[Skyhigh]

Which vehicles are those illustrations for?

To use BMW's language as above - transferring more than 50% torque to the front is "virtually impossible" with the TCU in our F series! It is simply mechanically not possible to disable the rear axle!

The topic has been discussed extensively before as well. Once again:
Clutch fully closed: 50:50
Clutch fully open: 0:100

You can limit torque by wheel through the ESP system and the brakes. But the xDrive in most BMWs (newer smaller models excluded) CANNOT send more than 50% to the front axle.

I think you are confusing torque and power…

[HighlandPete]

Originally Posted by Skyhigh

Which vehicles are those illustrations for?…

Covers E/F series. Both illustrations are in multiple technical documents.

And into the G-series... with the following BMW Technical Training quote for the G12, which is the cross reference for many of the G-series xDrive models.

The multidisc clutch in the all-wheel drive transfer box allows the torque to be distributed to both axles within certain limits. Seen statistically, the torque distribution between the front and rear axles on the current BMW all-wheel drive vehicles is 40:60. In the G12, the torque distribution to the two drive axles was split equally in the direction of 50:50. In terms of dynamics, however, other important parameters such as different wheel slip values play a part. It is no longer possible to speak of a 50:50 torque distribution with different wheel slip values at the two drive axles. In this case, the drive torques are distributed variably in the range between theoretically 0:100 and 100:0 corresponding to the driving situation.

BMW's words not mine. I see it as the difference in statistical torque distribution (F-series; 40:60, G-series; 50:50) and in terms of dynamics, (0:100 and 100:0) as do BMW, in the above quote.

[Skyhigh]

Trusting words (I.e. marketing) is good, trusting mechanics is better

You may as well believe what you read, but please also pay special attention to words like "virtually", "theoretically" and so on…

P.s. what I quoted earlier is also from BMW

[HighlandPete]

Originally Posted by Skyhigh

Trusting words (I.e. marketing) is good, trusting mechanics is better

You may as well believe what you read, but please also pay special attention to words like "virtually", "theoretically" and so on…

P.s. what I quoted earlier is also from BMW

I think we are talking at cross purposes here, just as BMW are talking two things, in your and my quotes. Torque split/bias and "Apportion up to 100%"

BTW, I'm not in any way disagreeing in my comments with a 40:60 or 50:50 mechanical bias on a closed clutch.

https://www.awdwiki.com/en/torque+split+ratio/

Understanding Torque "Apportion Up To 100%"
What does "torque apportion up to 100% to the axle with traction" mean? Imagine the same Subaru Legacy MT with 50/50 split "under normal conditions". Now imagine the rear wheels are on ice, on rollers, or being raised in the air. If you press the accelerator pedal, the rear wheels will attempt to spin without meeting any resistance. Because there is no resistance, the torque that is applied to the rear wheels is close to zero. The Subaru that we are using in the example has a viscous coupling locking center differential. The viscous coupling heats up and locks the center differential. This prevents the rear wheels from spinning, and transfers engine torque to the front wheels. When rear wheels are in the air, and we assume that the viscous coupling locks fully, 0% of the available engine torque goes to the rear, and 100% of the available torque goes to the front wheels. This is what we mean when we say "torque apportion up to 100%". This Subarus' "default" torque split is 50/50, but torque can be transferred in the range from 100/0 to 0/100 front to rear, depending on which axle loses traction.

Now let's take a vehicle with automatic all wheel drive systems as an example (assume the vehicle is front wheel drive under normal conditions). When in front wheel drive mode, the torque transfer is near 100/0 – most of the power goes to the front wheels. When front wheels slip, the transfer clutch attaches the rear axle. At full lock, torque split becomes 50/50. Now, if front wheels lose traction completely (ice, rollers, or raised in the air), 0% torque goes to the front wheels, 100% of torque goes to the rear wheels, but the ratio stays 50/50. Understand the two things: torque split ratio can vary from 100/0 to 50/50. But torque apportion can vary from 100/0 to 0/100.*

Note that we are talking about torque distribution between the axles, not to an individual wheel. To transfer torque from wheel to wheel you need a lockable differential installed in the axle. To be able to transfer 100% of torque to every single wheel, you need a fully lockable center differential and a fully lockable differential in each of the axles.

© www.awdwiki.com

[HighlandPete]

Originally Posted by CrimsonMoonLight72

What about side to side traction? I have this big ice spot on the side of my street and if I go over that ice spot ONLY with driver side wheels, either front or rear driver side wheels, what should the PASSENGER side wheel(s) do on the dry pavement as the driver side wheels or wheel is spinning on the ice? Do the passenger side wheels spin at same rpms on the dry pavement as the driver side wheels that are spinning on the ice? Or do they turn at a slower rpm than the spinning opposing wheels over the ice?

We would need locking differentials on both axles to get the best single wheel torque transfer. Individual wheel braking is used with xDrive to assist torque transfer to the wheel with grip.

[Skyhigh]

xDrive and the snowy slopes

[Handren]

This winter was the first in which I could try my F30 in the snow and I can say I am really pleasantly surprised. It was handling without any problems. But then again the snow wasn't that much. Compared to my previous car, so far I am really happy with my F30.

Running with 17inch tires by the way.

[J555]

I've heard such complaints few times. Usually the guys asked why their BMW drifts all the time, while their wife's SUV does not. In all those cases, the reason was the same - driving on snow in Sport+ mode...

[kehmann]

I've driven twice in the snow this year and it's amazing how I could feel the front wheels pulling me along.

[BlueB58]

Factory runflats are notoriously bad in the snow. Even worse than standard all-season non RFTs.

[Billfitz]

My OEM Conti RFT weren't bad at all for the first 10,000 miles. With xDrive they were much better than FWD with snows all around. But the tread wear after 10k was pretty bad, so their usefulness in snow deteriorated. I replaced them at 22k, not wanting to run them in winter again.

[nurgburgring]

all seasons tires are like summer tires if not even worse.. with real winter tires you r gonna smoke evry quattro at redlight.

[Billfitz]

Yeah, that will impress all the rest of the high school kids.

[J555]

Originally Posted by BlueB58

Factory runflats are notoriously bad in the snow. Even worse than standard all-season non RFTs.

According to all reputable comparisons I've seen, all winter tires from well known brands are very similar in grip in the snow. The only RFT winter tires I had were the Continental's, and they performed perfectly fine in the snow. Indeed, they suffered from all of the usual RFT drawbacks, and the dry and wet performance was pretty poor.

[Skyhigh]

Strongly disagree. There is MAJOR difference in the performance of reputable winter tires!!
Example: Michelin X-ice are the worst winter tires I have ever driven, on any car.
I had to find out that "X-ice" means "Not suitable for ice"!

[HighlandPete]

Originally Posted by CrimsonMoonLight72

What about side to side traction? I have this big ice spot on the side of my street and if I go over that ice spot ONLY with driver side wheels, either front or rear driver side wheels, what should the PASSENGER side wheel(s) do on the dry pavement as the driver side wheels or wheel is spinning on the ice? Do the passenger side wheels spin at same rpms on the dry pavement as the driver side wheels that are spinning on the ice? Or do they turn at a slower rpm than the spinning opposing wheels over the ice?

My observation when experimenting with an X3 on a snowy slope, individual wheel braking does a lot to stop the 'loose' wheel spinning, ensuring torque goes to the wheels with grip. Quite impressive watching the 'wheel' action, from a good vantage point, as the X3 was driven up a steep slope.

[KDW4him]

Originally Posted by BingoTheClown

Last year I purchased a 2018 440i xDrive GC. This is my first winter with it. Previously I have watched lots of youtube vids about xDrive in the snow. I was very excited to see how well it seemed to handle in this weather.

Although it has been brutally cold here in upstate NY, we have only had 2 small snow storms where I live. First one was just a bit more than a dusting of snow on the roads. And my 440i was all over the place. Even slow turns the rear would slip out.

Second storm: just about 1.5" on the ground. Roads semi-plowed and slushy but not icy. Again - my 440i was awful on the roads. Really had a hard time keeping control, even slow driving.

Now, I have to put things in perspective. I drove a huge Escalade for many years. Obviously there is a big big difference in snow handling. But I didn't expect it to be this awful for AWD car.

Second - I have the runflats. and YES - this is probably the issue at hand. Better tires will improve things. But, the RF's were brand new and lots of tread. I don't love the RF's, for sure. But I want to get my money out of them before I upgrade my tires. So, I will push through this winter and replace them before next winter. Hopefully that helps - but I still feel a bit lackluster over xDrive AWD.

My BMW is better in the snow than my 4wd work truck.

What specifically don't you like?

Mine out accelerates my wt, goes straighter than the wt when slipping.

[auburnf30x]

It's probably apples and oranges, but I find the xDrive to be very capable in poor traction settings, such as mud. I have yet to find anything that I can't get through with it. Traction isn't what I have to watch out for, just ground clearance.

Never realized just how much offroading kayaking forces you to do sometimes. The looks I get crawling past stuck trucks in my little blue Bimmer are great, though.

[schlyter]

thanks for alle the help i think the next car will be x-drive

[rdt22]

Originally Posted by BlueB58

Factory runflats are notoriously bad in the snow. Even worse than standard all-season non RFTs.

Can confirm this.
Exchanged them for non run flats, winter approved ones and the handling improved a lot in snow.
In my case it was the continental wintercontact ones, really good tires.

[Reshagen]

Originally Posted by CrimsonMoonLight72

Yes in that regard there probably are differences....the thing that drives me nuts in when after driving in wet packed snow for a bit the amount of snow that sticks in clumps in wheel well. It’s gets so bad that I worry about the snow pushing into and jamming wheels as I’m driving. I’ve pulled over many times just to break apart the snow and ice that collects in wheel well.

As I am Swedish and brought up on winter roads with plenty of ice and snow, I promise you that there is no need to pull over to clear the wheel wells on the go. Just clear the build up before you park the car so it doesn't freeze completely.

[CincyBearcats]

Originally Posted by thisismikeyb

a proper LSD in the back.

New F31 owner here. Plan to use it to get to skiing on deep days, and the roads in NM are often slow to get plowed. I am often forced to drive through a foot of snow. I will add snow tires for sure, but what LSD do you recommend?

If I'm honest, I'm not super familiar with the xDrive system. I assumed that it has open front, center, and rear diffs and uses electronically controlled braking to assist with loss of traction.