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BMW X5 AWD brake disk explodes with OE biscuit wheel


I was driving back from vacation on the Motorway, and got a Tyre pressure warning on my iDrive. I drive a BMW E70 X5 40d with X-drive. I pulled into the emergency shoulder and checked my tyre I could see no damage so reset my tyre monitor. A short while later I heard a noise from my rear left tyre only to discover I had warn through the run flat and got to the steel belt. At this point I decided to change to the OE spare wheel.

5km later at about 60km/hr, I heard an explotion, which made me immediately pull over (still on the Motorway). I discovered that the rear left disc brake was on fire and had completely exploded.

The car was collected by BMW on-call, and they have assessed the situation, they are saying that the damage was due to the stability control system (DSC) due to diameter differences of the spare wheel.

I’m wondering if anyone else has heard of anything similar happening on a BMW E70?

I have questions for you.

  1. You “checked” your tires for damage… did you check them for pressure? (I’d guess not) If not, why not?
  2. You replaced the RR wheel with an OE wheel, so the wheels and tires on the BWM were NOT OE? (I’d also guess not)

It appears as though you ignored the tire pressure warning telling you a tire was low in pressure, reset the warning and drove on. When your run-flat tire failed froma lack of air pressure, you installed a wheel and tire that did not match the others on a vehicle with AWD, traction and stability control. The difference in diameter confused the stability or traction control so much, it started applying the brakes to the RR. That is how those systems work. You didn’t notice this tugging nor the obvious lights on the dashboard and drove it until brake disk got SO hot it exploded.

This is all on you because you did not read all the warnings in the owners manual nor did you heed the warnings your own car gave you.

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Hey Mustangman

  1. I was on a motorway between 2 towns, so I checked the tires by looking and kicking the tires, but I did not have a tyre pressure tool. I would have stopped at the next garage but the garage was about 80km from where the warning came on. This all happened within 35km.

  2. I replaced the Rear Left wheel, with the OE spare wheel in the boot of the vehicle. The Emergency spare save wheel that was supplied with the vehicle. The wheels that I had on the car where also OE, They were Star-spoke styling 210, 255/55 R18.

The tyre warning did tell me there was a problem, but there wasnt anything I could do about it, but drive to the closest garage.

The spare wheel was supplied by BMW for this vehicle, and the dimensions should match the wheels on the vehicle.

I agree with that the spare should be compatible with the rest of the wheels. If his spare and his wheels and tires are all standard BMW provided equipment, then they should work. If they failed then this is not his or her fault, and blaming the driver is not right.

If BMW had some complex set of instructions about how to enable or disable complex electronic controls to avoid this, then shame on BMW for creating a system too complex to be used by the average purchaser.

You could have stopped the car and had it towed to the nearest service center. You should also pay attention to the low pressure warning rather than just re-set it.

As for #2, I think BMW carries a chunk of blame here if what you say is correct. A question comes to mind - if you had runflats on the car why was there a spare? The reason for runflats is to remove the need for a spare. Not having the owners manual, is there any special procedure for letting the car know the spare is installed?

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The Owner’s Manual should cover this aspect. I couldn’t find one for a 40d but did find one for the 30d.
It speaks to the run flat tires and also the compact spare provided. Interestingly, they do not specify a mileage limit in the manual but do specify the maximum speed (which you did not exceed)-

I’d be using this to point out that you did not exceed any of the limits defined in the Owner’s Manual.
FWIW- you may want to look at the embossing on the run flat or spare for limitations molded right into the tire sidewall that may differ or enhance the info in the manual…

What’s interesting is all the warnings are about the handling and performance, they don’t mention that it will cause the cars electronic DSC to malfunction

I don’t know what country you come from, but why bother buying expensive run flats and a spare wheel if every time you get a tyre warning you call a towing company.

He’s just countering the comment you made saying there was nothing you could do about it. There are always alternatives although they may not be desirable. Both run flats (when compromised) and the compact spare have limitations on speed and distance. I’m quite surprised I didn’t read any warnings to that effect in the manual I was able to locate. You could certainly use that to your advantage in your negotiations with BMW corporate…

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My issue is there is repair, and solving the problem. The repair is fairly straight forward. But I don’t think that will have solved the problem. So if this vehicle has tyre trouble again. I don’t want to use the spare.

How far did you drive on the spare and how fast?

If the compact spare is rated for 50 miles at max speed it’s likely to go 100 miles at a much lower speed and with less possibility of collateral damage. But I would want to hear from corporate regarding their stance on the affect (or lack thereof) to the drivetrain…

I drove for 5km at about 60km/hr. Kept the speed below the 80km/hr maximum as I was looking for a garage to check the tyre pressure

What caused the wear on the tire? Frequently when the steel belt shows through the tread it is because the tires are worn badly due to use and should have been replaced long before the incident took place. I don’t know if this is the case, but it can be inferred from your description.

Is the spare tire you used the same diameter as the other tires? Or is it one of those intsy bitsy tires used to save trunk space ? The kind to use at a low speed just to get you to the next service station, where you either get the first tire fixed or replace it with a new one.

If it is one of those small diameter tires, suggest you show your shop or bmw dealership the procedure how you replaced the tire. Let them watch you as you repeat the tire change right there in their shop. There might have been something you did that the car took exception to for some reason. We’ve seen photos here of people bolting those small spare tires on the hub backwards for example. So the tire sticks out too far to the side. Also those small tires usually require a much higher pressure than the regular tires. They’ll sit in the trunk for years unused and the air will leak out. I checked the mini-spare on my Corolla last month, hadn’t checked it in several years, it was down to 20 lbs. It’s supposed to be 65 lbs, something like that. So low pressure on the spare could be involved too.

Glad no accident was involved, no one was hurt. The problem looks pretty big, but I expect it actually won’t be too much of a big deal to repair.

The tyres were causes by mileage, the car is on 90000km. There was some tread left on the tire but I only looked at the outer edge, the garage informs me both tyres have wear down to the canvas on the inner side. Which sounds like I have a suspension issue too.

Here the specs of the spare tyre they supply with my set of wheels. According to this the rolling dimensions are exactly the same.

I don’t know what happened and I have never seen a rotor like that, also since you compose lucid sentences, I doubt you put the spare on backwards. Even if someone did that, I don’t see how that could do that to a rotor. Sorry about your misfortune, If you ever find out what happened , I would love to hear about it.

I would amend what BMW said. The problem is related to your inattention to the tires. They should be inspected and rotated front to back every 10,000 km. If this was done, you probably would not have experienced the failure because your tires would have been replaced several months ago. In the future, take a little time to inspect the tread wear at 10,000 km intervals and replace them when the wear bars are the same height as the tread. I assume your tires have wear bars as we do in the USA.

Our tyres do have wear indicators, and the part of the tyre I could see was still within the legal limit of a tyre. It does turn out that the tyre was wearing un-evenly, but I don’t think that has any relevance. I had a tyre related problem fine, not blaming anyone for that. The problems occure when I use the spare wheel that is provided with the Vehicle.

This car is regularly serviced, and it had a “holiday check” 5000km before this incident. Tyres do fail and need to be replaced. But in situations like that you should not get your Brake disks exploding as they did for me. Surely car design should design for the fact that this scenario will occur.

I’m tempted to just drive with the spare wheel after it has been repaired, to prove that this problem has in fact been fixed. I think i’m perfectly within my rights to drive on the spare wheel, although I would obviously have to adhere to the speed limitation

At any time during this ordeal, did you check the pressure in the spare?

Is BMW paying for the repair?