brakes. That's on the motorway, if on a two lane road in the twisties, we'd have needed some brakes. The heavy trucks all geared down and used their compression brakes, but they did so by staying in the same gear. Downshifting is what you do as a result of the car slowing, not what you do to make the car slow.

As far as control goes, all the engine braking does is put a little braking force on whatever wheels they're attached to. As you slow, the compression braking diminishes to where it becomes inconsequential. If you're braking heavily, say on corner approach on the race track, and you have an old school three pedal setup, you get to do maximum braking while downshifting, since you need to be in the right gear by the time you reach the apex. To further complicate the issue, if you have an H pattern gearbox, you'll probably need to double clutch as well. That takes practice. Mismatching engine and transmission speed while doing maximum braking is a good way to spin the car, it's something best learned on the track. If you're needing maximum braking to avoid an incident, I'd not worry about shifting at all just avoid the incident, you can get the right gear later. And if you're needing to do this more than once a year, you're probably not looking far enough ahead, better to not be in the situation to need heavy braking at all, unless you're on the track.

To sum it up, don't put more wear on your expensive clutch and more expensive transmission synchronizers to reduce the wear on your cheap brake pads. Brakes are for stopping, clutches are for disconnecting the engine from the transmission.

[FormerFF]

Freewheeling is stupid and dangerous.
In neutral you have no control. Keeping your hand on the stick means nothing, you will also have to rev match and think - that's the split second that kills you or someone else.

What happens if your engine stalls?

While in neutral you WILL waste more fuel, because the injector will be feeding fuel to the engine to keep it alive. Coasting downhill in gear, the injectors will pretty much stop pumping fuel to your engine.

The less time spent in neutral the better.

I will agree with you that there is no need for excessive freewheeling, but I'm not seeing the dangerous part. I've been driving for 40 years, and I can't think of a situation where you'd need to go from deceleration to acceleration instantaneously. Can you think of an example?

[SGWilko]

I will agree with you that there is no need for excessive freewheeling, but I'm not seeing the dangerous part. I've been driving for 40 years, and I can't think of a situation where you'd need to go from deceleration to acceleration instantaneously. Can you think of an example?

Front wheel Drive vehicle losing traction on a wet/greasy bend - powering out generally helps

[wedge]

I will agree with you that there is no need for excessive freewheeling, but I'm not seeing the dangerous part. I've been driving for 40 years, and I can't think of a situation where you'd need to go from deceleration to acceleration instantaneously. Can you think of an example?

Lift-off oversteer :D

[wedge]

I will agree with you that there is no need for excessive freewheeling, but I'm not seeing the dangerous part. I've been driving for 40 years, and I can't think of a situation where you'd need to go from deceleration to acceleration instantaneously. Can you think of an example?

Lift-off oversteer :D

[Jag_Warrior]

Wimps! What I do is use the car in front of me to slow down. As long as you don't tap him too hard and pop the radiator, that method is golden!

[FormerFF]

Lift-off oversteer :D

I would never think putting the transmission in neutral unless I was planning on coming to a stop. i guess that's why I didn't think of those situations.

[driveace]

The idea of downshifting is of great advantage with a fully loaded car or van on a very long,steep downhill gradient,SO you take a lower gear and use cadence braking,this saves the brakes by using engine braking ,you can avoid the brakes overheating,where the pads and the discs become glazed,by the heat generated,so becoming less efficient !
It's OK for truck driver who can downshift and use the exhauster brake,or as the yanks call it ,compression brake .In a coach you would generally use the Telma,an electronic mechanism that works on the prop shaft,by usung large magnets !Coasting is dangerous as anyone taking the Theory Test in the UK will tell you as there are numerous questions on that Test as to why is coasting dangerous !

[driveace]

The idea of downshifting is of great advantage with a fully loaded car or van on a very long,steep downhill gradient,SO you take a lower gear and use cadence braking,this saves the brakes by using engine braking ,you can avoid the brakes overheating,where the pads and the discs become glazed,by the heat generated,so becoming less efficient !
It's OK for truck driver who can downshift and use the exhauster brake,or as the yanks call it ,compression brake .In a coach you would generally use the Telma,an electronic mechanism that works on the prop shaft,by usung large magnets !Coasting is dangerous as anyone taking the Theory Test in the UK will tell you as there are numerous questions on that Test as to why is coasting dangerous !