TECH TIP Technical Index

Balancing Act

by Mike C. -

Wheel Shimmy Ė I

There is perhaps nothing much more aggravating than out-of-balance wheels on your VW. The entire car may look like a million bucks and the engine may be the fastest thing on the planet, but if your wheels are out of balance, it will ruin the whole driving experience. Beetles with their lightweight front ends are particularly susceptible to imbalance and Super Beetles are notorious for making owners pull their hair out and eventually give up. Iím here to tell you that it doesnít have to be that way, and even Super Beetle owners can have a smoothie and you can keep your hair in as well. I wonít go through the step-by-step procedure as far as the actual balancing goes since most folks donít have the equipment (sometimes very expensive) to properly balance the tire/wheel assembly, but I will list the causes and solutions to each problem the best way I know how. I will be focusing on the old air-cooled VWís but you can apply much of the theory to all cars out there.

Rotating Assembly

Iíll start by talking about your rotating assembly. This simply means the tire/wheel combo and the brake rotor and/or drum. After all, if something isnít right about them, they will transmit that problem all the way through, no matter the condition of the rest of the suspension.

  • Drums & Rotors - Begin by making sure your drums and rotors are straight. I mean, take the wheels off and mount a dial indicator to something solid, position the indicator contact point on the surface where the wheel actually mounts (donít put the contact point in-line with the lug bolt holes) and rotate the disc or drum. You ideally donít want any needle movement (called runout) on the dial indicator. You probably will though, and limit this runout to 0.002" inch. This may not sound like much, but 0.002" will become a lot bigger number by the time you get to the outer edge of the tire when it is mounted on the car. If you have more than 0.002", take the disc or drum to a machine shop that has a lathe and they can get this surface true. You may even be able to get your automotive brake shop to do this for you. Do this for all the discs and/or rotors.
  • Wheels - Now turn to the tire/wheel assembly. Mount them back on the freshly-machined brake discs or drums. Spin them and watch to see if the rims are bent. You can take the dial indicator and do the same thing you did with the brake drums, only make sure you donít scratch the rim with the indicator contact. Make sure you measure at the outer edge of the rim. Again, I donít like to see any runout here (no more than 0.002" to 0.003"). If you didnít use a dial indicator, watch carefully. If you can visually see that the rim is bent (wobbling side-to-side) then that is too much. Donít let the motion of the tire fool you. If the rim appears to be going up and down (radial runout), then either the holes in the rim were drilled off-center, the holes in the brake drum were drilled off-center, or in the case of an aluminum rim the tire mounting surface may have been incorrectly machined. Most likely, this type of runout is caused by the lug holes in the brake drum being off-center. There isnít much you can do about radial runout except to try different drums or rims. Whenever possible, try to stick with German brake drums or rotors, as the Brazilian and Mexican-made units tend to be of much poorer quality. I went through this before, and have seen as much as 0.010" or more runout in these parts. Aluminum rims are far less likely to be out-of-true than steel rims, as the aluminum rims are machined to size. Again, beware of the steel rims, as you canít get new original-style steel wheels from der Motherland anymore. There are shops dedicated to building and straightening steel wheels, but there are none locally that Iím aware of.
  • Tires - Tires are the last things between the road and you, so runout is critical in these, too. You check these while checking the wheels, and in the same way. The tires ideally should have no runout, both lateral (side-to-side) and radial (up and down). Youíll have to do a visual check to verify this, as a dial indicator would not work well on a tire. Again, if you see the runout, itís too much. All you can really do with tires is make sure you buy a reputable name brand if possible, like B.F. Goodrich, Goodyear, or Michelin. If you are sticking with stock 165SR-15ís, you wonít likely find them in any of these brand names. Just ask around with fellow VW owners about what they are using and go with your gut. You can see from what you have to do with the possible problems of all rotating components that all the runout problems could "stack up" and cause big problems that youíll never solve with mere balancing. In fact, if your rotating assemblies are free of runout, you can get by with a lot more suspension wear since a worn suspension will actually magnify runout problems with wheels and tires.

Weíll finish up our balancing act next month with suspension and tire balancing.

Your VW Maniac &Tech Specialist,
Mike C.

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