EDITOR´S NOTE: Several readers responded to dealer Don Bewley´s March 27 letter in Tire Business stating that while his company used Hunter Engineering Co.´s new GSP9700 balancing unit, which also has the ability to measure road force variation, some customers still complained of tire vibration at highway speeds of 65-75 mph. Following are excerpts from those letters containing suggestions on how to eliminate such problems.

Although Hunter´s GSP9700 balancer is very accurate in determining weight position, amount of weight needed and also checks for radial force variation in the tire/wheel assembly, it is imperative the wheel be as perfectly centered on the balancer shaft as possible.

I suggest investing in a flange plate adapter kit to help center the wheel assembly on the balancer shaft. It simulates the exact way the wheel is mounted and torqued on the hub through the wheel´s lug holes. That ensures a more accurate balance, better repeatability and helps solve vibration problems.

An adapter such as this is available from Haweka Products in Cornelius, N.C., for four-, five-, six- and eight-lug wheels.

We´ve used such an adapter for some time now and it has dramatically reduced the number of vibration comebacks resulting in more satisfied customers and greater profitability.

Ron Huber
Manager
Michel Tire/Don Olson Tire
Cincinnati, Ohio

Unfortunately, Mr. Bewley´s letter did not provide enough information to pinpoint the exact solution to his vibration problem. Therefore, I can only offer some basic tips:

1) Hunter´s GSP9700 is a great machine, but it only will do what it´s told to do. Therefore, be sure that you´re centering the wheel assembly in the exact same matter it centers itself on the vehicle.

2) Is the wheel hub centric or bolt centric? If it´s hub-centric, make sure the mounting is from the back side.

3) In the event you have a bolt-centric wheel setup, place a tire dial indicator against the tire while still on the balancer. Take four readings at equal points marking the tire as it goes around. Place the tire on the vehicle, center and tighten the lug nuts with enough torque to keep it tight. Place the dial indicator on the tire and rotate it to each of the four points. Check your reading against what you wrote on the tire.

If you´re lucky, they will be the same. If not, reposition the assembly on the hub until you end up with the same readings.

Make sure you balance using the two-plane (weights on both sides) method.

5) If the vehicle in question has rear brake drums, have you checked the balance on them?

6) Check the axle and hub flanges for out of roundness. Anything over 1.5 thousands lateral runout (depending on the vehicle) could throw the assembly out of balance.

7) If the vehicle in question is front-wheel-drive, does the vibration change or even disappear under deceleration or acceleration. If so, there might be a motor-mount problem,

You indicated that 16-inch tires are causing most of the problem. I can only assume you´re talking eight-hole rims for light trucks. If this is the case, make sure you use the Dually spacer and back cone if possible.

And in answer to your last question, yes it is an industrywide problem. The biggest reason is lack of knowledge and understanding about balancing and the relatively high turnover in shop personnel.

If none of the above suggestions fix your problem, contact your Hunter representative or contact me directly. I´ll be glad to assist.
Dennis R. Franklin
Manager
Franklin Tire & Suspension
Yuma, Ariz.

We currently work with three machines. One is close to six years old, another is about seven years old and two men I work with, who have been at my store for nine and 13 years, said the third machine was here when they started.

I believe the problem described in Mr. Bewley´s letter is caused by operator error.

Our machines calibrated once a year by a qualified person. The only time we have vibration complaints is during certain times of the year and dealing with custom wheels.

We usually correct the problem on the rare second attempt. But if the problem still isn´t solved, we will use hub centric rings (in the case of a custom wheel).

Brian Young
Sales and service
Les Schwab Tire Center

Madras, Oregon

As for Mr. Bewley´s question concerning whether repeated complaints of vehicle vibration at highway speeds is a common problem throughout the industry. The answer is absolutely yes.

The source of the problem is not the balancer, faulty tires, cheap rims and not the service technician. The problem is the cone method in which the wheel is not centered and torqued on the balancing unit the way it will be centered and torqued on the vehicle. Period.

Several changes in the automotive industry are causing major issues with respect to smooth vibration-free vehicles:

1) Lighter vehicles,
2) More sensitive vehicle suspensions, 3) Growing SUV and light truck markets
4) Taller and wider wheels, and
5) Custom alloy wheels.

All these changes can be overcome using the proper flange plate adapters to center and torque the wheel correctly on the balancer. Proper centering solves vibration.

As opposed to balancing the wheel with a simple cone, which inherently causes the wheel to tilt and move off center from the balancer shaft, Haweka Flange Plate adaptors correctly center and torque the wheel on the balancer. This results in a perfect, vibration-free ride. Haweka Flange Plate Adaptors are available for all wheel balancers.

Scott A. Lepper
Regional manager
Haweka Wheel Balancing
Cornelius, N.C.

One problem is that no specifications have been published for use with the Hunter GSP9700 Roadforce Variation machine.

As a result, our company uses the following ``word-of-mouth´´ specs (maximum tolerances in regard to road force variation) based on discussions with Hunter sales reps and other users of the machine:

*18 lbs. (force variation as the tire rotates against the drum) in the case of passenger tires;
*24 lbs. for P-metric light truck tires; and

*32 lbs. for other light truck sizes (load range C through E).

Dick Keller
Owner
Keller´s Tire
Fort Walton Beach, Fla.