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TRUCK TIRE FAQ

Posted: August 1, 2014

Truck tires demystified.

Q. Why are there speed ratings on some medium and heavy-duty truck tires and not on others?

A. Tires that may be used in Europe will generally have a speed rating or symbol. In the United States, with a few exceptions, the only truck tire with maximum speed ratings posted on the casing will be local use tires, such as tires for dump trucks, concrete mixers, etc.

Q. Once the tread design is worn off the radial truck tire casing with a maximum 55 mph rating, is it legal to operate it at a higher speed after it has been retreaded with light, high speed tread designs?

A. I do not know of any law that addresses this, but it is not a good idea. The heavy-duty casing would likely become overheated and fail, if driven at high speeds.

Q. Is there a federal law regulating the minimum allowable tread depth for truck tires?

A. Yes, the federal law on minimum tread depth for truck tires is 4/32 inch on front axles and 2/32 inch on other wheel positions.

Q. Is there any situation where plugging a hole in a tire and not using a patch would be an acceptable industry practice?

A. Not according to tire manufacturers. Using a plug without a patch is a common practice for repairing tires that are not used on public roads because repairing a tire on a lawnmower, slow moving farm tractor, and similar types of equipment appears to present little risk. With that in mind, I would still recommend that the tire be removed from the rim and inspected before repairing for the safety of the tire technicians.

Q. When would it be acceptable to inflate a tire to the maximum pressure?

A. With truck tires this is a common practice because of the heavy loads they carry and the fact that most heavy-duty trucks do not have a placard in the vehicle that recommends a specific inflation pressure. The tire manufacturers and the tire and rim associations have a chart that recommends the correct inflation pressure for the weight that the tire is carrying. The inflation pressure for passenger tires is designated on a placard or owners manual in each vehicle.

Q. Is there a federal regulation requiring trucks to use new tires when hauling toxic waste?

A. No. There are no federal regulations that require new tires to be used on any truck.

Q. We are new to the retread business in our country and we wish to know how old a tire can be and still be retreaded or repaired.

A. There is no simple answer to you question, as in most cases a tire is rejected for retreading or repairing not because of its age, but because of its condition. Many tires may be unacceptable for retreading when they are only a year old, while others may be perfectly acceptable for retreading when they are close to ten years old. It all depends on how well the tire is maintained and how and where the tire is used. Some environmental and operating conditions can destroy even the best new tires very quickly.

Q. How will 20 percent overinflation in a steel radial truck tire affect the tire’s performance?

A. It depends on how the tire is used and the surface it is used on. If the tire runs on a smooth surface, it will likely develop some irregular wear. If it runs on gravel or travels over rough surfaces, the tire will likely experience severe cutting, chipping and other impact damage. Wet gravel makes the cutting and chipping worse. We recommend using only the inflated pressure required for the speed and load.

Q. I understand that the maximum allowable injury for a nail hole repair in a large radial truck tire is 3/8″(10mm), but I don’t understand why a 3/8″(10mm) injury in the sidewall requires a more costly section repair. Please explain.

A. The tread area of a medium radial truck tire features four to five layers of steel cord-three to four belt plies and one body ply-while the sidewall has only one steel body ply. Given those features, the tread area is heavily reinforced so that the repair unit for a 3/8″(10mm) puncture really only has to seal the injury. The sidewall offers much less reinforcement and flexes more than the tread, so it calls for the extra support of the larger unit required of a section repair.

Q. Is it true that any irregular tread wear pattern that develops in an original new tire will show up again when the casing is retreaded?

A. An irregular tread wear pattern is usually caused by operating conditions, the tread design, or poor maintenance of the tire or vehicle. The tire casing has very little effect on tread pattern wear.

Q. Can the new ultra-low profile truck tires that replace duals be retreaded?

A. Definitely. Both manufacturers have successfully operated retreaded tires in test fleets.

Q. Is it acceptable to use bias ply tires on the front of my dump truck if radials are on the tandem drive axles?

A. Yes

Q. How is minimum dual spacing measured?

A. Minimum dual spacing is measured from the centerline of one tire in a dual position to the centerline of the other tire.

Q. We perform free air pressure checks for truck drivers on a regular basis. We know that any tire with less than 80% of the recommended inflation pressure must be deflated, demounted and inspected before it can be returned to service. What do we do when a hot tire is underinflated but above the 80% threshold?

A. According to the Rubber Manufacturers Association/RMA, underinflated hot tires above the 80% threshold should be inflated to the cold inflation pressure plus 10psi. Once the tire cools to atmospheric temperature, the inflation pressure can be adjusted to the correct level.

Q. Can regrooved tires be used on the steer axle of a dump truck?

A. Yes. The only type of vehicle with restrictions on steer tires is a bus. A bus cannot be operated with regrooved or retreaded tires on the front axle, but other vehicles can. (TRIB does NOT recommend the use of regrooved tires on steer axle of any vehicle)

Q. How long does a truck have to sit before the cold inflation pressure can be read?

A. Generally, the cold inflation pressure can be recorded after the vehicle has been parked for at least 3 hours.

Q. How do you measure dual tire spacing?

A. Dual tire spacing is measured from the centerline of the outside tire to the centerline of the inside tire.

Q. We know that temperature changes have a direct effect on inflation pressures. What about altitude?

A. For every 1,000-foot increase in altitude, there’s a 0.5 psi increase in inflation pressure. So a tire that starts in Denver inflated to 100 psi will read around 97 psi at sea level and a tire inflated to 100 psi at sea level will read around 103 psi in Denver. In other words, it doesn’t have much of an effect.

Q. How many repairs are acceptable in a standard tubeless radial truck tire?

A. The number of repairs is unlimited, as long as the repair units do not overlap, and the same radial body cable is not injured more than once.

Q. At what point will a truck tire burst from overinflation?

A. Most new or undamaged medium radial truck tires can withstand three to four times the recommended pressure before bursting. In fact, the rim usually fails before the tire. ITRA has conducted several burst strength tests on new and used medium radial truck tires with special reinforced rims. The tires were pressurized with water. Most recently, three new tires and 13 used tires were “burst tested” with the lowest pressure burst recorded at 300psi and highest at 540psi for an average of 420psi. All of the test tires failed in the bead area.

Q. How do I know if my tires are suitable for retreading?

A. Only your retreader can make that determination after your tires have been inspected in the retread plant. Tires that have been run underinflated or have been pulled with less than 4/32″ of tread left are more likely to be rejected than tires that have been properly maintained and pulled with 5/32″ or more tread remaining. This is, of course, a good argument for properly maintaining tires. Before the retread process begins all tires are subjected to both a visual inspection and an inspection on a non-destructive testing machine (there are several equally good systems now in use). Only those tires that pass this stringent inspection are allowed to continue through the retread process.

Q. How many times can a steel radial truck tire be retreaded?

A. That depends on the condition of the tire and how much damage it has accumulated. Long haul, high-speed operations usually retread their tires two or three times. While fleets, such as garbage hauler and other local service operations that wear tires out very quickly, can sometimes retread their tires five or more times if they are properly maintained.

Q. Which are affected more by underinflation, radial or bias truck tires?

A. The extent of underinflation and the speed and distance the tire ran are factors to consider. Also, underinflation affects tubeless and tube-type tires differently. In fact, it causes so many conditions we think it best to state that underinflation causes damage to all tires and should be avoided. We do not recommend any tire as being better than another when run underinflated.

Q. Which type of nail hole repair does the best job, one, or two-piece?

A. If properly applied, both types work extremely well, but there is a difference in how the two can be used. A one-piece repair is appropriate if the angle of the penetration through the tire does not exceed 25 degrees. A two-piece repair can be used regardless of the penetration angle. When a single piece repair is installed with the stem angle at greater than 25 degrees, the stem often breaks off at the patch.

Q. I heard that before mounting a commercial truck tire that may have been run low or flat, it must be inflated to 20 psi above the recommended inflation pressure. Is this true?

A. The Rubber Manufacturers Association (RMA) recommended practice states that any tire suspected of having run low or flat must not only be inflated in a safety cage to 20 psi over its recommended inflation pressure, it must retain that pressure for 20 minutes. It must then be lowered to the recommended pressure before being returned to service.

Q. We know that underinflation shortens a tire’s life. Does overinflation do the same?

A. It depends on the type of tire, vehicle speed, travel distance and the surface it travels on. Overinflation can cause irregular tread wear, poor handling characteristics and severe impact and cut damage, on rough or rocky roads. Check with your vehicle manufacturer and tire supplier for their recommendations for your particular situation.

Q. Which surface wears a tire faster, a wet or dry surface?

A. If the tire is free rolling and not slipping, a wet surface lubricates and cools the contact area of the tire, thereby causing it to wear at a slower rate.

Q. What is the origin of the word rubber?

A. Believe it or not, in 1770 an English chemist named Joseph Priestly created the word “rubber” when he found the material could remove pencil marks from paper.

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