Tires and Wheels Vibration

Even though no problems may be found as the tire rotates on the balancer, when the tire experiences a load, the transition of the harder and softer sections of the tire may create a series of harmonic vibrations as the various sections of the tire contact and leave the road surface. Depending on conditions, this harmonic may occur once per tire revolution, or in a series of multiple vibrations per revolution. It's possible that this phenomenon may vary according to changes in tire pressure, vehicle speed, individual tire load and road surface conditions, all of which may serve to reduce and/or amplify the vibration problem. In other words, the vibration the driver feels may not occur at any one rate of speed, or on any particular road surface, because the problem may appear only under a specific combination of these variables.

If a tire/wheel will not balance properly, or if a vibration exists after a successful balance job, don't automatically blame the tire. If you haven't checked the hub and wheel for runout, you may be jumping to conclusions. If, however, all balance, static runout and chassis parts variables have been exhausted, then it may be time to suspect a radial force variation problem.

To check for and attempt to actually verify a dynamic radial runout condition, a spin-balancer with a built-in load roller is recommended. This type of balance machine places a load (which attempts to simulate road load) onto the tire as it spins, while monitoring and recording variances of runout. If load variation is found, it may be corrected to an acceptable level via balancing weights. In extreme cases, it may verify that the tire should be replaced.

Tires and Wheels match mounting

Tires and wheels match mounting isn't a cut-and-dried method. Your approach to match mounting will depend on several variables:

* whether the tire is runout- and weight-matched,

* whether the wheels low runout spot can be determined, and

* whether you have access to a loadapplying balancing machine.

Regardless of the specific approach you take, it's important to understand that "stacked-up" runout and imbalance conditions can be addressed. Of course, once tire matching has been accomplished, the mounted package must then be checked and corrected for dynamic balance.

There are two types of radial runout -static and dynamic. Static runout, as we noted earlier, refers to the high spot of the tire, a physical characteristic that can be measured with no load placed on the tire. Radial force variation, however, refers to a dynamic runout condition, which occurs only when the tire runs at speed, under load, due to variations in construction stiffness.

Radial force variation is so named because the radius of the tire varies according to vehicle speed and load. Of course, any tire, because of its pliability, will vary slightly in radius at the load spot during operation. Although a "radial force" might be the result of a runout area pronounced enough to affect the tires impact on the road, a radial "force variation" may occur if the tire has appreciably different "soft" spots and "stiff spots in the carcass and/or tread or in the sidewall construction. Given the precise quality control processes used by todays tire makers, it's rare that a force variation problem will occur. But when it does, it can be a tricky demon to chase.

CUSTOM WHEELS HANDLING

For decades, it was common practice in the aftermarket to mount a tire so its red dot aligned with the wheel's valve stem, since the valve stem area was normally assumed to be the wheel's lowest point of radial run out. Aligning the tires high point to the wheel's low point (theoretically) reduces or eliminates the chance of developing a radial force variation (RFV) in the tire/wheel assembly.' RFV (again, an issue of runout, not imbalance) can cause a vibration that might be mistakenly diagnosed as an imbalance problem.

Times change. With the advent of styled custom wheels, the valve stem location may no longer indicate the wheel's low radial run out spot. In other words, it may no longer be viable to assume that aligning a tire's.red dot to the wheel's valve stem will address any potential RFV issues.

Consequently, a procedure that was once easy has now become complicated. The only way to accurately match mount a tire to a wheel is to actually measure tire and wheel runout. The end goal remains the same: to align the tire's high point to the wheel's low point. The wheel itself can be easily checked for radial run out by mounting it to a hub and slowly rotating it while monitoring the rim edge with a rigidly mounted dial gauge. However, the only acceptable method to check the assembled tire/wheel package for radial uniformity under load is to use a state-of-the-art wheel balancing machine that features a load-roller that applies road-simulated load to the inflated tire. Such a machine will not only check for dynamic balance but will also locate the tire's high spot. If this high spot doesn't correlate to the wheel's low spot, the machine will let you know where to relocate the tire on the wheel to minimize RFV

If you don't have access to a road wheel type of balancing machine, and you don't know where a wheel's lowest radial run out spot is located, you can default to using the Weight Method, which involves aligning the tire's yellow dot to the wheel's valve stem.

Tires match mounting

Some of the most common types of work done on performance vehicles involve the wheels and/or tires. The wheels are one of the most visible parts of a vehicle, so any work done on them must be top-notch-meaning clean, pretty and accurate.

Custom wheel service can be broken down into two primary topics, essentially-tire match mounting and custom wheel handling.

Match mounting involves positioning the tire onto the wheel to minimize or eliminate the final combination of radial force variation and/or imbalance. One match mounting approach involves aligning the tire's point of maximum radial force variation (its high spot) to the wheel's radial low spot (where the wheel's radial runout is the lowest). This is called the Uniformity Method. The other approach involves simply aligning the tire's lightest balance point to the wheel's heaviest balance point, called the Weight Method.

OE tire suppliers are required to mark a tire's radial runout high point, and OE wheel makers are required to mark a wheel's radial runout low point. This makes it easy for the OEMs to match-mount tires to wheels from a radial force variation standpoint during production. In some cases, these marks are made with paint dots that help service technicians remount tires down the road. However, sometimes these marks are made using temporary stickers, which either fall off or are removed after mounting. This leaves no readily visible reference marks for the tire technician for future service.

If a tire does feature color dots on the sidewall, one or two dots may be used. A red dot indicates the tire's radial runout high point. A yellow dot indicates the tire's point of least weight, from a balance standpoint.

Alloy Wheels

Besides plus sizing, other factors should be considered before shelling out big bucks for wheels. The benefits of a good-quality alloy wheel are numerous. And, of course, many cars come with them as factory original equipment. Either way, you end up with reduced weight compared to steel wheels. This is a factor affecting a vehicle's road holding ability. Unsprung weight is the portion of a vehicle that's not supported by the suspension (i.e. wheels, tires and brakes) and therefore is most susceptible to road shock and cornering forces. By reducing unsprung weight, alloy wheels provide more precise steering input and improved cornering characteristics. The added strength of a quality alloy wheel can also reduce tire deflection in cornering. This is particularly critical in a car equipped with high performance tires where lateral forces may approach 1.0g. Better brake cooling is another benefit. The metals in alloy wheels are excellent conductors of heat and improve heat dissipation from the brakes. The risk of brake fade is also reduced under more demanding conditions such as spirited driving on a twisty mountain road. Additionally, alloy wheels can be designed to allow cool air to flow over the brake calipers and rotors. The lighter rotational weight of alloy wheels can even provide a slight increase in acceleration and fuel economy.

Changing wheels

There are two main reasons most people consider a wheel change. One is simply for looks. A better-looking wheel makes a world of difference on many cars and trucks.
Besides appearance, the plus concept is a key reason to switch wheels. Plus sizing your wheels and tires is the best way to improve both the performance and appearance of your vehicle. By using a larger diameter wheel with a lower profile tire it's possible to properly maintain the overall diameter of the tire, keeping odometer and speedometer changes negligible. By using a tire with a shorter sidewall, you gain quickness in steering response and better lateral stability. The visual appeal is obvious; most wheels look better than the sidewall of the tire, so the more wheel and less sidewall there is, the better it looks. If a car has a 15-inch wheel, then upgrading to a 16-inch wheel would be plus one and a 17-inch wheel would be plus two. You could also say that if a car has a 17-inch wheel (such as many performance cars do) then going to an 18-inch wheel and tire would be a plus one. If the car has 15-inch wheels, the 18s would be a plus three.

Tires tread design and Noise

Some tires tread designs are noisier than others and it varies significantly between tire brands and tread designs. If most of your driving is on lower-speed city streets, then this won't be much of a factor. But for highway driving, you'll want to consider your options, especially if you're driving a SUV or truck on pavement most of the time. At Victoria Tire our salespersons will be able to tell you which tires are quieter among those we are offering and you are considering. Even tires those of the same make that are in a different line can vary in road noise.