Advantages of 4WD on ordinary saloons?
Discussion
I've owned one 4WD car (Celica Carlos Sainz) and driven a few; owned two FWD cars and driven loads, and all my other cars have been RWD (4 x ME/RWD, 8 FE/RWD). Most of my driving is and has always been in rural Berkshire and Hampshire, so that means bumpy A, B and C roads, often wet, often leaves, and a week or two of snow per year, cleared on the main roads, but left white on the lanes. As far as I can tell these are the actual advantages of 4WD:
+ With high power, and especially with FE/RWD, it gives a more planted feel to the car in wet or otherwise slippery conditions (leaves, mid, gravel on tarmac roads etc). However, if a driver has sufficient care and sympathy with how they drive, then in my opinion even for fast driving this planted nature is purely a matter of taste, rather than a necessity.
+ Off road, it's highly desirable, especially if the car is FE/RWD. You obviously also need the ground clearance and appropriate diffs.
+ In snow, especially with FE/RWD, 4WD gives better traction for accelerating. For most people's use though, winter tyres are usually enough. Even with FE/RWD I manage fine on the lanes with winter tyres. Note that BMWs and Volvos are both manufactured in areas that receive heavy snowfall, and both are traditionally rear wheel drive - the key is that in those snowy areas, winter tyres are mandatory in winter.
And the downsides:
- Extra weight, which counts against you in a car in pretty much everything you do.
- If permanent 4WD, extra mechanical drag in the system, giving poorer bhp crank:wheels and wrose mpg.
- For some people, including me, the change in handling and 'planted feel' is not a nice thing. This particularly applies to cars that shuffle power about, which I find confusing and even dangerous.
- Packaging constraints in FE cars may mean that the front wheels can't be as wide as optimal (source: a top BMW engineer in an interview about X Drive in Autocar).
And some myths:
A myth that you hear repeated is that 4WD helps cornering grip, which of course is nonsense. Something that may perpetuate this myth is that many 4WD cars are given higher ground clearance than their 2WD equivalent (Panda, Volvo etc), plus of course many SUVs are 4WD, and the additional body roll and weight transfer from that higher ground clearance makes you feel like you're cornering faster than you actually are.
Another myth, popular in the UK, is that 4WD is the answer in the snow, even with the same standard tyres on the car. It will improve acceleration a bit, yes, but most people hit things because they can't corner or stop well enough, not because they can't accelerate, so safety isn't really improved, just your chances of getting stuck. Winter tyres really are amazing.
Finally, many people think that all 4WD is permanent. Most systems actually give you a 2WD car until you need the power.
+ With high power, and especially with FE/RWD, it gives a more planted feel to the car in wet or otherwise slippery conditions (leaves, mid, gravel on tarmac roads etc). However, if a driver has sufficient care and sympathy with how they drive, then in my opinion even for fast driving this planted nature is purely a matter of taste, rather than a necessity.
+ Off road, it's highly desirable, especially if the car is FE/RWD. You obviously also need the ground clearance and appropriate diffs.
+ In snow, especially with FE/RWD, 4WD gives better traction for accelerating. For most people's use though, winter tyres are usually enough. Even with FE/RWD I manage fine on the lanes with winter tyres. Note that BMWs and Volvos are both manufactured in areas that receive heavy snowfall, and both are traditionally rear wheel drive - the key is that in those snowy areas, winter tyres are mandatory in winter.
And the downsides:
- Extra weight, which counts against you in a car in pretty much everything you do.
- If permanent 4WD, extra mechanical drag in the system, giving poorer bhp crank:wheels and wrose mpg.
- For some people, including me, the change in handling and 'planted feel' is not a nice thing. This particularly applies to cars that shuffle power about, which I find confusing and even dangerous.
- Packaging constraints in FE cars may mean that the front wheels can't be as wide as optimal (source: a top BMW engineer in an interview about X Drive in Autocar).
And some myths:
A myth that you hear repeated is that 4WD helps cornering grip, which of course is nonsense. Something that may perpetuate this myth is that many 4WD cars are given higher ground clearance than their 2WD equivalent (Panda, Volvo etc), plus of course many SUVs are 4WD, and the additional body roll and weight transfer from that higher ground clearance makes you feel like you're cornering faster than you actually are.
Another myth, popular in the UK, is that 4WD is the answer in the snow, even with the same standard tyres on the car. It will improve acceleration a bit, yes, but most people hit things because they can't corner or stop well enough, not because they can't accelerate, so safety isn't really improved, just your chances of getting stuck. Winter tyres really are amazing.
Finally, many people think that all 4WD is permanent. Most systems actually give you a 2WD car until you need the power.
RobM77 said:
Another myth, popular in the UK, is that 4WD is the answer in the snow, even with the same standard tyres on the car. It will improve acceleration a bit, yes, but most people hit things because they can't corner or stop well enough, not because they can't accelerate, so safety isn't really improved, just your chances of getting stuck. Winter tyres really are amazing.
Paradoxically 4WD can be more dangerous to the less PH person. It allows you to accelerate "relatively normally", thus giving you a false impression of grip, cornering and stopping are only the same as a 2WD car. WestyCarl said:
RobM77 said:
Another myth, popular in the UK, is that 4WD is the answer in the snow, even with the same standard tyres on the car. It will improve acceleration a bit, yes, but most people hit things because they can't corner or stop well enough, not because they can't accelerate, so safety isn't really improved, just your chances of getting stuck. Winter tyres really are amazing.
Paradoxically 4WD can be more dangerous to the less PH person. It allows you to accelerate "relatively normally", thus giving you a false impression of grip, cornering and stopping are only the same as a 2WD car. 
A false sense of security. I'll hold my hands up and admit that I fell into this trap with my Celica CS a few times - you could drive off up a snowy road just fine, but then go anywhere near the brake or turn the steering wheel and it was like you were on ice.Leon R said:
I see how having to swap wheels and store them isn't ideal.
All-seasons?Hol said:
Would either of the terms: semi-permanent or non-permanent AWD be acceptable to you?
But clearly not Permanent AWD.
Except they are. They simply move the torque around automatically. There is always drive connected to all four wheels.But clearly not Permanent AWD.
Do any of the clever-diff AWDs have 100/0 normal torque split? Aren't they about 80/20 or 90/10 at a minimum? Either way, they're permanent in that nothing needs to be done to change from "2wd" to "4wd" - they are not part-time 4wd.
RobM77 said:
A false sense of security. I'll hold my hands up and admit that I fell into this trap with my Celica CS a few times - you could drive off up a snowy road just fine, but then go anywhere near the brake or turn the steering wheel and it was like you were on ice.
RobM77 said:
WestyCarl said:
RobM77 said:
Another myth, popular in the UK, is that 4WD is the answer in the snow, even with the same standard tyres on the car. It will improve acceleration a bit, yes, but most people hit things because they can't corner or stop well enough, not because they can't accelerate, so safety isn't really improved, just your chances of getting stuck. Winter tyres really are amazing.
Paradoxically 4WD can be more dangerous to the less PH person. It allows you to accelerate "relatively normally", thus giving you a false impression of grip, cornering and stopping are only the same as a 2WD car. A false sense of security. I'll hold my hands up and admit that I fell into this trap with my Celica CS a few times - you could drive off up a snowy road just fine, but then go anywhere near the brake or turn the steering wheel and it was like you were on ice.J4CKO said:
The more power you have in a RWD car, the less of if you can use in the wet, and with most BMW's, they are, on normal tyres, helpless if there is any snow.
I went from a TT with 4WD to an M135i, the TT could do full bore starts on snow, you could come off a roundabout in the wet and just aim and plant your foor, where the BMW goes a bit like Bambi on a frozen pond in comparison.
For a car you use all year round and do significant miles in, 4wd is the way to go, especially if you live anywhere snowier than average, hilly or a bit rural.
Failing that, get the right (Winter) tyres on any car and you are a lot better off, ultimate is winter tyres on something with 4WD, unstoppable, until of course you come across stranded BMW's across the road.
Yep. I went from a TT with 4WD to an M135i, the TT could do full bore starts on snow, you could come off a roundabout in the wet and just aim and plant your foor, where the BMW goes a bit like Bambi on a frozen pond in comparison.
For a car you use all year round and do significant miles in, 4wd is the way to go, especially if you live anywhere snowier than average, hilly or a bit rural.
Failing that, get the right (Winter) tyres on any car and you are a lot better off, ultimate is winter tyres on something with 4WD, unstoppable, until of course you come across stranded BMW's across the road.
Last car: V10 Audi S8. 265/35 Goodyear Eagle F1 Asyms all round. 444BHP. Full time proper 4WD (Torson diff) with 60/40 split. I would regularly boot that car on a straight road very close to where we live, from low gear, and it would hold a straight line and go. In all conditions. In fact I struggle to think I saw the TC light come on. Snow, ice, and maybe exiting very wet roundabouts once in a while.
Current car: V12 Vantage S. 295/30 Michelin PS4s on the rear. 565BHP. On that same straight road, in the rain at the weekend, roughly 1/4-/13 throttle in second applied - ahem - vigorously - had the rear wheels squirming and the TC lit up in a heartbeat.
Now obviously 444 though 4 wheels is going to be a lot more manageable than 565 through 2, but it was a bit of an eye opener as to relative stability in the wet. Though, according to something I saw last week, the V12VS is quite a bit closer to a GT3 in lap times in the wet than in the dry. Go figure.
ETA: the Vantage is a *much* nicer and better car notwithstanding its unruliness, and that's despite the S8 being pretty bloody top drawer itself.
Edited by anonymous-user on Monday 8th October 17:37
Nanook said:
I've been in 2 different snowy ditches when I lived in the countryside.
Once was in a Audi A4 Quattro Sport, the other time was in a Blob Subaru Impreza WRXPPP.
Both times a Shogun with appropriate tyres was used to retrieve the stricken car.
Tyres are everything in poor conditions.
TooMany2cvs said:
Except they are. They simply move the torque around automatically. There is always drive connected to all four wheels.
Do any of the clever-diff AWDs have 100/0 normal torque split? Aren't they about 80/20 or 90/10 at a minimum? Either way, they're permanent in that nothing needs to be done to change from "2wd" to "4wd" - they are not part-time 4wd.
The literature regarding my Insignia says:Do any of the clever-diff AWDs have 100/0 normal torque split? Aren't they about 80/20 or 90/10 at a minimum? Either way, they're permanent in that nothing needs to be done to change from "2wd" to "4wd" - they are not part-time 4wd.
Normal driving: 95% front, 5% rear.
During hard acceleration, up to 60% of power/torque is shifted to the rear wheels.
Sport mode: 40% front, 60% rear.
eLSD allows up to 50% of the power/torque going to the rear to be moved to either rear wheel (up to 30% of total).
WestyCarl said:
Paradoxically 4WD can be more dangerous to the less PH person. It allows you to accelerate "relatively normally", thus giving you a false impression of grip, cornering and stopping are only the same as a 2WD car.
Not exactly. You can still corner and brake better with 4wd. That is what gives 4wd rally cars such an advantage. GravelBen explained it earlier in the thread very well. 
blade7 said:
Handicapped with weight and ultimately banned. And someone claims modulating the throttle would negate it's advantage...
I never claimed that by the way. I said winters and smooth throttle modulation was better for me than a point and squirt on/off throttle solution but each to their own, I have no axe to grind, just different experiences and preferences.
The touring car Audi story is very different and is clearly not helping perception. As I am sure you know motorsport series run a minimum weight rule.
Which is were the Audi scored : they were the same weight as the 2wd cars and their cog was consequently lower. When a race car wins a race based on tenths and the 4wd adds zero penalty despite the added hardware, the balance had to be redressed and the loophole was closed. No 4wd road car would ever weigh the same as the equivalent 2wd model.
It's a bit like if I said that 4wd was useless on rally cars because the front drive Xsara group A beat the WRC cars on tarmac before the category was dropped. It would be twaddle.
All rather academic in the context of ordinary saloons anyway.
Edited by nickfrog on Monday 8th October 19:01
nickfrog said:
It's a bit like if I said that 4wd was useless on rally cars because the front drive Xsara group A beat the WRC cars on tarmac before the category was dropped. It would be twaddle.
Yip, being allowed to run over quarter of a ton lighter with the same power definitely helped. Even then they could only challenge the WRC cars on dry tarmac, in the wet it was a very different story.Edited by GravelBen on Tuesday 9th October 06:28
GravelBen said:
Yip, being allowed to run over quarter of a ton lighter with the same power definitely helped. Even then they could only challenge the WRC cars on dry tarmac, in the wet it was a very different story.Edited by GravelBen on Tuesday 9th October 06:28
nickfrog said:
GravelBen said:
Yip, being allowed to run over quarter of a ton lighter with the same power definitely helped. Even then they could only challenge the WRC cars on dry tarmac, in the wet it was a very different story.Edited by GravelBen on Tuesday 9th October 06:28
300bhp/ton said:
Not exactly. You can still corner and brake better with 4wd. That is what gives 4wd rally cars such an advantage. GravelBen explained it earlier in the thread very well.
You can apply power out of a corner better. The braking point is pretty much moot with modern ABS.300bhp/ton said:
nickfrog said:
GravelBen said:
Yip, being allowed to run over quarter of a ton lighter with the same power definitely helped. Even then they could only challenge the WRC cars on dry tarmac, in the wet it was a very different story.Often more specialised for tarmac too as 300 says, compared to the WRC car design being a compromise for a whole spectrum of events from smooth tarmac to snow to rough gravel and mud. At the opposite end of that spectrum a Dakar truck might beat a WRC car too! (if its rough enough)
otolith said:
You can apply power out of a corner better. The braking point is pretty much moot with modern ABS.
Nope, see GravelBens reply earlier in the thread. Think it was even quoted a few posts up. Braking isn't exclusive to using the brake pedal. There are other ways of slowing a vehicle.Gassing Station | General Gassing | Top of Page | What's New | My Stuff