[Closed] Engine Braking?

It will be acted on both wheels but the diff may mean it is not a dead 50/50.

I guess it's the same principle as accelerating. You're applying power through a differential, so if one wheel spins then there's no power getting to the other one. So with engine braking you're applying a braking force to both wheels so long as one of them isn't sliding.

A traditional differential will result in only one wheel receiving driving force, then one might assume that if the engine is acting as a retarding force rather than a drive force, then it too, acts only on one wheel.

In drive, when one wheel loses traction, "all" drive force goes to the spinning wheel.

Engine braking, when one wheel locks up, say, Im not sure what happens to the other though! Brain going fuzzy...

... in any case, engine braking will only apply to (usually) the front two wheels, where as the middle pedal goes to all four.

Plus, y'know, ABS. It's not 1980 any longer.

A traditional differential will result in only one wheel receiving driving force

If that were the case we'd all be driving in circles.

Engine braking in icy conditions seems mad to me. Foot brake, and if any hint of loss of traction, clutch down.

It's like the advice to pull away in second gear. Why? It's not like you need any less torque to move away from a standing start in 2nd than 1st.

If that were the case we’d all be driving in circles

we do anyway - otherwise we’d never get home

Descending hills in a lower gear, means higher revs and more engine braking, which controls your speed.

That's why it's a good idea. Because your speed will be lower, you need less actual braking which means less chance of locking up/losing control.

Go down a hill in 4th gear, with no braking.
Then do the same hill in 2nd gear with no braking. Your speed will be lower the 2nd time.

It’s like the advice to pull away in second gear. Why?

Probably because it makes it more difficult for people who can't drive very well to accidentally rev the tits off it.

Arguably though what you want is control not out and out stopping power.   Using the engine means you’re apply very gentle braking and trying to avoid a situation where any of the wheels are sliding so that the car is more likely to go where you point it. That’s the idea of abs too but under engine power the wheels are trying to turn (and in fwd are turning in the direction you’re pointing them) rather than just being prevented from locking

My Volvo xc60 doesn't do engine braking!

It has some fancy economy gizmo that let's it keep rolling.

So braking it is.

It has a hill descent button though for when it gets proper slippery.

Gotta be careful though. If you start slowing down sharply by using the engine and not the brakes then you risk a following driver ploughing into you.

Cars don't have enough engine braking to slow them quickly, motorbikes on the other hand...

Come off the throttle in 1st gear on my 1000cc vtwin and it feels like you've chucked an anchor out the back!

But for the OP, engine braking will almost never be powerful enough to lock up a wheel, so it will be acting on all the driven wheels.

Ooooh! A driving thread.

Back in a minute off for tea and biscuits.

Like people have said above, engine braking will slow the rate of rotation of the wheels down. Where as using the brakes will cause the wheels to stop rotating completely on a low friction surface (ice), thus causing a skid. Then the ABS will kick in and modulate the braking force.

^^ engine braking on ice can cause a skid too, which is more awkward than a braking skid in an ABS situation.

Can I raise a practical question at this point?

How would it work on a conveyor belt?

Cougar

Subscriber

… in any case, engine braking will only apply to (usually) the front two wheels, where as the middle pedal goes to all four.

Plus, y’know, ABS. It’s not 1980 any longer.

Anyone who's ever raced a car with ABS on track will know that it's not actually very good at stopping you when grip is at a premium. I ended up taking it off one of my production-based race cars years ago.

JP

down steep hills in snow I've always let it free in 1st gear and feathered the hand brake. No idea if it's best practice but always worked so far

Cars don’t have enough engine braking to slow them quickly,

I've had the 'pleasure' of driving '90s non turbo diesel fords when they were new. If you popped them into first and lifted the clutch when nearly stopped they would lock the front axle on a damp road.

My 951 broke the bellhousing at the gearbox end of the torque tube because of engine braking combined with a paddle clutch and hamfisted driver.

*Waves from Sweden*

Government advice is to use a lower gear and use the motor as a brake. You reduce the risk of locked wheels, or , as they put it..

Samma grundregler gäller som när du kör på hala vägar i övrigt. Försök att behålla väggreppet och undvik att hjulen låser sig. Moderna bilar har antisladdsystem som gör att tekniken känner av om ett hjul börjar slira. Då bromsar det hjulet in så att kraften och friktionen fördelas på alla de drivande hjulen.

I utförsbackar är det bättre att köra på en lägre växel, eftersom du då kan utnyttja motorbromsen. Då minskar risken att hjulen låser sig. Det är alltid bra att försöka motorbromsa, både ur säkerhetssynpunkt och ur miljösynpunkt.

I'd go with the Swedes on this one

Will a car skid through engine braking on ice?

Has shades of aeroplanes on tread mills.

Modern ABS is linked to the throttle and will tickle it open a tad when engine braking if it detects a wheel starting to slip.

Will a car skid through engine braking on ice?

Has shades of aeroplanes on tread mills.

I feared that ha ha.

My 'wisdom' was to engine brake in order to get to a general speed (or lack of), and then fine tune with the brake. But I did slide going down a reasonably steep hill (that others were spinning out on going up, and the road got closed shortly after). I was wondering if it was more the engine braking, actual braking (with ABS), driver, tires or a combination of all that caused the sliding 😀 I kept the vehicle under control by finding deeper snow right by the kerb and keeping the tiyres next to the kerb in the that. It'd be a good road to experiment on if it wasn't for the fact that you'd crash into oncoming traffic due to it having a bend near the bottom!

It’s like the advice to pull away in second gear. Why? It’s not like you need any less torque to move away from a standing start in 2nd than 1st.

In regular comfort mode my car never uses 1st to pull away. Automatic use fluid drive rather than a clutch plate so your not going to burn that out. Its slower to spin the engine up in 2nd so the power is put down smoother. In Icy conditions where smooth acceleration/braking is especially important slower revving makes it easier even in lower power cars.

So the point about engine braking is that it applies gentle braking force to the front wheels and they never actually stop, so in the old days this was a nice way to slow gently on ice. However you can't really control the braking force very well, so you could still have one wheel slip, and if that happens you've suddenly got nothing. Also, all the braking goes through the front wheels so they have to do twice the work, meaning they are more likely to slip in the first place. All it does is apply retarding force to the wheels same as braking, but it's uncontrolled and only on two wheels. So a bit of a bad idea really.

With ABS, the car applies braking force to all four wheels, and it modulates them independently i.e. if one skids, it reduces the force on that one until it grips again - the others are unaffected. It is possible to be unable to stop even with ABS, but this means that there just wasn't enough grip to slow down any quicker.

The flaw with ABS is that if all four wheels lock, the car thinks you're stopped, so it does nothing and you slide on. However, with modern cars they have ESP which means it knows you're still moving, and in which direction, so it can continue to modulate the brakes to maximise grip. This doesn't mean that you will always be able to stop, of course - there is a limit to the available grip - ESP just maximises it better than you can as a driver.

The reason you need to turn ESP off on a racing track is that you are not trying to stop, you're trying to corner, and a certain amount of slip is desired by the driver and it needs to be predictable. And you can't predict it with the computer controlling the brakes for you. I think some racing cars have ABS but I'd bet it's set up rather differently.

I've spun a car numerous times through engine braking (on a track). Any sudden change in velocity or direction will cause an in balance and possible skid.
Not saying what's best, just avoid a skid

Having had a DC2 Integra and an FD RX7 with lightened flys through multiple Winters, I can confirm it's a) possible and b) pretty****ingscary to lock up wheels on ice/snow through engine braking.
Never had it on a car with a normal fly though.

In response to the original question, jack up a 2wd car without an LS and leave one of the driven wheels on the ground, make sure it's in neutral, and you can turn the other driven wheel no probs.
Which logically extrapolates that yeah, one will lock up in the op's scenario.

Also, on snow, lock up are better for stopping in a straight line than ABS.

Will a car skid through engine braking on ice?

Yes, if you shift down and just dump the clutch - the trick is shifting down and feeding the clutch in slowly, so there’s no jolt that could unsettle the car; keeping everything smooth is golden. I’ve been using engine braking in every car I’ve owned since I started driving, in the mid-70’s, and I’ve only lost control once, where a junction had flooded then frozen, and I had to turn 90 degrees right. I slowed up gradually coming up to the junction, but as soon as I turned the wheel, the car just carried on until the grass verge stopped it.
Required some rocking back and forth to get clear, but I could easily have had the car do a 360 and go through the hedge if I’d just used the brakes, I’d got it down to walking speed just using the engine.

the trick is shifting down and feeding the clutch in slowly, so there’s no jolt that could unsettle the car; keeping everything smooth is golden.

But you can brake just as gently. And you'll get braking force from four wheels not two.

The brakes are for stopping, the engine is for going.

The brakes are for stopping, the engine is for going.

I see this trotted out a lot
Imho it's bad advice in areas with big descents. Getting halfway down a hill with glowing, overheated brakes that are starting to boil the fluid because they've been dragged the whole way isn't a nice feeling.
When I was leaning to drive I cooked my brakes doing exactly that in the bloody South Downs.

@howsyourdad1

We all know all you said there was CD rack and meatballs

Also, on snow, lock up are better for stopping in a straight line than ABS.

That's true for deep snow (and sand) where you can build up a pile of powder in front of your tyres to create a larger surface area. But 1) most of the snow we encounter here is hard-pack or only a few cm so that doesn't apply and 2) ABS helps you maintain control of steering as you're slowing down.

In modern cars with ABS and brakes that don't overheat too readily, it doesn't make any sense to force all your braking to be done via the wheels you also wish to steer with. So assuming a FWD car which most people have, advice to use engine braking is daft. IMO which is of no consequence at all.

The brakes are for stopping, the engine is for going.

I see this trotted out a lot
Imho it’s bad advice in areas with big descents. Getting halfway down a hill with glowing, overheated brakes that are starting to boil the fluid because they’ve been dragged the whole way isn’t a nice feeling.
When I was leaning to drive I cooked my brakes doing exactly that in the bloody South Downs.

Hence the 'use low gear' signs on steep descents.

Latest VW DSG gearboxes will coast when you take your foot off the throttle, but if you brake going downhill, the engine will brake for you...

They only make the things, perhaps they know how they should work...

My auto changes down gears when going slowish down steep hills, so I guess the electronics think that’s wise. Newish Audi Quattro.

Engine braking in icy conditions seems mad to me. Foot brake, and if any hint of loss of traction, clutch down.

I have an auto so I feel this advice probably won't help me, however...

... I also have a BMW so when faced with ice and snow, the only driver activated control that is of any use are the hazard warning lights. Closely followed by the airbag 😉

I asked my recently full licensed offspring what they were taught. They both responded with 'nothign at all'.

Any driver of a manual car that has never used engine braking either has never driven anywhere hilly or is a terrible driver.

Hence the ‘use low gear’ signs on steep descents.

But you're not stopping, just trying to regulate speed. If you need to stop, then let the brakes do exactly the thing they were designed for.

Obviously

When I was leaning to drive I cooked my brakes

When was that? How old was the car?

Hence the ‘use low gear’ signs on steep descents.

Not really related to the skidding on ice issue.

They only make the things, perhaps they know how they should work…

Indeed. Which is why mine have has engine braking option on the gear selection.

When was that? How old was the car

1998.
1998 Polo, 4 up on the approach to Friston from the East.
Take a look at most modern family hatches and they have small discs all round (some even still have drums on the back)
You can't change the laws of physics, with a full car it's relatively easy to cook the fluid or pads on most modern cars.
There's nothing wrong with engine braking. It's better than pumping unnecessary heat into the braking system.

Reference the abs and traction control in racing cars, I seem to remember the FIA banning such driving aids in F1 because they were deemed to aid the driver too much. Or am I thinking about something else?

Either way, moderate engine braking in slippy conditions enables speed control whilst maintaining drive through the driven wheels. Also using 2nd gear to start moving in icy conditions reduces the chance of wheel spin that is more easily achieved in 1st gear.

This thread neatly highlights why driving in the snow is best avoided. Even if you think you know how to control your car on a slippy decent it seems highly likely the numpty behind you hasn’t got a clue!

The instruction manual for my car explicitly warns against using engine braking. I suspect others are similar.

The instruction manual for my car explicitly warns against using engine braking. I suspect others are similar.

In everyday driving Continuously using the engine to brake rather than the brakes to brake I expect will put undue wear and stress on the engine, so to be avoided. However we aren't talking about everyday driving we are talking about exceptional circumstances. Also I think using heavy engine braking at speed is a bit different to using the engine as a 'crawler mode' or to regulate slow speed in snow (the assumption being that if you're facing downhill in snow then you shouldn't be going very fast in the first place anyway).

The instruction manual for my car explicitly warns against using engine braking. I suspect others are similar.

What car would that be? And how do they advise you drive down a road steep enough to have "Engage Low Gear Now" signs?

B.A.nana stop giving reasonable and thought out answers.

Engine braking can mean different things to different people. To some it means going down a gear, letting the clutch out so the engine revs high and then the car slows - I was taught this was not a good thing. Then there is gentle adjustments on the throttle but in the same gear to adjust the car’s speed as necessary - this was called acceleration sense when I was taught to drive (but I have seen it referred to as engine braking) and was considered a good technique.

The latter works particularly well on my Triumph but I can confirm it only does it on one wheel.

@colp I think you missed the bookcase. They're the biggest sellers.

Using engine braking to actually brake is not really the done thing these days as it's totally unnecessary - does not harm to the car, but just no point. Modern day brakes are so good no assistance form the engine is needed. So going down the box and engine braking in every gear is pointless. Just brake to the speed you want to get to and put the car in the right gear when you get there.

But using engine braking to regulate your car's speed when going down a long steep hill or down an icy or slippery hill is totally the correct thing to do. You still see signs at the top of long hills saying 'use low gear' or something along those lines, to regulate your vehicles speed and reduce the use of wheel braking.

I also have a BMW so when faced with ice and snow, the only driver activated control that is of any use are the hazard warning lights. Closely followed by the airbag

You can generally use the car bumper two inches ahead of yours to regulate your speed.

I'm not one of those BMW drivers Martin 🙂 In fact I let people out and refuse to practice passive/aggressive 'bumper humping'. It's the surprise on the faces of the people I try and be nice too which hurts the most 😉

Anyway as you were. Our (un-gritted) road was properly icy this morning. It's also on a hill. I'll see how the whole thing plays out at 5am tomorrow morning...

Flaperon +1. It's all changed now though, the only choice in the Zoé is do I use D or mode B.

Edit: and in fact you don't get the choice because mode B doesn't work when the battery is cold.

I have nothing to add except bravo to the OP for dangling this cheeky bit of catnip at STW.

[i]down steep hills in snow I’ve always let it free in 1st gear and feathered the hand brake. No idea if it’s best practice but always worked so far[/i]

Bad practise...vehicles that have dedicated handbrake shoes (such as a drum inside the disc) are not designed to do anything but hold the car stationary, so can overheat very quickly, or wear out very quickly. Its a problem in delivery vans when the drivers get into the habit of using the handbrake and starting to get out before the van has fully stopped.

Engine braking seems rubbish on modern cars, I think its to do with the EGR valve opening. However if my van works out that I want it to engine brake (1st gear, slow start and feet off the pedals), I can go down a 20% gradient near me (1 in 5) without touching the brakes, thats 5.5 tons of camper and horse trailer so its nice knowing that you don't need to cook the brakes and then find them lacking when needed.

Don't know about vans but heavy goods vehicles use engine braking all the time and since Diesel engines don't do engine braking as they don't have a throttle body, then they have a specific system that creates engine braking in the absence of a throttle body. Clearly they're very heavy so more need to reduce heat built up in the brakes. Cars tend to be massively over braked....even bog standard brakes fitted on small cheap cars can generate in excess of 3000HP of braking power so not so much of a problem in cars.

Definitely of use when descending long hills. Not so much for just slowing down for the traffic lights. And is better to use on icy slopes as you're not actually braking...the wheels are still being driven just at a different speed than the car so less likely to induce a skid as you could if you use brakes - ABS or no ABS. Just a bit more gentle.

There are various driveline brake systems on HGVs, some are a bit rubbish, others are better. Electromagnetic retarders and exhaust brakes are common, US trucks often can change the valve timing so that the engine turns into a compressor and these can create lots of braking torque (jake brakes).

My van doesn't have any of those, I wonder if it just closes the EGR or something as the revs climb over a certain threshold.

‘How to go down hills in snowy conditions’?

Slowly and with snow tyres. I found in snowy and icy conditions things can go from seeming pretty slow to ‘arrrrgh’ surprisingly quickly.

You can’t change the laws of physics, with a full car it’s relatively easy to cook the fluid or pads on most modern cars.

Easy is a strong word. Sure it's possible if your driving like a dick or your brake system needs over hauled.

But not something ive ever managed....and I've been over some steep and warm roads in heavily loaded vehicles.....

So by that definition it's hardly easy.

As for engine braking - waste of time in the van - stick. It in second and try to go down a hill and it just run round the rev counter till it's hitting the far side. It's simply too heavy for the engine to retard it.

You need first gear trailrat. Although I'm sure my 2013 has more engine braking than my 2005 (same basic engine but ECU map will be different). First gear may be a bit lower as it's a 6 speed versus the older 5 speed.

Also worth remembering it's rwd. The last thing I want to do is lock up the rear by jamming it into first on a slippy descent.

I use the brakes and the brakes are quick and easy to change designed for the purpose of stopping the vehicle. But I also fitted weather condition suitable tires for the bad weather which makes more difference than which friction plate you want to wear out.

like when I ride my bike I don't drag them all the time -which must be largely why I don't have the issue a significant number on here have with hope brakes.

I did fit brakes off a 2006 model though for more out and out stop power .....they are about 40mm bigger od and bigger calipers.

Meanwhile when I'm using my land rover off road in low traction situations I will use the engine more because it's a different set up and not so likely to spin me....plus the engine actually retards usefully.

I have nothing to add except bravo to the OP for dangling this cheeky bit of catnip at STW.

Ha! It was a genuine question, but the selection of replies on here sums up why I asked it 😉
Although in all seriousness, the whole 'you only engine brake with one wheel' didn't make much sense to me. I just figured that the relationship between the engine, diff and wheels was pretty well the same regardless of speeding up or slowing down.

Interesting thoughts above.
Fwd car, open diff.. I guess perhaps that might be the case. But only if one wheel gives up traction?.... Then if it does go to one wheel then presumably it's providing breaking to the wheel with traction?
Esc/stability control would also presumably monitor this and make corrections - if your talking a reasonably decent car post what, 2010?
Talking of esc, (summer tires club aside) this could well be part of the issue with cars not being able to get started up the icy hills. with this week's conditions I've tended to switch esc off at launch in deep slush, ice etc as it stops the car getting bogged down in computer braking confusion. Back on again for driving though as presumably it's more than just a **** light.

2 pages on a snow driving thread and only a half mention of winter tyres? STW letting me down today.

Surely the answer is a full set of winter tyres and carry on as you would in summer with no loss or grip?

Petrol engines produce more engine braking as they are pulling a vacuum when the throttle is closed. Diesel engines don’t do this when the throttle is closed. In a petrol you vary the amount of air entering the engine and the ECU supplies the fuel where as in a diesel you vary the amount of fuel you put in and the engine draws as much air as it needs. Diesel engines have a dedicated vacuum pump that creates the vacuum needed for the brakes. Diesels engines do produce engine braking just not as much.
As said above engine braking is used to control speed rather than actual bring it to a stop.

Diesel engines don’t do engine braking as they don’t have a throttle body

I definitely get a significant braking effect with the throttle closed on downhills (320d auto), I don't know what's doing it though.

*edited for clarity

I was once recommended to put the car in reverse gear when trying to set off and negotiate the likes of downhill slippery compact snow or icy patch. Then, rather than jamming the brakes, locking them and sliding you would bring the clutch up and the vehicle would descend very slowly but without skidding and sliding into the curb or worse another vehicle in front. Not sure if this actually constitutes engine breaking! 🙂

Clearly not great for your clutch long term, but I've used the technique on a couple of occasions and it does work very well.

Also useful to know how to turn into a skids and +1 for winter/all season tyres.
Probably not worth teaching Winter driving skills for much of the UK though ... these days we only seem to get a few days of actual winter!

I just figured that the relationship between the engine, diff and wheels was pretty well the same regardless of speeding up or slowing down.

As a complete sidetrack but related to this point...in the world of digital car racing/ sims ie: Forza 7 (if we accept the thinking that they are evolved enough to have a strong relationship to reality through their modelling) - then when you upgrade your car to the full 'race diff' then you get independently adjustable locking thresholds for acceleration and deceleration rather than a diff with set presets, and they can have an affect on on-limit grip both into and out of corners.  So my thinking is that it depends what type of diff is in the car (probably very basic in most cars) as to how it would behave in deceleration and it's ability to lock a wheel. I use the digital example as although I've been in a variety of fast sports cars on track at limit, I've never found myself thinking much about the diff unless  it's blatant ie: the way a Megane RS pulls into the apex under acceleration...perhaps a true real world driving god with deep experience of on limit chassis behaviour will be along to help out here....puts kettle on.

The diff would mean you only achieve the braking force of twice the minimum on the driven axle(s) assuming open diffs all round.

Also, if you were to lock up/stall you might not restart the engine under extremely slick conditions, which would lead to one wheel locking up. This could be even trickier if you have an LSD, and will make things very tricky on a RWD car - even under conditions with the engine running there's all sorts of contraptions to reduce engine braking and avoid a spin.

The engine does give a bit of control over speed, but for stopping you're best to just dip the clutch and brake appropriately I would think. That said, you can probably modulate engine braking better as the force available is far lower so as long as the driven axle has most of the weight over it, it still may be useful in practice/away from driving gods.

So, to summarise...

You should never, ever use engine braking, except, of course, to control your speed.

And it doesn't work with diesels, except when it does.

Seems clear.

Petrol engines produce more engine braking as they are pulling a vacuum when the throttle is closed. Diesel engines don’t do this when the throttle is closed. In a petrol you vary the amount of air entering the engine and the ECU supplies the fuel where as in a diesel you vary the amount of fuel you put in and the engine draws as much air as it needs. Diesel engines have a dedicated vacuum pump that creates the vacuum needed for the brakes. Diesels engines do produce engine braking just not as much.
As said above engine braking is used to control speed rather than actual bring it to a stop.

Ah also I missed off, there's a lot less engine braking on modern petrol engines as they have heterogenous charge (lean burn/direct injection) and often throttle-less running to boost fuel economy under idle/light loads, plus engine downsizing.

Often valve opening is used to some degree to mimic the throttle, and on some applications engine braking is optimised (HGVs) by setting valve lifts to restrict the flow of air through the engine and not injecting fuel, but I'm not aware of any light vehicles having engine braking built in. It's a design case for a lot of engine components as nothing gets nice, cool fuel sprayed all over it, potentially for the duration of an alpine descent.

This could be even trickier if you have an LSD, and will make things very tricky on a RWD car

Is this why you often see BMW's gracefully pirouetting down the road in fairly benign conditions?...though I've always expected it's the big lump of torque from a turbo motor to be the big culprit.

I'm confused....I would of expected an LSD to hunt for more grip in slippy conditions, is this not the case? Related to this...can someone tell me what something like a Nissan GTR with front and rear diffs and torque vectoring is like in the snow? is it amazing or awful? Obv's I need to know just in case...

I’m confused….I would of expected an LSD to hunt for more grip in slippy conditions, is this not the case?

More grip for traction, yes, but both wheels spinning at once which could reduce lateral grip once you're getting wheelspin (as 2 wheels are spinning instead of one). Also, rear wheel drive means you oversteer rather than understeer in that situation.

All an LSD does is redistribute some torque to the wheel that has more grip at the time. This can be done in various ways, but that's not really relevant here.

Most traction control systems these days will also mimic an LSD by applying the brakes a little to the wheel that's spinning. With an open diff, this feeds more torque to the other wheel. Of course with traction control, the amount of slip that one wheel will experience is limited, but that doesn't make it totally fool proof. Same goes for ESP (and automatic steering into the skid, which I can't remember what they call) which will try to bring stuff back into line, but doesn't make the car uncrashable if for example you over-correct or just react with blind panic.

Without an LSD you get exactly the same traction from both driven wheels and it's equal to the traction from the wheel with least grip. With an LSD you get the most traction from the wheel with most grip and some from the other one too. So when there's a difference in the grip between the two wheels it makes a lot of difference. It also means the car pulls under power as one wheel is pulling more than the other, so much so that in the days before power steering, FWD cars with LSDs required a firm hand to keep them in a straight line under power.

Probably because it makes it more difficult for people who can’t drive very well to accidentally rev the tits off it.

Probs the same people who brake on bends all year round...?

Yes, if you shift down and just dump the clutch – the trick is shifting down and feeding the clutch in slowly, so there’s no jolt that could unsettle the car; keeping everything smooth is golden.

The trick is really just to control your speed well in advance... whereas that's ALWAYS a good idea sudden ice its even more a good idea. Regardless emergency braking is going to be on the brakes anyway... by complete co-incidence I was driving through an icy new forest yesterday night when a pony emerged round a blind bend... I was going uphill at the time ....so not strictly relevant other than I was going an appropriate speed for the ABS to do its job... though perhaps because I'd need down the last hill using engine braking.

In other words all seems like a non-argument.... keep your speed down using the engine ... emergency brake with brakes.