4 wheel drive & the real world

[CGJJ]

Having read a lot of opinions on this thread i am keen to know why Porsche 911 Turbo's (4 wheel drive) are considered
safer all weather vehicles for everyday driving than the GT2 & GT3 derivatives with 2 wheel drive?

[Orangecurry]

CGJJ said:

Having read a lot of opinions on this thread i am keen to know why Porsche 911 Turbo's (4 wheel drive) are considered
safer all weather vehicles for everyday driving than the GT2 & GT3 derivatives with 2 wheel drive?

GT cars tend to be track toys which tend to have track-biased tyres. Therefore you use another form of transport in winter conditions.

Also the key word you used is 'considered'.

As was suggested about 12 pages ago, when you are on the brakes and off the power, tyres and driver make the difference, not the number of driven wheels.

[sleep envy]

Orangecurry said:

As was suggested about 12 pages ago, when you are on the brakes and off the power, tyres and driver make the difference, not the number of driven wheels.

This, unless you have fists of ham.

[Dave Hedgehog]

sleep envy said:

Orangecurry said:

As was suggested about 12 pages ago, when you are on the brakes and off the power, tyres and driver make the difference, not the number of driven wheels.

This, unless you have fists of ham.

parking and turning off the engine also resolves any traction issues


but its far better to have 4wd and just keep the the throttle nailed, so no need to compromise performance for the limitations of a single axle drive

[CGJJ]

Orangecurry said:

GT cars tend to be track toys which tend to have track-biased tyres. Therefore you use another form of transport in winter conditions.

Also the key word you used is 'considered'.

As was suggested about 12 pages ago, when you are on the brakes and off the power, tyres and driver make the difference, not the number of driven wheels.

Ah,Ok- got ya.So a GT3 will have as much traction as a 911 turbo if it is running the same tyres.

Thanks,that explains it.

[Orangecurry]

No - not unless I'm misunderstanding you. 'Traction' or the ability to 'go' will be better in AWD than 2WD.

I could 'go' anywhere in the Impreza if I had ground clearance, even on summer tyres.

But not 'safer' as it could 'stop' just as badly as everyone else (on the same tyres)

ETA and certain AWD systems like the 911s are rear driven with a VC and prop to the front wheels, power to the front is normally around 5%, which increases to up to 50% *after* the rear wheels start to slip. Opinions vary as to how effective such AWD systems really are in snow/ice.

Edited by Orangecurry on Saturday 1st February 00:19

[CGJJ]

So the GT3's nickname 'The widow maker' is underserved then because it has all the stopping power of the turbo,and cars only crash when they are braking?

[Orangecurry]

The GT cars have a bad reputation as they are (let's simplify this) very stiff and very fast, therefore they let go much quicker and with much less warning than the softer-sprung 'road' cars.... it's too late to write any more and the cat wants to come in out of the rain, but that's the general idea.

[GravelBen]

CGJJ said:

Having read a lot of opinions on this thread i am keen to know why Porsche 911 Turbo's (4 wheel drive) are considered
safer all weather vehicles for everyday driving than the GT2 & GT3 derivatives with 2 wheel drive?

Because Porsche engineers are all morons in comparison with the automotive expertise of PH of course...

I also have to wonder if the people commenting on 4wd not stopping or cornering any better than 2wd on slippery stuff have ever actually driven one...

Edited by GravelBen on Saturday 1st February 01:28

[Orangecurry]

GravelBen said:

Because Porsche engineers are all morons in comparison with the automotive expertise of PH of course...

I also have to wonder if the people commenting on 4wd not stopping or cornering any better than 2wd on slippery stuff have ever actually driven one...

Edited by GravelBen on Saturday 1st February 01:28

I have total respect for your experience Ben.

I didn't say it doesn't corner better. And the question was aimed at the 'non-driving-god' level of driving.

I said once off the power and on the brakes, there is no difference. We can argue about how much effect a permanent mechanical AWD system has on braking, but most AWD cars don't have it.

As to why I am commenting on this thread? I like to explore the 'edges of reason'.

I've also taken the BMW and the 911 out in the snow/ice, but obviously only stopped to take photos occasionally on certain outings and only when it was safe to do so.

Therefore I have experience of FWD, RWD (front engine) RWD (rear engine) AWD mechanical centre diff and AWD modern Subaru centre diff.

My early career was in Geophysical exploration, and have driven 109s and 110s extensively in mud and desert, which is very different from the OPs question.

This is me 'going' and steering (with accelerator and steering wheel) but stopping was no different from any other car.

Either on Rainsport2s or Falken 452s (can't remember which).



This is me not going anywhere due to ground clearance.



This is me going somewhere with winter tyres.



This is me going somewhere with 2WD and chains.

Edited by Orangecurry on Saturday 1st February 10:52

[jonah35]

I know on ph we are all driving gods and all drive 1000bhp tuned lamborghinis but I think arguably fwd is better than rwd for most 'normal' people.

Better in snow, safer, easier to drive fast without crashing, grip more etc.

Rwd is fun on track but I'm not sure its better in the real world.

[RobM77]

jonah35 said:

I know on ph we are all driving gods and all drive 1000bhp tuned lamborghinis but I think arguably fwd is better than rwd for most 'normal' people.

Better in snow, safer, easier to drive fast without crashing, grip more etc.

Rwd is fun on track but I'm not sure its better in the real world.

I don't think balance and poise can only be enjoyed on track. All three layouts offer pros and cons and it's down to an individual's priorities which they choose. There are some absolutes though, some measures of 'better' and/or worse, such as traction, it just depends whether people care or not. RWD is much better than FWD for traction, provided sufficient longitudinal acceleration is achieved, because that acceleration transfers weight down onto the rear wheels and off the front wheels. The only exception to this is very slippery surfaces where insufficient acceleration is achieved and you're stuck with the car's static weight distribution, such as snow or wet mud.

Objective Measures
Traction on wet/dry roads: 4WD best, RWD next, FWD worst.
Traction on snow, ice or wet mud: 4WD, FWD, RWD.
Balance: depends on layout, rather than the drivetrain, but with typical layouts, RWD first, 4WD next, FWD worst.
Drivetrain power losses: FWD best, RWD next, 4WD worst.
Weight: I think FWD would be slightly better (fewer housings, shorter driveshafts etc), RWD next, definitely 4WD last.
Production cost: FWD cheapest. RWD and 4WD I'd have thought would be similar
Interior space: Generally FWD will win this with RWD and 4WD similar, depending on the engine orientation chosen.

Subjective Measures
All three drivetrains have different handling characteristics, which depend largely on the mass layout chosen and how the car is tuned. Sadly though we can't design our own cars, so we have to buy what's typically available. Because of the above, most RWD saloons are built with handling in mind. FWD saloons with practicality, and 4WD saloons with low grip situations in mind. Generally speaking, a typical RWD saloon car such as a BMW will have poise and tiptoe balance, with FWD and 4WD cars having quite a nose heavy feel. Looking at our driveway I see differing priorities though; we have a Civic Type R built for fun and sporty driving, and a 320d built for family/rep use. The hot hatch feels much more lively, alert and keen to respond, but ultimately there is still that nose heavy feeling there when you push, and achieving balance requires corner entry commitment. The ordinary saloon that's RWD has a much lazier and less sporty feel, but it retains poise when you push and is largely well balanced at all speeds and all levels of commitment. So it's largely about chassis tuning, but when you really push, the raw differences come through. Obviously if two cars are designed with the same purposes in mind, those differences extend right back to everyday driving too - compare perhaps a GT86 with a Civic Type R.

Myths
RWD is all about power oversteer - no, it offers balance at all speeds. Balance is usually easier to achieve because of the distribution of weight.
FWD cars understeer - no, most balance in cars is achieved through management of weight transfer, not application of power. FWD cars can make this balance hard though due to the distribution of weight where everything's up front.
RWD is only worth it with high power - No, see myth 1. A 115bhp MX5 is lovely to drive, rain or shine.

The above pros and cons are quite complex, especially when you add the different designs of different cars into the mix, so it obviously comes down to personal preference and priorities at the end of the day. It's easy to see from reading the above that if a driver isn't particularly interested in handling and they want something versatile with good interior space and cheap to buy, that they're better off with a FWD car, which is why most cars these days are FWD. I reckon that if all manufacturers were to start afresh tomorrow, even BMW and Merc would probably go FWD, although I suspect most of the chassis engineers would walk out - profits rule the day, not the odd geek like me who cares about handling.

Personally, I've owned all three drivetrains and I've raced FWD and RWD. I enjoy all three, but primarily it's RWD that I enjoy the most. In an ideal world I'd have a RWD daily driver, a RWD GT, a RWD track car, a FWD hot hatch for fun and track days and a 4WD rally car for fun on the loose.

Edited by RobM77 on Saturday 1st February 11:49

[GravelBen]

Orangecurry said:

I didn't say it doesn't corner better. And the question was aimed at the 'non-driving-god' level of driving.

I said once off the power and on the brakes, there is no difference. We can argue about how much effect a permanent mechanical AWD system has on braking, but most AWD cars don't have it.

As to why I am commenting on this thread? I like to explore the 'edges of reason'.

I've also taken the BMW and the 911 out in the snow/ice, but obviously only stopped to take photos occasionally on certain outings and only when it was safe to do so.

Therefore I have experience of FWD, RWD (front engine) RWD (rear engine) AWD mechanical centre diff and AWD modern Subaru centre diff.

I guess it also depends if by 'on the brakes' you mean to the point of actuating ABS (in which case I agree about that) or braking in a controlled manner below that threshold, in which case I've found Subarus to trasfer load between wheels and resist locking up/triggering ABS better than 2wd cars (pedal feel makes a big difference there too). I've only had manual ones, the autos have a different centre diff setup and might not do it so well.

I think the silliest car I've taken out in the snow was the turbo MX5 on semislicks... roof down of course!

Edited by GravelBen on Saturday 1st February 11:44

[GravelBen]

RobM77 said:

Sensible stuff

I can't speak for whether 4wd Audis etc are the same, but Subarus at least I've found to retain a lot more poise and composure on rough as well as loose surfaces compared to most other cars I've tried. Its down to suspension tuning etc as well as drivetrain, but the traction is part of it and certain things often go together.

You often end up with a bit of a spectrum between (for example) a Rwd car optimised for smooth grippy roads, and an Awd optimised for rougher less grippy roads. On the smooth grippy road the Rwd car feels sharper and more balanced, while the Awd can feel a bit duller and less responsive. On the rough slippery road the Awd car feels eager and composed, while the Rwd car gets a bit flummoxed and out of its comfort zone. Both may be just as good at what they do, its just they're optimised for different things.

[Scuffers]

RobM77 said:

Objective Measures
Traction on wet/dry roads: 4WD best, RWD next, FWD worst.
Traction on snow, ice or wet mud: 4WD, FWD, RWD.
Balance: depends on layout, rather than the drivetrain, but with typical layouts, RWD first, 4WD next, FWD worst.
Drivetrain power losses: FWD best, RWD next, 4WD worst.
Weight: I think FWD would be slightly better (fewer housings, shorter driveshafts etc), RWD next, definitely 4WD last.
Production cost: FWD cheapest. RWD and 4WD I'd have thought would be similar
Interior space: Generally FWD will win this with RWD and 4WD similar, depending on the engine orientation chosen.

all this is very dependant on what the layout of the car is...

front engined FWD might have better traction then front engined rear drive, that's to do with weight distro, now throw a mid-engined RWD in the mix, it has better traction than FED hands down..

you can argue the same for balance, etc etc...

ie. it depends on the car.

[RobM77]

Scuffers said:

RobM77 said:

Objective Measures
Traction on wet/dry roads: 4WD best, RWD next, FWD worst.
Traction on snow, ice or wet mud: 4WD, FWD, RWD.
Balance: depends on layout, rather than the drivetrain, but with typical layouts, RWD first, 4WD next, FWD worst.
Drivetrain power losses: FWD best, RWD next, 4WD worst.
Weight: I think FWD would be slightly better (fewer housings, shorter driveshafts etc), RWD next, definitely 4WD last.
Production cost: FWD cheapest. RWD and 4WD I'd have thought would be similar
Interior space: Generally FWD will win this with RWD and 4WD similar, depending on the engine orientation chosen.

all this is very dependant on what the layout of the car is...

front engined FWD might have better traction then front engined rear drive, that's to do with weight distro, now throw a mid-engined RWD in the mix, it has better traction than FED hands down..

you can argue the same for balance, etc etc...

ie. it depends on the car.

Definitely, yes; sorry if I wasn't clear enough with that. I was talking as generically as I could. You'd need a pretty extreme layout though to give a FWD car more traction than a RWD car under moderate to hard (0.5 to 1.0g) acceleration.

Mind you, what I didn't say that you're quite right in pointing out is the ME or RE RWD has the static traction advantage of FWD (e.g. in snow), along with the dynamic traction advantage of RWD (e.g. wet or dry tarmac). Best of both worlds. Plus, RE/RWD offers the interior space of FWD as well. This is why the Beetle and 911 were and are so popular and capable.

[jamieduff1981]

tr7v8 said:

jamieduff1981 said:

In response to a mention of a diesel S-Type above, it's interesting because I've heard that a lot, but my 3.0 petrol auto S-Type has been with me for 5 years now and until this winter served me daily on P-Zero Assymetricos. It couldn't be driven with the carefree abandon of a Defender on chunky tyres, but it's never given me any trouble in snow.

I think the important word here is petrol! I think the turbo diesel spools up & spins the rear wheels up & that seemed to be the issue. I've driven loads of stuff in snow & the Jag wasn't going anywhere.

Yes that's what I mean I use a Jag specific forum too and the diesel owners do seem to struggle a lot more than the petrol owners do. It can only really be the power delivery at work here. The petrol and ZF combination does offer a particularly soft start which seems to work well on snow

[jamieduff1981]

goldblum said:

jamieduff1981 said:

The only car I've lost control of and slid straight over a cross-roads junction on snow in was AWD.

Some of Goldblum's friends must have seriously fast cars because I overtake in the wet all the time in the 4.5 Cerbera and don't have any trouble with wheelspin. Maybe it's my driving godliness though because it's got enough power that you simply don't need WOT for overtaking unless you're sticking with 4th or 5th gear or you're trying to overtake in gaps which aren't safe for overtaking and you're hammering it in low gears. It wont spin wheels in the wet in 4th or 5th gear, and it won't spin it's wheels in 3rd gear in the wet unless you are clumsy changing gear or reach the top 3rd of the RPM range where you're at automatic court appearance speeds.

You know what - you're right. The whole premise of fast AWD/4x4s is flawed. Despite billions of pounds of sales the world over, the popularity of WRC and it's lesser brethren, the entire soft roader market etc etc. Because you can drive a 4.5 Cerbera without wheelspin in all conditions. I'm surprised the rest of the world hasn't discovered this nippy little all weather sportscar and sales haven't rocketed.

Or perhaps they've just used a bit of common sense and realised there are other options available more suited to poor road conditions.

As for me - my AMG doesn't like snow and rain up here too much despite the Conti winters so like many others I have alternate 4x4 transport.

Silly me, I should have bought a Cerbera instead.

The point I'm making is that TVRs are far from well engineered and well road tested. Infact it's probably the worst possible ambassador for waving the "RWD is perfectly useable" flag. I'm genuinely surprised that all your friends struggle to overtake in the wet without chronic wheelspin problems in far more expensive and far better engineered cars which will have been tested and developed in various climates to ensure that they are safe and usable - as opposed to knocked together in Blackpool, driven round the block and put on sale. I'd have expected them to be far better at putting their power down than my silly car, not far worse. That leads me to suspect you either have an especially ham-fisted social group, or you may be exaggerating the limitations of RWD in slippery conditions somewhat.

[goldblum]

jamieduff1981 said:

I'm genuinely surprised that all your friends struggle to overtake in the wet without chronic wheelspin problems in far more expensive and far better engineered cars which will have been tested and developed in various climates to ensure that they are safe and usable - as opposed to knocked together in Blackpool, driven round the block and put on sale. I'd have expected them to be far better at putting their power down than my silly car, not far worse. That leads me to suspect you either have an especially ham-fisted social group, or you may be exaggerating the limitations of RWD in slippery conditions somewhat.

Do you need glasses?

This innocuous statement:

goldblum said:

"everyday folk who are bored of their performance car wheelspinning in the wet when pulling out of a junction or during a nippy overtake".

Has resulted in these comments from you:

"all your friends struggle to overtake in the wet without chronic wheelspin problems "
"you either have an especially ham-fisted social group"
"you may be exaggerating the limitations of RWD in slippery conditions"

Somehow you've managed comment on a scenario you've invented just for yourself.

[Carl_Docklands]

CGJJ said:

Having read a lot of opinions on this thread i am keen to know why Porsche 911 Turbo's (4 wheel drive) are considered
safer all weather vehicles for everyday driving than the GT2 & GT3 derivatives with 2 wheel drive?

I will have a go at answering:

- Tyres, by default most GT cars will be equipped with semi-slicks
- Suspension setup (improved ground clearance on the Turbo, only marginally with the Turbo aerokit although, you can easily remove the front splitter on the Turbo and the later GT3's did have a lift system as an option)
- Lack of under-floor protection on the GT car's means you should never drive it when the roads are gritted. The rust warranty only last for 3 years on the GT cars due to this
- Track biased electronics are slightly more playful at stock in the GT car's. If you hit standing water on the motorway, there is a higher risk of the car kicking out although, this is no problem if you are ready to catch it
- In 3 inches of snow it is less likely that a GT car will make it up an incline, the Turbo will make it, even in summer tyres
- Finally, the Turbo is 2WD unless you lose grip from the rears. This gives it almost all the benefits of 2WD with limited downsides.

All the above makes progress in poor conditions a more stressful experience in the GT cars, it can be done if you put the right tyres on but you will need to be alert if planning to drive at speed.

Out of all the crashed or written off Porsche car's we see posted on PH, one of the most common is a GTx car which has wiped out on Cup tyres in Winter or poor conditions. A crashed Turbo due to weather is a rare sight.