What 393.75(b) means in plain language
This regulation targets one of the most safety-critical tires on your truck: the steer axle tire. The rule requires that every tire mounted on the steer axle maintain a minimum tread depth of 4/32 of an inch across the major grooves. If an inspector measures any steer tire and finds the tread worn below that threshold, you are in violation of 393.75(b).
Why steer axle tires specifically? Because they control the direction of the vehicle. A worn steer tire dramatically reduces your ability to channel water away from the contact patch, shortens stopping distances, and degrades your steering response — especially at highway speeds or in wet conditions. The regulation treats these tires differently from drive and trailer tires precisely because the consequences of failure are so immediate and so severe.
The standard is simple to check and simple to violate. A tread depth gauge costs a few dollars, takes ten seconds to use, and is the difference between rolling through an inspection and being parked on the side of the road.
What our enforcement data actually shows
Across our database of 13 million+ roadside inspections, 393.75(b) has accumulated 10,962 all-time citations, ranking it 218th out of 3,036 FMCSR codes by citation volume. That puts it in the top 8% of all federal motor carrier safety codes by frequency — this is not a rare or obscure violation.
Of those 10,962 citations, 2,298 resulted in the vehicle being placed out of service, producing an all-time OOS rate of 21.0%. To put that in context, the all-FMCSR average OOS rate across every code in our database is 31.4%. So 393.75(b) runs about 10 percentage points below the average — inspectors do not place every cited vehicle out of service, but more than one in five vehicles cited for this violation get parked on the spot. If you are cited, the odds are roughly 1-in-5 that you are not driving that truck until the tire is replaced.
One important signal in our data: both the last 12 months and the last 90 days show 0 citations recorded. This reflects how citation data flows into our database and how coding practices shift over time — it does not mean this violation has disappeared from enforcement. The 10,962 historical records remain fully active in CSA scoring calculations.
Who gets cited most
The top vehicle makes in our citation records tell a clear story about where this violation clusters. FRHT leads with 876 citations, followed by FORD at 688 and FREIGHTLIN at 495. KW (Kenworth) accounts for 352 citations and INTL for 309. The pattern spans the full range of commercial vehicle types — this is not a problem isolated to one manufacturer or one segment of the fleet.
Among carriers, our data shows fleets such as CNC LOGISTICS S DE RL DE CV (USDOT 2726203) with 38 citations and RS TRANSFER SA DE CV (USDOT 1156825) with 31 citations leading the all-time count. Notably, large, well-resourced carriers also appear: FEDERAL EXPRESS CORPORATION (USDOT 86876) shows 26 citations and UNITED PARCEL SERVICE INC (USDOT 21800) shows 21 citations. The data makes clear that no fleet size or operation type is immune — steer tire wear is a universal maintenance challenge.
How severe is this compared to similar codes
Placing 393.75(b) alongside peer codes in the Vehicle Maintenance category shows it is a mid-volume violation with a meaningful OOS risk relative to some neighbors.
Consider 393.9(a) — Inoperable required lamps, which has 660,737 all-time citations at a 15.4% OOS rate. That code is cited roughly 60 times more often than 393.75(b), but its OOS rate is lower. Inspectors are more likely to park you for a steer tire violation than for a lamp violation.
396.3(a)(1) — Inspection, repair, and maintenance (general) sits at 236,919 citations with a 45.3% OOS rate — more than double the OOS rate of 393.75(b). That code is a catch-all for systemic maintenance failures; 393.75(b) is a specific, measurable defect with a defined threshold.
393.78 — Windshield condition defective logs 157,894 citations but carries only a 0.3% OOS rate, meaning inspectors almost never park a truck solely for a windshield issue. A steer tire violation at 21.0% OOS is substantially more likely to end your day.
The takeaway: 393.75(b) carries a CSA severity weight of 7 and an OOS rate that, while below the all-FMCSR average, is high enough that you cannot treat it as a paperwork issue. It stops trucks.
How to avoid it
Every one of these actions can be completed during your pre-trip inspection before you ever pull out of the terminal.
- Carry a tread depth gauge and use it on every steer tire, every trip. The legal minimum is 4/32 inch. A gauge that reads 5/32 means you have almost no margin — replace the tire before it reaches the threshold, not after.
- Pay extra attention on FRHT, Ford, and Freightlin platforms. Our data shows these vehicle makes account for the highest citation counts — 876, 688, and 495 respectively. If you operate one of these trucks, steer tire inspection should be a non-negotiable pre-trip step.
- Check tread depth at multiple points across the tire width. Uneven wear can leave the center of the tread above 4/32 while the shoulder is already below. Inspectors probe the lowest point. You should too.
- Look for signs of uneven wear during the inspection. Cupping, feathering, or one-sided wear signals a wheel alignment or suspension problem that will eat through a new steer tire just as fast. Fix the root cause, not just the symptom.
- Log your tread depth readings in your pre-trip notes. If you are cited and can demonstrate a documented inspection history showing gradual wear, that record supports your driver file and your fleet's safety management case during a DataQs challenge.
- Do not defer a steer tire that is close to the limit. The 21.0% OOS rate in our records means that more than 2,200 drivers were parked roadside for this violation. The cost of a new steer tire is a fraction of the cost of a delayed load, a CSA severity weight 7 hit, and a potential OOS order.