SUVs - Whats the point?

[Ares]

Nanook said:

Ares said:

But again....the use of engine braking, and the effect it has is incredibly marginal. I've never used engine braking. Always been advised against it on road and track.

Pre-ABS, Pre-Disc brakes, yes, it was a tool to be used. Nowadays, it's as effective and needed as Double-Declutching.

But...this was merely a comment that when the wheels are not being driven, all cars are no-wheel drive. Happy to accept on this very very rare occasions that you find yourself on a slippery slope, or have some other need to engine brake, having 4 wheels engine braking will be better than 2....but in that case, the 2WD would NOT be better than the 4WD (which was how this started)

You always use engine braking, unless you de-clutch or knock it into neutral every time you come off the throttle.

Do you understand what we mean when we talk about engine braking? That's not a snide attempt at sounding clever, but I'm not even convinced we're talking about the same thing here.

It was a while ago now, but I think this started because someone suggested a 2WD car would be lighter than a 4WD car, which is a fair assumption, and would have an impact on braking.

Yes. Using the engine to slow the car down. I'll grant you, a tiny tiny element of engine braking will occur when you brake normally, but as said before, it'll have less impact that aerodynamics and less impact than the battery recharge function on modern cars (EcoPro etc)

Engine braking is when you purposefully engage a higher gear to that the energy expelled in turning the engine over will increase the rate of deceleration, and repeatedly changing down a gear as you decelerate. Back in the 1950/60/70s it was standard practice because brakes were st. Even in the 80s when Emergency braking, you were taught to only dip the clutch at the last minute to gain that extra element of braking power.

With modern brakes, the effect of engine braking is so slight, and the need to save brake wear likewise, it is a practice that becomes less needed.

Volvo & Bosch both advised against using engine braking once catalytic converters became a standard feature, more so to avoid overheating and incomplete combustion. The risks were greater than the marginal benefit it brought.


Engine braking can also be/used to be advised for control down steep roads (the old fashioned sign 'Engage Low Gear') - again, as road car brakes were prone to overheat pre-discs.

Edited by Ares on Tuesday 20th June 16:42

[Hungrymc]

I suspect that Ares is talking about changing gears to reduce speed. Which I think is indeed no longer taught as good driving but could be wrong
(and I certainly use it sometimes anyway)

ETA these posts past in the internet somewhere.

Edited by Hungrymc on Tuesday 20th June 16:43

[Challo]

Nanook said:

So Ares, when racing you wouldn't change down through the gears on your way to say, a hairpin?

You'd what, leave it in 5th, until it was time to select 2nd? Or dip the clutch and coast?

Engine braking is not going to have less impact than aero, depending on how fast you're going. You're doing 30 in 3rd, you lift off all of the pedals, the car slows. This is engine braking.

We're not talking about ramming it into 2nd at 55mph and not touching the brakes, in order to slow a car. The conversation has become so warped I'm not sure any of us know what the point is anymore, except that I disagreed that under braking all cars are 0WD.

I think we can all agree up on that now, yes?

But do we know the point of SUV's?

[Ares]

Nanook said:

So Ares, when racing you wouldn't change down through the gears on your way to say, a hairpin?

You'd what, leave it in 5th, until it was time to select 2nd? Or dip the clutch and coast?

Engine braking is not going to have less impact than aero, depending on how fast you're going. You're doing 30 in 3rd, you lift off all of the pedals, the car slows. This is engine braking.

We're not talking about ramming it into 2nd at 55mph and not touching the brakes, in order to slow a car. The conversation has become so warped I'm not sure any of us know what the point is anymore, except that I disagreed that under braking all cars are 0WD.

I think we can all agree up on that now, yes?

No. I would change down, but not using the engine to slow me (it was a 400kg car), only chaining down so that I was in the right gear for exit.

And what I said was engine braking in terms of not selecting neutral/depressing the clutch was so minimal as to have less of an effect than Aero.

Using your example of 30mph/3rd gear. Most modern cars can decelerate from 30 in around 30ft (around 1.5 seconds). Slamming on the brakes at 30mph with the clutch depressed and comparing it with leaving the clutch engaged will have a minuscule difference, if any at all.


As for the 0WD. If the wheels are not being driven, then it is a no-wheel drive? (for what it's worth, the 0WD was Willie Green's terminology when instructing drivers of 4WD cars on track)

[Granfondo]

How does hill descent work on RRs is it engine braking or brakes or both?

[300bhp/ton]

Granfondo said:

How does hill descent work on RRs is it engine braking or brakes or both?

Depends how you ask the question. HDC as introduced on the Freelander 1 used the ABS to regulate speed to 5mph for steep descents. As a substitute for engine braking because it didn't have a low ratio transfer box.

On a modern Range Rover HDC will be built into the Terrain Response system. And will work along side the low ratio gear set. So you use engine and braking force to regulate speed.

As far as I know HDC systems use the same sensors as the TCS does. This means it can monitor and regulate braking force on a per wheel or per axle basis. Which is critical in helping prevent the vehicle yaw wildly on steep slippery descents. This regulation on a per wheel or axle basis you simply cannot do from the foot pedal. Which is why HDC is far more effective than simply braking when going down a steep slippery decent.

However anyone who has ever driven a truck, lorry, tractor or proper 4x4 in such conditions or with large heavy loads. Will know the virtues of engine braking and how useful it can be. But driving 4 wheels via engine braking will always give you more traction than only 2 wheels.

Case in point. Try and find the Tiff Needell review of the Westfield SEight. Not sure if it was an old Top Gear or early Fifth Gear. Anyhow on a race track, if he downshifted early, the V8 had enough torque to lock up the rear wheels. If it had been AWD it wouldn't have happened.


For snow driving engine braking in a 4wd vehicle gives them far greater abilities than engine braking in a 2wd vehicle. And can and does give you more control than simply mashing the brake pedal.

[venquessa]

300bhp/ton said:

Not the best vid. But a good example of engine braking. And even with 4wd there was still some wheel slip. If you did the same in a 2wd and used engine braking, it would have locked the wheels and skidded, largely out of control.

Please explain how it would do that. I mean, how does engine braking lock the wheels on a 2WD but not on a 4WD? Or are you talking out of your arse again?

[300bhp/ton]

venquessa said:

300bhp/ton said:

Not the best vid. But a good example of engine braking. And even with 4wd there was still some wheel slip. If you did the same in a 2wd and used engine braking, it would have locked the wheels and skidded, largely out of control.

Please explain how it would do that. I mean, how does engine braking lock the wheels on a 2WD but not on a 4WD? Or are you talking out of your arse again?

You are a pleasant fellow aren't you

Answer this riddle..

Why is it easier to wheel spin a 2wd car than a 4wd one?

And you'll have your answer.

[venquessa]

My point was... if the wheels lock, the engine stops. It won't happen under engine braking on 2WD or 4WD.

The only advantage, as you possible elude to, is that you get less engine braking per wheel (unless the 4x4 produces more engine braking from a big agro diesel under the bonnet).

However you don't need to lock the wheels all you need to produce more engine braking than the grip available and you are suddenly out of control. With a 2WD you lose two wheels, 4WD you lose all 4. There is even a potential that a RWD would be better here. Anyone who has mountain biked is familiar with dragging the locked rear wheel down a slope as a dead brake. The steering wheels are completely unaffected. Granted you will have less over all braking.

To loop back to the point in hand, with proper rubber you are much more likely to have enough grip to use engine braking or just brakes.

To loop back even further. My point has never been that 4x4s are particularly bad in snow, or that 2WD is better, my point was that too many people state the premise that for snow you want a 4x4 giving the impression to many that is all you need, a 4x4. It's a dangerous miss-conception that will lead to many accidents, getting stuck, ending up in a ditch. A BMW X5 on normal summer orientated road only tyres is just as dangerous as a Ford Focus is the same snowy icy conditions on similar tyres. Any advantage of the 4x4 systems are minimal if there is no grip to take advantage of them.

4x4 on summers, 2WD on summers - I'd take the 4x4.
4x4 on summers, 2WD on winters - I'd take the 2WD.
4x4 on winters, 2WD on winters - I'd take the 4x4.

When grip is the number one, defacto thing you need, I would favour the rubber. If rubber is more or less equal I'll take the 4WD.

Who owns a 4x4? Which of you dares to test your hill descent mode on normal road tyres down a steep muddy or snowy/icy slippery hill? Please post the video. Note AT and off road tyres don't count.

[Hugo a Gogo]

diesels don't give as much engine braking

[Hungrymc]

Hungrymc said:

venquessa said:

As a point in hand I would suggest that 90% of coupes are used for the purposes they are ultimately designed. Which therefore doesn't make a good argument when the main thing leveled against 4x4s and SUVs is that they aren't.

What would you say is the purpose of a coupe?

And looking at most modern SUVs, what do you think their ultimate design purpose was?

(I'll add that I think its way too simple to group all SUVs or indeed all Coupes together, but I appreciate you may have a different view).

venquessa, apologies if I missed it but I didn't see a response to this (also fair enough if you chose not to).

I think the debate about off road / poor weather and choice of tyres and car is a little at risk of derailing the thread from the original question. Some have 4x4s (or SUVs) for pretty serious low grip use - they generally fit appropriate tyres. Others have 4x4 and SUVs due to other aspects. I'd generally go along with your description of car / tyre combo on this page. But I'd disagree on the point of engine braking.... However, once again, that isn't going to be a major factor in many peoples choice of SUV..... And that takes me back to the question, what do you think their design intent is if you believe one is used for its purpose and the other isn't?

[A.J.M]

venquessa said:

My point was... if the wheels lock, the engine stops. It won't happen under engine braking on 2WD or 4WD.

The only advantage, as you possible elude to, is that you get less engine braking per wheel (unless the 4x4 produces more engine braking from a big agro diesel under the bonnet).

However you don't need to lock the wheels all you need to produce more engine braking than the grip available and you are suddenly out of control. With a 2WD you lose two wheels, 4WD you lose all 4. There is even a potential that a RWD would be better here. Anyone who has mountain biked is familiar with dragging the locked rear wheel down a slope as a dead brake. The steering wheels are completely unaffected. Granted you will have less over all braking.

To loop back to the point in hand, with proper rubber you are much more likely to have enough grip to use engine braking or just brakes.

To loop back even further. My point has never been that 4x4s are particularly bad in snow, or that 2WD is better, my point was that too many people state the premise that for snow you want a 4x4 giving the impression to many that is all you need, a 4x4. It's a dangerous miss-conception that will lead to many accidents, getting stuck, ending up in a ditch. A BMW X5 on normal summer orientated road only tyres is just as dangerous as a Ford Focus is the same snowy icy conditions on similar tyres. Any advantage of the 4x4 systems are minimal if there is no grip to take advantage of them.

4x4 on summers, 2WD on summers - I'd take the 4x4.
4x4 on summers, 2WD on winters - I'd take the 2WD.
4x4 on winters, 2WD on winters - I'd take the 4x4.

When grip is the number one, defacto thing you need, I would favour the rubber. If rubber is more or less equal I'll take the 4WD.

Who owns a 4x4? Which of you dares to test your hill descent mode on normal road tyres down a steep muddy or snowy/icy slippery hill? Please post the video. Note AT and off road tyres don't count.

I did use hill decent on my D3 on a steep hill on the very worn out tyres LR spec them from the factory.
Fronts were Pirelli Scorpions.
Rears were Goodyear Wranglers.

Tyres were at 3mm or so, so pretty worn out.
I was in low range, GGS mode selected on the TR and HDC on.

I got 1/3rd down the slope before the tyres slipped and I went into a slide. Which ended in a ditch, which I drove out of. We were on an off road track so away from traffic and other people.
The track was so bad that the Defenders that had went before me, couldn't reverse back up the section and they had to walk up.

Had the car been on fresher tyres, or not car 25 of 27 it may have been different.

Interestingly, those on mud tyres also had issues with the slope.

I now run Goodyear Wrangler Duratrac which is an aggressive AT tyre which has been designed to work in snow and icy conditions.


So, like anything. Tyres make a huge difference and while technology is great and helps out.
It can't defy the laws of physics.

[300bhp/ton]

venquessa said:

My point was... if the wheels lock, the engine stops.

Engine won't stop, if you are meaning it'll stall. Tyre may slide, until there is sufficient traction for them to rotate again.

venquessa said:

4x4 on summers, 2WD on summers - I'd take the 4x4.
4x4 on summers, 2WD on winters - I'd take the 2WD.
4x4 on winters, 2WD on winters - I'd take the 4x4.

The thing is, that's not a very good comparison, as it never happens. Why would someone have a 4x4 and then fit summer tyres to it and fit winter tyres to a 2wd car?

And it's a far more complex reality. Firstly a large percentage of 4x4's will be on M&S rated tyres anyhow or better.

But conditions would also make for a bit more pondering. If the snow is deep, then most 2wd cars simply won't have the ground clearance to cope.

And another important point is drivetrain. An open diff BMW with RWD will be almost useless in the snow, because it will instantly turn into 1wd, due to how open diffs work. One fitted with an LSD would be miles and leaps more capable.

For fwd you have a similar issue. Open diff and you get 1wd, although as you can slew the steering you can sometimes generate more traction, as you can often get both wills to turn on and off by doing this. Hence the reason many think FWD is better than RWD in the snow. Personally I'd take RWD with an LSD over FWD with an open diff in snowy conditions. The RWD might be harder to get off the line, especially if there is an adverse camber on the road, but once moving you'll have much more control.

FWD with an LSD has the potential to be fairly capable. But.........

Having used 4x4's and AWD vehicles in the snow, it's a no brainer. They are just so much better. For all the reasons mentioned previously.

Tyres can and do make a big difference. But winter tyres are not a miracle cure that suddenly give you the same grip and traction as hot dry tarmac does. So the fundamentals of the car and the drivetrain still come into play. And if you get a wheel spinning with winter tyres, 2wd and an open diff. You are still down to 1wd and on the wheel without much traction.

venquessa said:

Who owns a 4x4? Which of you dares to test your hill descent mode on normal road tyres down a steep muddy or snowy/icy slippery hill? Please post the video. Note AT and off road tyres don't count.

I have a number of 4x4's. Not really sure what you mean by 'test hill descent mode'. But I can assure you, on road tyres, using engine braking and or any other technology, 4wd will always out perform 2wd when going down steep slippery slopes/hills.

[FiF]

300bhp/ton said:

But winter tyres are not a miracle cure that suddenly give you the same grip and traction as hot dry tarmac does.

Nobody, but nobody, not even on the various winter tyre threads, has ever even remotely suggested this. Stop being stupid and coming out with irrelevant hyperbole like that, just making yourself look idiotic and sending the thread into full retard.

[Hugo a Gogo]

ground clearance difference between a 5 series and an X5, as an example, is about 1.5 inches
most of these SUV crossovers look higher, but aren't much

we're not talking about Defenders here

a small car with skinny wheels and 185/65s will deal with deep snow much better than something with 325/30 21s

[300bhp/ton]

FiF said:

300bhp/ton said:

But winter tyres are not a miracle cure that suddenly give you the same grip and traction as hot dry tarmac does.

Nobody, but nobody, not even on the various winter tyre threads, has ever even remotely suggested this. Stop being stupid and coming out with irrelevant hyperbole like that, just making yourself look idiotic and sending the thread into full retard.

It's implied enough times. And really why the insults?

[300bhp/ton]

Hugo a Gogo said:

ground clearance difference between a 5 series and an X5, as an example, is about 1.5 inches
most of these SUV crossovers look higher, but aren't much

we're not talking about Defenders here

a small car with skinny wheels and 185/65s will deal with deep snow much better than something with 325/30 21s

I don't know the difference in ground clearance on the BMW's. All I can say is, a Freelander has significantly more clearance than an Impreza does. And will make a difference in such conditions.

[Hugo a Gogo]

Freelander is 220mm, 20mm more than the X5, hardly a monster truck

[300bhp/ton]

Hugo a Gogo said:

Freelander is 220mm, hardly a monster truck

Exactly, but significantly higher enough that it actually makes a really big difference in real world applications.

A few years back, I went out for a drive very early one snowy morning. Went up Ivinghoe Beacon, which is one of the steeper and higher points in the area. At the top was a Vauxhall Astra that looked like it had been driven up there only a few hours prior. Quite impressed it had got that far tbh. But at the top the snow had drifted and you could clearly see the track it made in the snow dragging it's underbelly along, until finally the snow was too deep for the wheels to touch the road, and there it sat beached.

Latter that same day I came across almost the same scenario on Dunstable Downs, where a small van (Corsa/Escort thing) had the same issue, although the driver resolutely sat there with both wheels spinning, dangling in free air and refused the offer of a tow. (Van was there abandoned 24hrs later).

Something like a Freelander would have breezed through any such conditions. Even something like a Honda HR-V would have been a big step up, ground clearance and AWD.....


And yep, this comes from first hand experience.


The HR-V was stock, but riding on slightly taller AT tyres. It would be a huge stretch of the imagination to call it an off roader, but in the snow it was frankly brilliant. As was the Cherokee. Which latter this day was used to mount a 3 hour rescue mission to retrieve a stranded family member.



This was hugely capable in the snow. Did a 160 miles this day in conditions like this, plus a few detours for some photos.


This was completely unstoppable in the snow, even when driving through snow this deep. Something I truly doubt a 2wd car on winter tyres could have managed. And these photos aren't even the deepest bits of snow, some where as high as the bonnet.


Both of these were no bother in the snow, the p38a being on road biased tyres too.



My Impreza was pretty ok in the snow. It went everywhere you wanted it too, even on regular all season tyres. And the AWD system played a huge huge huge part in how it cornered, braked and drove in these conditions. That said, it was not as good as any of the 4x4's above. Some decent winter tyres would have improved it no end. But it did lack the ground clearance for such conditions.





All things considered, this went relatively quite well in the snow. RWD with an LSD and skinny'ish tyres. But it is leagues behind the 4x4/AWD's in these conditions and moving off the line without the back going sideways is always a challenge.



Likewise, I was also impressed with how my Camaro drove in such conditions, despite fat tyres, loads of low end grunt and an auto box. My TR7 is pretty hopeless though, but it has an open diff....

My smart Roadster went quite well, but really suffered with ground clearance.


Of the front wheel drive cars I've driven in the snow, I've been unimpressed with all of them. My brother did report his Rover 200BRM went fairly well, but that does have a front LSD, which is probably why, although I didn't drive it myself.



Basically, my experience says 4wd for the win! For such conditions. And is in many ways reason enough to own a 4wd of some kind.

[Hugo a Gogo]

the point you've missed, is that the difference between the ground clearance on the Impreza, and on the Astra and Escort van, compared to the Freelander, is only an inch or two, so maybe an hour's heavy snow?