If it's not too bad, you can sometimes rotate the tires, since the front tires will usually be worse than the back. If not, the flat spotted tires will have to be replaced. Again, tires shakes are very consistent, they will always shake at the same speed s. So if your tires have passed the first test, you can often tell what kind of a problem you have by the speed that the vehicle shakes or wobbles at.
Though this can be caused by a severely bent wheel, or severe cupping, the most likely cause is a separated tire. Separated tires are a very serious safety issue, and must be dealt with immediately, since it's just a matter of time before the tire blows.
A tire failure of this type almost always causes damage to the vehicle, but that's nothing compared to the many fatalities that are cause by this. Do not put this off! To test for this, simply drive the vehicle for a short distance at 15 to 20 mph. If the bad tire is in the front, the steering will rock back and forth, if it's in the rear, the rear of the car will wobble in a similar manner.
If you can find out which tire is separating, it may be best to put the spare on right then and there, so that you can actually make to the tire shop. The tire with the problem will have a bump along the tread face which is visible, or you can feel it with you hand. If you use the hand test, the tire should have a uniform profile except for the place where the separation is, which will be distorted, usually with part of the tread pushing away from the tire, ie. The pictures below illustrate this: The picture on the left is the "normal" side of the tire and is pretty uniform, while in the picture on the right, you can see the "bump" where the tire is separating.
This separation is pretty large, but they will always start out smaller, so you should look for even small distortions in the tread face. The most common cause of vehicle wobbles in this speed range is a bent wheel or mildly out of round tire. Transmission and drive line issues can also show up in this range, but tires are the first thing to check. Unlike the low speed wobble, this is usually not a safety issue.
In many cases, the tire can be better matched to wheel high spot to low sport, or vice versa and the wobble can be eliminated.
This is where the "Road Force Balancer" comes in, and we'll explain that at the end of this article. If that doesn't work, the problem tire or wheel should be replaced. If the tires and wheels spin true and you still have a problem, then you should have a mechanic look at the vehicle.
The most common cause of vehicle shakes at 50 mph or higher is tire balance. Again, transmission or drive lines can cause this, but the tires should be the first thing to have checked. A tire or wheel that is slightly bent or out of round can also be a factor here, and this can be checked while the tire is on the balancer. Obviously, the first thing to check is the tire balance, and only after the tires have a clean bill of health should you take it to a mechanic.
Over the years there have been various methods of balancing tires. Without going into the history, we will simply explain the types in common use today, and when you would use one method or another.
If you think of how your tires are mounted on the car, static balancing refers to balancing the tires only from up to down, or across the tire.
In most cases, this works pretty well. Though not used very much these days, bubble balancers and "on the car" balancers can only do this type of balance. Also, if you don't want weights on the outside of your wheels, you will often get this type of balance.
This is also called "single plane" balancing. Dynamic balancing will not only balance the tire from up to down, but also from side to side, and is often called "dual plane" balancing.
This can only be done by modern "computer" balancers, and requires weights to be put on both sides of the wheel. However, if you want a good balance, and either your wheels won't take weights on the outside, or you just don't want the see them, you can often still have a two plane balance.
Many modern vehicles are designed with "positive offset" wheels, which means that the bolt face is pushed towards the outside, so most of the wheel is inboard, towards the vehicle.
In this type of wheel, it is easy to put the outer weights just behind the face of the wheel and the inner weights on the inside edge. This allows for a proper dual plane balance and is the preferred method apart from weights on the outside edge. However, if you have a standard offset bolt face in center of the wheel or a reverse offset wheel bolt face toward the inside edge of the wheel , then you really can't get a good dual plane balance without putting weights on both sides of the wheel.
Now to dynamic balancing. Increasing a wheel's width creates a balancing conundrum. It potentially moves the imbalance and counterbalance points further away from the wheel's centerline.
A counterbalance added to the wheel's backside to counter an imbalance at the wheel's face would statically balance the wheel; however, that likely won't prevent a shake at high speeds. In fact, doing that might actually make the wheel wobble as if it were mounted to a bent shaft.
Imagine a driveshaft to understand why. If the tailshaft end were imbalanced at 12 o'clock then a counterweight added to the yoke end at 6 o'clock would statically balance it.
However, as momentum increased each end would follow its respective imbalance point. In fact that's how the earth spins: it wobbles. Now imagine if your wheels spun that way. Summary: Static balances almost always work adequately for narrow wheels; wider wheels almost always need a dynamic balance.
On-car balancing addresses imbalances throughout the entire rotating assembly, tire, wheel, brake, hub, and all. In fact, it'll eliminate the imbalance created by removing a counterweight from a Buick drum. This type of balancing has shortcomings: it balances only statically so it's most suitable for narrow wheels.
And it requires that all parts index so they go back together the exact way every time. But the worst shortcoming is availability; the machines and their operators got rare a long time ago. But balancing beads eliminate all but one of those shortcomings.
They're just tiny balls usually ceramic that freely roll around inside the tire or, if equipped, tube. As the tire spins it generates centripetal force that holds the beads along the inside of the tire or tube. Ultimately the beads gather at the point opposite the imbalance until they amass enough weight to offset it. At that point the wheel rolls true and the spare beads just distribute themselves equally along the inside of the tire.
When the vehicle comes to a stop they all come crashing back down to the bottom. Like on-car balancers they affect only a static balance; however, they're available everywhere mail order , don't cost much, transfer to new tires, and constantly correct imbalances over the life of the tire.
Imbalance that can be cured by static balancing. Vibration of the wheel while driving is shown at the right. At low speeds a wheel rotates around its principle axis of inertia, its axle blue line. But at speed a static imbalance can force the suspension to deflect so the wheel can follow another axis called the axis of rotation red line. Swing a bucket to experience the force a static imbalance can generate.
Imbalance that can be cured only by dynamic balancing. Vibration of the spinning wheel shown at the right. Imbalances away from the wheel centerline can generate an axis of rotation red irrespective to the axle itself blue.
When the axis of rotation is close to a wheel's centerline left the wheel won't wobble. But moving the imbalances apart right moves the axis of rotation further away from the centerline and a wobble is likely to follow. A narrow wheel balanced statically can have all of the counterweights on one side usually backside. But a wide wheel balanced dynamically requires weights on each plane with an imbalance, the face if one exists there. Imbalanced hubs, drums, and rotors nullify a wheel's balance.
Buick drums' weights may not be handsome but they're not as ugly as the shake that results from removing them. Most Buick-style drum covers aren't balanced. Personal experience indicates that some aren't even round. No amount of balancing will matter if a wheel rolls like an egg. Chris Sage at The Wheelsmith noted a few things that prevent a wheel from rolling true.
Because most wheels center on the lug nuts on older cars he recommends seating nuts by hand before tightening them. And some of us are responsible for a potentially ill fit. It's popular to mount Buick drums to old Fords. However, early Ford disc wheels with the 5. Because most of the Buick-style drum covers maintain the same external dimensions they too suffer the same problem as I discovered on my own car. If the wheel doesn't seat properly it possibly won't roll true. If the spark plugs are okay and their connections seem sound, then check your air filter next.
There are a few parts on front disc brakes that need to be replaced every so often — namely, the pads and rotors. The rotor is the round metal disc that attaches to the wheel. Over time it can become warped from heavy wear and tear. There are pads that press against the rotor in order to slow down the vehicle and these pads need to be a certain thickness in order to work properly.
If the pads have become too worn, it can cause the vehicle to vibrate. The caliper helps to squeeze the pads against the rotor to slow down and stop the vehicle. All vehicles vary on timelines for when brakes need to be replaced. On average, they should be replaced every 50, miles but many makes and models can last longer. In addition, whenever you get an oil change, have your mechanic visually check the condition of your pads and rotors.
These professionals can give you a better idea of when replacement is necessary. Most vehicles have 2 axles — one that connects the front wheels, and another that connects the rear wheels. Vibration can occur if either of the axles is bent or dented — which can happen in an accident or other mishap with the road — and vibration will usually increase in intensity as you accelerate if the problem is related to the axle.
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