Introduction

Any discussion of wheels inevitably involves tires. The most common reason for new wheels is for appearance, (custom wheels) or to use larger tires. The failure rate of wheels is small, but custom wheels are extremely popular. The subject of wheels can be complex and technical, but there are a few tips for those shopping around for new wheels.

The correct capacity, rim width, type of wheel, offset, bolt pattern and diameter all must be considered when selecting a replacement or custom wheel. Having the right wheel is just as important as having one that's not defective. At highway speeds, the wheels on an average vehicle will rotate close to 600 times a minute, about 10 times every second. The wrong type or size of wheel can destroy tires and bearings very quickly at that rate.

Wheel construction
See Figure 1

A wheel is made up of a rim and center member, known as a disc or spider. The rim supports the tire and the spider (disc) connects the vehicle with the rim.

Wheels are usually of two types-the Drop Center (DC) and the Semi-Drop Center (SDC). Drop center wheels are used on all cars and light trucks; semi-drop center wheels are usually only used with large multi-ply, heavy-duty tires on over-the-road trucks. The SDC wheel has a removable outer ring that allows easier installation and higher inflation pressure. Above six plys, tires would be extremely rigid in the bead and be very difficult to mount on a single-piece wheel without damaging the bead.

Most passenger vehicle wheels fall into two types. The all-steel wheel is the type found on many vehicles as original equipment from the factory. Custom or "mag" wheels were named for their resemblance to magnesium racing wheels. True magnesium wheels are too porous to hold the air pressure of a street tire and never should be used on the street. Custom wheels are a cast aluminum alloy, a steel rim with cast aluminum alloy spider or a two-piece steel wheel.

Just as tires have a maximum load capacity and inflation pressure, so do wheels. Any wheels you install should have a greater load capacity and inflation pressure capacity than the tires, or you could have problems. Obviously, the load-carrying capacity of the vehicle is only as strong as the weakest part. If you have selected your tires to carry an anticipated load of, say, 1500 lbs., then the wheel should be capable of carrying at least that, preferably more.

Wheel dimensions

Size
See Figure 2, 3 and 4

Wheel sizes are determined by three measurements-rim diameters, rim width and flange height. A typical wheel size might be 14 x 7J. Rim diameter and rim widths are always expressed in inches, so this wheel is 14 inches in diameter and has a rim width of 7 inches. The letter combination following the rim width indicates the flange height in inches. A J rim has 0.68 inch high flange while a K rim has 0.77 inch high flange. The circumferences on which the centers of the wheel bolt holes are located is the bolt circle. It is usually shown as a double number: 5-5½. The first number indicates the number of holes, and the second, the diameter of the bolt circle.

The rim width will be dictated by the tire section width and/or the tread width. The general rule is that the flange-to-flange width of the rim should be a minimum of three-quarters of the tire section width. The maximum flange-to-flange wheel width should be equal to the width of the tire tread. Narrow tires on wide rims tend to make the outer edges of the tire curl in toward the center. The result is less tread on the road, increased tire wear and a harsher ride. At high speeds, centrifugal action can pull the tire beads away from the bead seat on the rim.

Wide tires on narrow rims create a poor bead seal and force the tread to assume a convex shape causing abnormal tire wear, reduction of control with a somewhat smoother ride.

The general rule is that the tire and wheel combination is satisfactory if, when the tire is flat, no part of the underside of the vehicle touches the ground. This will prevent a shower of sparks, should a blowout occur.

Offset
See Figure 5

Another important dimension to be considered when looking for wheels is offset. Offset is the distance from the mounting face of the wheel spider to the rim centerline. Offset is positive when the mounting face (lug circle) is outboard of the centerline and negative if the lug circle is inboard of the centerline. All wheels are designed for either positive, negative or zero offset, usually for disc brake clearance or for handling characteristics.

Generally, you should not increase the offset more than 1/2 inch (12mm) or tire width by 1 inch (25mm), or you'll create further problems. Increasing offset 1/2 inch (12mm) or tire width 1 inch (25mm) will put the entire extra tire width 1/2 inch (12mm) to the outside, where it may not clear the wheel well. Increasing the offset also has the effect of loading the front wheel bearings past their design limits and can actually "cock" the bearings causing rapid wear or premature failure.

Occasionally, disc brakes cause a mounting problem; some wheels were not designed for use with disc brakes and will not clear the brake caliper or will interfere with the disc. Be sure to check before buying wheels, especially used wheels, that they will fit your vehicle. Be sure that the tires on wider wheels will clear the wheel wells, especially when turned at full lock, and that the tires do not interfere with suspension travel.

Tire mounting
See Figure 6

Most steel wheels require little care. But, more and more vehicles have been equipped with aluminum and custom wheels. Tires must be mounted carefully to avoid scratching any wheel which is not hidden by a wheel cover. Wheels with steel rims and alloy spiders can be somewhat easier to work with than all-alloy wheels, but many service facilities charge extra to mount tires on custom wheels, or will refuse to work on them at all.

Aluminum and custom wheels are balanced in the same way as steel wheels, but adhesive backed weights are often used instead of the hammered on type. Adhesive weights must be checked more frequently than the others, and, as with mounting tires, many service stations charge extra to dynamically (spin) balance custom wheels, or will not do it at all.

Wheel and tire removal and installation
See Figure 7

1. Park the vehicle on a level surface.
2. Remove the jack, tire iron and, if necessary, the spare tire from their storage compartments.
3. Check the owner's manual for the jacking points on your vehicle. Then, place the jack in the proper position.
4. If equipped with lug nut trim caps, remove them by either unscrewing or pulling them off the lug nuts, as appropriate. Consult the owner's manual, if necessary.
5. If equipped, remove the wheel cover or hub cap. In most cases there is a groove along the cover's edge, insert the tapered end of the tire iron in the groove and pry off the cover.
6. Apply the parking brake and block the diagonally opposite wheel with a wheel chock or two.

Wheel chocks can usually be purchased at your local auto parts store, or a block of wood cut into wedges may be used. If possible, keep one or two of the chocks in your tire storage compartment, in case any of the tires has to be removed on the side of the road.

1. If equipped with an automatic transmission/transaxle, place the selector lever in P or Park; with a manual transmission/transaxle, place the shifter in Reverse.
2. With the tires still on the ground, use the tire iron/wrench to break the lug nuts loose.

If a nut is stuck, never use heat to loosen it or damage to the wheel and bearings may occur. If the nuts are seized, one or two heavy hammer blows directly on the end of the bolt usually loosens the rust. Be careful, as continued pounding will likely damage the brake drum, rotor and/or wheel bearings.

1. Using the jack, raise the vehicle until the tire is clear of the ground. Support the vehicle safely using jackstands.
2. Remove the lug nuts, then remove the tire and wheel assembly.

To install:

1. Make sure the wheel and hub mating surfaces, as well as the wheel lug studs, are clean and free of all foreign material. Always remove rust from the wheel mounting surface and the brake rotor or drum. Failure to do so may cause the lug nuts to loosen in service or may allow the wheel to all but freeze onto the surface making future removal difficult or nearly impossible.
2. Install the tire and wheel assembly and hand-tighten the lug nuts.
3. Using the tire wrench, tighten all the lug nuts, in a criss-cross pattern, until they are snug.
4. Raise the vehicle sufficiently to withdraw the jackstands, then lower the vehicle.

If a torque specification is not available for your lug nuts, use a torque wrench to measure the lugs on your other wheels. Find the average specification and match it on the wheel you are installing. Remember that the nuts must be tightened enough to prevent loosening in service and, most importantly, they must be tightened EVENLY.

1. Using a torque wrench, tighten the lug nuts in a criss-cross pattern to specifications.
2. If so equipped, install the wheel cover or hub cap. Make sure the valve stem protrudes through the proper opening before tapping the wheel cover into position.
3. If equipped, install the lug nut trim caps by pushing them or screwing them on, as applicable.
4. Remove the jack from under the vehicle. If you have just finished changing a flat, place the jack and tire iron/wrench in their storage compartments.
5. Remove the wheel chock(s).
6. If you have removed a flat or damaged tire, place it in the storage compartment of the vehicle and take it to your local repair station to have it fixed or replaced as soon as possible.

Tightening wheel lug nuts
See Figures 8 and 9

Although it is frequently done for speed, wheel lug nuts should not be tightened with an electric or air impact gun. ALWAYS hand-tighten them with a cross-type wrench, then torque to specifications using a torque wrench.

Torque specifications for lug nuts should be adhered to and applied evenly in a criss-cross pattern. Over tightening lugs can lead to broken studs. Over-tightening, uneven tightening, or tightening in the wrong sequence can lead to warped brake drums or rotors.

If a torque specification is not available for your lug nuts, you can use a torque wrench to measure the lugs on your other wheels. A beam type wrench with a needle indicator works best for this, but a dial-clicker type can also be used. When measuring with a clicker, dial a torque that you are pretty sure is below the specification , say 50- 60 ft. lbs. (68-81 Nm), and test it on a lug nut. If the wrench clicks without turning the lug, keep increasing the torque by 5 ft. lbs. (7 Nm) increments until the nut begins to turn. Then, check that setting on other lugs. Be sure to properly loosen and retorque the test lug nuts when you are finished so that no lugs are over-tightened.

Keeping your wheels clean
See Figures 10 and 11

For more information on cleaning of wheels please refer to the section on "Body Care."

Oxidation and theft are the main enemies of custom wheels. Oxidation is caused by a chemical reaction between air and water that causes the alloy to pit. Various waxes and cleaners are available to hold the oxidation process to a minimum and keep the wheels looking like new.

Remember that many aluminum wheels are painted or clear-coated to help prevent corrosion. Use of harsh chemicals or abrasives will remove the coating allowing for oxidation to occur. Also, remember that exposure to dirt, gravel, cinder and road salts will eventually take their toll on even the best coated wheel, but proper care can provide significant protection while beautifying your wheels.

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