If you’re not already sold on the necessity of wheel rim and tire balancing at your shop, think about the forces involved in a collision, the way a vehicle is tossed around and the lightweight construction of wheels and rims. Even in a slight fender bender, you can bet a vehicle’s wheel balance has been affected.
A veteran tire shop owner told me that even with current anti-lock brake systems, he still finds that panic stops can alter the position of the tire to the rim and change the balance. This means that even if you did nothing to service the wheels or rims, failing to check for this problem may mean the customer comes back with a valid complaint that can hurt your reputation and your bottom line.
How do you prevent such related collision damage from damaging your profits and customer satisfaction index? Consider installing a computerized wheel balancer and offering tire and rim service instead of subletting it to the shop down the street.
The Bare Facts
To understand why a body shop should consider getting into the wheel balancing business, let’s take a look at some ride quality basics:
1. Vehicles with lightweight suspensions don’t absorb road forces readily.
2. Struts and rack and pinion steering are both “straight line” vehicle commodities. They don’t soak up any force or vibration; they simply transfer it in a straight line, most often directly up to the driver.
3. Lower aspect ratio tires use ultra-lightweight wheels with larger diameters and have an acute tendency toward distortion and imbalance.
4. Dynamic forces, including those set up by brake system feedback from anti-lock brakes or traction-control devices, affect tire forces that, in turn, affect balance characteristics.
5. Ride quality is “advertised” by vehicle manufacturers as being a primary reason to buy and continue to own their products. This means the vehicle must continue to ride and handle like its showroom cousins after it leaves your collision facility.
If you’re starting to get the picture as to why you need to control your own destiny regarding wheels, tires and balancing, this article is doing its job.
The Wheel World
The most basic level of balance for an object that’s at rest or “static” is the single plane or single point static balance. The item – in this case, the wheel – is considered to be in a state of equilibrium while at rest. However, if the wheel is placed in motion, it may experience dynamic feedback or vibration that will affect the vehicle’s driveability.
Static balancing was previously accomplished with equipment that used a balancing scale or bubble plane. Today, computer balancers are designed to allow for a static balance setup primarily from the true center-line of the tire, though this operation is confined to very special wheels and applications that don’t benefit from high-speed dynamic balancing or wheel and tire tuning. An example might be the 50-inch mudders on a monster truck that would bounce a driver out of the cab were it not for a static “patch” weight glued to the inside of the tire at the centerline.
Dynamic balance accounts for all the relative forces as well as the motion of the tire and wheel as they roll along the road. Although dynamic characteristics are assumed to be side-to-side or in-and-out motions, static or up-and-down bounce problems are addressed at the same time.
Identifying the dynamic weight planes is an important part of understanding weight placement on most, if not all, of the newest types of rim and tire combinations. The creation of separate planes and the establishment of an overall diameter is significant when inputting data to an off-the-car computerized balancer. This input becomes even more obvious and is critical to achieve a fine high-speed balance when weights other than standard clip-ons are in use.
The list of special features on many of the high-end computer balancers seems to be endless. The better package you can afford to place under your shop’s roof, the better the chance you’ll have to perform perfect balancing jobs with no comebacks.
The set-up basics, however, are pretty much the same for most high-quality equipment. Accurate wheel-to-balancer-shaft mounting begins by looking at how the wheel rim is attached to the vehicle:
- Hub-centric is a method that uses the rim pilot hole and a corresponding lip or machined flange on the vehicle hub to establish true concentric mounting rim to hub.
Hub-centric front/back cone mounting utilizes the hole in the rim centerline to establish a true and concentric mount. Always try to use the smallest cone possible, and place it from the inside to provide for the highest centering accuracy. Occasionally, a custom or heavy-duty steel wheel may need the cone placed from the outside. The wheel may also require a spacer on the balancer flange to provide an offset for the tire and rim to clear the body of the balancer.
These set-ups are sometimes trial and error exercises, and the safety aspects come into play once the wheel is spinning with the balancing machine’s power behind it. Be sure to lock down the wheel clamping device – be it with a nut, a clamping cup, spring plate and wing nut or any other positive attachment device that’s supplied by the manufacturer of the balancer. Most balancers will automatically shut down the motor and apply the balancer brake if a wheel spins on the shaft because of a loose or improperly clamped rim-to-balancer attachment.
- Lug-centric is the alternative method seen more often these days. It involves the actual centering of the wheel to the vehicle rim lug-bolt circle, which is assumed to be centered in and around the concentric plane.
Many of the newest and most popular wheel designs using low-aspect ratio tires have no center hole at all. This means that a lug-centric adapter must be used to mount them on the balancer. A uni-lug with a universal flange plate may be used to match the bolt circle as well as the number of studs. The circle itself may range from an average of 3.75 to 8.45 of an inch, and the amount of lugs are changeable to attain any given diameter. The balancer stub shaft will replace the ordinary shaft assembly and is required to accommodate the holeless wheels.
Typical tire candidates for a lug-centric adapter are Acura, Audi, BMW, Chevrolet custom wheels, some Chrysler and Dodge products, Daihatsu, Fiat, Fomoco factory custom, Ford F-350, Honda low-aspect designs, Hyundai, Isuzu, Lincoln/Mercury specialty tires, Maserati, Mazda, Mitsubishi, Nissan, Peugeot, Renault, Saab, Toyota, Mercedes and certain Volkswagen products.
Setting Data Parameters
After a successful mount to the balancer, most equipment companies will provide a choice of either full or partial automatic data input – including the position of the wheel on the shaft, the diameter of the wheel or the rim width and diameter. Manual data input is still standard on a few units, but that trend is in decline.
Rim dimensions are gauged from the outside of the flange at the tray area on the rim to the corresponding area on the inside of the rim. Note that when using custom wheel balance procedures and adhesive-style weights, the procedure is different and manual over-ride is necessary on some equipment to establish rim data input.
Placing the Weight
Set-up of the rim on the balancing machine is dependent upon the type and style of wheel and weights being used.
- Typical hammer-on weights are called clip-ons and come in a dozen or so styles to accommodate specialty wheels of various lip or flange designs. Many of these clip-on designs are coated to prevent a dissimilar metal corrosion or stain from marring the wheel. Another method is to use white or black liquid rubber to act as a sealer or barrier on the contact portion of the weight at the rim flange.
Handy “rim gauges” are available to help identify specialty rim flange-design clip-on weights. Abbreviated aluminum flange series specialty weights such as ALCEN, ALCFN, ALC and ALCW can be identified by placing the gauge against the rim flange, rotating it to the best fit and then selecting the appropriate weight.
- Adhesive or stick-on weights are nothing new. I was placing them on custom wheels during the era of on-the-car spin balancing (which is called finish balancing these days).
It’s good to place adhesive weights on wheels that need a narrow plane separation or unique hiding of the weights for show or beauty purposes. Some of these rims work well with a static balance, but most still shake badly unless you provide a dual-plane dynamic balance situation that would be impossible to arrive at without adhesive weights.
Keep in mind that calipers can rub and pull off or displace weights, causing damage to brakes or rims. Also, be careful with weight placement. Allow adhesive weights to set well if you’re augmenting self-stick weight pads with super glue or stronger adhesives. Some shops use duct tape to help hold the weights on during the drying period. Have the customer return in a day for you to pull off the duct tape and re-check the wheel balance.
Balancing Equipment for the Body Shop
When installing a balancer in your shop, the environment is a big factor in selecting the specific design. If space is a problem, then a mobile, hand-spin model may be your best option. The limitations on wheel capacity may be a factor here, but that’s something to decide for yourself.
When selecting a balancer, consider the following as well:
All of the newest balancer designs offer tire matching that’s useful in finding the optimum tire-to-wheel position. In addition, rim and/or tire diagnosis can be accomplished using several of the equipment options available. Automatic parameter entry is a good feature, and the high-end machines all have this as an option at the very least. The design of the motor, circuit board, and strain gauge or digital sensors was a concern we had to carefully examine 10 years ago. Today, all of the balancers I looked at used hearty industrial components.
A roller-arm loaded tire and wheel can alter the balance parameters enough to create a wheel shake that you wouldn’t find using an ordinary balancer machine. But equipment and diagnostic gear that will find such defects in tires and rims – as well as act as a balancer – are very expensive. Many tire shops are just now realizing the wisdom of having these types of equipment, so you may not want to spring for them just yet.
Regardless of the specific manufacturer, the amount of damage or the color of the finish, the vehicles that grace our repair bays these days have one thing in common: They all have at least four wheels. And more than likely, the wheel balance on a vehicle that’s involved in even a minor fender bender has been affected.
That means there’s money to be made when it comes to wheel balancing. So why continue subleting it to the shop down the street? Keep the work in house, keep the profits for yourself and keep your customers happy by giving them a complete, quality repair.
Writer Bob Leone, a retired shop owner and contributing editor to BodyShop Business, is ASE three-way Master Certified and is a licensed secondary and post-secondary automotive instructor in the vocational school system in Missouri. He is also a former NAPA A.S.E. Technician of the Year.
Accurate wheel-to-balancer-shaft mounting begins with a look at how the wheel rim is attached to the vehicle.
Understanding Force Variation Technology
Reliable BMW in Springfield, Mo., may cater to the Bimmer crowd, but certified technician Scott Hohgrefe also operates a “come one, come all” high-tech chassis service area under the dealership banner. Hohgrefe says the force variation balancer the dealership owns is constantly kept busy, and has been in place with almost zero down-time for more than three years. What are the big sources of balancing business for the equipment? Body shops that don’t perform this particular service. “Body shops that dress up the chrome and do a visual inspection only on a tire or wheel that’s been in a collision situation stand to loose more often than not,” he says.
During my visit to his service area, Hohgrefe showed me a few tricks of the trade with regard to force variation balancer technology. “The correct set-up for clip-on or mixed weights will net a perfect balance every time,” he says.
The force variation system uses tests for tire defects including unequal sidewall stiffness, distorted bead centers and collision-damaged carcass. This is done by applying more than 650 pounds of force to the tread area of the tire while the tire is spinning on the balancer. The machine Reliable BMW uses has a roller that makes contact with the tread surface and then systematically checks for mounting error, run-out and force variation. It also performs other simple diagnostics.
The force variation balancer technology in place at Reliable BMW may not be a standard fixture in shops today and may not be the right piece of equipment for your body shop, but Hohgrefe believes that once the industry produces a few different versions of this type of equipment, you’ll see more shops getting into the balancing game. But the cost will likely need to come down. Reliable’s equipment cost more than $9,000 – three times as much as a traditional balancer.
“Like mechanical shops, body shops can’t continue to practice procedures that offer only a ‘get by for now’ solution,” says Hohgrefe. “The cost of liability and damage to your reputation will make investment in advanced equipment a necessity 10 years down the road.”
|Force Variation – Wheel alignment and chassis experts explain force variation as the effect that would be present if a series of springs were positioned between the rim and the tire tread area. If some of these springs were very stiff wire while others were finer wire, a non-uniformity would exist. Such a condition would represent a force variation problem, which can create vibration on a vehicle. Incidents such as this can occur even if the tire and rim are perfectly balanced.
Static Balance – The most basic level of balance for an object that’s at rest or “static” is the single plane or single point static balance. The item is considered to be in a state of equilibrium while at rest, but if the wheel is placed in motion, it may experience dynamic feedback or vibration that will effect driveability of the vehicle.
Dynamic Balance – This accounts for all the relative forces as well as the motion of the tire and wheel as they roll along the road. Although dynamic characteristics are assumed to be side-to-side or in-and-out motions, static or up-and-down bounce problems are addressed at the same time.