Why do worn-out tires result in wobbly rides?

By Ferman Lao
 

Hi, Ferman!

My family owns a 2009 Hyundai Tucson 2.0 CRDi. My usual speed whenever I cruise along NLEx (North Luzon Expressway) 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.

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 imbalanced, 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 they lead to uneven wear and 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 while your doing your inspection.

Keeping your wheels properly aligned and camber adjusted also helps prolong the life or 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 have tires frequently balanced.

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 in NLEX the speed limit 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 being doing 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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Filter comments by:
  • GBfive Jul 24 2011 @ 05:39am
    ff-up question: is it true that an old but unused tire(8y/o spare tire inside the trunk) will also turn oblong?
  • 17Sphynx17 Jul 24 2011 @ 07:24am
    I actually had an experience with our old tire before. It wasn't worn out as we still had a good amount of tread to it and very visible grooves that provided the grip. However, i was in fact around 4 years old since the time we bought it.

    I drove the vehicle and parked it near the curb, however, it got a little too close and nudge the sidewall of the tire against the curb's face. Lo and behold, the tire blew.

    My assumption to the occurence is that our tire lost most of its elasticity that is what caused the rupture when pressure was directly applied onto the sidewall.

    It is still rubber which I believe means it does lose its elasticity over time.

    Am I right in believing so?
  • aargh Jul 24 2011 @ 08:25am
    Buti di ka pa nahuhuli sa nlex for overspeeding..
  • Ads Jul 24 2011 @ 09:39am
    I've seen Mitsubishi Montero Sports clock at 170 kph on SCTEX and NLEX.
  • 997 GT2RS Jul 24 2011 @ 09:49am
    Driving a car with worn out tyres at high speed is just asking for trouble. I have seen a few SUV's and other cars rolled caused by blown tyres.SUV' s are the worst because of it's high centre of gravity.
  • maranello_5775 Jul 24 2011 @ 10:32pm
    bilis talaga mapudpod ng stock turanza tires ng tucson tsktsk
  • Danny Ricohermoso Jul 30 2011 @ 10:02am
    It is the likes of Gabriel who worries us responsible drivers/motorists that we see often not only at NLEX. Also at SCTEX and SLEX. Or if they see an opening, will zoom like crazy (mostly just for show).

    Not minding the law and the others around them. And worse, some drivers like him drives like mad even if it is raining hard and/or the visibility is poor.

    Hope you will learn your lessons early. Not after something worst happen to you.

    Thank you Mr Lao for reminding Gabriel and his bunch to respect the law and the benefit they will get from it. At least we could drive calmly if one less Gabriel will be away from this group.

    To Gabriel, no harm intended. Just watch your speed and manners on the road.
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