DOT roadside guy wrote up one of our customer's dump trucks for tires.

For commercial vehicle tire tread depth requirements, here are the key minimums per FMVSS No. 109 and DOT regulations:

Steer (Front) Tires:

• Minimum tread depth: 4/32 inch (3.2 mm) across one full tread width.
• Applies to the outermost groove and must be continuous.

Drive and Trailer (Rear) Tires:

• Minimum tread depth: 2/32 inch (1.6 mm) across one full tread width.
• This is the same as passenger car tires.

Additional Notes:

• Tread wear indicators (if equipped) must be visible when tread reaches the minimum.
• DOT inspections (per 49 CFR Part 396) require tires to meet these minimums.
• Retreaded tires must also meet the same tread depth standards.

Practical Tip:

Use a tread depth gauge to measure at the deepest point of the main groove. If the truck is in a state with stricter laws (e.g., California), check local regulations—some states adopt 4/32 inch for all positions.

If the DOT cited your customer for tires below these thresholds, they likely failed the tread depth requirement during a roadside inspection. Advise replacing tires before the next inspection to avoid out-of-service orders.

FMCSA 49 CFR §393.75 sets the federal minimums (most states adopt these verbatim):

| Axle Position | Minimum Tread Depth | | :--- | :--- | | Steer (Front) Axle | 4/32 inch (measured in any major groove) | | All Other Axles (Drive, Trailer, Tag, Pusher) | 2/32 inch (measured in any major groove) |

Critical Enforcement Details:

1. "Any Major Groove": If one major groove hits the limit, the tire is OOS (Out of Service). You cannot average grooves.
2. Measurement Point: Measure in the groove nearest the centerline of the tire, avoiding tie bars, humps, or stone ejectors.
3. Steer Tire Damage: Any exposed belt/cord, sidewall cut exposing ply/cord, or tread separation is an automatic OOS violation regardless of depth (§393.75(a)(1)–(3)).
4. Regrooved Tires: Allowed only on non-steer axles if marked "Regroovable" on the sidewall (§393.75(d)). Never allowed on steer axles.

Practical Tip: If the DOT officer measured 3/32" on a steer tire, the ticket is valid. Replace the tire before the truck moves under its own power (or have it towed) to clear the OOS order.