Prevention FAQ — FMCSR 393.75C: Tire Tread Depth (Other Axles)

Inspectors use a tread depth gauge to check non-steer axle tires — drive axles on the tractor and all trailer axles — against the 2/32-inch minimum. They probe the two major tread grooves at multiple points around the circumference, specifically looking for worn shoulders, uneven wear patterns, and cupping that a quick visual sweep misses.

Our inspection records show Texas alone generated 10,476 citations for this code in the last 180 days, dwarfing every other state. Illinois is a secondary hotspot: only 170 citations, but a 15.3% OOS rate — more than triple Texas's 4.5% rate — meaning Illinois inspectors are more likely to escalate when they find a violation. North Carolina adds a 6.0% OOS rate on 283 citations. If your fleet runs TX-IL-NC corridors, the probability of encountering this citation is materially higher than average.

Build these steps into the non-steer axle section of your DVIR form:

1. Gauge every drive and trailer tire with a calibrated tread depth tool — not a visual estimate. Flag any tire at or below 4/32 inch as a watch item requiring shop review within 72 hours; flag anything at or below 2/32 inch as a no-dispatch condition.
2. Check inner duals — inspectors reach between them with probes, and drivers skip them most often.
3. Look for uneven wear patterns: feathering, one-sided wear, and center wear each point to different mechanical causes that will consume tread faster on the next segment.
4. Record the measurement, not just a pass/fail checkbox. A written depth creates a trend baseline your shop can use to project replacement intervals.

With 23,963 citations in the last 12 months, a generic "tires OK" line on the DVIR is not a defensible prevention practice.

Drivers should carry:

• The current trip's signed DVIR showing the specific tread depth measurements recorded that morning.
• Any recent roadside or shop inspection report for the unit confirming tires were within specification.

Carriers must retain:

• Maintenance records showing tire inspection dates, measured depths, and the technician who signed off — retained for the life of the tire plus 12 months minimum under 396.3.
• Tire replacement work orders with odometer/date stamps so you can demonstrate proactive replacement before a citation window.
• PM schedule records that show each unit's tire inspection interval.

If a driver cannot produce a DVIR reflecting a tire check on the day of inspection, the inspector has no paperwork to counter — and the citation stands without any mitigating record for your DataQs challenge or SMS review.

The co-occurrence data from our last 90 days of inspection records reveals three strong patterns:

1. Inoperable Required Lamp (393.9) — 1,668 shared inspections: The most frequent pairing by far. When a lamp and a tire are both deficient on the same inspection, it signals a maintenance program that relies on driver reports rather than scheduled shop inspections. Drivers notice lights; they rarely measure tread depth proactively.

2. Windshield Condition Defective (393.78) — 788 shared inspections: Cosmetic defects and tire wear appearing together points to deferred-maintenance culture — repairs get prioritized by urgency rather than by scheduled interval, so slow-degrading items like tread depth fall through.

3. Brake Tubing/Hoses Inadequate (393.45B2UV) — 730 shared inspections: Brake and tire defects co-occurring in 730 inspections suggests units returning from long runs without shop review. Brake and tire wear both accelerate under heavy use; if neither is being caught between runs, periodic inspection intervals are too long or not being executed.

Verification must be independent of the technician who performed the replacement:

1. A second technician or shop supervisor gauges all non-steer axle tires after the replacement is complete — not just the replaced tire. A unit that had one worn tire often has others approaching limit.
2. Record the gauge readings on the work order alongside the technician's name and the date. This creates a documented baseline for the next inspection cycle.
3. Confirm wheel torque is within spec — a post-mount torque check prevents early irregular wear that will bring tread down faster.
4. Update the DVIR for the next driver to reflect the new tires and the measured depths, so the incoming driver has a starting point rather than an unknown.
5. For units that generated a citation, attach the repair work order to the original inspection report in your management system so the post-event audit trail is complete and retrievable if the violation is disputed.

Run a structured four-step review within 48 hours of the citation:

1. Pull the unit's full maintenance history. Determine the last dated tread depth measurement in your records. If there is no measurement on file, that is the root cause — your PM process does not capture depth, only visual checks.
2. Audit all other units in the same assignment pool. Our inspection records show this code ranks #83 out of 3,036 FMCSR codes by citation volume, meaning inspectors cite it routinely. A single citation is usually a signal that other units share the same condition.
3. Interview the driver. Was the tread marginal at pre-trip and not reported? Was the DVIR measurement recorded? The answer changes whether this is a training gap or a process gap.
4. Log the corrective action — replacement, updated PM interval, or driver coaching — in your safety management system with a due date and an owner. A citation with no documented corrective action is a liability in any future SMS review.

This code carries a CSA severity weight of 5, which is mid-range. Points are time-weighted within the 24-month SMS window, so recent citations decay in value over time but remain visible throughout that window.

The code is not OOS-eligible under normal circumstances — our database shows an all-time OOS rate of only 4.3%, compared to the all-FMCSR average of 31.4%. That lower OOS rate means citations accumulate quietly in your Vehicle Maintenance BASIC without the operational disruption that might force immediate attention.

With 23,963 citations logged in just the last 12 months across all carriers, this is a high-frequency code. Carriers that allow chronic exposure — like the top-cited carriers in our database, some with over 200 citations — build a BASIC profile that can trigger an investigation threshold without ever having had a truck placed out of service. The danger is accumulation, not single-event severity.

Our inspection records show Freightliner (FRHT) accounts for 12,854 all-time citations under this code — more than double the next highest make, Kenworth (KW) at 5,359. Utility trailers (UTIL) contribute 4,059 citations, and Wabash National (WANC) adds 3,431.

The Freightliner concentration suggests that fleets operating FRHT tractors need to specifically train drivers on the drive axle tire inspection steps for that platform — dual spacing on certain FRHT configurations makes inner dual access awkward, and drivers skip what is hard to reach. The UTIL/WANC trailer volume indicates trailer tire inspection is being skipped or rushed at drop-and-hook points.

Training topics to build:

• How to use a tread depth gauge correctly on duals, including inner tires
• How to identify uneven wear patterns and what they indicate
• Why trailer tires at drop yards deteriorate faster and need measurement, not just visual inspection
• How to document depth on the DVIR rather than recording a binary pass/fail

A DataQs challenge is appropriate only when you have documented evidence that the citation was factually incorrect — not simply that the violation was minor or quickly corrected. Grounds with the strongest success probability:

1. The DVIR from that morning shows a recorded tread depth above 2/32 inch on all non-steer axle tires, with the driver's and supervisor's signatures. This is direct contradicting documentation.
2. The inspection report identifies the wrong axle or tire position — if the cited axle doesn't match the actual unit configuration, that is a recordable error.
3. A shop inspection completed within 24–48 hours of the citation documents all tires as compliant at the time of inspection, and you have reason to believe the inspector misread or mis-gauged the tire.

Do not file a challenge simply because the tire was replaced after the citation — replacement confirms the violation existed. Illinois's 15.3% OOS rate on this code also suggests inspectors in that state are applying stricter judgment; a challenge there requires especially solid documentation to succeed.

Our inspection records show citation volume for this code is sustained and growing: the last 12 months logged 23,963 citations, and the 90-day count of 5,491 annualizes to roughly 22,000 — consistent with the full-year pace. Monthly counts have ranged from 1,871 to 2,391 citations across the most recent full months, with no seasonal dip that would suggest a safe period to relax scrutiny. October 2025 and February–March 2026 were the three highest months, each above 2,300.

Recommended audit cadence:

• Every PM cycle (or every 25,000–30,000 miles, whichever comes first): shop-level tread depth measurement recorded on the maintenance record for all non-steer axle tires.
• Monthly spot audit: Pull 10% of active units for a shop tire measurement independent of driver DVIR entries. Compare results against DVIR records to test whether drivers are actually measuring or estimating.
• Post-border-crossing review for cross-border Mexico corridor units: our carrier data shows the most-cited carriers in our database are cross-border Mexico operators, where vehicle condition management across two regulatory environments creates gaps that a consistent PM schedule must close.