The rollercoaster that is the upper Midwest winter is moving along at a breakneck pace.
One day, the high temperature was in the single digits. Two days later, the high was pushing 50. In a few days, temperatures are forecast to drop 20 degrees, with snow on the way.
The changes in temperature can be a shocking experience for the most hearty of souls.
You can be in for a real shock, too, when ambient temperatures change abruptly or wheel ends experience extreme temperature changes.
These swings in temperature have a great impact on wheel-nut torque and clamping force on hub-piloted disc wheel systems.
You may find that wheels are running loose and even coming off vehicles rolling down the road shortly after a tire/wheel assembly change on which you were sure the torque was properly checked, but which experienced an extreme temperature variation between the time of the tire/wheel installation and the vehicle's return to service.
Just what is going on?
Three factors may be the culprits in situations like this.
The first is that flange nuts used in hub-piloted disc wheel systems require two drops of motor oil be applied between the nuts and flanges and two drops to the last two or three threads at the end of each stud.
This is required to ensure the proper clamp load is attained to hold the wheel assemblies on the vehicle.
However, the characteristics of lubricants vary greatly across a temperature range of sub-zero to extremely hot temperatures, which will affect the clamp load attained.
When the axle end is extremely hot, fasteners may be greatly over torqued due to changes in lubrication characteristics at elevated temperatures and may lose clamping force when the wheel end returns to normal ambient conditions.
Second, wheel-end assemblies with different metal components, such as aluminum hubs with aluminum wheels and steel studs, behave much differently than wheel-end assemblies equipped with all-steel components.
This is due to the different thermal expansion characteristics of different metals. When installed at temperatures below 0 degrees, tire/wheel assemblies may end up over torqued at normal ambient conditions.
And thirdly, normal torque measurement procedures do not produce accurate tension/clamping force measurements at extreme temperatures as compared with normal ambient conditions.
So even though you used a calibrated torque wrench to check the torque on the wheel fasteners, it probably isn't right if it was done at extreme cold or hot temperatures.
When the wheel-end temperature returns to something more normal in the 60- to 70-degree range, the wheel assembly will become loose.
I mention hot temperatures here because if a wheel end has been super-heated due to a frozen wheel bearing, for example, and you install a tire/wheel assembly on it and torque it to 450-500 ft. lbs., the tire/wheel assembly probably will become loose when the temperature drops to normal again.
This is because torquing wheel nuts at temperatures above normal shop conditions can result in damage to fasteners that could lead to loose wheels. So extreme hot as well as extreme cold temperatures are a bad thing and should be avoided when installing tire/wheel assemblies on vehicles.
So what do you do when faced with changing a tire/wheel assembly in the middle of a polar vortex?
The answer is, if possible, to wait to install tire/wheel assemblies until the wheel-end temperature reaches normal shop maintenance conditions for the geographical area you are in.
As a general rule, the normal temperature range for performing maintenance on wheel-end components is between 0-150 degrees, with the middle of this range being ideal. (This can vary depending on fleet vocation, environmental considerations and geographic location.)
So, if it is minus 40 degrees, get that vehicle into the shop, grab yourself a cup of hot chocolate and let both you and the axle end warm up before performing service on it.
If it is impossible to wait until the wheel-end temperature returns to "normal" conditions, install the tire/wheel assembly and get yourself inside to warm up.
Then the wheel end should be retorqued as soon as it reaches normal temperature. This may be after it has gone down the road a ways.
The proper way to retorque wheel nuts in this situation is to loosen the wheel nuts and then torque them to 450-500 foot pounds.
If you just put a torque wrench on them to check the torque, you will further overtorque and damage them.
Wheel manufacturers recommend that wheel ends be retorqued if large temperature swings of 150 degrees or more exist or are anticipated.
If the wheel nuts are not retorqued, fasteners can be damaged, therefore be sure to inspect fasteners for damage during every tire/wheel assembly change.
Winter can be terribly cruel in the northern regions of North America such as in Juno, Alaska, Green Bay, Wis., and even Detroit.
Make sure you bundle up warm to face the ravages of commercial tire service in the winter and take steps to ensure that tire/wheel assemblies are installed and torqued properly, taking into consideration the swings in ambient temperature and overheated axle ends.
Peggy Fisher is president of TireStamp Inc. and is based in Troy, Mich. She can be reached via e-mail at [email protected].