What 393.75B-OOS means in plain language
When an inspector cites you for 393.75B-OOS, they've found that a tire on your steer axle has less than 4/32 inch of tread depth. This is a federal requirement under FMCSR Part 393—your steering tires must meet this minimum threshold to stay legal on the road.
Steer axle tires are critical because they control your truck's direction and stability. Worn tread reduces grip, especially in rain or snow, and increases stopping distance. The 4/32 inch standard is the federal floor; many fleets and insurance companies enforce higher standards internally, but 4/32 is the legal limit.
If your citation is issued at roadside, the inspector will likely measure the tread depth with a penny or gauge. If tread is confirmed below 4/32, you'll receive a citation and, in most cases, an out-of-service order (OOS) that prevents you from operating the truck until the tire is replaced or repaired.
What our enforcement data actually shows
Across our 13 million+ inspection records, 393.75B-OOS is ranked #1109 of 3,036 FMCSR codes by citation volume. We see enforcement intensity increasing: 138 citations were issued in the last 12 months, with 28 in the past 90 days alone.
The enforcement consequence is severe. Our data shows that 73.1% of all 393.75B-OOS citations result in an out-of-service order—that means 207 out of 283 all-time citations led to the truck being pulled from service. This rate is far above the all-FMCSR average of 31.4%, making this one of the more likely codes to trigger an immediate roadside shutdown.
The trend over the past 12 months shows volatility: May 2025 saw a spike with 24 citations (16 OOS), while recent months have settled lower. February 2026 recorded 12 citations with 9 OOS placements, and March 2026 saw 15 citations with 11 OOS orders.
Who gets cited most
Geographically, our inspection records show three states dominating 393.75B-OOS enforcement over the past 180 days: North Carolina (21 citations, 85.7% OOS rate), Illinois (12 citations, 66.7% OOS rate), and Iowa (11 citations, 90.9% OOS rate). The OOS rate variance is material—Iowa's 90.9% is significantly stricter than Illinois' 66.7%—suggesting more aggressive enforcement or different inspection practices across these jurisdictions.
By carrier, our data shows fleets such as EZ CARGO INC (USDOT 3077844) and SOUTHVIEW SANITATION SERVICES INC (USDOT 4183417) with 3 citations each in our all-time records. Several smaller operators have 2 citations each. These numbers reflect inspection frequency and fleet size variation rather than any pattern of negligence; they simply appear in the data because their trucks were inspected and found non-compliant.
How severe is this compared to similar codes
Within the vehicle maintenance category, 393.75B-OOS sits in a middle tier for OOS consequence. Compare it to three peer codes: 393.9(a) — Inoperable required lamps has 660,737 all-time citations but only a 15.4% OOS rate, far lower than 393.75B-OOS. By contrast, 396.3(a)(1) — Inspection/repair/maintenance general has 236,919 citations with a 45.3% OOS rate, still below 393.75B-OOS. And 393.78 — Windshield condition defective has 157,894 citations with a 0.3% OOS rate, nearly never resulting in out-of-service.
The data indicates that steer tire tread depth is treated as a safety-critical defect: inspectors and enforcement agencies view a worn steer tire as an immediate hazard, not a minor cosmetic issue. Your likelihood of being sent OOS is dramatically higher with this code than with lamp or windshield violations.
How to avoid it
Prevent 393.75B-OOS by making steer tire inspection part of your daily pre-trip routine:
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Check tread depth before every departure. Use a penny test (insert Lincoln's head into the tread) or a dedicated tread-depth gauge. If you can see the top of Lincoln's head, your tread is below 4/32 inch. Do not operate the truck.
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Inspect steer tires for uneven wear or balding. Wear patterns reveal suspension or alignment issues. Trucks with FRHT, INTL, FORD, and KW makes—the top four vehicle makes in our citation data—should get extra attention because they represent the highest volume of steer-tire citations.
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Conduct a complete tire and lighting walk-around. Our data shows that 393.9 (Inoperable Required Lamp) co-occurs in 9 of the last 90 days' 393.75B-OOS inspections, and 393.78 (Windshield condition defective) in 5 shared inspections. If your truck failed pre-trip inspection once, multiple defects often cluster. Address one issue and systematically check the rest.
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Replace steer tires proactively, not reactively. Don't wait until tread is marginal. Most professional fleets replace steer tires at 6/32 inch or higher to build in a safety margin and avoid roadside citations.
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Verify your carrier's tire maintenance schedule. If you're an owner-operator, maintain documented tire rotations and inspections. Our data shows that 396.17C (No proof of periodic inspection) co-occurs in 3 recent 393.75B-OOS cases, indicating that lack of maintenance records accompanies tire failures.
If you've already been cited and placed out-of-service, replace the tire immediately and request re-inspection before moving the truck. An OOS order is a hard stop—operating with one can result in additional fines and CSA points that affect your safety rating for years.