:popcorn:

In reference to the replicas, there is also no data that says they are unsafe. My point is just that people shouldn't blanketly assume they are not safe. You need to do your own due diligence (i.e. ask for certifications, speak with the vendor, get references, etc.) and determine if you believe that particular wheel is safe.

Also, I have no problem with BMW making money on wheels. My point was that because they are 1/2 of BMW's price doesn't mean they are 'cheap' in terms of quality. The price difference is part profit, part overhead on BMW's part.

Agree. Especially on the (important) distinction between the through bolt type... essentially all spacers are 'painted' with that one brush.

I once had morons at an Americas Tire store refuse to work on my E39M5 because the fronts had (gasp) 3mm spacers! three-friggin-millimeters. the width of this O. They did the rears, and I jacked the car up in the parking lot myself and handed them the bare wheels.

Now, I will make two comments about spacers on the track- they reduce the thermal transfer from rotor to wheel, AND they CAN make the lug bolt loading more complex and increase these stresses. However, this is an X5 forum (so we aren't talking track) and the situation where this kind of consideration comes into play is pretty high up on the performance curve even with track use.

And some technical inspectors won't allow spacers due to the safety risks, particularly on front wheels with their higher braking loads.

I would agree that bolt-on adaptors are safer, but I don't think they are as safe as having no spacer. You have introduced an additional failure point, as well as changing the load on the wheel bearing, and suspension components. That has to count for something.

I think that loose spacers are far less safe. It doesn't matter if the lugs are a higher strength steel, unless you calculate both the bending moment and the fatigue limit and make sure both are still reasonable. One calculation I saw showed that a 1/8" spacer (3 mm) reduced the safety factor by two. I consider that a significant reduction in safety.

Good previous discussion here, with my link to another thread in the GT40 forum. http://www.xoutpost.com/bmw-sav-foru...l-spacers.html

I completely agree with your assessment of slip-ons (loose), as the bending moment will affect the loading on the bolts more.

However, it's difficult to get on board with the idea that bolt-ons would decrease an MTBF by a factor of two. Follow this thought process:

1) The only thing you are introducing is a slab of aluminum. Granted, you are adding 5 more bolts to that wheel hub, so technically, there would be your MTBF reduction by 2, but that's subjective much like many reliability calculation methods.

2) The idea that you are imposing more load on the axle and hub are nearly moot due to the nature of differing wheels themselves. Obviously the loading on the hub is different with the sport 20's vs. the stock 18's. The 18's have a higher offset and are tucked in more. To think that a safety factor is not used would be crazy.

3) I know the right way to build a widebody track car would be to replace the axle, hubs, and associated suspension arms, but not everyone does this. The cheaper and more popular way to achieve the stance is to purchase very low (in the negatives) offset wheels, which are effectively much further off the hub than what you'd get with spacers.

What I'm trying to get at is that if anyone has a cause for alarm for even a 1" (25mm) spacer on their wheels is ludicrous in my book. But if it does make one feel uneasy, then simply don't buy them. :)

I may be wrong, but I don't consider mean time between failure to be directly related to safety factors. I relate MTBF to availability, more than reliability. Safety factors are designed to improve reliability. With an issue like a wheel coming off a vehicle at speed, even small differences in safety factors (reliability) can matter due to the extreme consequences.

I don't think that the offset point is moot, since the correct offset should put the centreline of the tire at the same point as the axle bearing. Anything that changes this creates a bending moment. What about scrub distance? Is that a concern, particularly with the negative camber of the X5?

I suppose that one could assume that the original engineer put in a healthy safety factor, and that one is free to spend it without consequence, but I guess the engineer in me rebels against that approach. My E53 was designed for 17" wheels. I suppose that the E70 was designed for 18" wheels. Anything over that puts additional load on the suspension, and is using up some of that original safety factor, IMO.

Agree completely that the cheapest way to deal with it is to install spacers, as opposed to buying the correct wheels. I just don't think that makes them as safe. Maybe it makes them safe enough. But in the consideration of systems that I would want to reduce safety in, wheel retention isn't one, due to the potential consequences of failure of that retention system.

I agree that this is more of a risk on track vehicles. However, when one poster asked a while ago if there had ever been a problem on a street vehicle, it didn't take long to provide the story of a Jeep (CJ or YJ, not sure which) that had a wheel pass the driver on the highway.

Interesting discussion.

What really scares me is this look. This isn't ok with me since I'd need to have it on from December through March in MN.
http://www.xoutpost.com/bmw-sav-foru...18-set-up.html
http://www.xoutpost.com/attachments/...p-100_1829.jpg[/QUOTE]



Hi All - Sorry do dig up an old thread, but I would like continue the discussion of using wheel spacers to push narrow wheels further out toward the end of the fenders do avoid the look mentioned above. I may opt for truck tires instead of winter tires because I live in SF where the weather is quite temperate and I travel frequently to Tahoe where there is a lot of snow. Snow tires around the bay area can wear out quite fast and truck tires might last a bit longer.

Anyhow...is there anyone out there who has successfully used the smaller width wheels and use spacers to push the wheel/tire out and closer to the edge of the fender? I also want to avoid the look of the car bulging out over the wheels!