What 393.75B means in plain language
Every steer axle tire on your commercial motor vehicle must maintain a minimum tread depth of 4/32 of an inch. When an inspector measures your steer tires and finds the tread worn below that threshold, you're looking at a 393.75B citation. The steer axle gets its own stricter rule — separate from drive or trailer axles — because those are the tires directly controlling your steering response.
The 4/32-inch requirement isn't a gray area. Inspectors use a tread-depth gauge, place it in the major tread groove, and either the measurement clears 4/32 or it doesn't. There's no rounding up, no wiggle room for "close enough." If it reads low on even one steer tire, you're cited.
The practical implication is straightforward: worn steer tires don't just invite citations, they directly affect your stopping distance and directional control, especially on wet or uneven pavement. This code exists because a steer tire failure at highway speed is a catastrophic event, not just a maintenance inconvenience.
What our enforcement data actually shows
Across our 13 million+ inspection records, 393.75B has generated 2,959 all-time citations, placing it at #442 out of 3,036 FMCSR codes by citation volume. That's a meaningful enforcement presence — not a rarely-enforced obscure rule. Over just the last 12 months, our inspection records show 1,796 citations issued under this code, and 380 of those came in the last 90 days alone, indicating this is an actively enforced violation right now.
While 393.75B is classified as OOS-eligible, our data shows inspectors exercise significant discretion here. Of all 2,959 all-time citations, 474 resulted in an out-of-service order — a 16.0% OOS rate. For context, the all-FMCSR average OOS rate across all codes in our database is 31.4%. So while being placed OOS is absolutely possible with this citation, it happens at roughly half the rate of the average violation. The other 2,485 cited vehicles — about 84% — were allowed to continue operating after receiving the citation.
Looking at monthly trends, our inspection records show a consistent enforcement cadence throughout the year. Citations peaked at 191 in October 2025 and stayed elevated through early 2026, with 170 citations each in both February and March 2026. The CSA severity weight for 393.75B is 7, which means every citation lands on your safety record with real scoring impact, even when you're not placed OOS.
Who gets cited most
Breaking down the last 180 days geographically, three states dominate enforcement activity for 393.75B in our database. Texas leads by a wide margin with 719 citations, and 124 of those resulted in OOS orders — a 17.2% OOS rate in that state. If you run cross-border corridors through Texas, this code should be on your pre-trip checklist every time.
Iowa comes in second with 31 citations, but inspectors there placed vehicles OOS at only a 6.5% rate — more than 10 percentage points below the Texas rate. Illinois follows with 27 citations and a 7.4% OOS rate. That 10+ percentage point gap between Texas and the other two states is material: Texas inspectors are significantly more likely to put you on the side of the road for this violation than their counterparts in Iowa or Illinois.
North Carolina recorded 16 citations with a 0.0% OOS rate over the same period, and New Mexico showed 8 citations, also with a 0.0% OOS rate — though lower citation volumes make those percentages less statistically stable.
Our data shows fleets such as CNC LOGISTICS S DE RL DE CV (USDOT 2726203) with 21 all-time citations and TRANSPORTADORA NORTE DE CHIHUAHUA S A DE C V (USDOT 711125) with 20 all-time citations have accumulated the highest totals in our records. The heavy concentration of cross-border Mexican carriers in the top-cited list aligns with the Texas enforcement dominance — the border crossing inspection corridors are where this code is being enforced at volume.
How severe is this compared to similar codes
Putting 393.75B in context within the Vehicle Maintenance category, compare it against a few peer codes from our database. Inoperable required lamps under 393.9(a) has generated 660,737 citations — more than 223 times the volume of 393.75B — with a 15.4% OOS rate that sits close to 393.75B's 16.0% rate. So on OOS risk, these two codes behave similarly, but lamp violations get cited at a dramatically higher frequency.
Look at 396.3(a)(1), covering general inspection, repair, and maintenance obligations: 236,919 citations in our records with a 45.3% OOS rate. That OOS rate is nearly three times higher than 393.75B's 16.0% rate, meaning a general maintenance failure citation is far more likely to park your truck than a steer tire tread citation.
Windshield condition under 393.78 shows 157,894 citations with a 0.3% OOS rate — an enormous citation volume but almost no OOS placements. By comparison, 393.75B's 16.0% OOS rate is substantially more dangerous to your operating status than a windshield citation, even though 393.75B is cited far less often overall.
How to avoid it
The co-occurring citation patterns in our data tell you exactly where to focus your pre-trip. In the last 90 days, 393.75B appeared alongside 118 inspections that also cited inoperable lamps (393.9), 65 inspections that added other-axle tread violations (393.75C), and 60 inspections involving windshield defects (393.78). That pattern points to a vehicle that wasn't walked around carefully before departure. Here's how to break that cycle:
- Check steer tire tread depth with a physical gauge before every trip. Eyeballing tread wear is not reliable at 4/32 inch. Carry a tread depth gauge and use it. If you're close, you're already in violation territory.
- Inspect all axle tires at the same time. Our data shows 65 inspections in the last 90 days caught both 393.75B and 393.75C together — steer and other-axle violations in the same stop. If one set of tires is worn, the others often are too.
- Walk the full perimeter and check every light. 118 inspections in 90 days paired this violation with an inoperable lamp citation. If inspectors are stopping for one thing and finding another, the pre-trip wasn't thorough.
- Check your windshield and glazing while you're at the front of the truck. With 60 inspections co-citing 393.78 and 37 co-citing 393.60C (glazing obstructions), front-end condition checks are clearly being done incompletely.
- Pay extra attention on Freightliners and Kenworths. Our records show FRHT trucks cited 755 times and KW trucks cited 385 times under 393.75B all-time — the two most-cited makes by a significant margin. If you're driving either platform, tread wear history on your specific unit is worth tracking.
- Don't defer the replacement conversation with your fleet. With a CSA severity weight of 7, every 393.75B citation is scoring against both your record and your carrier's BASIC score. A set of steer tires is a known, budgetable cost. A string of severity-7 violations is not.