Need engineers thoughts on wheel offset

[Passin_Thru]

Travel trailer wheels have either a centered or outside offset. My question is this. I have outside offset wheels and have sheared off wheel bolts on 2 different wheels I have weighed everything and I am 500 Lb/axle below MGWR on each axle. If I move to a centered offset, how will it change the torque and shear on the bolts. I believe that it is being caused by too high a torque load when cornering to the outside at higher road speeds on I 81 in Pa and NY. Will this drop the torque on the bolts and tire? Thanks I am an A&P Mechanic but havent worked much with shear forces.

[JIMNLIN]

Good picture....shows how the wrong offset can contribute to sheared or broken lugs. Some where on Dexters old website they had the same wheel pictures but showed the inner and outer bearing placement located between them.

I've seen several haulers use GM 6 lug std steel automotive wheels on 6 lug trailer axles. After many miles lugs would start to break or shear off at the wheel/hub interface.

[Kayteg1]

The title is misleading as OP talks about wheel centering.
Centering is determinate by hub design and you can't change it other than changing the hub.
In case of lug shearing, when they were torqued to 90 ft-lb I can only guess they were over-torqued in the past and now break with metal fatigue.
Would order quality bolt and that should solve the issue.
Wheel bolts usually have safety factor about 5, so it takes a lot to have one broken.

[Passin_Thru]

Chum lee, Thanks for the insight. Understand it. Correct taper according to Dexter. They carry the axle, wheel, bolts and nuts installed. 1/2 in Dia. bolts.
Screwed on freely. Dexter says 90 to 120 ft lb is adequate torque.
http://www.dexteraxle.com/docs/default-source/default-document-library/light-duty-wheels-and-tires.pdf?sfvrsn=2
Waiting on Aluminum wheels to arrive. Will try them as they have a 0-Offset. Thanks again to all of you who answered. Its neat to pick others noggins for ideas when one gets stuck and I worked with Engineers at Flight Test for years.

[Charlie_D_]

What size studs? Seems a little light on torques values. Does the nut screw on freely to the stud?

[Passin_Thru]

I tightened mine according to A&P Mechanics training. You loosen everyone and retighten with a Calibrated Torque Wrench. Mine is a Snap-On and I torqued to 90 ft lbs.I was doing 65 through Scranton when it sheared off on a curve to the right. I had been on Rt 11 from NY line to 20 N of Scranton, rough twisty windy. My lug bolts came form Dexter Axle, on the trailer. Knew about the L and Right hand threads. Chrysler had them for a long time. will call Dexter tomorrow and talk with their engineers. I may buy titanium bolts.

[Chum_lee]

I know it seems counter intuitive, but cornering loads or offset wheels DO NOT increase the loads on properly torqued wheel studs until they become so substantial that the wheel deforms/deflects enough to cause it to lose contact with the hub. That will add tensile forces to the stud. Think about it. Suppose each stud provides 1000 lbs. of clamping force when properly torqued. That's what puts tension in the stud. The only way to add more tension to the stud is to deflect (stretch) it more. You could do that by adding torque to the lug or by pulling the wheel away from the hub which would increase the tensile force on the lug. (very difficult to do) Each lug would need more than 1000 lbs. of force (in this example) to counter the load all ready on it and stretch it further.

As correctly previously mentioned, the clamping force between the wheel/hub creates static friction which clamps/holds the wheel to the hub. Hub centric hub/wheel designs or conical lugs are only there to provide locating action. That's why everything goes bad when the lugs become loose or become over stressed due to being loaded (over torqued) beyond their yield strength.

Overly offset wheels will substantially add loads to wheel bearings though. Especially double row ball bearings typically used in front wheel drive cars. Trailer wheels less so but it does effect them. It also changes the vehicles stability concerning its center of gravity.

Chum lee

[Charlie_D_]

Have you checked the taper on the nuts? Not all nuts have the same taper. Another issue I had was installing acorn nuts that did not clear the bore of the hole. By that I mean the edge of the hex on the nut contacted the side countersink of the hub. That did not allow the taper of the nut to contact the area of the hub that it should have.
Heard a noise when slowing down. Found that 3 studs had broke and wheel was wobbling. Lucky I caught it before the wheel came off.

[Lynnmor]

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

He asked about torque and shear on studs as well. There has been some good discussion, and it is all part of the big picture.

[hotpepperkid]

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

[JIMNLIN]

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.

[Lynnmor]

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.

[babock]

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.

[pickjare]

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.

[pickjare]

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.