2011 E70 40d - Rear disc brake exploded with biscuit!

Craig_Za

New member
Hey, I was driving back from Durban and had the following happen to me just past Villiers on the N3.

I got a warning light about tyre pressure. I pulled over and checked the 4 tires r18 255/55. They all appeared fine at the time, and been the side of the highway. I reset the warning and headed for a garage.

About 15mins later @ ~100km/hr, I heard a tyre noise so pulled over to discover the rear left tyre had worn to the canvas, presumably I've been running on the run flat tire since the tyre warning. I decided to replace with the OEM spare supplied with the car.

Less then 5km @ 60km/hr my rear disk completely exploded which caused me to immediately pull over. The disk was completely in flames and bits of brake disk fell into the veld beside the highway and started small fires. We used the small amount of drinking water to put the flames around the disc out, and proceeded to stomp out the veld fires started by bits of molten disk. I then sat on the side of the motorway for 3 hours waiting for BMW to come tow the vehicle. It's still under Motorplan (not that helps much).

BMW South Africa have come back saying this was caused by the cars stability control and tire size differential caused by the spare wheel. The cars currently sitting at Boksburg, been "investigated".

I've a couple photos of what the brake disk looked like and parts of the brake disc we recovered. Unfortunately didn't get the camera out in time to catch the fire.
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Clint@MMS AUTO

BMWFanatics Advertiser
Official Advertiser
So its true that BMW's do catch on fire...

sorry about your experience, hope you get it sorted.
 

tman

Well-known member
Not quite sure how the differential or the stability control can cause a disk to shatter?

For the disk to get so hot, I assume the pad must have been touching the disk for a period of time?
 

Blue Shirt

Well-known member
The traction control (part of the stability controls) will apply brake pressure to a wheel that it perceives to be slipping. If the spare wheel is not the same diameter as the other wheels, it will turn faster than the other wheels hence fooling the stability control. Continuous brake pressure will overheat the brake disk with the results that you experiences.

That is my theory and I stick with it.
 

ChefDJ

///Member
What Blue Shirt says sounds plausible.

I am curious as to what BMW will say. Please keep us updated?
 

VictorMike

///Member
Blue Shirt said:
The traction control (part of the stability controls) will apply brake pressure to a wheel that it perceives to be slipping. If the spare wheel is not the same diameter as the other wheels, it will turn faster than the other wheels hence fooling the stability control. Continuous brake pressure will overheat the brake disk with the results that you experiences.

That is my theory and I stick with it.

Most probable. But wouldn't the TC warning be constantly on the dash while this was happening?
 

Craig_Za

New member
Blue Shirt said:
The traction control (part of the stability controls) will apply brake pressure to a wheel that it perceives to be slipping. If the spare wheel is not the same diameter as the other wheels, it will turn faster than the other wheels hence fooling the stability control. Continuous brake pressure will overheat the brake disk with the results that you experiences.

That is my theory and I stick with it.

Ye I agree, I'm sure the spare has a smaller circumference, (although this is the OEM spare provided with the vehicle so surely it should be tested). So I'm sure the Diff was doing it's job of keeping the spare going the same speed as the rest of the car.

Presumably this means some electronics see's this differential and then applies the brake to the spare wheel to try stop the slip. But then WHY NO DSC traction control light on the dashboard. I mean if you see the DSC coming on the hole time surely you realise there is a problem.

Second point is what is the effect on the spare wheel? Surely that would not like been slowed down.

The hole thing seems like a design flaw or Software flaw.
 

AshG108

///Member
Gee whiz, glad you and your family are ok bud, kak ordeal and would never wish it on anyone.

Hope it works out in an amicable manner and in your favor.
 

Blue Shirt

Well-known member
Craig_Za said:
Blue Shirt said:
The traction control (part of the stability controls) will apply brake pressure to a wheel that it perceives to be slipping. If the spare wheel is not the same diameter as the other wheels, it will turn faster than the other wheels hence fooling the stability control. Continuous brake pressure will overheat the brake disk with the results that you experiences.

That is my theory and I stick with it.

Ye I agree, I'm sure the spare has a smaller circumference, (although this is the OEM spare provided with the vehicle so surely it should be tested). So I'm sure the Diff was doing it's job of keeping the spare going the same speed as the rest of the car.

Presumably this means some electronics see's this differential and then applies the brake to the spare wheel to try stop the slip. But then WHY NO DSC traction control light on the dashboard. I mean if you see the DSC coming on the hole time surely you realise there is a problem.

Second point is what is the effect on the spare wheel? Surely that would not like been slowed down.

The hole thing seems like a design flaw or Software flaw.

The 4.0d has more than enough torques to keep the car going despite the brake pressure on the affected rear wheel. The whole point of traction control is to allow the car to move forward by applying just enough brake pressure on the spinning wheel to maintain the wheel speed in relation to the other wheel.

I also postulate that the speed differential was not big enough to trigger the DSC lights. If you have ever driven your car in slippery conditions (like I have with my previous X5), you will notice that the DSC light is only triggered when a wheel is actually freely spinning.

I agree that it seems like a software design flaw. It would be interesting to hear the dealer's explanation.
 

osiris

///Member
A solid piece of steel set on fire... That's actually quite impressive!
Glad you guys are alright.

If its an OEM spare wheel then you were within your right to fit it in case of a puncture etc so I can't see there being any complications from BMW with regards to this catastrophic failure.
 

B///Moodley

Events Organiser
Yasis that is bad. Glad you're ok bud. I see why it's a good thing our spare wheel still has the sticker on it.

I always wondered how going from a 275 or 315 to a 19X would affect the XDrive system and I see that was not a good idea.


Sent from my iPhone using Tapatalk
 

tman

Well-known member
Blue Shirt said:
The traction control (part of the stability controls) will apply brake pressure to a wheel that it perceives to be slipping. If the spare wheel is not the same diameter as the other wheels, it will turn faster than the other wheels hence fooling the stability control. Continuous brake pressure will overheat the brake disk with the results that you experiences.

That is my theory and I stick with it.

Certainly plausible.

I would also assume, if you are using cruise control, you wont "feel" that the brakes are applied.
 
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