6ul wheels

[breakaway500]

Not looking for the last word Troy, I actually enjoy a good debate. The 6UL wheel is an inexpensive lightweight wheel,and not built to DOT standards.I don't know if I would call this a design flaw..more like a design limitation. It is what it is. Many racers run them every week without incident:if there were a design flaw,I am sure we would be hearing about a lot more failures. The strongest lightweight wheels are forged,and they cost more. Some cast wheels are stronger than others,and usually heavier,for the same size. One must balance the amount of risk involved against the advantage of having less unsprung weight. You pay for what you get..

[TroyV]

word

[Chrispy]

Many racers run them every week without incident:if there were a design flaw,I am sure we would be hearing about a lot more failures.

Most of these "incidents" seem to mysteriously vanish from the internet, wonder why this is? No one likes bad press, but cover up instead of full disclosure is not a company that I would want to be dealing with when your safety is on the line.

[paultg]

Many racers run them every week without incident:if there were a design flaw,I am sure we would be hearing about a lot more failures.

Most of these "incidents" seem to mysteriously vanish from the internet, wonder why this is? No one likes bad press, but cover up instead of full disclosure is not a company that I would want to be dealing with when your safety is on the line.

Couldn't agree more, and was glad WIllM quoted the info. I posted from my phone and could not do so, meant to come back to it, because in the past these types of links with info do in fact get pulled rather quickly. - Paul G.

[breakaway500]

I agree Chris,and Paul,a cover-up of a potential safety issue would be cause for alarm. Another train of thought would be these incidents "disappear",or no longer have any forum value,because there is no "dirty laundry" to tell..? Maybe the driver was interviewed and stated three laps earlier,he went 4 wheels off. Maybe the other wheels were inspected and found to have been damaged by someone putting on the new track tires?(it happens..) Maybe the guy tied his car down to a trailer with chains through the wheels (don't laugh,I've seen it) I really don't know the rest of the story,but I honestly don't believe 949 Racing has the ability to control what goes out on the net any more than you or I. If the 6UL wheels were crap,wouldn't more people be screaming bloody murder,considering how many of them are out there? I guess I am also having a hard time believing anyone would try and cover up a real safety issue...

[joncowen]

Something that hasn't been touched on much is fatigue. Aluminum wheels all have a finite life. Some longer than others. If the wheel is strong enough so that the stress is low enough, the number of load cycles before a fatigue crack may be high enough that no one ever breaks one.

These wheels may be strong enough under static loading, but are likely failing due to fatigue.

There have been many debates about the strength of aftermarket track wheels in the BMW track community, as there have been lots of failures in the last 5 years or so, by a few manufacturers. One specifically as of late.

The particular manufacturer that is having problems lately, is denying that there is anything wrong with the wheel. Yet, we see pictures of heavily cracked or broken wheels almost weekly. Some of the wheels are said to have had only 5 track weekends on them before catastrophic failure.

So, this manufacturer isn't the only one with problems like this....

Everyone should check all their aluminum wheels before every track day. Even heavy OEM wheels will fail eventually, given enough high stress cycles.

[horizenjob]

Most DOT rated wheels are substantially stronger than a "track" rated wheel.Sacrifices are made in weight and design for most track wheels,and so is their ultimate strength.

Again, it's the fatigue issue. A street wheel would have to be designed for more then 200 million load cycles. That would be 200,000 miles give or take. So when the engineer designs the wheel, they derate the strength of the aluminum based on the number of load cycles. A track rim could be assumed to have nearly 100 times fewer load cycles. It is not clear that one would be any stronger near the end of it's life then the other.

if there were a design flaw,I am sure we would be hearing about a lot more failures.

Designers need to be very careful, especially when operator safety can be an issue. It is very attractive to use "typical" values for calculations, but this is a serious error. A designer needs to use "worst case" numbers at every point of the process. This includes understanding your raw materials, your manufacturing process and inspection process. The raw material, heat/age treating, the manufacture dimension tolerance and inspection quality all would have published tolerances. You can't use average values in production, you must use the worst case in each of these steps. Then you need to provide a further allowance. This is what produces "Safety Margins". Among other things it's how airplanes manage to be light and also strong and safe (and aluminum).

That wheel broke near where the spokes meet the hub, which would be the highest stress area. The spokes should be larger there. This wheel appears to be designed to be good looking, and it is. The minilite style wheels have a spoke design that would have to be much stronger because of their larger size.

If that wheel had the same amount of material in half as many spokes of the same basic shape, they would be four times stiffer.

Construction method really shouldn't matter or indicate a strength difference. The design process and safety margins should be the same. A stronger process would yield a lighter wheel. Possibly a lighter wheel has more invested in the design and better engineering. It shouldn't though.

I have no qualms about the quality of engineering available in other countries but there seems to be a real failure in Americans that simply desire to make money by buying cheapest possible stuff and then selling it on.

[Chrispy]

I'd guess that most of the failures are due to fatigue, although if you go back to page 4 you'll see the FWD fellow from Australia that broke a wheel on his 3rd track day with them. The FWD cars are probably the worst case scenario for the reasons that Mark pointed out earlier, but to me that would indicate an inherent weakness in the design to break in such a short time span even under these worst case conditions.

Jon, the BMW case sounds equally disturbing, especially the denial part. Although even OEM BMW rims have a reputation for being "soft" and easily bent, or is that more of a short suspension travel issue?

The OEM forged wheels for the 370Z seem to be pretty strong, there have been many pictures of people crashing into curbs, tearing of suspension parts etc, but not a single breakage reported. Might not be the ultra lightest but definitely strong.

[zchris]

Even the best wheels fail with time. A friend of mine has a GT1 mustang with BBS centerlock wheels. A couple years back he started having problems with the rim hitting the lower balljoint. His wheels are probably 10+ years old. Wheel bearings are all new. Ball joints are good. The wheels have just got to the point where they are fatigued and flex to much. At $800+ per he is in no hurry to replace them. Instead he has parked it.
Chris

[TroyV]

I think we all agree that it is reasonable to expect to replace wheels after a suitable amount of use. I don't think this is that.

[savage217]

Jon, the BMW case sounds equally disturbing, especially the denial part. Although even OEM BMW rims have a reputation for being "soft" and easily bent, or is that more of a short suspension travel issue?

The OEM forged wheels for the 370Z seem to be pretty strong, there have been many pictures of people crashing into curbs, tearing of suspension parts etc, but not a single breakage reported. Might not be the ultra lightest but definitely strong.

I have not heard of any reputation of BMW wheels "bending easily." One thing I will say is that BMW manufactures and engineeres a variety of wheels with different processes. My current street and track wheels are the Motorsport Forged aluminum wheels. These came on a limited amount of M3's and are known to be the strongest wheel BMW made on the e36. So far they have been fanatastic. None are bent, and they are relatively light compared to the other options they produced. Jon's wheels are the most common e36 M3 wheel, which was a cast wheel IIRC. These wheels may have a couple of bends in them from time to time but nothing out of the ordinary when comparing to similar cars. In my opinion it is the relatively low sidewall accompanied by potholes and various bumps that cause the wheels to bend. I would rather have a wheel that is known for bending than one known for cracking/ catastrophically failing.

[Chrispy]

I have not heard of any reputation of BMW wheels "bending easily." One thing I will say is that BMW makes many wheels manufactured and engineered with different processes. My current street and track wheels are the Motorsport Forged aluminum wheels. These came on a limited amount of M3's and are known to be the strongest wheel BMW made on the e36. So far they have been fanatastic. None are bent, and they are relatively light compared to the other options they produced. Jon's wheels are the most common BMW wheel, which was a cast wheel IIRC. These wheels may have a couple of bends in them from time to time but nothing out of the ordinary when comparing to similar cars. In my opinion it is the relatively low sidewall accompanied by potholes and various bumps that cause the wheels to bend. I would rather have a wheel that is known for bending than one known for cracking/ catastrophically failing.

Bending is definitely better than cracking I'll agree. The forged wheels that you have are going to be much stronger than the typical OEM wheel so those are a great set to have. The data I have on bent BMW wheels is far from scientific, just an aggregation of comments from friends having to have their wheels straightened (in some cases 3 out of 4 on the car). Like you said it may not be the wheels but rather a combination of other factors such as lower than average profile, crappy NE roads and firm ride.

[cfossum]

I have not heard of any reputation of BMW wheels "bending easily."

Car and Driver magazine has mentioned bent wheels on their BMW test cars on several occasions.

[Shawn624]

Having owned several BMWs and put many of their wheels to my own subjective testing (I let my wife and daughters drive them), I found that none of them bent except the E36 16" sport wheels. I had three of them straightened, straightened replacements, and declined to buy used replacements that also needed straightening. I've never had this happen with any of the other BMW wheel styles on the E36s or any other model, but that one version just didn't seem to hold it's shape.

[TroyV]

I cracked a wheel on our 08 335xi, but I blame that on the use of those ridiculous run-flat tires. Whoever came up with that shit should be shot on site. They might as well be solid rubber tires.