Direct Answer
49 CFR 393.75(a)(3) is a federal tire regulation requiring that no tire on a motor vehicle be operated when its tread depth is less than 2/32 of an inch on any major tread groove on a steering axle. A violation of this standard is an Out-of-Service (OOS) condition: the vehicle cannot move until the tire is replaced.
What This Means
When a DOT roadside inspector finds a tire on your steering axle with a tread depth below 2/32 of an inch, they cite the driver under 393.75(a)(3). This is not a warning. It is an immediate Out-of-Service order. The vehicle stays parked until the defective tire is replaced and the driver is cleared to continue.
For non-steering axles (drive and trailer axles), the threshold is 1/32 inch under 393.75(b). Violations there are also cited but are not automatically OOS conditions, though inspectors may still place the vehicle OOS if multiple tires are near the threshold.
Regulation Context
- CFR Reference: 49 CFR 393.75(a)(3)
- Full Rule Name: Part 393: Parts and Accessories Necessary for Safe Operation, Subpart H: Tires
- Enforced by: FMCSA, in conjunction with state patrol officers during Level I, II, and III roadside inspections
The regulation covers all commercial motor vehicles (CMVs) operating in interstate commerce. It applies to every tire on the vehicle (including steer, drive, and trailer tires) with different thresholds depending on axle position.
Severity & OOS Impact
| Axle Position | Minimum Tread Depth | OOS Condition? |
|---|---|---|
| Steering axle | 2/32 inch | Yes, immediate OOS |
| All other axles | 1/32 inch | Conditional (inspector discretion) |
| Any tire (flat/audible leak) | N/A | Yes, immediate OOS |
| Any tire (visible ply/cord showing) | N/A | Yes, immediate OOS |
An OOS violation is the most severe outcome of a roadside inspection. It stops your truck, costs hours or days of delay, and triggers mandatory review in the FMCSA's SMS (Safety Measurement System).
CSA / BASIC Impact
393.75(a)(3) violations count against the Vehicle Maintenance BASIC in the FMCSA's CSA (Compliance, Safety, Accountability) program.
- BASIC affected: Vehicle Maintenance
- Severity weight: OOS tire violations carry a severity weight of 10 (highest tier on a 1–10 scale)
- Time on record: Violations stay on your BASIC score for 24 months from the inspection date
- Threshold: FMCSA places carriers above 80% in Vehicle Maintenance under intervention consideration
Multiple tire violations across inspections will rapidly push your Vehicle Maintenance BASIC percentile into alert territory. A single OOS tire violation on a small fleet with few total inspections can cause a significant percentile jump.
Corrective Action Steps
- Remove the vehicle from service immediately. Do not allow the driver to continue operating with the cited tire.
- Replace the defective tire with one meeting 49 CFR 393.75 standards before the vehicle moves.
- Complete a post-inspection repair order documenting the tire replaced: size, brand, tread depth at time of replacement, technician name, and date/time.
- Conduct a fleet-wide tire audit within 48 hours. Pull tread depth readings for all steering axles across your active vehicles.
- Document findings. Record readings for every tire inspected. This creates audit-ready evidence even for tires that passed.
- Update your pre-trip inspection checklist to require drivers to record tread depth readings, not just mark "OK."
- Create a tire replacement threshold. Most fleets replace steering tires at 4/32 inch to stay well above the legal floor.
- Brief your drivers. Ensure every driver understands that a tire violation at or below 2/32 on steer axles means OOS.
Evidence Checklist
- ☐ Copy of the original inspection report (DataQ or paper form)
- ☐ Repair order showing the specific tire replaced (axle position, size, brand)
- ☐ Tread depth measurement at time of replacement
- ☐ Technician name, certification, and date of repair
- ☐ Post-repair vehicle inspection sign-off
- ☐ Fleet-wide tire audit results (all vehicles, all axles)
- ☐ Updated pre-trip inspection form showing tread depth field
- ☐ Driver training acknowledgment (if retraining was conducted)
- ☐ Any photos taken at time of inspection or replacement
Prevention Tips
Implement a tread depth program. Set internal replacement thresholds at 4/32 inch for steer tires, 2/32 above the legal minimum. This creates a buffer and removes judgment calls from drivers on the road.
Use calibrated tread depth gauges. Issue one to every driver and require its use during pre-trip and post-trip inspections. Record readings in your inspection log.
Schedule regular tire rotations and inspections. High-mileage routes wear steer tires unevenly. Build tire inspection into your PM (preventive maintenance) schedule every 15,000–20,000 miles.
Train drivers on what to look for. Beyond tread depth, drivers should flag exposed cords, sidewall bulges, and audible air leaks immediately. All are OOS conditions under 393.75.
Track violations by driver and vehicle. If the same truck keeps generating tire violations, it may indicate a maintenance workflow problem, not just bad luck.
Frequently Asked Questions
Q: Does 393.75(a)(3) apply to trailer tires? Yes, the regulation applies to all tires on a commercial motor vehicle, including trailers. The threshold for non-steer trailer tires is 1/32 inch under 393.75(b), not 2/32.
Q: Can the driver continue after a 393.75(a)(3) violation if the tread depth is close to 2/32? No. A tire at or below 2/32 inch on a steer axle is an automatic Out-of-Service condition. The vehicle cannot move until the tire is replaced and the driver is cleared by the inspector.
Q: How much does this violation affect our CSA score? Tire violations carry a severity weight of 10, the highest in the Vehicle Maintenance BASIC. A single OOS tire violation will have a meaningful impact on your percentile, especially for smaller fleets with fewer total inspections.
Q: How long does a 393.75 violation stay on record? 24 months from the date of inspection. After that it drops out of the 24-month SMS calculation, though it remains in the FMCSA inspection history.
Q: What if we think the violation was issued in error? You can contest the violation through the FMCSA DataQs system at dataqs.fmcsa.dot.gov. Submit evidence including photos, inspection records, and repair documentation. Successful DataQs challenges remove the violation from your SMS record.