Tire Mounting, Repair, and Balancing

Tire work looks simple, and that is why it goes wrong. A wheel run down with an impact gun can stretch its studs and warp a rotor. A plug pushed in from outside can hide damage that lets go at highway speed. A bead forced on with too much air can explode. This is the hands-on job from the moment the wheel comes off the car to the moment it goes back on.

What You Will Be Able to Do

• Dismount and mount a tire without damaging the bead, wheel or sensor.
• Seat a bead safely and stop at the pressure limit.
• Find a leak and decide whether a tire can be repaired.
• Make an industry-standard puncture repair.
• Balance a wheel and torque it correctly.

Rules That Apply to Every Tire

The OSHA rim wheel standard, 29 CFR 1910.177, covers large vehicles such as trucks, tractors, trailers and buses, and does not apply to rim wheels on cars, pickups and vans. It requires employers to train anyone who services those large rim wheels, and requires a restraining device or barrier for inflation. Do not touch a truck wheel or a multi-piece rim until you have had that training. A split rim or lock ring can fly apart with deadly force.

Passenger and light truck tires can still seriously injure you. The US Tire Manufacturers Association (USTMA, formerly the Rubber Manufacturers Association) publishes the wall charts most shops follow. Tire and machine maker instructions come first when they are stricter.

Warning: Keep your head, hands and body out of the path of a tire during inflation. Never lean over it. Use a clip-on air chuck with a remote valve so that you can stand back.

Dismounting a Tire

1. Mark the tire's position if it is going back on the same vehicle.
2. Remove the valve core and let all the air out. A tire that still holds air can break loose suddenly.
3. Note the valve and sensor location. If the wheel has a TPMS sensor, keep the bead breaker and the demount tool away from it, and begin the bead break opposite the valve.
4. Break both beads with the machine's bead breaker. Do not pound on the tire with a hammer.
5. Lubricate both beads generously with approved tire lubricant.
6. Set the mount head at the proper gap from the rim, lift the top bead over it and rotate. Repeat for the bottom bead.

Dry dismounts tear beads and scratch alloy wheels. Check the machine's instructions for reverse-mount wheels and low-profile or run-flat tires, which need extra care.

Mounting a Tire

1. Inspect the wheel. Reject cracks and bends. Clean the bead seats, because corrosion on an aluminum wheel is a common cause of slow leaks.
2. Inspect the tire. Match its size to the size stamped on the wheel. A 16-inch tire on a 16.5-inch rim is a known cause of explosions at inflation.
3. Service the valve. Fit a new rubber stem on a non-sensor wheel, or a new service kit on a sensor.
4. Lubricate both beads and the rim with approved tire mounting lubricant.
5. Check the direction. Directional tires must turn the way the arrow shows, and asymmetric tires must have the side marked "outside" facing out.
6. Mount the tire and keep the bottom bead in the wheel's drop center, so that the top bead can slide over with little force.

Only use a lubricant made for tires. Silicone spray and petroleum products can harm the rubber or let the tire slip on the wheel. Dish soap and similar substitutes can leave residue that contaminates the bead or corrodes the rim, and the bead may not seal correctly.

Seating the Bead

1. Remove the valve core for a faster, more even air flow.
2. Add air in short bursts and watch both beads. Stand back from the tire.
3. Check the thin molded ring near the bead. It must sit an even distance from the rim all the way around, on both sides.
4. Refit the core and set the pressure to the vehicle placard.

Warning: Never exceed 40 psi to seat a bead. If both beads are not seated at 40 psi, deflate the tire completely, reposition it, lubricate it and try again. A popping sound alone does not prove a bead is seated. Check both sides.

If a bead will not seat by 40 psi, the cause may be poor lubrication, a mismatched size, a damaged bead or a bent rim. More pressure is never the fix. This limit comes from USTMA procedures, and some tires, such as agricultural tires, have a lower limit. Follow the maker's figure if it is lower.

Finding a Leak

1. Inflate to the placard pressure.
2. Spray soapy water on the valve stem, valve core, bead, tread and sidewall.
3. Watch for bubbles. Big foam means a large leak, and fine fizz means a slow one.
4. Check the valve core. Cores fail with no visible damage.
5. Dismount the tire and look at the inner liner under good light. A tire driven while low shows a wrinkled or powdery ring inside the sidewall, and it must be scrapped.
6. Check the wheel's bead seat for corrosion pits. Clean to bare metal and use a bead sealer if your shop approves it.

Repair or Replace

Use the USTMA puncture repair procedures for passenger and light truck tires. The tire must come off the wheel, because you cannot see internal damage from outside.

Worked example: a tire has a 1/8 inch nail hole in the middle of the tread, with a clean liner inside. It passes all the checks, so you can repair it. A screw in the same tire that sits at the edge of the outer tread block and angles into the shoulder cannot be repaired, even though the hole is small.

Making the Repair

A plug alone or a patch alone is not an acceptable repair. A proper repair fills the injury with a rubber stem or plug and seals the inner liner with a patch. A one-piece plug-and-patch unit is the common way to do both.

1. Mark the injury, remove the object and dismount the tire.
2. Inspect inside and outside. Probe the angle of the injury.
3. Clean and buff the liner around the injury, following the repair unit maker's instructions.
4. Fill the injury with the stem and fit the patch, using the specified cement and curing time.
5. Roll or stitch the patch down firmly and seal the buffed area.
6. Remount, inflate, check for leaks and balance the assembly.

Check tire maker rules for run-flat tires and for speed ratings after a repair, because some makers limit or do not allow repairs on certain tires. An outside-in plug on the wheel may get a customer to the shop, but it is not a permanent repair.

Balancing

A wheel and tire are never perfectly even. Balancing adds small weights to cancel the heavy spots, so the assembly can spin smoothly at speed.

Balancing Step by Step

1. Remove old weights, stones from the tread and mud from inside the wheel.
2. Clean the wheel's mounting face and center bore.
3. Mount the wheel on the balancer with the correct cone or flange. A wheel that is off center gives a false reading.
4. Enter the wheel dimensions or use the machine's arm.
5. Spin it. The machine shows the amount and the location for each plane.
6. Fit the weights at the positions shown. Clean the wheel with the correct cleaner before using adhesive weights.
7. Respin to confirm. Most machines show zero, or a value under about 0.25 ounce, on each plane.

Choose weights to suit the wheel. Clip-on weights fit steel wheels, and the clip must match the rim flange. Adhesive weights are preferred on alloy wheels, because they do not damage the wheel's finish and can be hidden behind the spokes.

When Balance Does Not Fix It

If a vibration stays after a correct balance, use a road force balancer. It presses a roller against the tire as it spins to measure how evenly the tire holds the load. It can find a stiff spot in the tire or an out-of-round wheel that a standard spin cannot detect. The fix may be to match-mount, which means rotating the tire on the wheel to line up the tire's high spot with the wheel's low spot.

Other causes of a comeback:

• Mud, debris or an old weight left on the wheel
• A bent wheel, or a dirty hub or mounting face
• Cupped or unevenly worn tires
• Worn suspension or driveline parts

Installing the Wheel and Torquing It

Clean the hub and the wheel's mounting face, and thread each lug nut by hand first. A typical spec for passenger cars is 80 to 100 ft-lb, and light trucks often run higher, but the right number is the one in the service information for that vehicle.

1. Run the nuts down by hand or with a low-torque setting until they are snug.
2. Lower the vehicle until the tire touches the floor and can no longer spin.
3. Tighten in a star pattern with a calibrated torque wrench, in two passes.
4. Recheck each one at the final spec.

Do not finish lug nuts with an impact gun. Guns deliver uneven and often excessive torque, which can stretch studs until they fail, distort the rotor and cause pedal pulsation, and leave a wheel that has to be cut off at the roadside. Torque sticks help control an impact gun, but they do not replace the final pass with a torque wrench.

Do not oil the threads unless the service information says to. Lubricated threads turn the same torque reading into far more clamping force.

Alloy wheels can settle on their seats after the first drive. Many shops put a retorque reminder on the steering wheel or the driver's window, asking the customer to return in 50 to 100 miles for a free retorque.

Before the Vehicle Leaves

• Confirm every wheel was torqued, and record it on the repair order.
• Set all tires to the placard pressure, including the spare.
• Check that the tire pressure warning light is off.
• Clean any grease from the seat, door and wheel.
• Hand the old tires back or dispose of them as your state requires.

Common Mistakes

Check Your Understanding

1. A tire is at 40 psi and one bead still will not seat. What do you do? Deflate it completely, reposition it, relubricate and try again. Check for a mismatch or a bad bead if it fails again.
2. A customer asks for a quick plug on a screw in the tread. How do you respond? Explain that the tire must come off to be inspected, and the repair needs both a plug and a patch. If it passes, you make the repair inside the tire.
3. After balancing to zero, a car still shakes at 65 mph. What is the next step? Check the wheel and tire for runout, then road force test the assembly. Inspect suspension parts as well.
4. You are about to fit adhesive weights, and the wheel is coated in brake dust. What do you do first? Clean the area so that the weight bonds. A weight on a dirty surface can fall off.

Key Takeaways

• Stop at 40 psi when seating a bead, and keep out of the tire's path.
• Large truck rim wheels fall under OSHA 1910.177 and need specific training.
• A permanent repair needs the tire off the wheel, and both a plug and a patch, in the tread area only.
• Use only approved tire lubricant.
• Balance removes shake from weight, and road force finds what a spin balancer cannot.
• Finish every wheel with a calibrated torque wrench in a star pattern.