The 2008 NASCAR season is about to start and the testosterone is flowing. Now is the time to remind your technicians that installing wheels on passenger vehicles is not like being on a pit crew for a racecar.
We all see how quickly a pit crew can change four tires, usually in 14 seconds or less including filling a tank of fuel. If we aren’t careful, this same aggressive style can infiltrate our own shops.
The types of wheels and lug studs used in a hard-core race car are significantly different than the ones used in passenger vehicles, plus they get replaced after a few hundred miles. The wheels, lugs and studs on a passenger vehicle have to last for hundreds of thousands of miles, which includes multiple removal and installation procedures. How do we improve the safety in our shops and have higher customer retention at the same time? The answer to both of these questions is eliminating “wheel-offs.”
Wheel-off claims hurt your business in many ways but can be avoided by properly installing wheels. Here is some information to help you understand why proper centering and torque procedures are necessary and tips on how to do it correctly.
To start, take a look at the mounting surface. When a wheel is removed from a vehicle’s hub, a visual inspection should be made of the surface of the rotor, hub and mounting pad. Before other work is performed, these surfaces should be cleaned with a wire brush or abrasive pad.
Any debris must be removed so the wheel can mate to the hub of the vehicle properly. If these two parts are not properly cleaned, debris can loosen from between the wheel and hub during cornering, which may create a gap that can reduce the clamping force applied to the wheel.
If performing maintenance on a vehicle that has custom wheels and a centric ring, inspect the centric ring as well. The ring should feel snug on the hub, with no slack.
Many centric rings are plastic, which over the course of time will deform and no longer properly center the wheel onto the hub. These are too cheap to repair, so replace them as needed. In some instances the vehicle may have aluminum centric rings installed. Inspect them as you would the hub. Pay close attention to aluminum centric rings as sometimes corrosion can begin to form when aluminum and steel are in contact, especially when moisture and salt are present.
Next, inspect the lug nuts and the lug holes of the wheel for galling, burs or elongation. Galling and burs would indicate possible damage to the lug nut or wheel, while elongation would indicate that several lug nuts came loose while the vehicle was traveling down the road. In this instance, the lug nuts should be replaced and the wheel should be sent to an authorized repair center or replaced.
This leads us to the most overlooked inspection component of all: the lug studs. In many cases, wheel-offs can be linked to weakened lug studs. Make sure to inspect each stud individually from all angles. Visual inspection will show damage to the threads but you can’t visually detect if the integrity and strength of the lug stud has been compromised.
To understand how a lug stud works, we need to understand a few key terms. First is the elastic region. This is the portion of the stud that stretches slightly as torque is applied, which is how we attain a specified clamping force, measured in foot-pounds.
A point to be made here is even though many vehicles have the same diameter lug stud, such as 12mm, there are variations in the amount of torque to be applied depending on the specific vehicle manufacturer’s recommendations. These variations are due to how the lug stud was manufactured and its metallurgical properties. It is recommended that some 12mm studs be torqued to only 75 foot-pounds, whereas others can be torqued to 100 foot-pounds.
The other term is called the yield point, which indicates the point when a stud has reached its maximum clamping force. Once a lug stud has reached its yield point, torqueing the lug nut further will actually cause the clamping force to diminish. If this has occurred repeatedly over a number of years, the risk of a lug nut backing off can greatly increase.
This is why it is so important to use proper installation techniques, including using a calibrated torque wrench and either maintaining a record of the torque applied, using some of the newer computerized torque wrenches that record the amount of torque applied to each lug nut, or at the very least having a training manual in place that specifies how to properly install lug nuts.
I like to have the customer actually watch me as I do this. The reason for this is a previous shop or the vehicle owner could have over-torqued the lug studs. If a problem with a lug nut backing off doesn’t occur until after you have serviced the vehicle you have nothing to prove that you followed industry recognized procedures except your word and the word of the technician.
I would also highly recommend that you have each employee be certified through the Tire Industry Association’s (tireindustry.org) ATS program, which includes a segment on wheel retention. There are other companies who offer excellent training material on this and other related topics. For more information, e-mail me at [email protected] and I’ll forward the information to you.
Over the years, I have worked on a wide variety of vehicles ranging from new to 70 years old. A few years ago, I was working on a 1953 Chevy truck. The front suspension had been replaced with components from a late 1970s truck and the rear was a Ford 9-inch taken from a Lincoln in a junkyard.
The owner had worked on this truck for 10 years and one of the final details was to install some custom wheels and tires. We chose a set of Cragar SS wheels, which require a mag shank lug nut. During the installation process, we broke a lug stud. After replacing it, we broke another one. If you ever find yourself in this situation, stop and look for any number of possibilities. At first we questioned the lug nuts. We were concerned that if the threads were cut wrong or irregular that this could lead to the lug nut shearing the lug stud.
I took a handful of new lug nuts and threaded them onto new studs. What we found was that the lug nut started to bind about half way down the threads of the lug stud. We found one lug nut that worked very well on one lug stud and used it on a number of others.
Eventually, we tested over 50 brand new lug studs to find 20 that were straight enough for us to use. We installed all of the lug studs that weren’t out-of-spec and haven’t had any problems since. As I researched this, I found that there had been several instances where inferior out-of-spec lug studs had made their way into the country.
At this point, we have inspected and replaced any component found to be defective. To finish this job we have to install the wheel correctly. When installing a set of custom wheels, there are several items to consider:
1. Remove any Tinnerman clips that may be present. These are the small round clips that fit over the lug studs that are designed to hold the rotor/hub on the vehicle as it is being assembled. OE wheels have a relief on the mounting surface to accommodate the clips. Most custom wheels do not have this relief.
2. Put the hub centric ring in place.
3. After placing the wheel on the hub, begin installing the lug nuts by hand. This is the only way that you can detect a problem.
4. Continue threading the lug nuts by hand while rotating the wheel. This lets the wheel settle and allows the lug nuts to fully engage the wheel. Don’t expect a plastic or thin metal centric ring to hold a 50-pound assembly dead center. Engaging the lugs while rotating will nearly eliminate a potential vibration.
5. Impact guns using torque limiters can be used to secure lug nuts while the vehicle is in the air, but do not rely on any pneumatic tool to apply consistent torque, unless it is a computer controlled version. Remember to use approved star patterns.
6. Lower the vehicle until the tires just touch the ground or use a tire chuck to hold the tires while applying the final torque using a calibrated torque wrench. Check reference or owner’s manuals to determine the amount of torque required. If you use a “clicker” style wrench, hold it by the handle only and apply torque slowly and smoothly. Stop immediately when you hear the click.
I hope this helps many of you to lower your risk and improve customer satisfaction. It’s an age-old problem, but with new hires and turnover, it bears repeating.
