Quattro 4 wheel Drive vs Rear Wheel Drive

[Snake Pliskin]

There has been a couple of threads lately concerning the RS3 vs BMW's which are of course rear wheel drive.

There has been some debate as to the all weather usability of the rear wheel drive cars and whilst out yesterday in frankly terrible road conditions which consisted of .... sleet & snow, heavy wind, wet saturated roads, standing water etc it got me thinking about my Quattro all wheel drive car and how I was glad I didn't have a rear wheel drive Bimmer or the like.

Travelling on a long B road I was experiencing a lot of slow trucks and the like, with the high perfortmance quattro the car felt planted and never lost traction at any time enabling me to safely overtake slower traffic with ease and never worry about the back end losing grip or snapping out.

There is no way you could be that confident in a high powered rear drive car the same as you feel in an Audi Quattro in road conditions like we had yesterday. Yes you would get by, but I am pretty sure you would have to adjust your driving style to suit the rear drive car and you would not have the same level of confidence overtaking either.

 

[u3sport]

AWD with winter tyres are best for driving with that weather conditions, sure.
RWD better for fun, track, drift, cornering, driving experience...

Anyway, quattro isn't everything... RWD with winter tyres > AWD with summer tyres.

 

[Snake Pliskin]

AWD with winter tyres are best for driving with that weather conditions, sure.
RWD better for fun, track, drift, cornering, driving experience...

Anyway, quattro isn't everything... RWD with winter tyres > AWD with summer tyres.

Unsuprisingly "ASPORT" you have totally missed the point here !!!

Fit winter tyres to an Audi Quattro and you have epic grip.

Fit winter tyres to a rear wheel drive Bimmer and yes you can get about instead of being stranded.

This thread was about a standard audi quattro car (yes fitted with summer tyres) vs same tyres and conditions rear wheel drive car.

 

[billyali86]

As you know Snake, I made the change. It takes some getting used to, I haven't pushed the new car as roads are really greasy and icy at the moment. You get odd wee squiggle from the rear, but if you drive sensibly and take the conditions into account you should be ok

 

[Snake Pliskin]

As you know Snake, I made the change. It takes some getting used to, I haven't pushed the new car as roads are really greasy and icy at the moment. You get odd wee squiggle from the rear, but if you drive sensibly and take the conditions into account you should be ok

Hey ... I've had a Bimmer, a 330i M sport back in 2006, lovely engine and gearbox and for the time I had it the weather wasn't so bad as I recall and the winters certainly were not bad as they never really factored in me buying a car.

For 95% of the year, I am sure the rear drive Bimmers will be fine and on blazing hot sunny days you will have monumental grip and with front tyres just left to do the steering, they do feel sweet.

I think the thing is like you say, with standard summer tyres fitted - in conditions like I drove in yesterday - you would have to adjust and drive to suit the conditions in the Bimmer and yes you would be fine and safe ... I found with the quattro though that I could literally flaw the throttle for overtaking, getting max power and the car still felt safe & planted. It did cross my mind at one point that it did feel unusual being able to overtake and power on with such ease considering the horrible conditions but that is what made me think that the quattro 4 wheel drive DOES make a difference in winter for those of us like me who never change to winter tyres and give the car that added all weather security .. and hey I am no speed freak, these were just controlled bursts for overtaking safely on a b road.

The other issue with winter tyres in the UK is the variable weather and temperatures up & down. I'm sure winter tyres need to have temps below a certain level to operate safely ? The UK summer this year has seen very unusual highs so not sure where you would sit with winter tyres fitted on days where the temp is 16 degrees C ?

 

[msdmjb]

Last weekend I put my spare set of wheels with winters on the S3, incredibly secure even on icy roads, make sense here as grit and salt isn't really used. Where I live in Europe some roads are only open for cars with winters and the S3 is awesome, some of the locals use winters all year and even in a Med summer offer plenty of grip...........OK they are not ideal and not designed to be pushed hard in heat but it is suprising how well they do hang on so don't worry about 16deg.

 

[CraigI]

What you want is Torsen AWD.
That gives the best of both worlds, proper AWD (not like Haldex) with a true rear bias so that driving has the fun element.

 

[simond72]

Unsuprisingly "ASPORT" you have totally missed the point here !!!

Fit winter tyres to an Audi Quattro and you have epic grip.

Fit winter tyres to a rear wheel drive Bimmer and yes you can get about instead of being stranded.

This thread was about a standard audi quattro car (yes fitted with summer tyres) vs same tyres and conditions rear wheel drive car.

The problem is that many people feel that with AWD you don't need to worry about winter rubber, and that is not necessarily true. However, in the South of England, I doubt winter rubber is really needed on an AWD car as long as your tyres have sufficient tread to clear standing water...in the north, I'd expect winter rubber to have more benefit and be more necessary.

So I'm looking forward to lazy winters in the south where I don't have to bother swapping wheels in autumn and spring...and of course the space saving in my garage

My only criticism of the RS3 is that it's still too FWD oriented, it would be a better performance car if it was RWD oriented and only sending traction to the front when necessary.

 

[Spaceman_RS3]

Like a skyline of old.

 

[CraigI]

The problem is that many people feel that with AWD you don't need to worry about winter rubber, and that is not necessarily true. However, in the South of England, I doubt winter rubber is really needed on an AWD car as long as your tyres have sufficient tread to clear standing water...in the north, I'd expect winter rubber to have more benefit and be more necessary.

So I'm looking forward to lazy winters in the south where I don't have to bother swapping wheels in autumn and spring...and of course the space saving in my garage

My only criticism of the RS3 is that it's still too FWD oriented, it would be a better performance car if it was RWD oriented and only sending traction to the front when necessary.

That's what Haldex gives you.
I prefer a FWD with a good mechanical differential to a Haldex AWD system - much more rewarding drive and turn in.
Audi should really offer a front diff for the RS3 as part of the Dynamic Pack.
Would improve things no end!

 

[josedebardi]

The latest generation haldex, a la the 8V RS3 is rear bias. Albeit only a tiny bit and not 100% of the time, and certainly not enough to completely remove the under steer tendency. But compared to previous haldex systems I can say it's MUCH better.
A proper 'sport' front diff as Audi would call it would be a nice option, I agree.

 

[RGBARGEE]

Winter tyres are great when it's cold... Around here it's been +10 degrees most of the day. I really feel that this winter tyres thing is getting a bit silly. Yes of course if its really cold they are better but most of our winters it seems a bit of a faff fitting them.

 

[Gops]

Some people forget that Haldex is in more supercars than you know.. I.E The Veyron, Aventador.. etc. Haldex is more than capable and isnt fake 4wd.

As for RWD. I've recently bought an M135i and i have to say it isnt bad to drive in the wet, in fact its actually surprisingly good! With the optional Diff its much much better, where the S3 would slip or loose front end grip, the beema bites and gives you confidence. I love this bmw, its a lovely car, well made and its different. My S3 is far from standard but its nice to have both so you can understand the difference in drive. Granted in the snow the beema wont be as reassuring as a quattro, mine in the snow on its winters was awesome (off boost).

Both great cars in their own respect. I would encourage you to drive a new performance BMW to really see what its like. When my S3 is back, i'll be doing some back to back comparisons for fun!

 

[veeeight]

I think you forgot to mention that the Veyron is mid-engined, so couples the fronts when needed (the other way round to VW/Audi transverse engine cars), plus the Veyron has TWO Haldex units to do the job of one Torsen

 

[xpoweruk]

A Quaife diff (front) would make things much more interesting in the corners on the RS3/S3 I imagine.

Having had a FWD with Quaife ATB fitted the difference was night & day to the open diff

 

[veeeight]

The latest generation haldex, a la the 8V RS3 is rear bias. Albeit only a tiny bit and not 100% of the time, and certainly not enough to completely remove the under steer tendency.

I'm afraid that this is the number 2 Internet myth....
(Number 1 goes to the claim that DSG gearboxes can "learn" or "adapt" to your driving - they don't)


Gen V Haldex

The mechanical drive is only capable of a 50:50 split. Even in a RS3.
So whatever speed the front wheels spin at, the rear wheels will spin at.
There is no "static" rear bias, unlike Torsen.


If the front of the car is lifted in the air, with the front wheels spinning in the air, most of the dynamic torque (hence bias) available can be at the rear wheels. In this unique situation, it can be near 100% at the rear wheels, but you have to subtract the frictional losses going through the front half of the drivetrain. Which may leave you at around say 95% at the rear wheels. A similar situation can be achieved by having the front wheels wholly on ice, and the rear wheels on grippy tarmac. In this unique situation, you can have "near" 100% of the available torque at the rear wheels.

"Being able to send 100% to the rear" is slightly misleading marketing speak, as this implies that somehow, magically, the car can de-couple the front wheels and make the car a power over steering rear wheel drive monster (on grippy tarmac, on the move). This can never happen, as the rear wheels can never turn faster than the front wheels. You can invoke the rears stepping out, of course, for example at take off out of a junction with steering lock applied, but this is a result of the front wheels slipping, rather than the rears spinning faster.

You can have a 50:50 drive split (as the S3/RS3 8V is) and still have differing torque at the front/rear (eg: 20/80) as torque at the tyre is a function of the surface friction coefficient and weight of the car at each wheel/tyre.

What Audi claimed to have done with the Haldex controller on the RS3 is that they have re-calibrated it to lock up quicker/sooner in more circumstances, thereby sending more of the available torque to the rear sooner. As a function of time. But not have any "rear bias" as the 50:50 mechanical coupling still determines 50:50 drive front:rear.


The graph below shows a HPA Race Competition controller, the most aggressive calibration available on aftermarket. Audi have tried to emulate this on the RS3 Haldex Controller calibration (whilst still making the car soft enough for everyday road use).

If you look carefully, captured on a 4 wheel dyno, the turquoise coloured line (Rear Wheel Pwr) is never above the yellow line (Front Wheel Pwr) across the whole rev range (despite the controller 100% locking the clutch pack), you can never have more than 50% drive being delivered to the rear wheels, and never more than a 50:50 torque split, if all 4 wheels are on grippy tarmac, with identical high mu surfaces.

The graph above is shown on a Gen 4 Haldex, the main difference between Gen 4 and Gen 5 is the deletion of the accumulator, and a revised pump with integral "centrifugal"(!) pressure control valve. Which means the pump speed determines how much or how little pressure is available to clamp the clutch pack. All other mechanical limitations remain the same.

In simple terms, On the RS3, Audi have changed the shape of the individual curves above, but not the ability for the turquoise curve (Rear Wheel Torque) to be higher than the yellow curve (Front Wheel Torque).

A Haldex car, no matter which generation, cannot ever drive the rear wheels faster than the front wheels, nor have any inherent "static" rear bias on the car.

(Of course, on a low mu surface, e.g.: on ice, you can get the car to behave differently, but this is a function of the surface friction, rather than any Haldex magic.)

 

[FBF01]

I currently drive a mk7 Golf R and I was at the lights last Friday and a c63 pulled up beside me. Knew he was up for a wee blast from the lights as he came out of nowhere behind me, no idea what speeds he must have been hitting. Anyway, I get the jump on him but after we are climbing the gears he pulls past me with the rear end of his car all over the shop!!!!! Admittedly I'm sure he was having great fun, but I wouldn't have swapped cars if you paid me!!!! The confidence and traction you have from an all wheel/haldex etc car has meant there's no chance il consider the likes of a RWD or FWD car again.

 

[Snake Pliskin]

I currently drive a mk7 Golf R and I was at the lights last Friday and a c63 pulled up beside me. Knew he was up for a wee blast from the lights as he came out of nowhere behind me, no idea what speeds he must have been hitting. Anyway, I get the jump on him but after we are climbing the gears he pulls past me with the rear end of his car all over the shop!!!!! Admittedly I'm sure he was having great fun, but I wouldn't have swapped cars if you paid me!!!! The confidence and traction you have from an all wheel/haldex etc car has meant there's no chance il consider the likes of a RWD or FWD car again.

Nice observations FBF.

Yeah whilst rear wheel drive is great 'on track' ... Driving on public roads is not a 'race track' ... so I will take my safe & secure Quattro any day of the week, or year and get my power down whatever the weather ... & if that's boring, I will happily take boring

Rear end squirming on public roads is not my idea of fun ! & all this malarkey about 4wd front / rear distribution ... again I am really not fussed, it works end of and I'm quite happy with how Audi's Engineers have set the cars up for Jo Public.

 

[RGBARGEE]

I agree absolutely Snake.. TBH I cannot be ***** with all this debating around 'ultimate' grip and handling. If I wanted a track car it certainly wouldn't be an Audi or a BMW. I too am happy with what the Audi engineers have developed which will inevitably be a compromise for the experts 'real' or pretend! Beer however is a different matter... just enjoying a dose of Butcombe Rare Breed ;-)

 

[FBF01]

Nice observations FBF.

Yeah whilst rear wheel drive is great 'on track' ... Driving on public roads is not a 'race track' ... so I will take my safe & secure Quattro any day of the week, or year and get my power down whatever the weather ... & if that's boring, I will happily take boring

Rear end squirming on public roads is not my idea of fun ! & all this malarkey about 4wd front / rear distribution ... again I am really not fussed, it works end of and I'm quite happy with how Audi's Engineers have set the cars up for Jo Public.

Yeh this word "boring " is thrown about way too much with AWD cars, which becomes a tad tedious to take after a while.

A chap with similarly strong views over on the R forum has just chopped his in for a Boxter S as he just couldnt get to grips with the lack of enjoyment/fun factor. Many of us, and me included, like predictability in a day to day car. That's why there is such a thing as weekend cars for those who seek sideways action round roundabouts ha. I just don't particularly see the attraction of such a thing, but each to their own. People expect way too much from cars nowadays. It can't be everything to all people.

 

[billyali86]

Yeh this word "boring " is thrown about way too much with AWD cars, which becomes a tad tedious to take after a while.

A chap with similarly strong views over on the R forum has just chopped his in for a Boxter S as he just couldnt get to grips with the lack of enjoyment/fun factor. Many of us, and me included, like predictability in a day to day car. That's why there is such a thing as weekend cars for those who seek sideways action round roundabouts ha. I just don't particularly see the attraction of such a thing, but each to their own. People expect way too much from cars nowadays. It can't be everything to all people.

I had a tt rs and and rs3 before my m4. I went out on many back road blasts with the tt rs and had great fun keeping gtr's honest

 

[Eigdoog]

If i had a RWD i think i would end up in a ditch and you would be reading about me in the papers... AWD is where I'm at!

 

[Terminator x]

My previous car was a 130i. Loved it and one of my favourite cars for sure. Seriously **** in the snow and ice though!

TX.

 

[SHOTTA GTR]

Audi really should consider dropping the haldex system, in favor of the gkn twinster system found in the Evoque and Focus RS.

 

[tankclark]

Can you get about safely in Britain with RWD high powered cars? Yes fine.
Can you use all the power in a high powered RWD Car in Britain as much as a 4WD car? Absolutely nowhere near, even in Kent which is the driest place in Britain it rains on average 1/3 of tech year, take snap mornings , cold mornings etc and you could easily up that to 50% of the year