February 8, 2006
By Jim Kerr
Tis the season when our vehicles start to shake and shimmy. No, it’s not the latest dance – it’s something out of balance or out of alignment on your vehicle. Rough winter roads, slushy snow and cold weather all create conditions where problems occur more frequently. Often, city drivers may not notice a problem for many days. Then they drive the vehicle at highway speed and it begins to shake.
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Sometimes the shakes begin after the vehicle has been parked or driven through deep snow or mud. Often, it is caused by ice, snow or mud trapped on the inside of a wheel. The heavy weight throws the tire out of balance. Taking the vehicle to a wand-type car wash and cleaning the wheels thoroughly may be all that is necessary to fix the problem. It can take some time to wash the wheels in freezing weather. The thick metal wheel and heavy rubber tire take a while to warm up before the ice can be washed off.
Other times, a vibration starts after the vehicle has bounced through a pothole. A bent wheel may be causing the vibration, but also look for missing wheel weights. Clip-on weights will usually leave a mark on the wheel when they come off. Self-adhesive weights will leave some of the adhesive behind. Look carefully and you may visually find the cause of the vibration.
When you get tires balanced, a technician will spin them on an automatic balancer. The machine measures the amount and position of weight that needs to be added on both the inside and outside edges of the wheel. This is called dynamic balancing. Static or stationary balancing positions weight on the wheel opposite the heavy spot, but this doesn’t work well on today’s wider tires. Dynamic balancing positions weight on both sides of the wheel to balance it side to side as well. Most tires will be balanced with 3 to 4 ounces of weight although sometimes a tire may take more to balance it. If the tire is out of balance by as little as– ounce, you may feel a vibration on smooth highways.
Radial force variation is another cause of vibrations. This refers to variations in the flexibility of the tire sidewall. Occasionally, incorrect tire construction can cause this variation in flexibility. This will be noticeable as soon as the tire is installed and the only repair is to replace the tire. Good tires can develop this problem if operated at low pressures or suffer an impact that can damage tire sidewalls. Again, the only repair is to replace the tire.
Water inside a tire can cause a vehicle to shake. The tire can be balanced with the water inside, but when it stops spinning, the water is distributed differently and the tire is out of balance again. It’s not common to get water inside a tire, but it is possible. Water may enter when air is put in to the tire if the air compressor pressure tank isn’t drained of water regularly.
Slippery, icy streets make it all too easy to slide into a curb. Damage may not be obvious, but you may have bent parts. Even aluminum alloy wheels can be bent in the centre without any marks or damage visible to the eye. The wobble or run-out of the wheel at the outer edge should not be greater than about .75 mm or .030 inch. Accurate tools are needed to measure this small amount. Run-out greater than this can cause vibrations.
Even if the wheel is good, it is possible the axle shaft may have been bent in an impact. This would also cause the tire/wheel assembly to wobble, so before replacing a wheel, the wheel flange on the axle should be measured for run-out. As little as .005 inches (about the thickness of 3 hairs) run-out is enough to cause a vibration.
Keeping tires inflated properly and slowing down over rough roads can reduce the chance of vehicle damage that causes vibrations. Quality winter tires can help keep you on track instead of bouncing off a curb, but even good drivers make mistakes. Driving with a vibration can cause tires to wear unevenly and suspension joints to wear prematurely. If you feel a vibration in your vehicle, it can save you money in the long term to get it fixed sooner rather than later. Keep the shake, rattle and roll on the dance floor.