Lesson 1.2 — Tires

Why this matters

Tires are the #2 reason trucks get put out of service at the roadside. In the 2025 CVSA International Roadcheck, tires accounted for 21.4% of all vehicle out-of-service orders — 2,899 trucks shut down in 72 hours.

Tires also cause 53.5% of all roadside breakdowns — the single biggest reason trucks stop on the side of the road.

If a tire fails inspection, you stop. The load stops. You don't drive until it's fixed. This module shows you the checks to do on every tire before every trip so it doesn't happen to you.

4/32" Steer tires (front tires only). Below 4/32" = out of service.

2/32" All other tires — drives, trailer, dolly. Below 2/32" = out of service.

Measured in the main tread groove. A tread depth gauge costs less than $10 and takes 15 seconds per tire. Do not eyeball it. A tire at 3/32" on a steer axle looks fine but is below the limit.

1 Air pressure

1. Use a calibrated air pressure gauge. Not your foot. Not a thump with a tire billy.
2. Check when tires are cold (before driving, or sat 3+ hours).
3. Compare against the pressure stamped on the tire sidewall and the load you are carrying.

Out of service: any tire below 50% of the maximum pressure stamped on the sidewall. A tire stamped 105 PSI max is out of service at 52 PSI or less.

If you hear a hiss or feel air leaking — STOP. Audible air leak is automatic out of service.

2 Tread depth

1. Use a tread depth gauge. Push the probe into the main tread groove.
2. Measure at two points per tire — wear is often uneven.
3. If any major groove is below the limit, that tire is out of service.

Steer tires: 4/32" or more in every major groove.

Drives and trailer: 2/32" or more in every major groove.

If below — STOP. Write it on the DVIR.

3 Sidewall

1. Look at the side of every tire. The side, not the bottom.
2. Check both sides — inner and outer. For inner duals, you must look between the wheels.
3. Run your hand over the sidewall if it is safe. Feel for bulges.

Out of service:

• Any bulge bigger than 3/8 inch (the internal cords are torn).
• Any cut or crack that shows the cord or belt material underneath.
• Any visible separation of the tread from the sidewall.

If you see any of these — STOP. A sidewall failure at 65 mph is a blowout.

4 Inner duals

1. Most drivers skip these. Most violations come from here.
2. Use a flashlight. Look between the two tires of each dual pair.
3. Check the inner tire's pressure with a long-hose gauge or valve stem extender.
4. Make sure the two tires of a dual pair are not touching each other — that means one is under-inflated.

If you can't reach the inner tire to check it — fix that first. Get a long-hose gauge. Or install valve extenders. An inner dual at 30 PSI is an out-of-service condition you cannot see from outside.

Tire is visibly flat — any visible flatness on a loaded tire means under-inflation. STOP and gauge it.

Audible hiss — listen near each valve stem and each sidewall. Any hiss you can hear means an air leak that is OOS. STOP.

Exposed cord or wire in the tread or sidewall — looks like fabric mesh or thin steel wires showing through worn rubber. Automatic OOS. STOP.

Sidewall bulge or "egg" — a swelling on the side of the tire, larger than 3/8 inch. Internal damage. Automatic OOS. STOP.

Wheel rust trail or shiny lug nut threads — means the wheel is moving. Could lose a wheel. STOP.

Missing valve cap — not OOS by itself but lets dirt into the valve core and causes slow leaks. Replace it.

Center-only tread wear — tire is over-inflated. Won't fail inspection but ruins the tire.

Both shoulders worn, center fine — tire has been running under-inflated. Check pressure now.

1. Carry a tread depth gauge and a pressure gauge. Both cost less than $20 together. Keep them in the cab.
2. Walk every tire before every trip. Eighteen tires. Look at every one. Both sidewalls.
3. Check inner duals every time. An inner dual at 30 PSI is a roadside OOS that costs you a day.
4. Listen for hiss. If you hear it, the inspector will hear it. Find it first.
5. Write it on the DVIR. If you see a worn tire or a slow leak — write it down. The DVIR shifts the load off you and onto the shop.

• ○ 2/32 inch
• ✓ 4/32 inch
• ○ 6/32 inch
• ○ 8/32 inch

• ○ 1/32 inch
• ✓ 2/32 inch
• ○ 4/32 inch
• ○ 6/32 inch

• ○ 90%
• ○ 75%
• ✓ 50%
• ○ 25%

• ○ Drive slowly to the next service station
• ✓ Stop, write it on the DVIR, and do not drive — an audible leak is out of service
• ○ Add air and continue
• ○ Ignore it if the gauge still reads above 80 PSI

• ○ Steer tire tread depth
• ○ Trailer tire sidewall
• ✓ Inner dual pressure
• ○ Valve stem caps