High-Speed Problems

High-Speed Problems
Eliminating vibrations on vehicles like this Porsche is a must. (Photo: Porsche)

Eliminating vibrations from low-profile tires can sometimes be a real challenge.

While it’s business as usual to balance the wheels for the family SUV, a vehicle that’s made for more adventure may be more challenging.

According to Ron Racine, Training Manager for North and Latin America, Snap-on Equipment, balancing the wheels for a high performance vehicle starts with the right machine. “Your normal balancer can do weight or mass,” he says. “But they’re blind, they cannot see the shape of the wheel, so you need a machine that can handle weight and shape, or you need a run-out machine. These can measure the eccentricities of the assembly with a laser ray or a camera, or even a roller or gauge.”

Standard passenger cars with a high aspect ratio, like a 65 or 55 series, will absorb a lot of the impact caused by vibration. However, lower profile tires, such as those found on high performance vehicles, like a 35, 40 or 25 series, have virtually no sidewall. “That’s when shape comes into play,” explains Racine. “You have vibration that’s caused by mass, which is when the wheel is out of equilibrium, but it can also be caused by shape, where the wheel is not round.”

Wheel vs. tire

When a wheel is not round, the challenge is to determine whether it’s the wheel that’s causing the eccentricity or the tire. “From experience, in 90% of cases, it’s the tire that’s not perfectly round,” says Racine. “If it’s a new wheel, it’s rare for it to be out of round more than maybe a millimetre. Once it’s been installed and driven through some potholes, now it may have a shape problem.”

On a high performance vehicle, which is driven at higher speeds, the shape really comes into play. “If it’s shape, vibration will kick in at about 120 to 140 kilometres per hour,” says Racine. “If it’s weight, it’ll kick in at around 90 kilometres per hour.”

Machines that can read the run-out will read the run-out on the wheel and on the tire simultaneously but separately, and the machine will tell you what amount is caused by the wheel versus the tire. “If it’s 95% in the tire, then that’s a bad tire and you just need to replace it,” says Racine.

This equipment is expensive, and Racine estimates they cost from about $12,000 to $25,000, but the return on investment is less than a year. Also, the equipment manufacturers will provide the advanced training for techs.

Following OEM process

Grading tires, making sure they’re matched to the right rim, and following OEM process for mounting and installing tires also go a long way to eliminating vibration.

“Match mounting the tires is done at the OE level, whether it’s a Chevy Cruze or a Corvette,” says Dino Hatz, Business Development Manager at Hunter Engineering Company. “What changes is the allowable tolerance. Our RoadForce balancer can copy what the manufacturers are doing and applying it in an aftermarket situation.”

Each individual tire has its own personality, Hatz explains. “They’re not solid or perfectly round objects. They have a substructure that supports the vehicle through the flexibility in the sidewall. The spring rate or flexibility can vary around the circumference of the tire.”

He also recommends using the correct tire lubricant during the mounting process. “It’s critical,” Hatz says. “When you inflate the tire, you want it to properly seat itself to the rim.” Tire lubricant should be applied to the beads of the tires as well as the wheel. It should remain slippery during the mounting and inflation process, but it should be dry by the time the vehicle is put back on the road.

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