Tire Inspection
Dual Tire Inspection Checklist
Dual tire assemblies create an inspection problem: one tire is easy to see and one is not. The inside tire is hidden from a casual walk-around and can be underinflated, damaged, or near removal limits without any visible sign from outside the truck.
This checklist treats both tires in a dual set as separate inspection items, not as a unit where checking the outside tells you anything about the inside.
Dual inspection sequence
| Step | What to do | What to look for |
|---|---|---|
| 1 | Check outside tire tread depth with gauge | Depth at both shoulders and center; record the lowest reading |
| 2 | Check inside tire tread depth — use gauge through the gap | Inside tread depth may differ from outside; record separately |
| 3 | Check outside tire pressure | Record reading; compare to target |
| 4 | Check inside tire pressure — valve must be accessible or a pressure extension is needed | Pressure may differ significantly from outside tire; a difference of more than 5 PSI indicates a likely slow leak in the lower tire |
| 5 | Inspect outside sidewalls — both sides of the outside tire are accessible | Cuts, bulges, cracking, bead damage |
| 6 | Inspect inside tire sidewall — use flashlight through gap | Bulges, cuts, heat marks, bead area condition |
| 7 | Check valve stems on both tires | Missing caps, bent stems, corrosion, hissing |
| 8 | Check dual spacing | Sidewall contact or clearance significantly narrowed by tire size change |
Pressure in dual assemblies
Both tires in a dual set should be within 5 PSI of each other. A larger difference means one tire is carrying more of the load and wearing faster. The lower reading controls the decision: if either tire is below the target, both may need attention. Never bleed pressure from the higher tire to equalize — investigate why the lower tire is low.
Tread depth matching in dual sets
Industry guidance generally calls for dual mates to be within 4/32 inch of each other in tread depth. A larger difference means the two tires have different circumferences, causing one to drag against the road. When replacing one tire in a dual set, verify the remaining tire's tread depth is within an acceptable range of the replacement before mounting.
Inside dual access
- Some valve configurations allow pressure checks through the gap between duals without disassembly.
- Where inside valve access is limited, a flexible valve stem extension can make regular checks practical.
- Tread depth can be measured through the gap with a probe-style depth gauge.
- Sidewall inspection requires adequate light and a deliberate look, not a passing glance.
Step-by-Step Checklist
- Measure tread depth on both tires in each dual set — not just the outside.
- Check pressure on both tires separately.
- Inspect the inside tire sidewall with a flashlight.
- Check both valve stems and caps.
- Record any depth or pressure difference greater than the matching threshold.
FAQ
Why is the inside dual so often overlooked?
The inside dual is physically harder to reach and less visible from the normal pre-trip walk-around position. A driver working through a standard pre-trip may check the outside dual quickly and move on, not realizing the inside tire is significantly low or damaged. The outside tire can look and feel correct while the inside is underinflated, worn to the removal limit, or has a sidewall bulge. This is why dual inspection requires deliberate effort with light and a depth gauge, not just a visual pass.
How do I check the inside dual tire pressure if I cannot reach the valve?
Flexible valve stem extensions — available from tire supply vendors — thread onto the inside valve and route the valve outside the assembly for practical access. Some wheel designs position the inside valve at a location reachable through the gap between duals. If neither is available, a tire gauge with a long probe can sometimes reach inside. Valve stem extensions are inexpensive and make regular inside dual pressure checks practical for daily inspection.
What happens if the inside dual runs significantly low?
The outside tire — which is at correct pressure — carries more than its share of the axle load, wearing faster than it should. The inside tire, running underinflated, generates excess heat and may experience edge wear, potential sidewall fatigue, or, in severe cases, tread separation. The inside tire's lower pressure is often invisible until the tire fails or is measured. Regular inside dual pressure checks prevent an avoidable failure from developing unnoticed.
Source Notes
- Government 49 CFR 393.75 - Tires
- Government 49 CFR Part 396 - Inspection, Repair, and Maintenance
- Government TireWise Tire Safety
- Site note TruckTireGuide.com editorial notes