Part 393

Section § 393.75: Tires.

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Question 1: If a Commercial Motor Vehicle (CMV) has a defective tire, may the driver remove the defective tire from the axle and drive with three tires on an axle instead of four?

Guidance: Yes, provided the weight on all of the remaining tires does not exceed the maximum allowed under §393.75(f).

Question 2: May a Commercial Motor Vehicle (CMV) be operated with tires that carry a greater weight than the weight marked on the side wall of the tires?

Guidance: Yes, but only if the Commercial Motor Vehicle (CMV) is being operated under the terms of a State-issued special permit, and at a reduced speed that is appropriate to compensate for tire loading in excess of the rated capacity.

Question 3: May a vehicle transport HM when equipped with retreaded tires?

Guidance: Yes. The only Commercial Motor Carrier (CMV) that may not utilize retreaded tires is a bus, and then only on its front wheels.

Question 4: May tires be filled with materials other than air (e.g., silicone, polyurethane)?

Guidance: §393.75 does not prohibit the use of tires filled with material other than air. However, §393.3 may prohibit the use of such tires under certain circumstances. Some substances used in place of air in tires may not maintain a constant physical state at different temperatures. While these substances are solid at lower temperatures, the increase in temperature from highway use may result in the substance changing from a solid to a liquid. The use of a substance which could undergo such a change in its physical characteristics is not safe, and is not in compliance with §393.3.