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      01-30-2013, 06:52 AM   #1
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Does it have limited slip differential?

All cars I owned in the past with stability/traction control had limited slip differentials. Does anyone know if X1 has one too? This is important if one plans to use small spare tire.
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      01-30-2013, 08:48 AM   #2
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Rear drive BMW (non-M) BMW vehicles typically do not have LSDs. The dynamic stability control uses the brakes instead. AWD vehicles are a different story of course. What are your worries using a spare?
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      01-30-2013, 09:07 AM   #3
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It's impossible to have LSD in an AWD car. Maybe in a 4x4 where both axles are locked.
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      01-30-2013, 09:58 AM   #4
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Originally Posted by ACZakka325i View Post
It's impossible to have LSD in an AWD car. Maybe in a 4x4 where both axles are locked.
Hehe, your example would be a locking differential, not a limited slip. The S4, Evo, STI and even the X6 have either rear or front and rear LSD's.

As for running a mini spare, it's never a good idea on any awd car because the system will try to allocate less power to the smaller tire to compensate for lacking traction (a faster spinning tire). This can lead to additional wear. Add an LSD into the mix (on awd, fwd or rwd) and you greatly increase the odds of damaging rather expensive internals, especially on clutch based LSD's most non race cars use.
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      01-30-2013, 11:37 AM   #5
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Originally Posted by nospam View Post
Rear drive BMW (non-M) BMW vehicles typically do not have LSDs. The dynamic stability control uses the brakes instead. AWD vehicles are a different story of course. What are your worries using a spare?
If the spare is smaller than the regular tire one would end up wearing out LSD. Probably not an issue for the very short trip though.
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      01-30-2013, 11:49 AM   #6
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Quote:
Originally Posted by ACZakka325i
It's impossible to have LSD in an AWD car. Maybe in a 4x4 where both axles are locked.
I don't think this is correct. My understanding was that many AWD systems are FWD based with LSD in the back.

BMW AWD systems are RWD based (until the next generation of the X1). I don't know how the X1 AWD system works. I believe that because of the way BMW DSC works and the fact that the M Sport use DSC torque vectoring (performance control) that using a donut spare is safe for emergency use (low speed, short distance).

I definitely plan to do more research since I plan to remove the RFTs and carry a donut.
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      01-30-2013, 12:02 PM   #7
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I pulled this from WikiPedia
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Instead of a permanent torque split (which the earlier systems exhibit), xDrive provides variable torque split between the front and rear axles through the use of a multi-plate wet clutch located in the gearbox on the output to the front drive shaft. This setup allows xDrive to modulate the torque split between the front and the rear axles, which is normally split at 40:60 ratio. If wheel slip is detected by the ABS/DSC system, xDrive can react within a tenth of a second to redistribute up to 100% of the engine power to the front or rear axle.[1] The wet clutch is applied through a high speed electric servo motor turning a cam shaped actuator disc.

xDrive is connected to the ABS and DSC systems. In the case that wheelspin or directional instability still occurs while xDrive is or has been modulating the torque split, DSC will brake independent wheels to regain traction and improve directional stability without driver intervention.

The front and rear differentials in xDrive vehicles are an open differential design, thus relying on brake application by the DSC system to transfer power from the slipping wheel to the wheel with traction.
I believe it is safe to use a donut spare for emergency use since the system uses open differentials and DSC braking to modulate individual wheels.
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      01-30-2013, 12:05 PM   #8
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Originally Posted by nospam View Post
I pulled this from WikiPedia

I believe it is safe to use a donut spare for emergency use since the system uses open differentials and DSC braking to modulate individual wheels.
What about sDrive? That's what I have on order.
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      01-30-2013, 12:07 PM   #9
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This is a topic for a different thread, but I will never understand the desire to carry a donut. Many of us who've had M Cars, Corvettes or any BMW with the runflats removed have been dealing with this for over ten years now, with nothing more than an air compressor, a plug kit and road side assistance. I've been towed one time in fourteen years of non-RFT, non spare driving and it was due to a sidewall rupture on a heavily tracked tire that was a serious pain to mount and I'd known it was likely to blow out, but kept driving it anyway, entirely my fault.
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      01-30-2013, 12:09 PM   #10
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Originally Posted by xyz100 View Post
What about sDrive? That's what I have on order.
S Drive has the same issue, you will have an open diff, but DSC will still brake the other wheel trying to get things back in order. You can completely disable DSC (hold the button for 10+ seconds), which will help, but this is still a very temporary fix and should really be avoided if at all possible.
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      01-30-2013, 12:11 PM   #11
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Originally Posted by nospam View Post
I don't think this is correct. My understanding was that many AWD systems are FWD based with LSD in the back.

BMW AWD systems are RWD based (until the next generation of the X1). I don't know how the X1 AWD system works. I believe that because of the way BMW DSC works and the fact that the M Sport use DSC torque vectoring (performance control) that using a donut spare is safe for emergency use (low speed, short distance).

I definitely plan to do more research since I plan to remove the RFTs and carry a donut.
Offhand, I can't think of a single fwd based setup that uses a mechanical LSD in the front or rear.

Again, the X6 has an available LSD for the rear, which I believe makes it the only non-M BMW with an available LSD of any sort.
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      01-30-2013, 12:17 PM   #12
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So, will DSC detect "slippage" when running on donut and try to apply brakes? Probably the solution would be - donut with DSC disabled.

Whether having the spare or not - it is likely personal preference. On the long trips I would rather have a spare than patch kit. I had way too many beyound repair punctures. And I do not want it to be towed.
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      01-30-2013, 12:31 PM   #13
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Fair enough, I guess I don't get the fear of being towed (as BMW provides flat beds) and don't really travel often with the space for a full size wheel and tire inside the car, but as you said, it's personal preference.

Just curious what sort of beyond repair punctures you're dealing with? If I can't fix a puncture with a plug, there's a really good chance that the rim is bent, and I rarely have seen one rim bent without the one in front/behind it also being destroyed, and I have yet to encounter a car with two spares.

Some of you worry too much...
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      01-30-2013, 12:35 PM   #14
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Quote:
Originally Posted by xyz100 View Post
So, will DSC detect "slippage" when running on donut and try to apply brakes? Probably the solution would be - donut with DSC disabled.

Whether having the spare or not - it is likely personal preference. On the long trips I would rather have a spare than patch kit. I had way too many beyound repair punctures. And I do not want it to be towed.
I don't think the DSC will detect slippage on the donut at low speeds. You will see DSC light up in your cluster if it activates. If it does activate, I believe the better solution for sDrive would be to always put the donut on the front and move a front tire to the back temporarily if needed.
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      01-30-2013, 12:39 PM   #15
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Quote:
Originally Posted by Red Bread View Post
Offhand, I can't think of a single fwd based setup that uses a mechanical LSD in the front or rear.
I believe both the Subaru Forester and Outback use this setup (and have come with donut spares). I've read they have a fuse to disable AWD and switch to FWD system when using the donut.

Just google SUBARU, AWD, and DONUT.
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      01-30-2013, 12:42 PM   #16
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Originally Posted by nospam View Post
I don't think the DSC will detect slippage on the donut at low speeds. You will see DSC light up in your cluster if it activates. If it does activate, I believe the better solution for sDrive would be to always put the donut on the front and move a front tire to the back temporarily if needed.
Excellent point, whenever you're using a compact spare, you should always put it on the non-drive end, provided you're not dealing with an awd car. Even then, you're less likely to encounter issues if you put it on the end with less power distribution, or the front for the X1.

This means that if you got a flat on the rear of any X1, s or x drive and you have a compact spare, your best bet would be to remove a front wheel, place the donut on the front and the replace the flat rear wheel with the full size front. Even if you have staggered wheels, this will be preferable to just slapping the donut on the back.

Just to continue to needle, you could also just plug the flat and drive on until the nearest tire repair place where you should really get a patch installed.
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      01-30-2013, 12:43 PM   #17
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Originally Posted by nospam View Post
I believe both the Subaru Forester and Outback use this setup (and have come with donut spares). I've read they have a fuse to disable AWD and switch to FWD system when using the donut.

Just google SUBARU, AWD, and DONUT.
That doesn't mean that the have an LSD, which aside from the STI, I'm reasonably certain no Subie does.
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      01-30-2013, 12:44 PM   #18
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Quote:
Originally Posted by Red Bread View Post

Just curious what sort of beyond repair punctures you're dealing with? If I can't fix a puncture with a plug, there's a really good chance that the rim is bent, and I rarely have seen one rim bent without the one in front/behind it also being destroyed, and I have yet to encounter a car with two spares.

Some of you worry too much...
Over last year my wife managed to ruin the tire with hole so big that it went flat in an instance. Twice. I don't blame her. Too much garbage on the roads.

Besides I can not expect her to patch the tire with the kit. AAA offers two options - towing or spare tire. Both times they installed the spare. So it worked quite well.
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      01-30-2013, 12:53 PM   #19
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Just to continue to needle, you could also just plug the flat and drive on until the nearest tire repair place where you should really get a patch installed.
Thank you for adding this important point. I don't trust plug kits. Tires need to be repaired by an expert: http://www.tirerack.com/tires/tirete....jsp?techid=77

Quote:
Any repair attempted without removing the tire from the wheel is improper. Without inspecting the inside of the tire for hidden damage comes the risk of returning a weakened tire to service. Punctures in the tread area that looked repairable have revealed upon further investigation that the object that punctured the tire had been long enough to cut the tire's sidewall from the inside. Without dismounting the tire, the hidden damage would have been missed.
A donut is simply extra insurance. Never had to use the donut, hopefully never will.
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      01-30-2013, 12:57 PM   #20
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Originally Posted by nospam View Post
Thank you for adding this important point. I don't trust plug kits. Tires need to be repaired by an expert: http://www.tirerack.com/tires/tirete....jsp?techid=77


A donut is simply extra insurance. Never had to use the donut, hopefully never will.
Yep, I'm not recommending plugs as a long term solution, only as a more convenient alternative to carrying around a spare, jack and lug wrench that don't really have a home in the X1, not to mention the potential of slinging a dirty full size wheel and tire back in.

Since this is also my wife's car, as was the 135i without RFT's, her solution would just be to call BMW roadside and wait for the tow truck to materialize. Of course she has been taught to request a tow to the nearest Discount Tire, not the dealer, which AAA is just fine with, since they're who actually answers when you call BMW Roadside.
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      01-30-2013, 01:01 PM   #21
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WIFE!!! This is why I choose to carry the donut. We have both BMW Assist and AAA. My wife is a physician and works late nights at times. I won't put her at risk of having to ride with the tow truck driver. When we did have her 128i towed due to a failure of the RFT (so no donut), I went and picked her up.

BMW assist will only tow to a dealership...not America's Tire or home.
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      01-30-2013, 01:04 PM   #22
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BMW assist will only tow to a dealership...not America's Tire or home.
Interesting, as I have used them twice to do exactly that. I know that's what the official information says, but once a tow truck driver shows up, they don't really care, especially if the tire place is closer than the dealer. When I was living in Laguna Beach, I had my M Coupe towed from Anaheim to the America's Tire in Orange and I'm 99% certain they just billed BMW for towing it to Crevier.

As for going to pick your wife up with a flat RFT, was she more than 50 miles from home? That is sort of the point of RFT's, for just the situation you described.
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