Run-flat tires cause wheel cracking?

[Michael5155]

I saw a guy is seling his run-flat tires so his wheels don't crack. Is this a common or uncommon problem? Does it happen only on certain wheels?

[09cbb]

Originally Posted by Michael5155

I saw a guy is seling his run-flat tires so his wheels don't crack. Is this a common or uncommon problem? Does it happen only on certain wheels?

296 style wheels crack. At least for me, going for non-run flats solved the issue so far.

[Michael5155]

Originally Posted by 09cbb

296 style wheels crack. At least for me, going for non-run flats solved the issue so far.

How do I know if I have the 296 style wheel. I've got a 2009 Z4 30i.

Did 296 style wheels come standard with the car? Is BMW covering under warranty?

[Al Blue4.6l]

Originally Posted by Michael5155

How do I know if I have the 296 style wheel. I've got a 2009 Z4 30i.

Did 296 style wheels come standard with the car? Is BMW covering under warranty?

its these wheels.

[Michael5155]

Going to look right now!

[rfx45]

If they look like this, then they are 296 style.


Here's the current wheel options for the Z4.

[Michael5155]

Thanks for the fast feedback and the photos of the various styles. While I wish I had the 296s because they, I feel, are the best looking of the wheels shown above, I have 290 style. Whew!

What is BMW doing for people who have this problem? New wheels?

[Michael5155]

Quick question about run-flat tires. So if I get a flat, what do I do?

Drive to any mechanic and have the tire plugged? Or do I have to get a whole new tire?

[Auraraptor]

296 wheels crack because they are a large simple cast wheel with a small amount of rubber...rubber which itself is very very stiff (runflat).

The dirty truth is any simple cast wheel in 19 or 20 in with 35 or 30 series tires WILL easily crack. You don't hear about this much (yet) in the aftermarket world since the total sample population for a given wheel is small, coupled with drivers generally treating their wheels 'gentler' vs OEM.

326M are a much stronger wheel as they are forged.

The 290 wheels are on the opposite end of the spectrum...lots of rubber to help cushion the wheel, and are the least likely to crack of the wheels presented here.


BMWs response to cracked wheels varies location to location.

[jparnes1]

Originally Posted by Auraraptor

296 wheels crack because they are a large simple cast wheel with a small amount of rubber...rubber which itself is very very stiff (runflat).

The dirty truth is any simple cast wheel in 19 or 20 in with 35 or 30 series tires WILL easily crack. You don't hear about this much (yet) in the aftermarket world since the total sample population for a given wheel is small, coupled with drivers generally treating their wheels 'gentler' vs OEM.

326M are a much stronger wheel as they are forged.

The 290 wheels are on the opposite end of the spectrum...lots of rubber to help cushion the wheel, and are the least likely to crack of the wheels presented here.

BMWs response to cracked wheels varies location to location.

Are all M wheels forged? I have the 325M's.

[jparnes1]

Originally Posted by Michael5155

Quick question about run-flat tires. So if I get a flat, what do I do?

Drive to any mechanic and have the tire plugged? Or do I have to get a whole new tire?

Technically you can plug or patch it if the hole is not near the sidewall. But if you use the runflat as it's designed, to be driven while flat, you'll damage the sidewall and a new tire is in order. So more likely than not, you'll need a new tire.

[rfx45]

Originally Posted by Auraraptor

296 wheels crack because they are a large simple cast wheel with a small amount of rubber...rubber which itself is very very stiff (runflat).

The dirty truth is any simple cast wheel in 19 or 20 in with 35 or 30 series tires WILL easily crack. You don't hear about this much (yet) in the aftermarket world since the total sample population for a given wheel is small, coupled with drivers generally treating their wheels 'gentler' vs OEM.

326M are a much stronger wheel as they are forged.

The 290 wheels are on the opposite end of the spectrum...lots of rubber to help cushion the wheel, and are the least likely to crack of the wheels presented here.


BMWs response to cracked wheels varies location to location.

While bigger wheels with low profile tires are more susceptible cracks and bends I think that is giving too much credit to BMW. There just seems too many reports/cases of these wheels cracking. Porsche also offers 19" and 20" options and you rarely hear any cracks about them and I doubt you can say those are ridden more gently than BMWs.

There are also plenty of aftermarket wheels that crack reported online but those tend to be the cheap ones, you rarely hear it from the more dependable brans like BBS for example.

RFTs definitely plays a role though but I am convinced that the 296 styles are just flawed based on everything I've been seeing/reading.

[kernelkraut]

Hi Guys,

For those of you with 296 rims, I feel your pain. I have exactly the same problem.

There is an interesting post on the forum where apparently two users have received replacement 296's from BMW - These new rims seem to be a "Second Generation" of the 296 and they appear to be much thicker.

Check out the link and keep posting your experiences:

http://e89.zpost.com/forums/showthre...296+redesigned

[GunSpeed]

Originally Posted by rfx45

If they look like this, then they are 296 style.


Here's the current wheel options for the Z4.

FYI, none of the above wheels are forged... the 326M is even heavier than the 296!!!

[jparnes1]

where do you get your info about construction and weight?

[Mr. ///M3 RD]

Originally Posted by jparnes1

where do you get your info about construction and weight?

I think the wheel vendors (even if you go with original OEM) will provide you with the weights of the different style wheels to help you decide what wheel to select. As you know weight of your wheels and or brakes will add to performance and handling as the item I found below demonstrates, I will let it speak for itself ...

Schnitzer Quote ....

Weight reduction in unsprung mass

35 kg less weight in the parts (or thereabout) directly connected to the wheels, such as wheels, tyres and brakes, leads to a perceptible gain in agility and driving pleasure. The latest forging techniques using materials from the aerospace industry guarantee strength and an unbeatable weight saving. For example, the AC Schnitzer lightweight 4-pot high performance brake system with retraction system for the front axle, and the lightweight brake discs on the front and rear axles, ensure the shortest braking distances.

Or the Type VIII one-piece high-strength forged rims used on the AC Schnitzer 99d. These weigh in at just 7.9 kg per wheel and are connected to the vehicle with titanium wheel bolts. Experts say that measures to reduce the unsprung mass have a benefit of up to four times the weight saving. This means that in terms of agility, the AC Schnitzer 99d feels like a vehicle which overall weighs 335 kg less.

End Quote ....

[richard in NC]

My theory why the 296 is more suseptible to cracks is the spoke design. they connect to the very outside edge, allowing tremdous torquing against the inside rim area. Coupled with the stiffness of the RFT, an odd angle pothole strike could easily cause a rim deflection great enough to crack it. Most rims' spoke designs have a flare towards the center of the wheel for added strength.

[Mr. ///M3 RD]

Originally Posted by richard in NC

My theory why the 296 is more suseptible to cracks is the spoke design. they connect to the very outside edge, allowing tremdous torquing against the inside rim area. Coupled with the stiffness of the RFT, an odd angle pothole strike could easily cause a rim deflection great enough to crack it. Most rims' spoke designs have a flare towards the center of the wheel for added strength.

Yes that is part of it for sure ... however, only the wheel manufacturer and BMW know for sure and they are NOT telling us ... I think it has several factors that all lead to the same end result. If we were to express it in a ID/text formula then it would look something like this ...

Cause of BMW Style 296 wheel cracks;

Location of spokes on far outside edge + negative 2.5 degree camber + stiff RFT sidewall + fluctuating air pressure (sometimes too low) + going over uneven road surfaces (bridge and overpass road splits meant for expansion) + going thru minor potholes *** = Build up of stresses into the outer most edge of the inner wheel rim


It can be followed that the stresses that collect over time due to the above mentioned factors will eventually need to release (much like bending a paper clip back and forth it will then break) and when this happens the first indication will be Hairline Cracks I have seen 2 hairline cracks in my case and the air pressure still holds. Once the hairline crack has developed further inductions of the above mentioned conditions will then lead to an open crack and loss of air pressure.

*** Larger Potholes of course will advance this process and BMW will declare your wheel bend and not replace it. BMW can detect this bend condition provided they have the right tire machine. They have a build in measuring device (like a dial indicator) that can measure wheel out off roundness, expressed in another term TIR = Total Indicator Reading. I understand the BMW Tolerance for TIR is 3 mm or 0125"

Bottom Line ... return your wheel to BMW once you have a hairline crack you may then have a chance to get a replacement.

Tip ... Make sure whenever you have tire changes done on your soft alloy wheels that this work be done by qualified people having the right tire machine. The tire machine should in no way make contact with your wheel to cause damage. In my case BMW Idaho Falls used a local Tire Shop as a sub-vendor to do this work since they did not have the people or equipment to change tires or wheels. That sub-vendor damaged my wheel by using two (2) tire irons to remove the stiff RFT. Naturally this action bend my wheel. So make sure you know the location of a propper tire machine when you need it and don't let anyone near your wheels with tire irons.

Here is an example of an acceptable tire change machine ---> CLICK to see the Link

I've seen a similar machine in action at the Toronto International Auto Show in 2011. It is very slick, it makes no contact whatsoever with your expensive wheel/rim.