New drivers in the snow.

berliner

They don't learn to change down assisting braking ( old school) they just brake in top then stick it neutral then first to go. Yikes.
My kids scare me. But what can I say ?? They've learned the correct way.??

Ollieda

Well if their driving that way then they had a bad instructor.

Engine braking is the way I was taught a few years ago and it's the way some of my friends were taught very recently. AFAIK it's still considered the correct way as you maintain more control of the vehicle.

With most modern cars there's no difference for fuel in coasting in or out of gear so putting the car into netural and coasting doesn't decrease fuel consumption (something that used to be classed as the main pro of not using engine braking!)

desweller

Ollieda wrote:

Well if their driving that way then they had a bad instructor.

Engine braking is the way I was taught a few years ago and it's the way some of my friends were taught very recently. AFAIK it's still considered the correct way as you maintain more control of the vehicle.

With most modern cars there's no difference for fuel in coasting in or out of gear so putting the car into netural and coasting doesn't decrease fuel consumption (something that used to be classed as the main pro of not using engine braking!)

I went on one of those driver improvement courses in July, and I can confirm that the officially approved technique is to brake without shifting gears, then go straight into the gear you're going to use.

Like you, I was taught to use engine braking - I had quite a heated argument with the instructor about it!

kettrinboy

In my car, in the snow and ice its essential to use the gears to slow down as i find the ABS keeps kicking in even with the lightest pressure on the brake pedal and the stopping distance actually increases,i,d be able to stop quicker with a non ABS car thats for sure modulating the brake pedal pressure, but i,d still use the gears as well.

mrushton

the Police aren't taught to use engine braking either. we don't get enough snow in this country so people aren't used to driving in the conditions that ar e out there. Snow/studded tyres and chains are de rigeur in Europe and allow people to drive more normally albeit with care whereas in the UK we think that we need a £50k 4 x 4 to get about

inkyfingers

My parents are on holiday so I borrowed their Freelander but feel so self conscious driving it and have managed perfectly well in my Golf when we've had fairly heavy snow in the kent the last couple of years.

jc4lab

Attended a Speeding fine safety course instead of 3 points..You get a two hour advanced driving lesson teling youn how crap you are instead.Its a good thing really...Tyres and Tarmac when queining is screamed at you etc..... ...They call it coasting when you dont use gears to slow you down..and mine was picked up straightaway...Passing the test is not the end..just the beginning of learning to drive..motorways entering & leaving i,distance drinvins etc is not covered..Siimalerly icy roads..Nothing like insurance claim against you and increased insurance to make you drive more carefully

keef66

We get a half day driver safety training every other year. All the instructors are ex traffic cops. No engine braking; you get nagged if you go down the gears approaching junctions etc. "Brake pads & discs are easier / cheaper to replace than clutches & gearboxes" (sounds like budgetary considerations are what shapes police driving policy)

Appropriate speed / distance and smooth braking, steering and acceleration are what keeps you safe in the snow. No amount of engine braking will help you once you're careening sideways down a hill into oncoming traffic.

inkyfingers

jc4lab wrote:

..Nothing like insurance claim against you and increased insurance to make you drive more carefully

On a similar note, nothing makes you check your blindspot better better than reversing into a very solid fencepost

beverick

Few drivers understand the term "engine braking". They think that changing down and lifting the clutch without first increasing engine's revs is engine braking. It's not. That's clutch braking and leads to the familiar 'whine' (from the clutch) as it tries to slow and potentially destabilised the vehicle.

True engine braking (to make a relatively small scale reduction to the vehicle's speed by adjusting the accelerator) should be very used carefully in slippery conditions because the braking effect is only applied to the driven wheels. You need to ensure that the revs of the input and output sides of the clutch are matched at all times and 'feather' your foot's pressure from the accelerator. The vehicle's speed should decay gently and you should only declutch and change down to an appropriate lower gear when you have slowed to your desired speed.

Remember that in using engine braking you don't have use of the electronic safety gismos and gadgetry that's fitted to the braking and suspension systems on even entry level vehicles these days such as ABS, automatic brake force distribution and even automatic adjustmens to the suspension damping.

There is also the fact that, in applying the brakes, you're also telling the road user behind you that you're slowing and hence giving them more time to react - and in poor conditions you need all the time you can get.

In a vehicle with front wheel drive (ie most cars and 'light goods' vehicles) agressive or over-use of engine braking is likely to cause the front of the vehicle to skid hence losing directional control especially as the vehicle's mass is thrown over the front wheels.

The situation is potentially not as bad in a rear wheel drive when, although the rear wheels may skid, you will probably still have directional control. However, rear wheel drive is no real advantage if you've just ploughed the vehicle rear end first into the scenery!

nb, Depending on the design and sophistication, engine braking on a 4x4 vehicle's may only be applied to either the front or rear wheels so you may get either of the above happening. You just may not know until one end of the vehicle brakes away.

Bob

Dancing Bear

its not just in snow and ice that engine braking benefits, its in dealing with the unexpected slippy road surface - I was taught to engine brake, raced on circuits in competition and shudder at the thought of relying on one braking system only

This wrong gear selection and brake and hope teaching is a nonsense

desweller

beverick wrote:

Few drivers understand the term "engine braking". They think that changing down and lifting the clutch without first increasing engine's revs is engine braking. It's not. That's clutch braking and leads to the familiar 'whine' (from the clutch) as it tries to slow and potentially destabilised the vehicle.

Would you mind explaining how the clutch can provide a retarding force?

turnerjohn

kettrinboy wrote:

In my car, in the snow and ice its essential to use the gears to slow down as i find the ABS keeps kicking in even with the lightest pressure on the brake pedal and the stopping distance actually increases,i,d be able to stop quicker with a non ABS car thats for sure modulating the brake pedal pressure, but i,d still use the gears as well.

Although ABS is rubbish in the snow, theres no way even a racing driver with lightning last reactions can break then ABS...the advances with EBD as well means the electronic braking systems are far faster to react then us mere mortals.

Gears are still the best way to "slow down" and increase grip due to engine breaking

billysan

Im probably wrong, so feel free to correct me.....

I thought the practice of enginer braking was from the days when a cars brakes were not to be 100% relied upon? for the same reason you still see 'use low gear' signs at the top of steep hills. The practice also carried more relevance when cars didnt have ABS. Proper engine braking also reduces the chance of locking a driven wheel.

Modern car brakes are excellent at bringing the car to a stop, regardless of the gear you are in, in most situations EXCEPT SNOW.

The reason for the change in tuition techniques comes from these increases in brake technology. And from the fact that until recently we didnt ever really get these extreme conditions (down south anyway).

If you learn on the continent in one of the countries that can and do cope with a real winter, they still teach it.

MattC59

DesWeller wrote:

beverick wrote:

Few drivers understand the term "engine braking". They think that changing down and lifting the clutch without first increasing engine's revs is engine braking. It's not. That's clutch braking and leads to the familiar 'whine' (from the clutch) as it tries to slow and potentially destabilised the vehicle.

Would you mind explaining how the clutch can provide a retarding force?

It doesn't (I assume your commend was tinged with an element of sarcasm )

The clutch just links the engine to the wheels, via the transmission. The engine naturally wants to return to it's idle speed, and in doing so, will slow the wheels.

schweiz

It's not just in the UK, and it's not just in winter.

<rant>
I drives me mad when people drive down a mountain pass in top gear and their brake lights are flashing like a mobile disco! Their brakes must be roasting by the time they get to the bottom.

Stick it in third or fourth and you'll be limited to 60-70 km/h so there's no need to brake until the hairpin and you're already in the right gear to accelerate out of the bend.

Keeping the foot brake pressed when stopped at th lights is another bugbear of mine. I don't want to be blinded by your high intensity brake light when I know you've stopped, and I've stopped behind you! Handbrake on, release foot brake and maybe even select neutral and release your clutch! Your brake disks will thank you for it too, especially if you've been riding the brakes down the aforementioned pass and your pads and disks are cooked!

</rant>

markos1963

beverick wrote:

.


In a vehicle with front wheel drive (ie most cars and 'light goods' vehicles) agressive or over-use of engine braking is likely to cause the front of the vehicle to skid hence losing directional control especially as the vehicle's mass is thrown over the front wheels.


Bob

Not sure I would agree with this, the need to throw the weight of a car over the steering wheels is a good thing. Increased force will improve traction and as long as the wheels don't lock up steering will be enhanced. This is one reason racers brake deep into bends and don't lift off the brakes until they have turned into the bend. Obviously speeds are relative and you wouldn't be throwing a car around to the same extent

bexley5200

heavy snow and ice is a problem for most cars around here i just put my boots on and walk on by easy

rake

abs is very fast acting but im not sure its sensitive enough pressure wise on very reduced traction, i know someone who went out of a junction at walking speed because the abs wouldnt apply the brakes with the tiny amount of grip when skidding would have stopped it.

desweller

It's all about coefficients of friction. If the value of mu available to a rolling tyre is higher than to a sliding tyre, ABS will work. If it isn't, it won't.

On ice, it isn't.

rake

i didnt know that was the case on ice, ive learned something new today.must be usefull for skiing, or maybe not

desweller

I think it has something to do with dissipating energy by melting ice rather than via the braking mechanism. Snow is a slightly different matter though.

beverick

markos1963 wrote:

beverick wrote:

.

In a vehicle with front wheel drive (ie most cars and 'light goods' vehicles) agressive or over-use of engine braking is likely to cause the front of the vehicle to skid hence losing directional control especially as the vehicle's mass is thrown over the front wheels.

Bob

Not sure I would agree with this, the need to throw the weight of a car over the steering wheels is a good thing. Increased force will improve traction and as long as the wheels don't lock up steering will be enhanced. This is one reason racers brake deep into bends and don't lift off the brakes until they have turned into the bend. Obviously speeds are relative and you wouldn't be throwing a car around to the same extent

I agree that, in certain circumstances, having the mass move forward (in a controlled manner) may be beneficial but, in general, I'd say that this is only in conditions where grip can be relied upon. In most cases of very poor grip (ie ice and snow) I'd prefer to balance the mass as near to the centre of the vehicle as possible.

Irrespective of where the centre of mass lies you only have the same amount of grip available to you so where the mass lies is key to maintaining stabiity and directional control (bearing in mind that a rear wheel skid will lose directional control as much as a front wheel skid will of course).

Racing drivers will usually brake BEFORE a bend and then try to get the power back on as they enter the bend. Partially to maintain the stability of the car and secondly to 'balance' the effect of steering (ie control the forces being exerted on the vehicle's mass).

That said, as you get used to a circuit and want to squeeze the lap times you can brake later and let your braking trail off into the first section of the bend (aka braking 'deep' into the corner) but you need to have ultimate confidence in your vehicle and the grip available. You probably wouldn't want to do it in a front wheel driver car or any that understeers to a substantial amount.

The general rule is that if you brake on a corner at speed and there's only one place you're going and that's into the scenery.

Bob.

desweller

beverick wrote:

DesWeller wrote:

beverick wrote:

Few drivers understand the term "engine braking". They think that changing down and lifting the clutch without first increasing engine's revs is engine braking. It's not. That's clutch braking and leads to the familiar 'whine' (from the clutch) as it tries to slow and potentially destabilised the vehicle.

Would you mind explaining how the clutch can provide a retarding force?

If the input side of the clutch is spining slower than the output side when you release the clutch pedal the friction generated between the clutch plates will provide a retarding force until either the power from engine's compression is overwhelmed and the revs increase to match the road speed, or until the force being transmitted from the roadwheels is overwhelmed and the vehicle slows to match the speed of the engine (usually a combination of the two). in both cases, the initial braking effect is provided by the clutch which generates heat in the clutch and, in extreme cases, smoke.

Engine braking is only utilised fully when the clutch plates are no longer slipping.

That is certainly a novel analysis. Using your logic, during acceleration the clutch is providing the accelerating force until the crankshaft speed matches the gearbox input shaft speed.

captain_chaos

Ollieda wrote:

Well if their driving that way then they had a bad instructor.

Engine braking is the way I was taught a few years ago and it's the way some of my friends were taught very recently. AFAIK it's still considered the correct way as you maintain more control of the vehicle.

With most modern cars there's no difference for fuel in coasting in or out of gear so putting the car into netural and coasting doesn't decrease fuel consumption (something that used to be classed as the main pro of not using engine braking!)

With the continued demand on fuel economy all modern gasoline & diesel vehicles (upto 5-10 years old) will go into fuel cut when the pedal is closed and the engine is driven by the vehicle - i.e. in gear. Fuel cut means exactly that - no fuel. The only difference between vehicles is how aggressively the fuel cut calibration is implemented.

On the European drive cycle (which is relevant to most of the forum users) there is quite a lot of opportunity to be in fuel cut and hence get fuel economy improvements and hence a vehicle manufacturer will take every few % they can get. I know this as it is part of my job. I can also significantly improve the fuel economy in any manual vehicle by deliberately driving to maximise fuel cut periods

In addition, all electronic systems, safety or otherwise, interact and hence being in gear and braking is an accepted vehicle operating mode and the systems will be calibrated for this.

The bottom line is that all these systems make significant improvements to driving safety. The 2 issues that reduce this are the driver and the fact that, to quote Scotty - "you cannot defy the laws of physics". I suggest that the driver is the most unreliable, inconsistent and dangerous part of the vehicle

Smokin Joe

Speaking as someone who spent 20 years as an ADI Beveric hit the nail on the head when he said few drivers understand engine braking. It is NOT changing down the gearbox to slow the car down, which is both dangerous (two wheel braking only) and damaging to the transmission. The correct technique is to ensure you are in the correct gear for the conditions, whether a slipper surface or a downhill gradient, so that you have sufficient revs to allow the engine speed to drop and let it's compression retard the speed of the vehicle.

Too many drivers use too high a gear under the false impression that it saves fuel. The correct gear to be in is the one that lets the engine spin at it's optimum RPM, so that it is neither labouring nor over revving and you have enough throttle control to both accelerate and slow down by use of the accelerator.

MattC59

DesWeller wrote:

It's all about coefficients of friction. If the value of mu available to a rolling tyre is higher than to a sliding tyre, ABS will work. If it isn't, it won't.

On ice, it isn't.

I was just trying to think of a way of conveying the physics as succinctly as this, but couldn't............ well done 8)

ddraver

So how do I/we find out our engines optimum RPM?

I hear what you re saying though Joe, perhaps i have been engine braking wrongly - presumably the quicker deceleration as I lift the clutch is not the aim of the game...The ABS on my Scenic (quiet!!) though has a really nasty habit of stopping all braking on snow/ice which is a horrible heart in mouth moment cos it feels more likes that brakes have failed than the ABS is kicking in!

rake

Smokin Joe wrote:

Speaking as someone who spent 20 years as an ADI Beveric hit the nail on the head when he said few drivers understand engine braking. It is NOT changing down the gearbox to slow the car down, which is both dangerous (two wheel braking only) and damaging to the transmission. The correct technique is to ensure you are in the correct gear for the conditions, whether a slipper surface or a downhill gradient, so that you have sufficient revs to allow the engine speed to drop and let it's compression retard the speed of the vehicle.

Too many drivers use too high a gear under the false impression that it saves fuel. The correct gear to be in is the one that lets the engine spin at it's optimum RPM, so that it is neither labouring nor over revving and you have enough throttle control to both accelerate and slow down by use of the accelerator.

its more the pumping losses of the engine trying to suck air through a closed throttle plate that causes engine braking . the stroke after compression pushes the pistons down again due to the pressure built up, unless you have a peterbuilt truck with a decompression 'jake' brake.
pumping losses make it more efficient to drive round in a high gear(within reason) because the throttle is open more thus the engine doesnt have to waste as much energy sucking its air supply in. This is where much of the extra fuel efficiency of a diesel engine comes from, there is no throttle plate so they waste not much energy sucking the air in.

daviesee

ddraver wrote:

So how do I/we find out our engines optimum RPM?

Drive along normally and note the rev counter reading or listen to engine note if you don't have one.

Can you accelerate? If yes then you are okay, if not you are in too high a gear with no power (or too low a gear and on the rev limiter but you would probably notice that ).

If you take your foot off the accelerator pedal does the car slow down? If yes then you are okay, if not then you are in too high a gear.

The useable RPM will be quite a wide band but with practice you should automatically know within around +/-500 rpm. Optimum RPM takes practice and knowledge of the vehicle. In slippery conditions in a petrol driven car i usually keep it at around 2500 rpm but cars vary and diesels are usually lower.

kettrinboy

ddraver wrote:

So how do I/we find out our engines optimum RPM?

I hear what you re saying though Joe, perhaps i have been engine braking wrongly - presumably the quicker deceleration as I lift the clutch is not the aim of the game...The ABS on my Scenic (quiet!!) though has a really nasty habit of stopping all braking on snow/ice which is a horrible heart in mouth moment cos it feels more likes that brakes have failed than the ABS is kicking in!

I know exactly what you mean, i have a 2010 Renault Scenic and the the ABS on mine is just how you say, I thought it was just me, last week on braking for a junction from about 20 mph the ABS would not let it brake and i had to steer the car off the road to avoid hitting a car waiting to turn up the back, this was the very first time i had braked in this car on solid ice so ive learned a lesson,ABS may well save lives when used at higher speeds in the dry or even wet conditions by letting you steer during heavy braking, but on ice i think it could well cause a few accidents in some situations.