And why, balancing of tire and wheel assemblies should be the first step in solving any ride complaints:
All vehicle suspensions have a natural rebound frequency, or up and down motion as the vehicle travels down the road. Truck suspensions have a natural rebound frequency of 10Hz, (600 times per minute at 60 mph). Hertz are a measurement of waves, or the up and down motion in times per second. 10 times per second is called 10 Hz, or the up and down hop of the suspension in this case.
An out of balance wheel or heavy spot (heavier side of the wheel) pulls up and down on the suspension at every revolution. These revolutions are measured in revolutions per minute (RPM)
The average commercial truck size tire travelling at 65 mph has a revolution of 10 times per second, equalling 600 Revolutions Per Minute (RPM). So at 65mph, the out of balance portion of the wheel assembly (the complete axle end) is pulling up and down on the suspension at the same frequency as the natural rebound of the suspensions.
The resonate coupling of these two frequencies, meaning when the heavy spot of the wheel’s up and down motion synchronizes with the up and down motion of the rebound frequency, the resulting inertia multiplies the out of balance portion of the wheel assembly, enough to bounce the axle of a fully loaded truck and trailer up and down sending vibrations through the complete vehicle.
The consequences are a substantial reduction of tire life, premature wear of suspension, wheel and shock components and increased fuel consumption. These resonating vibrations cause a rough ride overall, damaging the vehicle and it’s cargo and have also been shown to negatively effect the vehicle’s handling.
A STRONG VIBRATION AFTER HITTING A BUMP is caused by the out of balance wheel assembly, from the bump compressing the axle spring at the rebound resonating frequency of the suspension and RPM of the tire. The out of balance tire at the resonating frequency will keep on bouncing forever unless the speed/RPM changes below or above the rebound frequency. Don’t expect your shock absorbers to prevent this from happening.
There is only one way to stop this from happening besides changing speeds, and that is balancing the complete axle end.
The resonating frequency is in a narrow range of highway speed or RPM of the wheel assembly. When the wheel RPM is below or above the rebound frequency of the suspension, it prevents the resonate coupling that creates the vibration.
Tire balancing or wheel balancing are the same, usually describing balancing the tire and the rim only.
This method of balancing does not always solve the problem, it can actually make the situation worse in some cases. The reason is that by not knowing the out of balance portion/weight of a brake drum; you are gambling with your results and the expenses.
The same applies when match mounting a tire and rim. Again, you do not know what out of balance portion you are matching, plus the question of the rest of the wheel assembly and all its moving parts.
The solution is balancing the COMPLETE AXLE END the whole wheel assembly; that is everything that’s turning with all the intolerance's and imperfections being accounted for. This includes the tires and rims, the brake drum or rotors, the hub, all balanced after being assembled as one piece.
NOT ALL BALANCING METHODS WILL WORK
Conventional machine tire balancing off the vehicle, only balances half the axle end. Balancing only half a wheel assembly with no consideration for the intolerance's and imperfections of the heavy part of the brake drum and mounted tire will actually make it worse, because the two heavy spots exacerbate the out-of-balance situation. Balancing the mounted tire and rim in such a manner would make the situation worse.
Match mounting Tire and Rim is just that…mounting the tire and rim with no consideration for the acceptable intolerance of the brake drum, hub and other moving parts of the axle end.
Why it is so important to balance the complete axle end?
It only takes a minor out of balance axle end to cause major problems.
A 6oz out of balance axle end will multiply to 60 lbs at 60 mph through centrifugal force alone; that is like a 60 lb hammer hitting your wheel at every revolution 600 times per minute. If you think that’s bad you’re right, but it gets a lot worse when that out of balance wheel rpm reaches the rebound coupling frequency of the suspension. This resonate coupling multiplies this to 600 lbs, to a force strong enough to move a fully loaded axle up and down several inches. This is "the wall" and all the damages that it causes.
ABC lowers them all: Fuel savings, tire longevity, reduced maintenance expenses
Tire/Wheel assembly balancing has traditionally been used to address driver ride complaints, reduce vehicle vibration, and to minimize premature and irregular wear.
More recently, data has shown that balanced tire/wheel assemblies can have a significant, positive effect on fuel economy especially in high-speed line haul applications.
More and more Fleets are considering balancing tires not only as a ride complaint solution, but also as an opportunity to improve fuel economy and to maximize tread life through the reduction of irregular wear.
Different axles may contribute differently to fuel economy and tread wear in various operations.
To get maximum benefit from balancing tires for improved tread wear and fuel economy, fleets with line haul operations should start with balancing the trailer tires first, then drive tires, and finally steer tires since their contribution to fuel economy and tread wear are the greatest in that order.
Tire Balancing Benefit Summary
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