Big weak points Quattro ?

[The Pretender]

I'm not sure what to think about this.
Is it nomal or is something broke on the Quattro system.
Is BMW's X-drive much better then Quattro. ?
Take a look at these video's:

http://www.youtube.com/watch?v=crnAn-mt1Ks
http://video.google.com/videoplay?docid=9072883197544018466
http://www.youtube.com/watch?v=Oo9GV4mSnRQ&feature=related

Jarod.

[LOWR1D3R]

That´s what it looks like. :doh:
There was this R8 donut clip on this forum that made me think why doesn´t the frontwheels spin. This is the only reasonable explanation for that.

[gabbby69006]

This is torsen central dif. It cannot do a 100% torque distribution, only + or - 25%. But it still being the better dif for all wheel drive because it is mechanical and not electronical. In regulare snow condition it will be a big gap wetween an electronical system and a mechanical system, because the mechanical system is a lot more sensitive, and permit to the tire to maintains the grip...

On a Q7, there is probably the two approach combined : with the brake (and ABS sensors), the system can slow down the slipping wheel to distribute torque to the other wheels. Then, you have the better of the two world. You cannot be stopped like this...

There is a video that demonstrate the absolute superiority of the expensive torsen dif, where we see an alroad that climp a skiing track, where BMW SUV cannot.

Think

[gabbby69006]

This is torsen central dif. It cannot do a 100% torque distribution, only + or - 25%. But it still being the better dif for all wheel drive because it is mechanical and not electronical. In regulare snow condition it will be a big gap wetween an electronical system and a mechanical system, because the mechanical system is a lot more sensitive, and permit to the tire to maintains the grip...

On a Q7, there is probably the two approach combined : with the brake (and ABS sensors), the system can slow down the slipping wheel to distribute torque to the other wheels. Then, you have the better of the two world. You cannot be stopped like this...

There is a video that demonstrate the absolute superiority of the expensive torsen dif, where we see an alroad that climp a skiing track, where BMW SUV cannot.

Think that the torsen is mounted in the best AWD cars : Subaru Impreza, Evo...

[PeterJohn]

Audi has a "Torque Sensing" centre diff lock, aka Torsen. On the rollers, there is zero torque, thus zero lock. Acceleration or a tap on the brakes would activate the diff lock.

The A6 in the snow was actually sitting on a snow bank, with virtually no weight on the tyres.

BMW has a speed sensing diff, using sensors. The downside is a delay in reaction, which you could see on the video. An Audi diff can predict slippage, while a BMW diff reacts to it when it has already occured. The upside is that it works on rollers, without having to tap the brakes or accelerator pedal.

The BMW vid seems like a con to me. Some brakes, or actuall acceleration, and the car would have had no trouble getting of the rollers (as you can see in the A4 video). You can see the car inch forward, and then he throws on the brakes. Put these cars on wet grass, and the BMW with it's slower reaction time will have a much harder time.

[The RS6]

There is a video that demonstrate the absolute superiority of the expensive torsen dif, where we see an alroad that climp a skiing track, where BMW SUV cannot.

Here it is...
http://youtube.com/watch?v=8zfKRdgoRo4

[Tanner]

You know that the allroad had much better tires than the others? The better way to do that test is to ensure that all vehicles are using the same exact tires - willing to bet that most of the cars would have made it to the top.

Honestly, I have not gotten stuck in deep snow. If you're running all seasons, there are limits to how much traction it can get. Winter tires are a must. Of course, if you're hooning around in a parking lot and end up getting into deep heavy/wet snow, you're just going to beach yourself and end up getting stuck.

[GeCcO]

You only need to use the handbrake and your of the rollers. This is so apparently a clip made to get BMW look good. And this is so much more close to theory than the actual practical use of a 4wd system. Come on, where would you find a spot where both wheels have NO friction, that just aint gonna happen in a real life situation ;)

[raulg]

You know that the allroad had much better tires than the others? The better way to do that test is to ensure that all vehicles are using the same exact tires - willing to bet that most of the cars would have made it to the top.

Honestly, I have not gotten stuck in deep snow. If you're running all seasons, there are limits to how much traction it can get. Winter tires are a must. Of course, if you're hooning around in a parking lot and end up getting into deep heavy/wet snow, you're just going to beach yourself and end up getting stuck.

How do you know that? Maybe they changed all tires to one specific model.

Or maybe all had winter tires - I expect that, or that test is irelevant.

[raulg]

You only need to use the handbrake and your of the rollers. This is so apparently a clip made to get BMW look good. And this is so much more close to theory than the actual practical use of a 4wd system. Come on, where would you find a spot where both wheels have NO friction, that just aint gonna happen in a real life situation ;)

I've been on ice for the last 2-3 weeks, heavy winter here in Chicago with plenty of icy spots -especially where I work, cause they don't use any salt ... And even if I keep my rear tires on ice and front on dry pavement I still have no issues to take off. I guess ICE has much more resistance than those rollers. Lucky me there are no rollers on the street at all.
I should record it .. a short video may convince people .. :)

[PeterJohn]

You know that the allroad had much better tires than the others? The better way to do that test is to ensure that all vehicles are using the same exact tires - willing to bet that most of the cars would have made it to the top.

Honestly, I have not gotten stuck in deep snow. If you're running all seasons, there are limits to how much traction it can get. Winter tires are a must. Of course, if you're hooning around in a parking lot and end up getting into deep heavy/wet snow, you're just going to beach yourself and end up getting stuck.

Since when are tyres not a part of the car?

[Tanner]

The point I was making, if you want to do a fair comparison of the various AWD systems, standardize on the same set of tires on all of the vehicles.

The video of the hill climb is a few years old, but there were a fair number of comments on this video. A lot of people commented on how the test was done and hence many suspect including myself that some had all season tires. All season tires of course are a compromise to begin with.

Besides, how many of us would even have the opportunity to try and climb a ski hill with their car... would be fun and interesting, but not sure about going down the hill!

[RS246]

This video is a fake..... i do not i my wildest dreams belive that crap....

the quattro system in this A8 has 50% distrubution on the senter diff...
Wich means tha the car have to spin on one wheel at the front and one at the back....