At a glance
| Topic | Rule | Why it matters |
|---|---|---|
| 393.75(a) | No exposed ply or belt, tread or sidewall separation, flat tire, audible leak, or cut exposing cords. | These are direct unsafe-condition triggers. |
| 393.75(b) | Front tires on a truck or truck tractor need at least 4/32 inch of tread depth. | Steer tires are inspected more strictly because failure risk is more severe. |
| 393.75(c) | Other CMV tires generally need at least 2/32 inch of tread depth. | This covers drive, trailer, and many other non-steer positions. |
| 393.75(e) and (i) | Certain regrooved tires are restricted on front wheels, and tires must be inflated for the load carried. | Position-specific tire use and inflation both matter, not just tread. |
What matters most
Drivers should know the items inspectors commonly find under 393.75: low steer tread, flat or leaking tires, exposed belt or ply, cuts, separation, and low inflation for the load.
Fleet teams should treat 393.75 as a maintenance-control rule, not just an enforcement rule. Replacement timing, inflation programs, and axle-position controls should all map back to it.
If a driver or fleet manager only remembers one FMCSA tire citation number, 393.75 is the practical one. It is where condition, tread, and inflation expectations come together in a way that directly affects roadside inspections.
That does not mean every tire problem is complicated. The value of knowing the rule is that it gives the shop, dispatcher, and driver a common standard for what must be fixed before the truck is released.
Steer tires are treated differently because a steer-tire failure can be more dangerous at highway speeds and under loaded conditions. That is why the tread-depth minimum is higher on the front wheels of a truck or truck tractor.
This also changes replacement planning. Fleets often need separate steer, drive, and trailer replacement standards instead of one generic tread target across the whole combination.
A tire can look acceptable and still be noncompliant if it does not have the cold inflation pressure needed for the load. That is one reason fleets with good inflation discipline usually avoid a large share of avoidable roadside tire violations.
If your route, cargo, or trailer configuration changes often, inflation programs and training should be part of the compliance system, not an afterthought.
Checklists
Pre-trip or driver checklist
- Inspect steer tires first and separately from the rest of the combination.
- Confirm tread depth in major grooves, not on tie bars or humps.
- Check for cuts, exposed cords, separations, and air loss.
- Verify tire inflation against the actual operating load or fleet standard.
- Flag regrooved or retreaded front-position issues before dispatch.
Fleet owner or manager checklist
- Set axle-position replacement rules that match 393.75 thresholds.
- Document inflation targets by tire size and route load assumption.
- Control regrooved and retread casing placement on front positions.
- Audit shop practices for when a tire is repaired versus replaced.
- Use roadside inspection data to spot repeat 393.75 violations by terminal or account.
Avoid common roadside problems
What gets trucks in trouble
- Steer tires worn below 4/32 inch.
- Trailer or drive tires worn below 2/32 inch.
- Visible belt or ply from impact or wear.
- Underinflated or audibly leaking commercial tires.
- Using a prohibited tire type on the front axle.
What to do before an inspector sees the truck
- Know which tire positions are subject to the higher front-axle tread rule.
- Do a last walkaround focused only on the defect list in 393.75(a).
- If the route is loaded differently than usual, re-check inflation assumptions.
- Be ready to show that listed DVIR tire defects were repaired before reuse.
Related pages
Return to the main Tire University hub.
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Open pagePre-trip tire inspection checklistUse a tire-first pre-trip routine before dispatch.
Open pageFind steer tiresBrowse steer-position commercial tire pages.
Open pageFind drive tiresBrowse drive-position commercial tire pages.
Open pageFind trailer tiresBrowse trailer-position commercial tire pages.
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Open pageQuestions people ask
01What is 49 CFR 393.75?
It is the FMCSA tire rule that covers unsafe tire conditions, tread depth, front-tire restrictions, load carrying, and inflation pressure for commercial motor vehicles.
02What tread depth does 393.75 require on steer tires?
At least 4/32 inch in a major tread groove on the front wheels of a truck or truck tractor.
03Does 393.75 cover underinflation?
Yes. The rule says a tire cannot be operated below the cold inflation pressure needed for the load being carried.
04Can a leaking tire be cited under 393.75?
Yes. A flat tire or a tire with an audible leak is directly listed in 393.75(a).
05What should fleets do with 393.75?
Translate it into axle-position replacement rules, inflation controls, DVIR repair closure, and roadside trend review.
Official sources
Check the primary sources when a compliance decision matters.