Keeping Things in Balance with Hunter Engineering

Your passengers are questioning whether you’re having trouble affording your car payments, and thinking they must be joking, you ask, “Why?” Their response comes as a bit of a shock, “Because it feels like your car is trying to shake the loose change from my pockets!”

The problem started and grew so gradually that you didn’t even notice, but sure enough, now that you’re actually paying attention to the vehicle’s ride characteristics, you do notice a rather unpleasant vibration. Where’s it coming from? Looks like it’s time for a trip to the tire shop.

The burly gentleman with the bushy mustache who’s standing behind the local tire shop’s counter diagnoses the problem before you even finish telling him the situation. “Yer tires need to be balanced,” he says. “It’ll be forty-two dollars and we’ll have ya’ outta’ here in ’bout an hour.” You pass the time in the “quaint” waiting room, leafing through a two-year old copy of Field and Stream, and sure enough, your car’s ready to go in no time.

Problem solved, right? Well, maybe not entirely. How well do you know your tire shop and its employees? Are the technicians ASE certified? Do they have additional specialty training? Are they using equipment that’s state of the art, or does the shop bear a striking resemblance to Gomer Pyle’s garage? These are important questions, and they could make the difference between a repair that’s fixed right the first time or the beginning of a long and stressful repeat problem relationship.

Roadfly was fortunate to have spent a full day at the world-renowned Hunter Engineering headquarters in St. Louis, Missouri, where we met with the folks who know more about vehicle dynamics than Brett Favre does about football. They gave us the full tour, and we were able to pick their collective brains about the proper way to mount and balance a wheel and tire. What they told us might surprise you…let’s read on.

“Most people don’t realize that both the wheel and tire have high and low spots,” began Dave Scribner, Product Manager of Hunter’s wheel balancers, tire changers and brake lathes. “The general notion is that a tire might have a high spot, so people pound weights on a rim to counterbalance that high spot.”

Denny Bowen, Hunter’s Director of Product Management chimes in, “Static balancing has long been a standard for balancing, but a true two-planed, dynamic balance will really make a difference to any vehicle.” We’re standing in one of Hunter Engineering’s shop facilities, surrounded by hundreds of thousands of dollars of world-class automotive equipment.

Scribner leads us to one of Hunter’s finest pieces of equipment, the Hunter GSP9700. As he places a wheel and tire assembly on the machine, he talks about the additional factors that play a key role in proper tire and wheel balance. “You can have a wheel that reads completely balanced and still have a vibration. That drives customers and technicians nuts,” he says with a bit of a knowing smile and as he places the wheel on the machine, we get the impression that he’s done this a time or two before. “Wheel force variation can cause a vibration that most balancers won’t detect, and it’s one of the main reasons drivers feel a vibration in their vehicles.”

Jim Huhn, Director of Marketing and Communications for Hunter Engineering adds, “With today’s extremely modern and well engineered suspensions, drivers can detect vibrations that they were never able to detect before. It’s something that can be both a blessing and a curse.”

We watch as Scribner attaches Hunter’s exclusive “Inflation Station” device to the tire’s valve stem. The Hunter GSP9700 is capable of determining the proper tire pressure for a particular wheel and tire combination, provided the operator supplies data about the vehicle from which the wheel came from. The machine detects that this particular tire is under-inflated by almost 7-PSI. It automatically corrects the tire pressure.

With the tire properly inflated, the machine starts itself up and attempts to determine the wheel’s state of balance. Within a matter of seconds, it’s determined that the wheel is severely out of balance and that it’s suffering from excessive wheel force variation. Scribner makes a few marks on both the rim and tire with a grease pen, then removes the assembly from the machine.

“What’s happened here is that the rim has a high spot, as does the tire. To complicate matters, the tire has its own ‘stiff and weak spots.’ As the assembly rotates, there are various forces working against the tire. Air pressure is supporting the tire, while the road surface is pressing back against the tire. When there’s a stiff spot, it can act like a ‘hard spot’ and cause a vibration.”

Bowen seems to be reading Scribner’s mind because he continues, “Dave is going to deflate the tire, break the bead and spin the tire so that the high spot on the rim matches with the low spot on the tire. That should correct the problem.”

We follow along with Scribner as he rolls the wheel assembly over to another one of Hunter’s fine pieces of machinery, the top of the line TC3500 Tire Changer. Having spent many years mounting and balancing tires myself, I was awed by Hunter’s latest and greatest equipment. The attention to detail, the quality construction and the amount of computerization was nothing short of amazing.

As Scribner deflated the tire and broke the bead, we arrived at a somewhat startling discovery. The wheel that we had been working with was a 19″ magnesium alloy wheel from a Ferrari, and much to our surprise, the inside surfaces of the wheel were heavily gouged and scraped. “That’s from a technician using a shovel breaker improperly,” said Scribner rather nonchalantly.

Apparently the Hunter folks were well aware of this, and explained that on traditional tire changers, a metal shovel squeezes the tire against a nylon block while breaking the bead of the tire (that’s where the tire mates to the rim to create an air tight seal). If the operating technician isn’t careful, the shovel will drag across the inside of the rim. “The scary part of this is that the customer would never know it happened, but anyone with a basic understanding of chemistry will know that magnesium doesn’t like water,” says Bowen, “And the inside of tires can collect moisture and water rather easily.” The result could be catastrophic were the damage and moisture great enough – the wheel could easily collapse at a very inopportune moment.

“We can build the greatest equipment in the world,” says Jim Huhn, “But if the tech’s don’t know how to use it properly, it won’t matter how good our equipment is. We place a lot of emphasis on proper technician training, and offer classes here on a regular basis (for industry technicians).”

Within a just a few seconds, Scribner has the wheel free of the rim, has spun it to align his marks and is inflating the tire. The beads seat with a loud “pop!” and with the press of a pedal, the wheel is released from the non-marring jaws of the rim clamps. We head back over to the Hunter GSP9700 machine, and watch as Dave Scribner mounts the assembly to the machine once again.

“This is another problem for a lot of technicians,” he explains as he places the wheel on the balancing machine. “A guy uses the wrong centering cone, or manages to clamp the wheel so that it’s slightly out of square, and he’ll be chasing balance issues all day.” With the wheel mounted (square and true) to the balancer, Scribner once again checks the tire pressure and waits for the machine to properly inflate the tire. Within seconds, the air hose is removed and the wheel is being checked by the GSP9700. Bowen adds that Hunter has an optional attachment for the GSP9700 that will help to automatically center the wheel assembly on the balancer.

The machine winds down and Scribner lifts the protective lid. “We need to add three-quarters of an ounce to right about…here,” says Scribner as the machine rotates the wheel assembly automatically to the proper position. He makes a note of the location, cleans the inside of the rim (as close to the center of the rim’s width as possible, and applies a weight. He fires up the GSP9700 once again and smiles, “Perfect.”

The Hunter GSP9700 tire balancer really is a marvel of modern day engineering and Hunter has every right to be proud of it. With a large, CRT-style display, computerized menus and functions, and Hunter’s exclusive “road roller” (a drum that rotates against the tire to simulate road conditions and measure wheel force variation), the GSP9700 makes all other tire balancers look like toys.

The road roller can supply up to 1400-lbs of pressure against the tire to detect non-balance, radial force-related vibrations and is a key component to the success of the GSP9700. The GSP9700 can also determine if excessive “run-out” (effectively a side-to-side variation) is tire or rim related. But the most amazing option available to the Hunter GSP9700 (at least in our minds) is the “StraightTrak Lateral Force Measurement System.”

This incredible piece of technology can detect tire pull, and suggest the ideal corner on which to mount the wheel and tire to negate a tire pulling effect. Tire drift was one of the most difficult problems to properly diagnose, that is, until Hunter developed technology to detect and correct it. It’s nothing short of amazing. Why? Prior to this technology being made available, a technician had only a few options available to help correct a vehicle’s drifting problem – perform a vehicle alignment to counteract the tire pull, or try to guess which tire was causing the problem and then, through trial and error, place the tire in the proper location on the vehicle to correct the pull.

Neither of those options is very efficient, especially if the vehicle’s owner rotated his tires regularly. If a vehicle is aligned to correct a tire drift problem, the drift will resurface when the tires are rotated, creating a “repeat problem” for the shop and vehicle owner.

“Tire drift problems just became a thing of the past,” says Bowen. “The StraightTrack LFM system helps a lot of shops solve problems that were once nearly unsolvable.” We watched as Scribner demonstrated how compounded tire pull could result in more than 21-pounds of pull to the left in a simulated example. Jim Huhn commented, “You’d notice that sort of pull pretty quickly and most tech’s would suggest an alignment to correct it.”

Scribner then asked the GSP9700 to determine the ideal placement of each wheel and tire assembly on the vehicle, then re-ran the simulation with the proposed changes in effect. After the corrections were made, the pull force registered 2-pounds of pull to the left – an entirely acceptable figure.

Despite spending the better portion of a day with the guys from Hunter, we had run out of time and wished we could have had more time to talk tires. We finished the tour with a trip through the company’s mini-museum, and marveled at the dozens of Duesnebergs, Lincolns, Rolls Royce and other fine cars from the ’30s and ’40s. Lee Hunter, Jr. founded the company in the mid 1930s when he invented the world’s first quick-charge battery charger for automobiles. Prior to Hunter’s invention, battery charging took days – Hunter’s machine could charge a battery in just a few hours.

From there, Hunter was called off to World War II. Upon his return in 1946, his company went on to develop many industry leading products – from alignment machines to electronic, drive-on brake and suspension testers. Today, Hunter Engineering products are the finest in the industry.

Of course, as the good folks from Hunter were quick to point out earlier, a properly trained technician is the key to getting the most from any Hunter equipment. So, do yourself a favor the next time you need to have your tires mounted, balanced or aligned – locate a shop that utilizes Hunter equipment, and make sure the technicians are properly trained to use the equipment.

For more information about the amazing line-up of Hunter Engineering equipment, or to locate a shop that utilizes Hunter equipment, please visit them on the web, at:

The editors of Roadfly wish to send a hearty and sincere thank you to Jim Huhn, Denny Bowen and Dave Scribner for taking the time to share their knowledge with us, and for allowing us to spend so much time at their world-class facility in St. Louis, MO.

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