What is BMW sDrive - the dynamic rear-wheel-drive system

[mopartodd]

Newb question. New to the forum and BMWs.

I've done a couple searches but can't seem to find out if this is a mechanical differential type system, or strickly a computer/braking controlled system. How does this system work?

Thanks for any information.

[prash]

There is no system. Its just a name that BMW made up to note the difference between all wheel drive (X-Drive) and rear wheel drive (S-Drive.)

Thank God the M Division didn't get saddled with that name or they would be called the S-Drive M5 or maybe the M S-Drive 5.

[Kevlar]

Non-M BMW's uses an electronic rear differential setup... it applies brake pressure to slow the spinning wheel which in turn sends wheel to the opposite side of the car (the one not spinning as much). It's a simulated limited slip differential setup.

M Cars use a mechanical limited slip differential which has an internal pump which reroutes power to the wheel with the most grip through some wizardry which I can't explain at the moment.

[mopartodd]

Thanks for the replies. Thought for sure these cars would use a mechanical differential rather than the open diff/computer/brake set-up.

I suppose then that the X-drive set-up is much the same.

[mryakan]

Thanks for the replies. Thought for sure these cars would use a mechanical differential rather than the open diff/computer/brake set-up.

I suppose then that the X-drive set-up is much the same.

No xDrive is quite a bit more complicated and it depends how much so on which generation it is. The latest generation xDrive (e.g. on X6) uses torque vectoring among other things to distribute power to the wheels.
http://www.caranddriver.com/features...ks-up-handling

[mopartodd]

Wow, that system is pretty involved. Unfortunately, I'm not in the market for anything like an "M" as a Daily Driver.

[pizzaman09]

Thanks for the replies. Thought for sure these cars would use a mechanical differential rather than the open diff/computer/brake set-up.

I suppose then that the X-drive set-up is much the same.

The computer aided simulated differential is not too new of an idea for BMW either. The traction control system in my 01 740iL uses the brakes to simulate a limited slip differential in a high slip situation such as one tire on ice. It works wonders, if that car didn't have the system it would be pretty much undriveable in the winter. With the system I have been able to make it through 11 winters living in the snow belt off of Lake Erie driving an e38.

[r33p04s]

eww using brakes to simulate a LSD...why not just stick a LSD in there and call it a day...sounds like more computer crap for the sake of making it more complicated (expensive)

[mopartodd]

eww using brakes to simulate a LSD...why not just stick a LSD in there and call it a day...sounds like more computer crap for the sake of making it more complicated (expensive)

This is how I feel as well. Wonder why BMW and other companies are going this route. I know in other car circles, owners are replacing these systems with a mechanical set-up when available because they are less invasive.

[Kevlar]

eww using brakes to simulate a LSD...why not just stick a LSD in there and call it a day...sounds like more computer crap for the sake of making it more complicated (expensive)

Electronic controlled limited slip differentials are

* Cheaper to operate
* Cheaper to install
* Cheaper to replace
* Quieter in operation
* Can be easily tweaked to application without retooling
* Lighter
* Smarter

I am sure the list goes on and on... but those are the ones I could quickly think of.

[90turbo1]

This is how I feel as well. Wonder why BMW and other companies are going this route. I know in other car circles, owners are replacing these systems with a mechanical set-up when available because they are less invasive.

because with a real LSD rear end you are fixed. you can make them loose to some extent with a viscous coupling lsd but a mechanical lsd is more or less fixed, what you have is what you get. When they use computer controls to brake the spinning wheel it is completely variable. thats why they are going that route.

unsuspecting driver with true lsd on ice is in for a suprise. let the car do the job with electronics and the customer is safe and feels like a rock star on ice.

and it is cheaper like said, they are simply using existing equipement and programming it to do things like this.

[pizzaman09]

Electronic controlled limited slip differentials are

* Cheaper to operate
* Cheaper to install
* Cheaper to replace
* Quieter in operation
* Can be easily tweaked to application without retooling
* Lighter
* Smarter

I am sure the list goes on and on... but those are the ones I could quickly think of.

They are also more efficient. Theoretically with a limited slip diff there is energy lost in the "brake pads" in a corner.

[jumperdono]

sounds like more computer crap for the sake of making it more complicated

[r33p04s]

Electronic controlled limited slip differentials are

* Cheaper to operate
* Cheaper to install
* Cheaper to replace
* Quieter in operation
* Can be easily tweaked to application without retooling
* Lighter
* Smarter

I am sure the list goes on and on... but those are the ones I could quickly think of.

I just replaced my open diff with a LSD from an //m w/ ~120k on it...no noises here

cheaper to install and replace? these are bmw's just putting the thing on a lift will cost you a benjamin or 2... same with connecting it to a laptop and coding a battery

I can't imagine them breaking without being severely abused before 150-200k/mi... I understand the flexibility but on cars like these there aren't many shared components beyond the driveline and even then @ 200k who cares if it breaks its way past warranty anyways... do we really want them 'tweaking' one part to use for another application instead of designing something bespoke the dynamics of a 3'r is different than the dynamics of a 7'r and as such should be using different equip and systems... smarter? yes but computers can't think they just process inputs and output based on their known parameters

because with a real LSD rear end you are fixed. you can make them loose to some extent with a viscous coupling lsd but a mechanical lsd is more or less fixed, what you have is what you get. When they use computer controls to brake the spinning wheel it is completely variable. thats why they are going that route.

unsuspecting driver with true lsd on ice is in for a suprise. let the car do the job with electronics and the customer is safe and feels like a rock star on ice.

and it is cheaper like said, they are simply using existing equipement and programming it to do things like this.

flexibility is a legit reason but i feel like bmw (just like all other corp's) are simply pushing the tech to increase the bottom line and decrease costs, not improve the product... safer for the customer? i can't comment i live in sunny sofla never driven on ice other than patches of the black stuff 1yr in atlanta

im of the school of thought that whenever possible you use the real deal, dont cut corners and dont 'simulate' anything if you cant do it at x price you cant do it and you charge x+y price for the feature

do they use these fancy electronic diff's (computer managed dynamic rear braking) on the //m cars? or do they still equip them with the real deal mechanical lsd...that should be a pretty definitive answer as to what is the better setup

either way they will continue on this path of increasingly complicated and electronic cars...

[yankee2]

Electronic controlled limited slip differentials are

* Cheaper to operate
* Cheaper to install
* Cheaper to replace
* Quieter in operation
* Can be easily tweaked to application without retooling
* Lighter
* Smarter

I am sure the list goes on and on... but those are the ones I could quickly think of.

I cannot quite believe that BMW dies ANYTHING because it is cheaper! In general, it seems (haven't been an owner for long, but I hear horror stories) that BMW repairs typically cost as much as 4-5X as much as my old Toyota cost, I recall thinking THEY were costly to repair! Better, perhaps, but cheaper???

[yankee2]

Easier to configure, cheaper to manufacture, sell for more, generate more profits! To slap an s-drive badge on the side of their cars which have 2WD must be the cheapest system ever invented for a car! I have to wonder how many buyers gushed "ooo! s-drive!" not long before signing the papers?

[BimmerBreaker]

Easier to configure, cheaper to manufacture, sell for more, generate more profits! To slap an s-drive badge on the side of their cars which have 2WD must be the cheapest system ever invented for a car! I have to wonder how many buyers gushed "ooo! s-drive!" not long before signing the papers?

I'm curious what part of "S-drive" made you think of anything other than a 2WD platform?

[asphalt4463]

I cannot quite believe that BMW dies ANYTHING because it is cheaper! In general, it seems (haven't been an owner for long, but I hear horror stories) that BMW repairs typically cost as much as 4-5X as much as my old Toyota cost, I recall thinking THEY were costly to repair! Better, perhaps, but cheaper???

In my experience, the total cost of ownership of my BMW's with warranty hasn't been unexpectedly high (definitely not 4-5x) and has been on-par with my VW's (even including depreciation). That's just an economic comparison not allowing for the better grade and driving experience of the bmw. The absolute best value IMO (re: including operating cost, insurance, etc.) and reliability is the Honda Accord (I've had 3). I wouldn't directly compare driveability of an Accord to a 3series but with good tires, I think they're pretty decent. That said, even the Honda has its economic surprises and ease-of-repair issues.