What they are
Centramatic Wheel Balancers use a very interesting concept to balance
the tyres and wheels. Truckers and big-rigs have used these types of wheel balancers for a long time but Centramatic has designed a variety of sets to fit light-trucks and certain SUVs. The Centramatics are 4 discs that go behind each of your tyres and mount to the hubs. The discs have rings at the borders that are filled with steel shots in oil. They work by making use of centrifugal force to distribute the weight inside the rings. This compensates for the dynamic tyre balance as the unit rotates. For example, let us assume that there is some excess weight present at a certain point of the wheel/tyre combination. As the unit rotates, this causes an acceleration of the wheel/tyre unit in the direction of the heavier spot. The steel shots (suspended in oil) in the ring of the disc will flow away from this acceleration until there is equilibrium. This centrifugal force holds the weight (i.e. steel shots) against the outside of the ring. The ring is located inside the rim; hence it is closer to the center of the wheel.
These types of balancers require a certain speed (usually about 30 mph) to be attained to work. This is not a problem at all because below that speed, tyre balancing and vibration is normally a non-issue.
Our experience with the Centramatics
Our Centramatic Wheel Balancers came in a box with the four discs, an instruction sheet and warranty/registration card. Each of the discs weighed about 5 pounds each. On the outer circle of the disc, there was a plastic ring, which contained the heavy steel shot in oil.
We tested the Centramatics on my 1985 Toyota 4Runner 4x4 running 35x12.50x15 BF Goodrich tyres. Installation is so simple that even a 12-year-old child could do it (although I would caution against it). Simply loosen the lug-nuts slightly, jack the vehicle up, remove the lug-nuts, pull the wheel off and slide the Centramatic Wheel Balancers over the hub. Then, re-install the wheel and tighten down all the lug nuts to spec. Centramatic claims that it is not necessary to have your wheels/tyres balanced prior to using their Wheel Balancers but it is advised to for optimum performance and a smooth ride.
Once under way, I noticed an interesting sound coming from the Centramatics the first time I drove with them on. This only occurred at slower speeds. I attribute this sound to the steel shots rolling around the inside of the ring. At faster speeds, they seem to quiet down. Since my BF Goodrich tyres were already balanced, they rode pretty well to begin with but with the application of the Centramatics, there was a noticeable additional smoothness. While the Centramatics had done their job effortlessly on these radial tyres, I decided to test them out a little more extremely by throwing on my other set of tyres, which were bias-ply 35x15.50x15 Super Swamper SX off-road tyres. These heavy bias-ply tyres have the reputation of being extremely hard to get balanced perfectly. This should be a challenge for the Balancers.
While the Swampers already had some wheel-weights on to try to balance them, there was always still quite a bit of vibration whenever I drove on them. The shop that had mounted them had told me that no matter what they tried, they could not get the Wheel Balancing Machine to "zero-out" and balance the wheels/tyres perfectly, regardless of how much weight they stuck on. The combination of the shop-balanced Swampers (that still vibrated) and the Centramatic Wheel Balancers made a huge difference at highway speeds. The almost unbearable vibrations that use to shake and rattle my truck is now a gentle shudder...quite the difference!
Used with regular-sized radial tyres, the Centramatic Wheel Balancers should provide you with an extremely smooth ride and will also increase the life of your tyres. My recommendation the next time you buy new tyres is to have them mounted up on your rims (but not balanced). Try running them with just the Centramatic Wheel Balancers and if they ride smoothly (as they should, if the new tyres are not too out of round and are within the Centramatics' capabilities), then you just saved yourself some money. The Wheel Balancers will be money well-spent because of the money you save from not having to shop-balance your tyres as well as the general increased tyre-life. You will also have a more comfortable smooth ride all-around all the time.
Currently, Centramatics are available for trucks, tractor/semi trailers, coaches, buses, delivery vehicles, motor homes, trailers, large pickup trucks, Jeeps, SUVs and police cars. They also custom build for application-specific centrifuges. For more information and to purchase the Centramatic Wheel Balancers, please go to www.centramatic.com.