Contrary to popular belief, all wheel balancers are not the same. When tires and wheels were of similar size and mass, it didn’t matter as much, but now, like everything else, things change.
Static and couple correction used to be done at the rim edges with clip weights on the majority of wheels. Now, most wheels are no longer using clip weights exclusively. This is now the era of adhesive wheel weight balancing.
In the 1980s, assembly line wheel balancers and garage tire balancing evolved from static correction to a combined static and couple correction (dynamic balance), thus providing better high-speed ride quality. It all worked better, but then wheels started to change. As vehicle applications proliferated, tires became heavier and larger in diameter, and dual correction weight locations moved away from rim flanges and became narrower. This caused issues.
Industrial wheel balancers automate the balancing process in production lots to fit specific OEM applications. Weights are often applied inside the wheel instead of at the rim edges with a clip weight, which changes weight calculation methods.
Today, tire construction uniformity, along with alloy rim quality, has become much better at reducing dynamic wheel wobble. As a result, large amounts of counter-correction (180° equal weight separated by equal distance) are not as necessary. Vehicles are also more sensitive, and static correction fine-tune balancing has become much more important to address.
Unlike pre-programmed industrial balancers, shop balancers had to evolve in a more flexible manner. As wheels changed, most garage balancers began to fall short in performance, and most still do not operate as efficiently as possible. Often used for clip-on weights, industrial tire balancing calculations come from the balancing standard ISO21940, and use the external rim flange planes placed far away from each other.
High-quality shop balancing OE software will also use the same balancing standard ISO21940, even if correction weights are not used at the furthermost edges of the rim flanges and adhesive weights are used inside the rim. This methodology, adopted by car manufacturers, saves time and eliminates the use of excessive couple correction counter weighting. Normally, wheels are considered balanced when residual unbalance is less than a specified tolerance of approximately ¼-oz. per plane on an approximate 15-in. diameter rim.
On-car high speed and also off-car wheel balancers (which came later) quickly allowed service centers to balance a wide range of vehicles.
Older software shop balancer designs have not followed this guideline in force measurement limits and calculation. This has caused problems with excessive counter-weight application when using tape-on adhesive weight.
When dynamic balanced, a traditional shop balancer with limitations in software may not compensate properly for static residual force. Residual imbalance may be hidden when less than 0.58-oz. (0.29-oz/plane) is in the same quadrant. This assumption is made with a fixed round-off weight increment and a fixed blinding function (always preset higher than the round-off to prevent weight chasing) and works independent of the chosen weight correction positions, rim dimensions and overall wheel mass.
Nevertheless, rim manufacturers make a clear distinction: correction planes, internal to the rim in case of adhesive weights, do not correspond to the reference planes for the evaluation of the residual unbalance, which are identified with the external planes of the wheel.
The drop-in balancer performance was related to the need to move correction weights inboard from the rim flange, which called for excessive amounts of counterweight (couple correction) and check spins.
Furthermore, heavier, large-diameter wheels and wide outboard decorative flange designs leave little space to apply two correction weight positions and achieve the same balance. The correct way to determine the couple force limit would be to use the rim edge flanges as the correction weight calculation and determine the couple force limit based on correcting from that area instead of two areas inside the wheel. These excessive and unsightly counteracting balance weights are incorrectly applied.
It’s also clear that a heavier wheel should be balanced differently. As an example, a 30-lb. wheel may vibrate with less than a half-ounce of static imbalance, but a truck wheel that weighs 170 pounds may not cause a vibration if the wheel is out of balance by 8 oz.
In the early 1990s, to improve dynamic balancing quality, changes in garage balancer dynamic wheel balancing algorithms were adopted from industrial balancing methods. Garage balancing algorithms introduced in the 1990s compensated each force (static and couple) separately. Correcting couple balancing force limits individually prevented excessive counter-weight when weights were placed inboard of rim flanges. Static force limits could be minimized to lower than an incremental correction weight as a result of shifting two balance correction weight locations in their phase angles to prioritize static force elimination over couple force.
Furthermore, balancing correction could shift from two weight locations to a new single weight location to perform a dynamic, two-plane balance more efficiently with a single weight. Industrial balancing software patents such as Bridgestone’s patent EP0509507B1 are now being used in leading aftermarket garage balancers to keep up with the best balancing practices to increase efficiency and improve ride quality.
All balancers today do not provide the same quality and efficient balancing capabilities when it comes to sensitive vehicle balancing, hidden weight alloy wheels and/or very wide, heavy on/off-road applications. A garage wheel balancer has a challenge to address a dauntingly-wide range of wheels that vary greatly in mass, diameter and correction weight locations.
Outdated balancer software algorithms are easily-written and perform poorly, and up-to-date software programs are difficultly-written, however, work well and are easy to use.
Well-written software on garage balancers with automatically-adapting calculations can instantly analyze and verify the residual unbalance on the external planes of the wheel, with the purpose of:
- Displaying data that shows the relationship between traditional balancer calculations and auto-adaptive software benefits.
- Calculating the actual acceptable unbalance and bringing back the residual unbalance values to factory parameters.
- Eliminating residual static unbalance from the hidden “check spin” residual errors.
- Saving both time and excessive use of wasted counterweights.
- Shifting to a dynamic balance, single weight new correction position saves over 40% labor time on over 70% of wheels balanced.
All wheel balancers are not the same; they do not all balance with the same results. Most shop wheel balancers are not up to date in the software improvements needed to allow them to work in the most efficient manner on a wide array of today’s wheel applications to save time, perform efficiently and provide the best ride quality.
Check out the rest of the October digital edition of Tire Review here.