F30 rear differential?

hi, anyone know whether the F30 is equiped with anything other than an open rear differential for the RWD? Is there an electronically controlled limited slip like on the 135?

Does the E9X 335is have a differnt differential?

Nope. Limited slip rear differentials are disappearing - except for dedicated track cars. They are substantially less valued than they used to be. The ability of modern cars like a BMW to use the DSC to control the geometry and dynamics is the reason. For example, most sophisticated new cars lightly apply the inside rear brake under hard cornering. Limited slip differentials have a number of disadvantages - including additional complexity and reliability issues. The new Mclaren MP4-12C does not have limited slip.

Originally Posted by TEAShea

Nope. Limited slip rear differentials are disappearing - except for dedicated track cars. They are substantially less valued than they used to be. The ability of modern cars like a BMW to use the DSC to control the geometry and dynamics is the reason. For example, most sophisticated new cars lightly apply the inside rear brake under hard cornering. Limited slip differentials have a number of disadvantages - including additional complexity and reliability issues. The new Mclaren MP4-12C does not have limited slip.

DSC braking is not good on a track at all. It slows the momentum of the car at a very critical point in the turn, where you are normally under power. To be fair, in the e90 you had to be carrying about 85 mph through a turn for it to interfere. It ruined my rear pads and rotors at Road Atlanta.

I don't think they're less valued than they used to be at all. It's true that if you are competitive in a 911 GT3 you're going to need to replace the clutches in the diff every other season. It's no news to anyone that going to the track is an expensive hobby and high end cars require a lot of maintenance to stay on track. Ask a Ferrari owner and he'll tell you it costs about $10 a mile just to drive the thing.

For differential technology look at the latest offerings from Porsche and Audi. On Porsche the option is called PTV (Porsche Torque Vectoring) and Audi calls it a sports rear differential. The uses magnets to disengage the inside half shaft and send all of the power to the outside wheel. It eliminates understeer without the need to dial in an insane amount of (tire destroying) negative camber on the front wheels.

Porsche/Audi may have the patent on this technology. I assume that if they were licensing it from someone BMW and Mercedes would be using this also, to be competitive.

I was thinking that slowing the inside wheel doesnt do anything for acceleration out of corners. It'lljust keep the car from spinning.
Doesn't the 135 have sort of electronic limited slip? I surprised the M Spt doesnt include some type of LSD.
How about X-Drive? How does it handle slip control?

Originally Posted by bimmerized

How about X-Drive? How does it handle slip control?

Electronic braking, although the X6 utilizes torque vectoring made by GKN Driveline. Neat system.

Originally Posted by westwest888

DSC braking is not good on a track at all. It slows the momentum of the car at a very critical point in the turn, where you are normally under power. To be fair, in the e90 you had to be carrying about 85 mph through a turn for it to interfere. It ruined my rear pads and rotors at Road Atlanta.

I don't think they're less valued than they used to be at all. It's true that if you are competitive in a 911 GT3 you're going to need to replace the clutches in the diff every other season. It's no news to anyone that going to the track is an expensive hobby and high end cars require a lot of maintenance to stay on track. Ask a Ferrari owner and he'll tell you it costs about $10 a mile just to drive the thing.

For differential technology look at the latest offerings from Porsche and Audi. On Porsche the option is called PTV (Porsche Torque Vectoring) and Audi calls it a sports rear differential. The uses magnets to disengage the inside half shaft and send all of the power to the outside wheel. It eliminates understeer without the need to dial in an insane amount of (tire destroying) negative camber on the front wheels.

Porsche/Audi may have the patent on this technology. I assume that if they were licensing it from someone BMW and Mercedes would be using this also, to be competitive.

Totally +1!

My Honda S2000 with it's Torsen differential totally spanks my 335is in the corners. It's amazing the way the back end on the Honda helps steer you around a corner.

Originally Posted by westwest888

DSC braking is not good on a track at all. It slows the momentum of the car at a very critical point in the turn, where you are normally under power. To be fair, in the e90 you had to be carrying about 85 mph through a turn for it to interfere. It ruined my rear pads and rotors at Road Atlanta.

I don't think they're less valued than they used to be at all. It's true that if you are competitive in a 911 GT3 you're going to need to replace the clutches in the diff every other season. It's no news to anyone that going to the track is an expensive hobby and high end cars require a lot of maintenance to stay on track. Ask a Ferrari owner and he'll tell you it costs about $10 a mile just to drive the thing.

For differential technology look at the latest offerings from Porsche and Audi. On Porsche the option is called PTV (Porsche Torque Vectoring) and Audi calls it a sports rear differential. The uses magnets to disengage the inside half shaft and send all of the power to the outside wheel. It eliminates understeer without the need to dial in an insane amount of (tire destroying) negative camber on the front wheels.

Porsche/Audi may have the patent on this technology. I assume that if they were licensing it from someone BMW and Mercedes would be using this also, to be competitive.

Doesn't the X6M have the same system?

Originally Posted by bimmerized

I was thinking that slowing the inside wheel doesnt do anything for acceleration out of corners. It'lljust keep the car from spinning.
Doesn't the 135 have sort of electronic limited slip? I surprised the M Spt doesnt include some type of LSD.
How about X-Drive? How does it handle slip control?

The inside wheel slip lets all of the power escape the system. In other words, if the inside wheel can only put down 90 ft/lb of torque than the whole drivetrain is lowered to that level.

X-Drive still has open diff in the rear, but it also has a center differential that sends power the front. It's not a fixed ratio but a varying 40-60 or 60-40 or 50-50, as power is needed. The front on the audi and the bmw x-drive have open front differentials.

how are people getting around this deficiency? What are the after market options and how expensive.

Was removing LSD a cost cutting measure? Which BMW still have LSD in the traditiona sense?

Originally Posted by bimmerized

how are people getting around this deficiency? What are the after market options and how expensive.

Was removing LSD a cost cutting measure? Which BMW still have LSD in the traditiona sense?

Not so much cost-cutting; it's always been an additional cost option. But for most people and most conditions (excepting tracking/rallying/xcross and some very limited snow conditions - see DTC), the use of the ABS system to detect wheel slip and brake that wheel to transfer torque to the other wheel works pretty well. BMW calls this system Automatic Differential Braking (ADB).

Only the M cars have LSDs, and they're electronically controlled so that it works with the DSC.

The center diff of the xDrive system, as mentioned, is electronically controlled to apportion torque front/rear. It uses a small motor to drive the clutch pack.

Originally Posted by TEAShea

Nope. Limited slip rear differentials are disappearing - except for dedicated track cars. They are substantially less valued than they used to be. The ability of modern cars like a BMW to use the DSC to control the geometry and dynamics is the reason. For example, most sophisticated new cars lightly apply the inside rear brake under hard cornering. Limited slip differentials have a number of disadvantages - including additional complexity and reliability issues. The new Mclaren MP4-12C does not have limited slip.

Quite the opposite:

2013 Ford Mustang added LSD as an option on all models (it was already on the Boss 302 & GT500)
2013 Subaru BRZ has standard LSD
2013 Cadillac ATS has optional LSD
Porsche added an LSD option to Boxster/Cayman in 2009 (I think)

Originally Posted by floydarogers

Not so much cost-cutting; it's always been an additional cost option. But for most people and most conditions (excepting tracking/rallying/xcross and some very limited snow conditions - see DTC), the use of the ABS system to detect wheel slip and brake that wheel to transfer torque to the other wheel works pretty well. BMW calls this system Automatic Differential Braking (ADB).

Is it true that more torque actually gets transferred to the wheel with more traction? I thought torque is reduced with the application of the brakes down to as much as the slipping wheel can take, which isn't much for an inside wheel when corning hard...

On the M cars with DCT off, the limited slip doesn't work? but I guess there's a track mode.

Originally Posted by Chris90

Quite the opposite:

2013 Ford Mustang added LSD as an option on all models (it was already on the Boss 302 & GT500)
2013 Subaru BRZ has standard LSD
2013 Cadillac ATS has optional LSD
Porsche added an LSD option to Boxster/Cayman in 2009 (I think)

So is LSD needed? It depends on the power being put down, the weight and balance of the car. The Mustang V8 puts out a lot of power and with it's solid rear axle, it really needs LSD. The Subaru BRZ is pretty light overall and very light in the back. Like my old Nissan 240SX, it needs LSD to put down the power. Cadillac will likely offer it on their most powerful engine to decrease lap times. Porsche....well, it's a higher hp performance car and you'd expect it.

The 3 series are very well balanced with medium hp so it's not really necessary most of the time. Obviously the M3 is a different story.

Originally Posted by micknugget

So is LSD needed? It depends on the power being put down, the weight and balance of the car. The Mustang V8 puts out a lot of power and with it's solid rear axle, it really needs LSD. The Subaru BRZ is pretty light overall and very light in the back. Like my old Nissan 240SX, it needs LSD to put down the power. Cadillac will likely offer it on their most powerful engine to decrease lap times. Porsche....well, it's a higher hp performance car and you'd expect it.

The 3 series are very well balanced with medium hp so it's not really necessary most of the time. Obviously the M3 is a different story.

My ZHP needs an LSD badly - it gets the 1-wheel peel badly, and sucks at accelerating and turning in snow despite snow tires. I haven't driven one of the newer cars with electronic diff, but since it's still an open diff, I'm pretty skeptical.

I think BMW doesn't use LSDs in the regular cars cause it's safer - driver's who mash the gas in a corner or wet/snow will just have one-wheel spin with minimal oversteer. If you know what you're doing, an LSD is safer cause it's more predictable, but that doesn't apply to most BMW owners.

Originally Posted by micknugget

So is LSD needed? It depends on the power being put down, the weight and balance of the car. The Mustang V8 puts out a lot of power and with it's solid rear axle, it really needs LSD. The Subaru BRZ is pretty light overall and very light in the back. Like my old Nissan 240SX, it needs LSD to put down the power. Cadillac will likely offer it on their most powerful engine to decrease lap times. Porsche....well, it's a higher hp performance car and you'd expect it.

The 3 series are very well balanced with medium hp so it's not really necessary most of the time. Obviously the M3 is a different story.

I can notice the lack of limited slip in almost any car I drive, FWD or RWD. Did BMW elimiate it for safety? they should left it as a cost option...

Originally Posted by bimmerized

I can notice the lack of limited slip in almost any car I drive, FWD or RWD. Did BMW elimiate it for safety? they should left it as a cost option...

Why not just get an aftermarket one then?

Originally Posted by tim330i

Why not just get an aftermarket one then?

Cause it's like $3500. I'm kicking myself for not doing it to my E46 when I bought it 6 years ago. Would seem kinda silly now.

Originally Posted by bimmerized

I can notice the lack of limited slip in almost any car I drive, FWD or RWD. Did BMW elimiate it for safety? they should left it as a cost option...

Well, it will teach you to use the throttle better then

Originally Posted by micknugget

Well, it will teach you to use the throttle better then

what makes you think I need to practice my application of the throttle. It's about putting as much power down out of corners to lower lap times.

Originally Posted by bimmerized

what makes you think I need to practice my application of the throttle. It's about putting as much power down out of corners to lower lap times.

For me it's not that at all, it's about going sideways around slow corners.

BMw has never been big on LSD's - neither has Mercedes. They can be useful for dedicated track cars but other than that they are really not seen as a good idea.

Originally Posted by TEAShea

BMw has never been big on LSD's - neither has Mercedes. They can be useful for dedicated track cars but other than that they are really not seen as a good idea.

The C63 AMG has gotten very serious. You can get the LSD as always, but now you can also get ceramic brakes and a full AMG engine package with light crank shafts from the SLS roadster. Also, the RS5 and RS4 will have ceramic rotors option, in addition to a very special center differential. They're behind rear LSD and focusing on higher level performance.

Originally Posted by floydarogers

.

The center diff of the xDrive system, as mentioned, is electronically controlled to apportion torque front/rear. It uses a small motor to drive the clutch pack.

Can anyone confirm this is true? A passive differential in the center is all I've ever heard of. On the sedans for sure. SUV tech I have no idea about. Link?

Originally Posted by TEAShea

BMw has never been big on LSD's - neither has Mercedes. They can be useful for dedicated track cars but other than that they are really not seen as a good idea.

Nonsense, are BMW M convertibles dedicated track cars? Cause they have mechanical LSDs.

Originally Posted by westwest888

Can anyone confirm this is true? A passive differential in the center is all I've ever heard of. On the sedans for sure. SUV tech I have no idea about. Link?

All you have to do is to actually LOOK at the parts for the transfer case: http://www.realoem.com/bmw/showparts...32&hg=27&fg=15

And, BTW, there has been a bunch of talk about the weakness of the little plastic gears on the X3 forums - they wear out easily.