§393.75 Tires

Question 1: If a 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(g).

Question 2: May a vehicle transport HM when equipped with retreaded tires?

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

Question 3: May tires be filled with materials other than air (e.g., silicone, polyurethane)?

Guidance: Section 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.

Question 4: Do tires marked ‘‘NHS’’ (not for highway service) mean that highway use is prohibited by §393.75?

Guidance: No, provided the use of such tires does not decrease the safety of operations (see Periodic Inspection Requirements, Appendix G to subpart B).