Wheel balancing (also known as ‘tyre balancing’) is a tricky task, and is the process of equalizing the weight of the combined wheel & tyre unit, so that it spins in a uniform fashion / smoothly at high speed revolutions. ‘Balancing’ involves putting the wheel & tyre unit on a balancing machine, which centers the wheel and spins it to determine where the weights should go.
Although of high manufacturing quality, it is inherent in their nature that wheels and tyres are rarely exactly the same weight all around. The wheel’s valve stem hole, for example, removes a small amount of weight from that side of the wheel. Tyres will also have slight weight imbalances, whether from a joining point of the cap plies, or a slight deviation from being perfectly round – believe it or not, that kind of perfection is nigh-on impossible to achieve due to the nature of the product and the manufacturing process. At high speeds, what seems to be a small, minor imbalance in weight can easily become a large imbalance in centrifugal force (rotational force of the wheel), causing the wheel & tyre to spin with a kind of “drunken” motion. This usually translates into a vibration in the car, often felt at the steering wheel, as well as clearly visible irregular tyre wear which can be both dangerous and costly.
Traditional Spin Balancing – the most common method:
To balance a wheel and tire assembly, we put it on a digital balancing machine. There are several ways to manually balance tires, and with over 30 years industry experience, we have utilised them all, but they frankly do not compare to machine-balancing in terms of ease, accuracy & precision. The wheel goes onto the balancer’s spindle through the center bore, and a metal cone is inserted to ensure the wheel is perfectly centered. The machine spins the wheel; and tyre at very high speed to determine the heaviest point, and signals our tyre fitters where and how many weights to place on the opposite side to compensate for this imbalance.
Important Balancing Tips:
• Balancing Is Necessary: A weight imbalance in every wheel/tire assembly is pretty much inevitable. Only once in a very blue moon do we see an assembly come out perfectly balanced naturally. Some say that the machine should ring and glow like a Las Vegas one-armed-bandit if a wheel ever does go on naturally balanced – It is important to note that discovering a ‘balance’ is just as much a function of the balancing machine as discovering an ‘imbalance’.
• Balance Changes Over Time: As tyres wear, the balance will slowly change over time. Many tyre fitters (such as Kwik Fit, Halfords Autocentres or ATS) will rebalance your wheels for you when rotating your tyres, or when changing your tyres for their winter set up, for example. We recommend rebalancing your tyres at least once to extend their lifespan and your safety on the road.
• Balancing Only Fixes Balance: Balancing will not prevent vibrations from a irregular wear, a bent wheel or an inherently unrounded tyre. Balancing weights can’t compensate for a rudimentary problem that is actually physically wrong with the product, they can only compensate for weight differences. As well, one of the first mathematical assumptions the balancer’s computer makes is that the wheel and tyre are both round to within a certain maximum deviation, so if a wheel is substantially bent, for example, the balancer may end up getting the weight placement wrong in the first place.
Road Force Balancing – a new method:
There are other reasons in addition to ‘balance’ which cause vibrations and unusual tyre wear. This led to the eventual birth of the “Road Force” balancer. This style of balancer, in addition to performing a traditional spin balance, also measures more details of both the wheel and tyre to determine if there are any further problems that would cause a vibration on the road. Generally, most balancers press a large roller against the tyre as it spins slowly, reading tyre pressure and radial runout / any deviations from perfect roundness. This will raise awareness of issues such as belt separation, where the steel belt inside the tyre has been bent and is delaminating from the surrounding layers of rubber.
Generally, both wheels and tyres will have high and low spots in terms of their runout – as aforementioned, perfection is almost impossible. If you can imagine pulling one point of a connected circle (such as the edge of a wheel) marginally outwards, you can see that some other point of that circle must move inwards to maintain the connection, creating an egg shape. This explains ‘high and low spots’ when it comes to radial runout. Imagine you then mount a tyre such that the high spots for both the wheel and tyre match up together: these high and low spots will actually add together, rather than canceling each other out. If balanced on a traditional balancer, this assembly will not only require more weight to balance, but will still probably cause a vibration when run.
The solution is to measure both the wheel and tyre, then move the tyre around on the wheel until the high spot of the tyre matches the low spot of the wheel. This process is usually called match mounting. Most modern tyres have small markers on the sidewall to indicate the point on the tyre that should match to the valve stem to get a decent match mount.
Bang-On & Adhesive Weights:
Initial balancing methods utilised bang-on weights. These were lead/zinc weights of various denominations with a soft lead flange that gets knocked onto the edge of the wheel with a soft plastic hammer. These weights were very good when used on traditional steel wheels, but when alloy wheels came to the fore, these bang on weights tended to break the laquer / clearcoat on expensive painted alloy wheels when hit onto the cosmetic face. This caused them to hold water against the break in the laquer, causing corrosion to the unprotected aluminum surface underneath.
This led to the invention of Tape-a-weights: flat, adhesive-backed lead/zinc squares, each weighing one-quarter of an ounce, which are cut to size with clippers and stuck to the inside of the wheel behind the spokes. The adhesive is very strong, but tyre fitters should always clean the surface where the weights will go to ensure it is free of brake dust, grit and road corrosives if at all possible. This will help prevent the weights from falling off. Often, racing technicians use duct tape to hold weights on wheels under heat conditions that would melt the weights’ standard adhesive!
In summary, always ensure your wheels are appropriately balanced. Thankfully, all our brand new wheel & tyre packages come ready fitted and balanced by our experienced team, using high tech, digital balancing equipment.
Source: Wheelwright Blog