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

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.

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?

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.

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

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.

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

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.

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

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 owner’s manual in each vehicle.

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

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

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.

There is no simple answer to your 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.

How will 20 percent over inflation in a steel radial truck tire affect the tire’s performance?

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.

I understand that the maximum allowable injury for a nail whole 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.

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.