Why are wheel spacers with their own studs the devil?

[Hokie]

Ok, here's my question. We all know, hands down, the wheel spacers that just slip over your studs are dangerous and can shear your lugs off and all of that bad stuff. My question pertains to the ones that have their own lugs, which you mount to the wheel and to the hub.

I know plenty of people have posted before on this topic, but I don't understand is how these can be any different than a wheel with less back spacing. Here's my thoughts...

The weight of my truck pulls my vehicle down, and my wheels push back with the same force. This normal force is enacted at the geometric center of the contact patch of my tire. If i add a wheel with less backspacing, the moment exerted on the hub is magnified by the distance that the wheels are pushed outward. (Moment=Force*distance)

Since the force on the hub (normal force to weight) will act at the end of the moment arm, how does it make a difference if the wheels are pushed out with by using less backspacing or by using the nice, hub centric spacers with their own lugs. They still mount to the face of the hub, so they don't run the risk of shearing the lug nuts off.

Any engineers out there that can explain why these are bad? B/c this engineering student can't seem to understand the difference between using these and offset wheels.

Thanks!

 

[Howard]

My thoughts would be:

A spacer (with own studs) adds a second shear point by being bolted to the hub and then the wheel bolted to the spacer. This give twice the possible failure rate and increases the shear force because the moment (wheel)is further from the support (hub). Therefore the studs on the spacer are taking a lot more load than the studs on the hub and the question is are they strong enough. Normal studs strip and break fairly easily as is is.

A reduced back space wheel does not introduce any addition shear points and all the additional stress is within the wheel itself, apart from the extra moment on the hub bearings.

 

[unabonked]

i've had my H&R 1.75" spacers on my stock rear wheels for well over a year. They work fine, even in mild offroading. I may take them off when my truck gets a lift, 32 mudders next week.

 

[BonesDT]

hokiebert,
i was thinking the same thing you were. i like howard's explanation. it seem like thats the only reason why these spacers would be 'weaker' than an actual wheel with an equal backspacing. hypothetically, if you weld the spacer to the wheel, so that the wheel and spacer are one, then it should be the same as a wheel with less backspacing.

but, really, do these additional studs make a weak enough part that would be significant. i would like to see a picture of someone ripping off these studs.

buy a high quality spacer and you'll be fine.

if there were people who have broken these things, it is probably because they compounded a spacer with a wheel that already had too little backspacing with a heavy truck with heavy tires and did some serious offroading.

 

[Rick]

This is how it was explained to me. Basically you want the tire centered over the wheel bearings. The science behind it... I have no clue

 

[Hartman]

Here's something that might help:

 

[Hokie]

"Since the tire is pushed out farther away from the rotor, the downward force creates extra pressure on the lugs and the lugs"

All they are saying in that diagram is that the stress on the lugs is greater because the force (weight) is pushed out further. Which is true for offset wheels and spacers. By spacing the wheels out further than stock, you will create a bigger bending moment that the hub and suspension must resist/counter-act regardless of how you do it.

I agree with Howard in that you bring in another place for failure by having an extra set of lugs. My truck is my DD so I don't wheel her hard.

(please understand I'm not arguing with anyone, I just started thinking about this today from an engineering standpoint ~ its scary that I can actually relate stuff that I'm learning )

Rick didn't you run H&R spacers on your truck for a while?

 

[BonesDT]

from the diagram it looks like originally the rim would rest on both the lugs and the hub, but with the spacer, the rim sits only on lugs. i dont know if this is true in the real world. spacers should then have a center 'hub' as well. this could be another area of weakness.

 

[BonesDT]

also, something is as strong as its weakest part. i would guess that your quality aftermarket lugs will be stronger than your factory lugs. so, adding spacers instead of a lesser backspaced rim wouldn't add much of another place for failure (that is if my hub theory above didnt apply)

 

[Robb]

Whenever I think about extra stresses and such, I always think of extreme examples. If it becomes obvious that the extreme creates extra stress, then milder examples will also create stress, just not as much. Confused yet?

Try to imagine using 10" wheel spacers. By picturing that, it should become obvious that a serious stress point exists at the top of the hub/bearing assembly (an extreme example of Hartman's right pic). Now, if 10" spacers obviously create a stress point, then any size spacer spacer should create the same stress point, just in differing amounts.

Now, whether or not a .5", 1", or 2" spacer creates enough stress to harm anything...........I have no idea.

 

[Hokie]

You look at the world in a wierd way Robb I don't doubt adding wheel spacers (or offset wheels) will add stress.

Anybody know what the smallest spacer (with lugs) thats out there? Or is 1" the limit for spacers with their own lugs? And what is this type of spacer called anyway? Am I gettin' annoying yet?

 

[Howard]

The point is that for every mm further out the moment increases significantly. Imagine a lever setup the further to one end that you move the pivot point the more force is applied to the short end. The diameter of the wheel being the long end and the lug the pivot and the hub the short end. Even with just a decrease in back spacing there is a lot more force placed on the bearings so much so that it can lead to early failure. The bearings were only designed to take so much. If you over load them they will fail earlier. Of course you can get away with it in the short term. But eventually you will be replacing the bearings sooner than normal. Providing you don't have a catastrophic failure in the mean time. I have driven a 4x4 with spacers fitted (unknown to me) and had a wheel come off. The resultant mess is not pretty and I was lucky to get out of the wreck in one piece. Luckily no one was hurt, but the 4x4 was a dead duck having rolled over a number of times down a steep hill. If Ford had designed the hub assembly to run further out then there would not be a problem, but we have to work to what we have. If you put on simply wider wheels, even on both sides of the centre line, then there is much less additional force involved.

 

[Robb]

Originally posted by HokieBert
You look at the world in a wierd way Robb I don't doubt adding wheel spacers (or offset wheels) will add stress.

Differing wheel offsets shouldn't create those stresses. With a properly designed wheel, no matter the backspacing (unless negative), the weight and forces should be concentrated directlly at the wheel flange. Even if the wheel had backspacing of 0" (again, like Hartman's pic), the forces would be concentrated directly onto the hub/bearing assembly, not creating the extra stress that a spacer would.

edit: I should rephrase that a little. Low backspacing would create some extra stress, but not nearly the amount that spacers would.

 

[Hartman]

Originally posted by Robb
Whenever I think about extra stresses and such, I always think of extreme examples. If it becomes obvious that the extreme creates extra stress, then milder examples will also create stress, just not as much. Confused yet?

Try to imagine using 10" wheel spacers. By picturing that, it should become obvious that a serious stress point exists at the top of the hub/bearing assembly (an extreme example of Hartman's right pic). Now, if 10" spacers obviously create a stress point, then any size spacer spacer should create the same stress point, just in differing amounts.

Now, whether or not a .5", 1", or 2" spacer creates enough stress to harm anything...........I have no idea.

That's exactly how I thought of it Robb.

 

[SteveVB]

How does everyone then feel about the spacers that are on the fronts of most dually pickups. With the off sets ythe rear wheels need for duallyness, the front axle usually has a large spacer to keep the tire in the correct location since the wheel has a large negative offset.? I believe the front axles are same SRW or DRW in most vehicles. My Chevy 1 ton manual shows huge spacers on the front for the wheels.

All of the above sounds great, but dont know if I agree with it.

I run 1" spacers on the front and have for a year or more with no problems. Check torques every so often and everything is working fine.

 

[Hokie]

Originally posted by Howard
I have driven a 4x4 with spacers fitted (unknown to me) and had a wheel come off.

Which type of spacer?

 

[Hokie]

Originally posted by Robb
the forces would be concentrated directly onto the hub/bearing assembly, not creating the extra stress that a spacer would.

Where does the spacer concentrate the force?

 

[Howard]

Originally posted by HokieBert
Which type of spacer?

They were ones with there own studs. Maybe they were defective or not installed correctly. All I know is that I rolled some 6 times and was lucky to get out in one piece. Of course even without spacers a wheel can come off but why take the risk.

There is no doubt in my mine that any kind of spacer affects both the handling and the safety of the vehicle. I understand that they are much cheaper to fit than new wheels and outwardly do not appear to any damage. But they are changing the design of the structure quite a bit and are potentially dangerous as a result. I'm sure most insurance companies would take a dim view against any claim caused by their use and we all know that they will do anything to get anyway with not paying out.

One thing that no one has mentioned so far is the fact that there is a big difference between fitting them on the rear and fitting them on the front. At the rear they just run parallel and only increase the width. At the front however they also have an effect with turning corners. The carefully engineered turning circle (one wheel turns by more than the other) is altered quite considerably. This could lead to excessive tyre wear and some scrubbing and even possible a loss of grip because of this.

This is just my opinion and you are all welcome to form your own. Just been there done that and won't do it again ever.

 

[Stomper]

I agree with you guys that to simply add spacers, whether with or without their own lugs, to widen your track will cause greater forces and shear stresses on all kinds of parts. The forces are increased because of the increased 'moment arm' (Force = Mass x Distance). Know how you use a longer wrench or put an extender pipe on your wrench to get more force to break bolts free.....same idea. If you use that equation and plug in the numbers for an Explorer for example:

Assume weight is 4000 pounds (divide by 4 wheels) and distance from the center to centerline of the wheel is approx 30 inches: Stock 1000# x 30in = 30,000 psi

Say you install a 1" spacer to widen the track:
1000# x 31in = 31,000 psi

By adding that spacer you just added a 1,000 pounds of pressure (per sq inch) to each mounting surface.

These are just relative calculations to give you an idea.

Buuut, if you get a wheel that offers a different offset than stock, then a spacer is a good thing to bring your track dimension back to original track width. Early in the summer I bought a set of 18"x9" Cobra R replicas with a healthy positive offset, and installed the 1.25" beefy spacers w/ lugs from performance wheel and tire to take up the slack. I haven't babied the truck and have enjoyed and excellent ride and no sign of problems (I've taken 'em off a couple times to inspect everything, clean the wheels, and rotate the tires).

Just like any aftermarket mod, whether for off-road or street use, there is a proper application for everything.

 

[Hokie]

Well.. sorta...

Moving the wheel out 1" with a working load of 1000# will increase your moment on the hub/bearing assembly by 83.3 ft-lbs ~ 1000#x(1/12 ft)

The pressure increase due to the said bending moment will be [pi(0.25)^2 x 1000#] (assuming the lugs have a diameter of 1/2"

The pressure increase is 196.3 PSI

Basically, the thing i thought about is, when you use wheels, the wheel contacts the hub/bearing assembly at the critical section and applies the moment and shear forces there.

When you use wheel spacers, the wheel contacts the spacer which then contacts the hub/bearing assembly. The bending moments at the critical section have a moment arm of 1" greater than before which places more stress on the lugs.