Need engineers thoughts on wheel offset

Properly torqued the studs do not experience shear force, neither lug or hub centric, offset or not. The studs are under tension only, clamping the wheel to the hub. The static friction between the wheel and hub due to the clamping force is huge and thus transfers all vertical force to the bearings. This is why you see more and larger studs the heavier the vehicle gets, the static friction between the wheel and hub has to be much greater than the vertical loading.

Problems occur when the yield strength of a stud has been exceed, whether due to over tightening or additional tension due to scrubbing. Once yield strength has been reached and the stud stretches, that's it, it's tensile strength is gone and it no longer contributes any clamping force and total clamping force is reduced.

If clamp force is reduced significantly, more than one stud breaks or the load is too much for the number of studs, then the static friction between the wheel and hub can be overcome and the wheel can move relative to the hub. In this case with a hub centric wheel the hub can take some of the vertical load. Lug centric will have the wheel start rattling around on the studs and quickly killing them.

I can provide more detailed examples if anyone is interested.


To answer the OP's question, centered or offset wheels make an insignificant difference in tension force on the studs. Offset is for aesthetic or fitment, i.e. with high positive offset you can stuff brakes and stuff into that space. I still love me some deep dish wheels!

Another thing that causes people to break studs is lubricating the threads before torquing the lug nuts. The specs for torque is with dry studs. You never want to lubricate the studs.

As far as offset goes, trailer hubs are designed with bearing sizes assuming zero offset wheels. If you change the offset of the wheel you change the loading on the bearings.

babock wrote:
Another thing that causes people to break studs is lubricating the threads before torquing the lug nuts. The specs for torque is with dry studs. You never want to lubricate the studs.

As far as offset goes, trailer hubs are designed with bearing sizes assuming zero offset wheels. If you change the offset of the wheel you change the loading on the bearings.

Reduce the torque values by 25% for lubricated fasteners.
Lubricated: coated with a lubricant such as engine oil, thread sealant or threadlocker.

Third thread on this. I hope you get what you want to hear.

ktmrfs wrote:

pickjare wrote:
Consider how many cars and trucks on the road have wheels with all sorts of different offsets. I am not an engineer, but if wheel offset caused, or cured, wheel studs from breaking, I think we would have learned this from them. look at your wheel lug holes real close. If any one is elongated or worn, the wheel needs replaced. If every hole is good you might try retorquing the nuts after towing 10 miles--or 100 miles or both.

well...... virtually all cars and light trucks on the road today have hub centric wheels. that is the wheel hub is a very tight fit to the axle hub. So..... the hub takes ALL the vertical load on the axle, the lugs keep it from sliding off and take any horizontal load.

Virtually all utility and travel trailers (U-haul is one exception, most or all uhaul trailers have hub centric wheels) have LUG centric wheels, so the center is a loose fit on the hub so the lugs must take ALL the vertical AND horizontal forces on the wheel. Big difference.

that's one reason retorquing is so important on trailers. And the OP isn't the first person to have problems with lugs shearing on trailer axles. if lug nuts get loose it doesn't take long for the lug centric wheel to beat the **** out of the lugs.

I suspect any non zero offset puts even more force on the lugs.

Hub centric or lug centric refers to how a wheel is centered to the hub so they rotate on same axis. If lug nuts are conical, then lugs decide where wheel centers onto hub--lug centric. If lug nuts are not conical--they have a flat washer built in to the lug nut--then the nut and stud don't position the wheel onto hub. In that case, called hub centric, and only that case, it matters that the wheel fits tight to the hub as this centers its axis to the hub as they turn. This is how ford super dutys have been for years. This is how semi trucks are--hub centric. But, pretty much every other car and truck out there will be lug centric. That center hole in the wheel and its fit to the hub have nothing to do with centering the two parts together. As lug nuts are tightened in the proper sequence, the hub and wheel axis are matched together.

I believe it is incorrect to say "virtually all cars and trucks on the road today are hub centric." Ford super duty trucks are only vehicle I know of that are hub centric. Everything else uses conical lug nut and that is what determines where a wheel lines up with a hub.

I know towing a trailer doesn't exactly compare to nascar. But consider in a nascar race the cars are turning left with a very high amount of force on wheels, tires, hubs, etc. It is interesting to note that all 4 wheels have same offset--whatever that is. Again, yes there are many differences in a race car and a camp trailer. But, It isn't the case that the left side wheel offset is different than right side in an important effort to keep wheel from coming loose.

In addition, when a race car has a loose wheel, what was the cause? Improperly tightened (I can't even call it torqued) lug nuts. Every single time it is improperly torqued lug nuts. Every time. Very different situation, but it is one that helps prove lug nut torque will cause a loose wheel, not wheel offset.

Old-Biscuit wrote:
Reduce the torque values by 25% for lubricated fasteners.
Lubricated: coated with a lubricant such as engine oil, thread sealant or threadlocker.

You still don't want to do that with lug nuts.

go to 7:20 in the video here:
https://www.youtube.com/watch?v=X3ndeXiZUeM

This is a good video that shows why you should be torquing your wheel lug nuts.

friend of mine is a mechanical engineer and he said never to put lube on a wheel stud if there is no lubricated spec. 25% is just a guess.

Good video, thanks.

Now a show of hands for the Ford Super Duty folks. Who puts that drop of oil between the two pieces of the lug nuts? :@

If you don't do that kind of work, did you ever see a mechanic apply the oil? :h

Did any of that oil ever get on the threads. :@

From your owners manual:
It is important to follow the proper wheel mounting and lug nut torque procedures.
On all two-piece flat wheel nuts, apply one drop of motor oil between the flat washer and the nut. Do not apply motor oil to the wheel nut threads or the wheel stud threads.

Its been my experience using a offset automotive wheels on a trailer can break or shear lugs....crack the wheels centers.....whip out the axle bearing in short order.

If your trailer has offset wheels that are OEM or a aftermarket wheel installed, I would call your axle mfg and get their input.

My inquiry to Dexter and Rockwell American axle mfg some years back says do not use offset wheels on their axles.

I think the OP was asking about off sets on the rims not hub or lug centering. You want 0 offset on you trailer