Why do worn-out tires result in wobbly rides?

Our tech guru has the answer
by Ferman Lao | Jul 23, 2011

Hi, Ferman!

My family owns a 2009 Hyundai Tucson 2.0 CRDi. My usual speed whenever I cruise along NLEX is 140kph to 160kph. But last week, whenever I tried to speed up to 120kph, the steering wheel and the front wheels are shaking, or more like vibrating. The wheels are stock Bridgestone Turanza and they are already  pudpod. Do these worn-out wheels have anything to do with the vibrations? Your answer will help a lot.

Thanks and more power!

Gabriel

Hi, Gabriel!

Your assumption is generally correct. What happened is that the mass on your tires is no longer evenly distributed across its surface and it needs to be balanced.

Unbalanced rotating masses produce a wobble on the rotating mass. In the case of your tires, the wobble is felt and perceived primarily as vibrations felt through the steering wheel once the vehicle reaches a certain speed. This can be from as little as 80kph to as high as 140kph on some wheel-and-tire combinations. The vibration normally goes away once the speed at which it is felt is exceeded, but that doesn't mean it's no longer wobbling. Apart from the discomfort, the increased vibration can also accelerate wear on your car's other components that are affected by the vibration--parts like wheel bearings and steering components, for example.

When tires are manufactured, they are inspected and checked on static and dynamic balancer machines. Tires that don't pass are rejected outright and those that make it on to our cars are products that have very minimal irregularities wherein each section of the tire is equal to every other section in their mass distribution across the tire.

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The tires that are mounted on our vehicles' wheels are then checked for balance again to minimize the vibration and oscillation felt on the vehicle and through the steering wheel. If there is an imbalance, a counter weight equal to the amount of weight that's causing the imbalance is attached to the wheel and tire combination opposite the location of the imbalance. This can be as little as half an ounce. The effect of slightly unbalanced tires can give cars a poorer ride quality that can result in passenger discomfort. This is why every car that comes out have all wheels balanced.

Over time as our tires go through their service life and are slowly worn down, everything they encounter on the road will eventually affect their balance. A skid, for example, would eventually flat-spot a tire if it keeps happening at the same relative spot on the rubber. When it does, not only will the tire be unbalanced, it will also have a flat spot that is felt when the vehicle manifests a slight up-and-down motion at low speeds.

Poor inflation can also affect tires as it leads to uneven wear. Consequently, the mass across the tire will also become uneven.

Keeping your tires inflated based on the manufacturer’s recommended pressure not only prevents this from happening but also helps you get better fuel economy. Periodically inspecting your tires for nails, screws or other sharp objects that may possibly lead to tire punctures, gives you the opportunity to remove foreign objects such as pebbles and whatnots stuck in between your tire treads.

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Keep your wheels properly aligned and camber adjusted. This helps prolong the life of the tire and helps reduce the need to frequently have your tires balanced. Essentially, anything that keeps your tires from wearing unevenly will let you avoid unbalanced tires.

Have your tires balanced every time they are dismounted from the wheel, even if they are correctly clocked when they are reinstalled. It's cheap insurance against uneven wear.

Finally, have both front and rear wheels balanced as any imbalance on one tire will pass on unusual loads to the other tires, which will eventually result in uneven wear.

Regards,

Ferman Lao
Technical Editor

P.S.
You do know that speed limit in NLEX is 100kph, right?

I personally don't agree with it. Cruising at anywhere from 80kph to 100kph doesn't require too much focus and for most people, attention tends to wander to the point that there is a big risk of falling asleep at the wheel. However, in these times of high fuel prices, the current speed limit range is the best compromise of pace and fuel efficiency. Observing it would do your pocketbook a favor. Then, you can use the money you saved from being economical by driving within the speed limit to buy a track car and unleash the speed demon in you at Clark International Speedway.

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