AWD Power Loss

[Just_me]

this is an intresting thread regarding dyno losses. Various cars being tested, like RS4 and M5

http://www.germancarzone.com/pit-gen...hat-seems.html (Power: it's not what it seems)

[Imhotep Evil]

Originally Posted by Just_me

Above 200km/h a M5 E60 is faster than a Gallardo
Above 200km/h M5 E39 is faster than RS6 with 450 hp

Thats the conclusion m5board.com done during various races.
I think AWD is one of the reasons for the losses?

The Gallardo was lucky for having a considerably lower mass.

Originally Posted by Martinbo

c. The auto-tranny two footed pullaway. In performance cars with a high stall speed torque convertor automatic hold the car with the left foot on the brake and dial up the rpm. Release the foot brake and mash the accelerator to the carpet. A fine way to break an automatic transmission if not done with a measure of precision and mechanical circumspection. NOT recommended for DSG's, SMGs and CVTs.

Understandable, perfectly, since they're not exactly automatics.

[martinbo]

Of course the real-world flipside to all of this is down to that age-old concept of...?

Compromise.

Proponents of the AWD benefits are all too aware of the disadvantages involved. However, a car that's used in the real world, by real world drivers is far more socially acceptable by virtue of its imperious dynamics in all weather conditions than how quickly it accelerates from 200 km/h to 300 km/h. In that sense we're talking absolutes...

And in terms of absolute performance nothing comes close to a very much AWD, quad-turbo, 16 cylinder Bugatti Veyron.

[Imhotep Evil]

Originally Posted by martinbo

Of course the real-world flipside to all of this is down to that age-old concept of...?

Compromise.

Proponents of the AWD benefits are all too aware of the disadvantages involved. However, a car that's used in the real world, by real world drivers is far more socially acceptable by virtue of its imperious dynamics in all weather conditions than how quickly it accelerates from 200 km/h to 300 km/h. In that sense we're talking absolutes...

And in terms of absolute performance nothing comes close to a very much AWD, quad-turbo, 16 cylinder Bugatti Veyron.

Except for Caparo T1. And you can be sure it will absolutely destroy it in the corners, unless the driver suffers from g-LOC.
And if the Veyron uses 320 Km/h+ speeds to gain the advantage, it's fuel tank will be empty in 12 minutes, and the tires can only resist 15 minutes (by logic it will be stopped due to lack of fuel).

So no real world advantages from here.

Well it's obvious, really. At lower speeds the engine power is consumed only by the AWD system. So 0-100 km/h, AWD cars put in a good showing. However, at higher speeds aerodynamic drag starts to consume more and more engine power as a greater portion of the output is put to work in overcoming this aerodynamic resistance. The added resistance of an AWD car merely compounds this wasteful consumption of power.

While this is true, the nature of S85 engine and SMG III have to be taken into consideration. That engine really comes alive at 180 Km/h and is still strong at 325+ Km/h.

[Imhotep Evil]

Martin, here's a question:

Is AWD the ultimate form of Traction Control ?!

[The Artist]

snap that post was killer martin.. thnx alot

about the RS4 i did that first start you told us about..
and there is NO freakin wheelspinn..that car will not loose grip..
i love it ... and hate it for that..

[Monster]

Originally Posted by Imhotep Evil

Is AWD the ultimate form of Traction Control ?!

Do you mean traction control as the electronic system, or just traction control?

I will say AWD is better than those traction control systems because AWD manages the distribution of power to increase grip while traction control simplely reduce the already distributed power to deal with the amount of grip available to the driven wheels. It doesn't actually increase traction in a way AWD system does.

Traction Control redcuce the load per wheel thus increase traction by actively reducing engine power or braking one or both driven wheel. AWD distributes power to all wheels and there for reducing the load per wheel, there is no need to cut engine power or brake the driven wheels.

So in a way AWD is the ultimate form of Traction Control.
I hope this make sense.

[Sunny]

Originally Posted by monster

AWD in general looses more power in the drivetrain simply because there are more components in the drivetrain to move, and there are increased frictional lose in the drivetrain because of those additional components

It is not just additional frictional loss, there is the much higher rotational mass. The engine has to now turn 4 wheels and tires instead of just 2 and of course 4 brake discs, an additional axle, a larger drive shaft and usually another clutch, another differential and even worse - a viscous coupling. And all this loss is in percentage, so the faster you go the higher the loss.

[martinbo]

Originally Posted by Sunny

It is not just additional frictional loss, there is the much higher rotational mass. The engine has to now turn 4 wheels and tires instead of just 2 and of course 4 brake discs, an additional axle, a larger drive shaft and usually another clutch, another differential and even worse - a viscous coupling. And all this loss is in percentage, so the faster you go the higher the loss.

Nice post Sunny. Concise and to the point...

[martinbo]

Of course not all AWD cars employ power sapping viscous couplings on the centre differential. Many use a planetary gear arrangement or a electro-hydraulic multi-clutch pack to apportion power and torque fore and aft.

Do I think that AWD is the ultimate form of traction control? Well from a purely mechanical and physics point of view vs two wheel drive then my answer would be yes. But it all depends on the type of AWD. If it's a permanent 50:50 or 40:60 split then yes, I'll agree. The more on-demand type systems that are predominantly FWD and only engage when slippage occurs are good in some instances but on the whole I'd rate a permanent AWD setup as being the superior form of mechanical traction control.

Naturally, when you bring advanced electronics into the picture such as throttle position sensors, yaw sensors, steering angle sensors and electronically operated differentials then AWD becomes a formidable form of vehicle dynamic (and not just traction) control.