lub bolt loosening on aluminum wheels 5

[lombo]

Can anyone explain the reasons for lug bolts loosening on aluminum wheels?
I have heard that it is recommended to re-torque after a few miles especially on new wheels. Nobody has given me a good reason why.

 

[TVP]

Bolt Load Retention (BLR) is the amount of load (actually it is the tensile force in the male threaded fastener) retained in a clamped joint after some duration. Typically it is expressed as a percentage of the initial fastener prelod, i.e. 75% BLR means that the joint has relaxed enough to reduce the tension in the male threaded fastener to 75% of its original value. Aluminum and magnesium are prone to reductions in BLR due to a combination of factors (creep, stiffness characteristics of the joint, etc.), especially if the service environment is characterized by variable amplitude loading and temperature fluctuations. The purpose of re-torquing wheel bolts is to keep the tensile force on the bolt as close to the specified level as possible, thereby maintaining the original clamping force on the joint.

 

[lombo]

Thanks for the info.

Can you tell me why is this more critical with a new wheel compared to a used wheel? Are you actually yielding the material directly under the bolt or nut contact surface?
Wheels are heat treated so there shouldn't be any appreciable natural aging to change the physical properties of the aluminum.

 

[evelrod]

I have noticed that. I have always just double checked the torque on new wheels several times at first and just never paid any attention to the fact that they required a bit more attention when new. I suppose there is always a bit of 'bedding in' with anything like this when new.

On the same theme---Aluminum wheels with steel inserts for tapered lug nuts don't seem to suffer from this phenomenon.
I prefer tapered nuts and steel inserts but that is not available in all wheels. When you use the sleeve nuts use only top quality (if you can determine that). If possible, and it should always BE possible , make sure that some threads of the bolt sticks out beyoud the face of the wheel. Sleeve nuts are not safe and WILL shear at the sholder if threads don't go past it. 3/8" to 1/2" minimum IMHO for street and completely PAST the end of the nut for competition!


Rod

 

[GregLocock]

Our OEM alloys use a tapered wheel nut, just like on a steel wheel. If you think about a taper - a little bit of surface roughness getting flattened out will lead to a LOT of disappearing tension. I think I prefer the other style of lug nut, with a captive flat washer to provide the clamping force, and the cone just provides a lead-in for alignment. Of course the styling guys and the cost guys would hate them, so engineering comes in the loser. As usual. I'd be interested to know how many loose nuts they find at PDI (assuming they bother to check). Cheers

Greg Locock

 

[TVP]

lombo, the answer to your question about yielding is a qualified "yes". It is not purely gross yielding, but a combination of things. Remember, at the microscopic level, nothing is perfectly smooth, flat, etc. which is why Rod and Greg mentioned things like "bedding in" and flattening of surface roughness. Coatings on the surface of the wheel and the lug nuts also play a roll in this process, as friction has a dominant influence on any assembly joined with threaded fasteners.

Natural aging is not really a consideration, as you mentioned. For all of the reasons mentioned previously, new wheels require some amount of "break-in" after which the surfaces remain more or less static with respect to each other.

 

[CoryPad]

Sorry to join this thread late, I was not subscribed to this group.

I hate to contradict TVP, but his last post is not entirely correct - aluminium wheels do experience gross yielding (one of the few joints that does). Because there are five (or more) fasteners, and because the tolerance on surface planarity across the five seating faces is large, it is typical for one or more of the joints to plastically deform before seating. Thus, in addition to the other factors listed above, it is a good practice to loosen and retighten wheel fasteners after their intial tightening.

 

[lombo]

Thanks to all the replies.

 

[Mac7000]

Sorry to join this thread so late, along the same lines, the mounting face of aluminum wheels typically has a small step in it (~.20mm). This step creates a "belvil" washer effect in the joint. Two (of many) questions arise:
1) Should the lug nut draw the wheel down (or the rotor&hub up) to close that gap? (effect on mounted LRO & wheel retention)
2) Does the wheel deform/take a set thereby reducing the gap & degrading wheel retention?

Anybody know where to get reference/research material on this topic?

 

[ogonzalez]

I've been part of the Aftermarket Design of wheels since 1997, and to answer Lombo’s question, Alloys have the tendency to expand, especially at height temperatures and speeds.
For this reason we create a .010 to .020 Concavity on the Mounting face of the wheel.
Re torquing may be ok or good safe instinct, but O don't think is need it.

 

[SusTestEng]

"Our OEM alloys use a tapered wheel nut, just like on a steel wheel. I think I prefer the other style of lug nut, with a captive flat washer to provide the clamping force, and the cone just provides a lead-in for alignment. Of course the styling guys and the cost guys would hate them, so engineering comes in the loser.
Greg Locock"

We are the opposite. Our OEM AL wheels use the captive flat washer nut. This being said....yes, we actually want to go to the taper nut to reduce the cost. The cost is about $2USD per vehicle. I acutally prefer the use of whell bolts like all the German vehicle manufacturers use.