1. If you are only replacing two tires on a vehicle, should they go on the front axle or the rear axle?

In most cases, they should be installed on the rear axle. When new tires are installed on the front and worn tires are left on the rear, it creates a handling imbalance that can cause the rear of the vehicle to slide outwards during turns. This condition is known as 'oversteer.' Be aware that certain manufacturers of AWD vehicles recommend that replacement pairs be installed on the front axle only.

2. Is it true that the speed rating of replacement tires has to be at least the same as the speed rating indicated on the tire placard?

YES. The speed rating printed on the tire placard represents the minimum speed rating for replacement tires. Although it's fine to install tires with a higher speed rating, installing tires with a lower speed rating is not an option.

3. If all replacement tire sizes must match the sizes printed on the vehicle's tire placard, why do we plus-size assemblies on custom wheels?

Remember, the vehicle's suspension and steering system has been designed specifically for the size tires listed on the placard. Changing tire diameter beyond this point can adversely affect vehicle handling, antilock brake operation, and speedometer accuracy. However, as long as the outside diameter of the original equipment tires is maintained within 3%, the plus-sized custom wheel assembly should not cause any problems.

4. Can speed-rated tires be repaired and still maintain their original speed rating?

It depends on the tire manufacturer. Some manufacturers allow tires to maintain their original speed rating following a proper nail hole repair. Always check the manufacturer's tire repair policies and inform the customer if any limitations apply.

5. Is it necessary to install four snow tires or studded snow tires on front-wheel drive vehicles?

YES. Front-wheel drive vehicles have a tendency to understeer. This is because most of their weight is concentrated in the front. Installing snow tires on both axles minimized understeer by providing equal grip at all four corners. Since the weight in a rear-drive vehicle is more evenly distributed, installing two snow tires on the rear axle is acceptable.

6. Is it true that the tires on 4WD and AWD vehicles should all be the exact same size and have the same tread pattern?

Yes, especially where AWD vehicles are concerned. This is because driving on mixed tires can damage drivetrain components due to the difference in circumference between the tires on the front and rear axles. That's why the tires on these vehicles must be identical, and why maintaining proper inflation pressure is so important. In fact, some vehicle manufacturers strongly recommend replacing tires in complete sets to ensure circumference is the same on both axles.

7. Can you mix radial and bias tires on the same vehicle?

Yes, but it is not recommended. As long as the vehicle is NOT a 4WD or AWD model. On front-wheel and rear-wheel drive vehicles, always install the bias tires on the front and the radial tires on the rear to prevent oversteer.

8. Can you mix aspect ratios on the same vehicle?

Not if the vehicle is a 4WD or AWD model. On front-wheel and rear-wheel drive vehicles, the tires with the lower aspect ratio should be installed on the rear axle to prevent oversteer.

9. If you are replacing one tire on a vehicle, where should it be installed?

Always pair the new tire with the tire that has the most tread depth, and then install both tires on the rear axle (except certain AWD vehicles). Be sure the replacement tire is the same size and construction as the other tires and has an equivalent or higher speed rating.

10. What causes some tires to smell like ammonia when the valve core is removed?

This smell is usually an indication that the tire contains 'fix-a-flat' or similar injectable sealant. Since many of these products are flammable, a spark generated within the vicinity of the tire can ignite the gas and cause an explosion. To prevent serious personal injury, it is vital that the gas be purged from the tire whenever an ammonia smell is detected. This can be accomplished by inflating and deflating the tire several times before unseating the beads. If the tire is going to be returned to service, clean the inside of the tire thoroughly, making sure all of the sealant has been removed.

11. What does it mean to 'double bead' a tire?

The term 'double bead' refers to installing both beads simultaneously. This is not an acceptable tire-mounting procedure and should not be attempted.

12. Is passenger and light truck tire service covered by OSHA Regulation 29 CFR 1910.177?

No. However, every business is covered by the OSHA General Duty clause, which states that every employer must identify all risks to employees, and provide the necessary training and safety equipment required to protect them from injury.

13. Is plugging a tire from the outside an acceptable method for repairing an injury?

No. Repairing a tire properly is actually a six-step process that involves cleaning the innerliner, removing the damage, filling the injury, buffing the innerliner, cementing the innerliner, and installing the appropriate repair unit (one-piece combination or two-piece). This procedure, which requires the tire to be removed from the wheel, is the only approved method for repairing an injury.

14. What is the best time of day to check tire inflation pressure?

Since inflation pressure should be checked cold, the best time to check tires is first thing in the morning with the vehicle parked in the shade. If the vehicle has been driven more than one mile, or has been sitting in the sun on a hot day, the tires should be allowed to cool up to three hours before checking inflation pressure.

15. How often should you check tire inflation pressure?

Since it is normal for tires to lose 1-2 psi per month, tire pressure should be checked on a monthly basis.

16. How often should the tires be rotated?

While rotation schedules may vary among manufacturers, the general industry standard is every 5,000 to 7,500 miles.

17. Can there be a leak on a tire that is difficult to locate?

Yes. During the wheel casting process, air bubbles can become trapped in the molten metal. Once the wheel hardens, the air bubbles create tiny pockets (porous areas) that can allow air to escape. These porosity leaks may be so slight that it takes several weeks for the tire to lose a substantial amount of air.

18. How do you repair a wheel porosity leak?

Some manufacturers recommend special adhesive/sealers to repair a porosity leak. These products are typically applied in a 1/8" layer to the porous area and require about 12 hours of drying time.

19. What is the difference between a thrust angle alignment and a four-wheel alignment?

During an alignment, two benchmarks are used to determine the relationship between the vehicle and the tires. The first is the vertical reference line: an imaginary line that runs through the center of the tire/wheel assemblies. The second is the centerline: an imaginary line that bisects the vehicle lengthwise. Ideally, the centerline and thrust angle will be the same. The thrust angle and centerline are different, the vehicle will dog track down the road and the steering wheel will be off-center. On vehicles with non-adjustable rear suspension, the thrust angle is fixed based on the position of the rear wheels. In a thrust angle alignment, the front wheels are aligned according to the measured thrust angle. This procedure is used for rear-drive vehicles with a solid axle. For vehicles equipped with adjustable rear wheels, a four-wheel alignment can be performed. During this procedure, the thrust angle is adjusted to zero (center) prior to aligning the front wheels.

20. Why do top fuel and funny car drivers perform 'burnouts' before every run?

The soft rubber compound used in racing slicks contains several heat-activated chemicals. The chemicals are designed to improve traction, which is essential for winning races. Performing a 'burnout' heats the slicks and allows these chemicals to be released. This causes the tires to become sticky, providing the traction necessary to complete the run and achieve a low ET (elapsed time).

21. Is it important to have the proper inflation pressure in your tires?

YES. It is important to have the proper inflation pressure in your tires, as under inflation can lead to tire failure. The "right amount" of inflation for your tires is specified by the vehicle manufacturer and is shown on either the vehicle door edge, door post, glove box door or fuel door. It is also listed in the owners manual.

22. Why is it important to have my wheels aligned?

Misalignment of wheels in the front or the rear can cause uneven and rapid treadwear and should be corrected by a tire dealer. Have you alignment checked periodically as specified by the vehicle owner's manual or whenever you have an indication of trouble such as "pulling."

23. When is the proper time to check my tire pressure?

When you check the inflation pressure, make sure the tires are cool - meaning they are not hot from driving even a mile. If you have to drive to get air, check and record the tire pressure first and add the appropriate inflation pressure when you get to the pump. It is normal for tires to heat up and the inflation pressure inside to increase as you drive. Never "bleed" or reduce teh inflation pressure when tires are hot.