Second thoughts on the Sport Activity Package - Need Opinions on these pictures

[finagle69]

If you do some research, you'll find that a large number of track cars run spacers due to larger BBKs and for the increase in track width.

Seriously, people have very misguided views on spacers. There are two types, extended lug bolts/nuts, or bolt-on type.

Bolt-on spacers are every bit as safe as running no spacer at all. Slip on (or extended lug) spacers are less desirable, but no less safe, as the extended lugs are of a higher strength steel.

[BGM]

[ard]

Originally Posted by finagle69

If you do some research, you'll find that a large number of track cars run spacers due to larger BBKs and for the increase in track width.

Seriously, people have very misguided views on spacers. There are two types, extended lug bolts/nuts, or bolt-on type.

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.

[JCL]

Originally Posted by finagle69

If you do some research, you'll find that a large number of track cars run spacers due to larger BBKs and for the increase in track width.

Seriously, people have very misguided views on spacers. There are two types, extended lug bolts/nuts, or bolt-on type.

Bolt-on spacers are every bit as safe as running no spacer at all. Slip on (or extended lug) spacers are less desirable, but no less safe, as the extended lugs are of a higher strength steel.

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

[finagle69]

Originally Posted by JCL

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.

[JCL]

Originally Posted by finagle69

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.