Discount Tire ******!!!...Over

[Photog]

I will have to look into that a bit further; but torsional loads that coils springs get are a different animal than the theoretical cyclic loads on a wheel adapter.

Coil spring failures are usually due to stress riser, reducing the torsional strength of the spring wire. Valve springs usually fail due to heat fatigue; heat caused by the the forces you mentioned, and no way to cool down. This is a very common issue in engines used for distance racing (LaMons, NASCAR, etc).

 

[misterquad]

Finally, people discussing spacers in engineering terms. Thank you. :lurk:

 

[ntsqd]

Consider what is happening in the adapter between where the nut holding the adapter to the wheel hub is and where the lug stud holding the wheel to the adapter is. Then consider what the actual shape of the metal between them is. Factor in simply rolling down a smooth street and going around corners, never mind the potholes or the rocks and obstacles on a trail.

Attached is an overly simplified model of the part with the forces that I see shown.

 

[modelbuilder]

Consider what is happening in the adapter between where the nut holding the adapter to the wheel hub is and where the lug stud holding the wheel to the adapter is. Then consider what the actual shape of the metal between them is. Factor in simply rolling down a smooth street and going around corners, never mind the potholes or the rocks and obstacles on a trail.

Attached is an overly simplified model of the part with the forces that I see shown.

Glad you are talking about adapters now and not spacers. Spacers are 100% safe.

 

[Photog]

ntsqd,
I understand the model you posted. There should be a section through the middle, that is solid (the lug seats are not in line with each other).

Also, the forces (shown in red) are only compressive, like the ones shown in blue.

The section of material between the inner & outer lugs is where there may be some true cyclic forces (maybe). This would be depend upon the amount of compression the intermediate material sees, as the two lug systems are tightend down. Does this make sense? Hard to put into words.

It is possible that the material between the inner & outer lugs will only see shearing forces. In that case it may only see forces between zero and what ever max is during use. Not true force reversal seen during fatigue life testing.

I have found limited info so far, on the different life spans based on full force reversal, zero to positive, and more/less positive forces. There seems to be a large difference in fatigue life; but I have not been able to track down the actual calculations yet.

More to come.

 

[C-Fish]

UPDATE...

Went to a different DTC location today and the manager confirmed that DTC cannot work on vehicles with spacers OR adapters. This is very recent policy enforcement (policy has been ignored for years).

Somewhere (he didn't have details) a tire came off on a customers car and that is why they have revisited their policy.

He offered me this...
5 wheels of my choice at cost.
Zero labor cost to make the change on my part.
Free lifetime balance and rotations (with correct wheels).


So...I might be looking at some wheels to replace the silverblades (which are 16x7 with 285's that DTC mounted for me :Wow1.




The engineers now have the floor to continue their discussion. :ylsmoke:

 

[MotoDave]

If it were me, i'd do the rotation myself and take the rims and tires to DTC off the truck for balancing/mounting

Think of it as an excuse to buy a nice floor jack!

http://imgs.xkcd.com/comics/duty_calls.png

 

[tacomadave]

I went looking on other forums to find images or stories of failed adapter/spacers. Everything i found related to broken studs, no threadlock, not using a torque wrench, too short studs on axle. Nothing about the actual aluminum failing. I have Spidertrax spacers, they seem like high quality pieces, I used threadlock and a torque wrench but still they are always on the back of my mind, Ideally i'd like some proper offset rims.

 

[C-Fish]

If it were me, i'd do the rotation myself and take the rims and tires to DTC off the truck for balancing/mounting

Think of it as an excuse to buy a nice floor jack!

http://imgs.xkcd.com/comics/duty_calls.png

I'm with you.
I have all the tools and have done rotations for years on my own cars. The only time it sucks is May to September...+100, I don't like to do much of anything.

 

[Pskhaat]

Interesting set of posts:

http://www.thirdgen.org/techboard/wheels-tires/547897-wheel-spacers-how-strong.html

 

[ntsqd]

Glad you are talking about adapters now and not spacers. Spacers are 100% safe.

No, they are not, but their relative un-safeness is small enough to not be worth talking about here. I've always been talking about adapters unless I specifically mentioned a shim style of spacer. I was using the terminology for them commonly used on 4WD oriented forums. Coming to off road from road racing I'm well aware of the difference, but using the correct terminology is more confusing than helpful.

I drew the red arrows uniformly for speed of assembling the picture, but I did not intend to imply that the tensile and compressive forces are equal. They may and may not be depending on the exact application. I did linearize and greatly simplify the model for expediency. Roughly what I modeled is the sequence of linear cross sections from one stud hole to the next, which were then laid out to be collinear rather than curvilinear.

Consider the loadings in a corner. The cornering force vectors generated by the tires point in the same direction, towards the center of the turn. Their magnitudes differ by a small amount due to weight transfer, tire slip angle etc., etc., etc. This cornering force has a lever length of the tire's true rolling radius, which imposes a Moment on, eventually, the spindle. To get there that same Moment is applied to all of the parts in between the tire and the spindle. I am expecting that the lowest elevation wheel stud will be seeing a that side's max compressive force on the outer tire and the max tensile force on the inner tire. The upper-most wheel stud will be seeing the max tensile force on the outer tire and the max compressive force on the inner tire. Since we are dealing with a rolling wheel & tire assembly the wheel studs are rolling through those regions of max tensile and compressive forces while those regions are fixed in those locations. That is where I see the reversing stresses arising.

 

[modelbuilder]

No, they are not, but their relative un-safeness is small enough to not be worth talking about here. I've always been talking about adapters unless I specifically mentioned a shim style of spacer. I was using the terminology for them commonly used on 4WD oriented forums. Coming to off road from road racing I'm well aware of the difference, but using the correct terminology is more confusing than helpful.

I drew the red arrows uniformly for speed of assembling the picture, but I did not intend to imply that the tensile and compressive forces are equal. They may and may not be depending on the exact application. I did linearize and greatly simplify the model for expediency. Roughly what I modeled is the sequence of linear cross sections from one stud hole to the next, which were then laid out to be collinear rather than curvilinear.

Consider the loadings in a corner. The cornering force vectors generated by the tires point in the same direction, towards the center of the turn. Their magnitudes differ by a small amount due to weight transfer, tire slip angle etc., etc., etc. This cornering force has a lever length of the tire's true rolling radius, which imposes a Moment on, eventually, the spindle. To get there that same Moment is applied to all of the parts in between the tire and the spindle. I am expecting that the lowest elevation wheel stud will be seeing a that side's max compressive force on the outer tire and the max tensile force on the inner tire. The upper-most wheel stud will be seeing the max tensile force on the outer tire and the max compressive force on the inner tire. Since we are dealing with a rolling wheel & tire assembly the wheel studs are rolling through those regions of max tensile and compressive forces while those regions are fixed in those locations. That is where I see the reversing stresses arising.

Still talk...no proof.

Nothing here tells me spacers are unsafe...according to you they should be breaking left and right and they in fact are not.

 

[cruiseroutfit]

Safe/unsafe... all relative. How about illegal in the state of Utah

Discount and many other chain/local tire stores won't deal with spacers or beadlocks. Spacers are specifically called out as 'illegal' in our state laws whereas beadlocks will cause a failed safety inspection. Regardless you can and will get turned away for having them at many tire outlets. Some Discounts won't even air up a beadlock tire, others will mount and balance them I had a Big-O that wouldn't put a 12.50 on a 7" wide wheel but they would mount balance/beadlocks, the Discount would mount the tire but wouldn't touch the beadlocks

Moral of the story, its a constant variable but due to legalities at least here in the State of Utah, you can't blame them for considering them unsafe... afterall the fine gents in our legislature thought otherwise. Other than that, remember not just the load on your wheel studs but your axle bearings, ball joints, knuckle bearings and steering. If an alternative can be found that eliminates the need for them, I personally go that route.

 

[misterquad]

I am reading this debate on a couple forums right now and it makes me think.

As a mechanical engineer, could I design a set of spacers or adapters that are safe and won't fail? Yes, at Cal Poly, SLO, we did this exact type of work.

As a mechanical engineer working in manufacturing, would I design a set to sell to the public. Nope! Never! Not going to happen! After 20 years in the field, if you design something to be idiot proof, they just find a better idiot. The idiots will figure out a new way to misuse your product and hurt themselves. The laws and company policies are there to protect the idiots from themselves.

 

[ntsqd]

Still talk...no proof.

Nothing here tells me spacers are unsafe...according to you they should be breaking left and right and they in fact are not.

You've been asked repeatedly to support your statements, and those requests have been ignored. From that I infer that all you're really interested in is trolling.

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Simply changing the material to a ferrous alloy would virtually eliminate the fatigue issue, but that isn't what is being sold to the uninformed/unsuspecting public. Were there room to design the adapter (spacer) more like those used on dually pick-ups then there would not be a problem.

Be clear that I don't have a problem with adapter (spacers) used for what they were originally intended for, to increase scrub radius on comp buggies as a traction aid. In that type of situation the risks are accepted, and really aren't all that great due to the low(er) speeds and limited operation time.
When someone take such a product and misapplies it then he or she is putting everyone around them at risk too. Should it fail and cause he or she to drive off a cliff then that was their choice. When driving off the cliff if they also take out Joe Average and his family, Now I have a problem with the misapplication. When this happens often enough the legislature will get involved, and then the whole situation will become really screwed up!

The thing about fatigue that I don't get the sense that most layman understand is that it is not an instant failure. "It works, don't worry about it" is the mentality. Just because it works right now does not mean that it will continue to work for the next 2-50 years. There are those who proudly state "I've been running them for X years without a problem!" Great, they don't appear to understand that this sort of failure is not something that happens instantly. It happens over time. That they've been running them for X years just means that they have X fewer years of life left in those parts. In short, the fuse has been lit, but no one knows exactly when the bomb will go off.