Proper wheel balance plays an important role in keeping drivers safe and comfortable while driving at highway speeds. Unbalanced wheel assemblies can cause unwanted and severe vibrations that can be very uncomfortable to the driver and dangerous to everyone on the road. But what causes wheel assembly imbalances and vibrations, and how can you take care of this problem?
Why Do Wheels Need Balancing?
Despite various solutions and many technical improvements in car design, some parts remained quite the same over the past decades. One of them is the wheel.
Found on any car in the world, a wheel assembly comprises a rim and a tire. When joined up, they rotate around their center axis, which attaches to the vehicle’s axle with lugs or nuts. When a wheel assembly rotates, it exerts a centrifugal force on the axle, which is most noticeable at high speeds.
The amount of this force depends on where the exact center of the wheel assembly is. In a perfect world, the exact center of a wheel assembly would be in the exact center of the axle. This would mean the assembly could spin without vibrations at any speed, with even weight distribution on all sides.
However, the production of rims and tires does not take place in a perfect world. Even though they are both built to tight tolerances, weight imbalances are unavoidable.
Almost every rim has some imbalance or heavy spot, and so do all the tires. In most cases, these weight imbalances are very minimal. Still, even a small imbalance can create serious problems, as it compromises the exact center of the wheel assembly and causes uneven rotation. To illustrate the situation, it helps to know that just a half of imbalance an ounce at highway speed creates an outward centrifugal force equal to that of a sledgehammer.
By balancing the tire and rim combo, we cancel out the forces that cause uncomfortable vibrations and ride harshness. To balance a wheel, a mechanic will offset any imbalance by placing a counter-weight on the wheel. Spinning the wheel at high speed at the balancing machine reveals both amount and counter-weight location.
How Do Wheels Come Unbalanced?
In most cases, roads and streets we drive on are anything but perfect. Rough and uneven pavement, sunk manholes, and potholes are just some things that wheels on our cars encounter every day. The suspension travel and deflections in the tire alone absorb most of these bumps. However, if you hit a deep hole or a curb at high speed, the impact force will be too high, causing damage to the suspension or wheels.
Sometimes, this can destroy tire sidewalls and cause bulging. And if the impact is severe enough, it can even bend the rim itself. Although being very sturdy, all rims will bend or buckle at some point. Any of these situations will upset the wheel balance. As a result, you may feel vibrations at motorway speed, and your steering wheel can shake.
Besides poor ride quality, damaged wheels can also impact handling capabilities and cause uneven tire wear. And because tires need a straight surface to form an airtight seal, bent rims can even cause a flat tire.
What Kind of Rims Are There?
Most rims on cars today fall into two main categories. The first one is a steel rim, and you can find on most commercial vehicles and some cheaper family cars. As the name would imply, manufacturers make them from pressed steel plates. The main advantage of steel rims is the low cost, as they are cheap and easy to produce. Also, thanks to a more durable and resilient structure, they are less likely to bend. Stil, steel rims have downsides of their own, as they are heavier and prone to surface rust.
Alloy rims use aluminum or magnesium mixed with nickel to create a lightweight wheel structure. The lower weight of spinning wheels means better performance, improved handling, and increased fuel economy. And, thanks to various design possibilities, most car owners find alloy rims more attractive. But they are not without their weaknesses, either. When compared to steel counterparts, alloy rims are not only more expensive to buy but also require regular cleaning and special care. In addition, because the aluminum or magnesium alloy is more fragile than steel, rims made from these materials bend and crack easier.
How to Check the Rim for Damage?
If your car developed vibrations, steering wheel shaking or wobbling all of a sudden, it is likely that one or more wheels are out of balance.
To check, start by looking for bulges on outer and inner tire sidewalls, as they are a sign of a damaged tire structure. Besides causing vibration, bulged tires are dangerous as they can even explode while driving. As this might cause a severe accident, replace such tires with no delay. Also, check if the wheel balancing weight is in place. Sometimes, these can fall off when going over a big bump.
Can I Fix Bent Rim by Myself?
After finding a damaged part of the rim, you must decide whether to replace it or try to fix it. In case of steel rims, replacement can be an easy and inexpensive option, as you can buy cheap second-hand rims at salvage yards or over the Internet. And because they all look the same, you will have a wide range to choose from.
With alloy wheels, things are not that simple. For a start, they can be expensive if buying a new one. And sourcing a used one can be difficult, as wheel design depends on the model of the car and trim level. This means that a rim repair is a better option.
Choosing how to repair the rim depends on how severe is the damage. Huge dents and large deformations can cause microscopic cracks, which can lead to rim falling apart at high speeds. Because of this, look for a professional help when fixing severely damaged wheels. Rim repair specialists have both knowledge and experience to assess if wheel repair is possible and has all the tools needed for the job.
However, if the damage is small and only limited to the edge of the rim, you can try to repair it yourself. All you need are a hammer and several pieces of 2×4 construction lumber or similar kind of wood. And, if repairing an alloy wheel, you will also need a blowtorch. This is because the aluminum alloy is brittle at ambient temperature, and it could crack when hammered. Heating it to around 150 °C makes the aluminum more flexible and easier to work with.
Start by letting out the air from the wheel and removing the tire from the rim edge. Next, if repairing the alloy rim, use the blowtorch to heat-up the damaged area. As not overheating the material is important, it helps to use an infrared thermometer at this phase. Lay the wheel at a soft surface, such as an old blanket, with damaged side facing up. While standing on the wheel and holding the piece of lumber against the bent spot with one hand, hit the lumber with a hammer. You will need to repeat this several times, gradually increasing hitting force until you have straightened the bent.
As you have learned from this article, vibrations and wobbling inside the car are a sign of a wheel related problem. The wheel assembly comprises a rim and tire, which both have their own inbuilt imbalances. To overcome this problem, we add small balancing weights at specific spots of the rim.
However, bad road conditions and poor pavement quality can cause damage to the rim or tire. Not only that this offsets the wheel balance and causes vibrations, but it also affects handling and may result in uneven tire wear. Because of this, it is important to replace damaged tires and repair bent rims with no delay. And while you can repair minor rim damage by yourself, any severe rim damage should be left to the professionals.