Balancing TPMS assemblies: The basics still apply, but what about that added weight?
Changes to the typical retail tire dealership that are associated with tire pressure monitoring systems have been well-documented over the last few years. From the complex and almost absurd recalibration procedures to the vast array of sensors and seal kits, companies are constantly being bombarded with the message that if the revolution hasn't arrived yet, it's just a matter of time before it rears its ugly head.
Some have chosen to jump in the game and learn the painful lessons today, while others are waiting until they have a negative impact on sales. Philosophies aside, at least everyone can agree that inevitable changes are on the horizon -- and every company related to the replacement passenger and light truck tire industries will feel the effects.
One area that has not received much, if any, attention is the effect a tire pressuring monitoring system (TPMS) will have on tire balancing. Vehicle suspension and ride control systems are becoming more sophisticated, and drivers are more likely to notice vibrations that can be attributed to tire and wheel assembly imbalance.
With rising expectations on ride quality, some dealers have invested in new technology that can measure and correct factors like runout and road force. In the hands of an experienced and well-trained technician, this equipment can create the best match of the tire and wheel so that the low spot of the wheel is mounted opposite the high spot of the tire, and/or the heavy spot of the tire is opposite the lightest spot on the wheel.
Match mounting is the first step toward achieving the best possible ride quality. Some tire manufacturers will place sidewall markings in the form of yellow or red dots to identify the critical mounting points.
For the most part, the yellow dot represents the heavy spot of the tire. It is aligned with the valve stem since that is the lightest spot on the wheel. The red dot indicates the high spot of the tire or the area of greatest stiffness and is aligned with the low spot of the wheel or the valve stem.
It is not inconceivable that tire pressure monitoring systems will alter those guidelines. Direct systems, which to date are the only systems that meet the federal guidelines for identifying under-inflated tires, require a sensor in every tire and wheel assembly. The overwhelming majority of vehicle manufacturers utilize a valve stem sensor, but certain 2006 and 2007 Ford models have incorporated a band-mounted sensor.
Regardless, these TPMS sensors have considerable physical weight that must be accounted for in the balancing process. The average valve stem sensor weighs between 30 and 40 grams, or 1 to 1.5 ounces, a considerable amount from the balance perspective, especially since most tire and wheels are fairly close to "balanced" in the first place.
As a result, the match mounting policies of the past may have to be adjusted when it comes to vehicles with valve stem sensors. After all, if a yellow dot indicates the heavy spot on a tire, it would make sense to align it opposite a 1.5-ounce valve stem sensor. (In the case of the new Ford models, the band-mounted sensors already are located opposite the valve stem, so the change in policy would not be necessary.)
No flange, increased vibration?
But the changes related to balancing TPMS assemblies do not stop with match mounting. Current trends in wheel design at the original equipment level have led to the elimination of the outboard rim flange. The resulting wheels have a much cleaner look, and some may even say they are more durable because the likelihood of catching a rim flange on a curb is greatly reduced.
For some dealers, the solution is a simple static balance since these wheels are always aluminum. However, when 1 to 1.5 ounces of weight are added to the assembly with a sensor, the chances for a vibration complaint are definitely increased when using this approach. Therefore, dealers must be able to perform a dynamic balance with the use of tape weights so the outer plane can be balanced.
Years ago, the tape weight dynamic balance procedure was basically one of trial and error. Newer balancers have made the process much easier and even enable the technician to place the weight behind a spoke in the wheel so it isn't visible from the outside.
For those who want to minimize ride complaints, the solutions appear to be relatively simple: purchase a new balancer with tape weight capabilities, continue the trial and error method with older equipment, or bring the old bubble balancer out of the closet and hope for the best.
If the goal is to eliminate all types of ride complaints, then an external "pin plate" system also should be implemented in addition to the tape weights.
Traditional cone centering on the shaft lends itself to a much wider set of variables. Misalignment and debris in the center hole of the wheel are just two of the issues that can be avoided with a pin plate. Once again, the addition of 1 to 1.5 ounces of weight associated with a TPMS sensor increases the chances of a vibration, and the proper usage of the proper equipment will eliminate additional external factors that can contribute to customer complaints related to imbalanced tire and wheel assemblies.
None of these approaches to tire and wheel balance are going to come cheap. Sophisticated balancing equipment that is capable of achieving a dynamic balance with tape weights in a short period of time is going to require a fairly significant investment. And there's also going to be the constant need for more in-depth training on these balancers because it takes a little more than just tacking a couple of weights to the inner and outer rim flanges.
One possible solution to the balance problems associated with a TPMS sensor that does not require a large capital investment is the use of internal balancing compounds or systems. These products have been used in the commercial truck tire industry for years, and some dealers swear by them. The basic premise is that centrifugal force will cause the compound to disperse throughout the inside of the tire and naturally settle opposite the heavy spot.
Most dealers aren't even aware these products exist for smaller tire and wheel assemblies. But their potential benefits are intriguing simply because there is virtually no additional equipment or training required.
Liquid sealants that claim to have "balancing properties," on the other hand, definitely will have an adverse effect on certain sensors, particularly those manufactured by Beru AG, which are found on many German automobiles like Audi, BMW and Mercedes. The Beru sensor utilizes a filter over the air pressure port in the sensor, and if it becomes clogged with any foreign material, the sensor must be replaced.
Other sensor manufacturers have indicated their products are more robust to moisture, but the consequences of using liquid sealants still can be expensive, so it may be best to avoid liquids inside tire and wheel assemblies with sensors altogether.
By now, retail tire dealers have to be tired of hearing how the use of tire pressure monitoring systems is going to change their business models. While some markets service tires and wheels with sensors on a daily basis, others may still be a few years away from seeing significant numbers of vehicles with this technology.
By the time the 100% phase-in period for all new cars begins this September, however, millions of sensors already will be in service, so the odds of avoiding TPMS will only get worse.
Since consumer expectations are on the rise because of advanced suspension and ride control systems, even the slightest vibrations are unacceptable and often blamed on the tires. If the dealer does not have equipment that easily can measure factors like run-out and road force, it's going to become increasingly difficult to pinpoint the problem. And with tire manufacturers more reluctant to adjust tires for ride complaints, the best approach is to minimize the number of assemblies that have the potential for a vibration.
It's going to take some investment, some training, and some additional time, but the payoff is a more satisfied customer and a product that performs even when additional weight is added by a TPMS sensor.