Tire Condition, Tread Depth, Size, and Load/Speed Rating Inspection

The short version — Tires are the only thing touching the road, so a proper inspection covers tread depth, wear pattern, physical damage, and whether the size/load/speed rating still matches the vehicle spec — and you always check inflation pressure first, before you try to read any wear pattern.

Why inspection order matters

Before you even look at wear patterns, check inflation pressure against the door placard, not the number molded on the sidewall. The sidewall number is a maximum, not the running pressure for that vehicle. If the tire is over- or under-inflated, the tread will show a wear pattern that has nothing to do with alignment or suspension condition — it'll look like a mechanical problem when it's really just an air pressure problem. Get pressure right first, then evaluate everything else.

Measuring and reading tread depth

Tread depth is checked with a tread depth gauge, inserted into the main grooves of the tire. Don't just check one spot:

• Check inner, center, and outer positions across the tread face.
• Check several points around the circumference, not just one.

The reason for multiple locations is simple — uneven wear only shows up if you compare positions. A tire worn evenly across the face and around the circumference tells a different story than one that's bald on the outer edge and fine everywhere else.

Every tire also has built-in wear bars (tread wear indicators) molded right into the grooves. These are raised rubber bars that sit below the tread surface when the tire is new. As the tread wears down, the bars stay the same height — so when a wear bar becomes flush with the surrounding tread, that tire is at its legal minimum tread depth. You don't need a gauge to catch this; if the bar is flush anywhere on the tire, it's done.

Reading wear patterns and visual damage

One specific wear pattern worth knowing cold: feathering. This is when the edges of the tread blocks are worn at an angle — run your hand across the tread one direction and it feels smooth, run it the other way and it feels sharp. Feathering points to a toe misalignment. This is a testable pattern-to-cause pairing — don't confuse it with other wear types.

Beyond tread wear, a full visual inspection covers:

• Cuts in the tread or sidewall
• Bulges or blisters in the sidewall
• Punctures or embedded objects
• Sidewall cracking (weathering)
• Irregular tread wear patterns generally

Any of these can mean structural damage underneath — cord damage you can't see just by looking at the outside — and can set up a tire for sudden failure. Sidewall damage or a bulge is a replace-it condition, not a repair-it condition. A repair on the tread might be fine for a puncture, but a compromised sidewall means the internal cords are damaged, and that tire needs to come off the vehicle.

Size, load index, and speed rating

The last piece of the inspection isn't about wear at all — it's about whether the tire is even the right tire. Tire size, load index, and speed rating are all printed on the sidewall, and they need to be checked against the vehicle manufacturer's specification — the door jamb placard, the owner's manual, or an equivalent tag. This is not optional cross-referencing; it's part of the inspection every time.

The critical rule here: a replacement tire's load index must be equal to or greater than the original specification. A tire with a lower load index than what the vehicle calls for is unsafe — it's not rated to carry the weight the vehicle can put on it, and that's true even if the tire "looks" like the right size or fits fine physically. Size alone doesn't confirm it's correct — load index and speed rating have to match or exceed spec too.

Easy to mix up

• Sidewall max pressure vs. placard pressure — the sidewall number is the tire's maximum rating, not the vehicle's recommended running pressure. Always use the placard for inspection and inflation checks.
• Wear bars vs. tread depth gauge — wear bars are a fast go/no-go check (flush = minimum depth reached). A gauge gives you the actual measurement and lets you compare positions to catch uneven wear early, before the bars show it.
• Feathering vs. general irregular wear — feathering has a specific feel (smooth one way, sharp the other) and a specific cause (toe misalignment). Don't lump it in with generic "irregular tread wear" from the visual damage list — it's a distinct diagnostic clue.
• Repairable damage vs. replace-it damage — punctures and embedded objects are inspection findings that may allow repair; sidewall bulges and cracking are structural red flags that mean replacement, not repair.

Check yourself

Question: You find a wear bar flush with the tread surface on the outer edge of a tire, but the center of the tread still looks deep. What does this tell you, and what should you check next?

The tire has reached its legal minimum tread depth at that location — a flush wear bar means minimum depth, period, regardless of what the rest of the tire looks like. Since it's the outer edge that's worn and not the center, check inflation pressure against the placard first (incorrect pressure can cause edge wear), and also consider it could point to an alignment issue depending on the full pattern.

Question: Technician A says a replacement tire is fine as long as it's the correct size, even if the load index is lower than the original spec. Technician B says the replacement tire's load index must be equal to or greater than the original specification. Who is right?

Technician B is right. Correct size alone doesn't make a tire safe to install — the load index must be equal to or greater than the vehicle's original specification. A lower load index is unsafe even on a tire that's otherwise the correct size.

Question: A tech runs a hand across a tire's tread and it feels sharp going one way, smooth going the other. What does this indicate, and where would you look for the cause?

This is feathering, and it indicates a toe misalignment. The cause is in the steering/alignment setup, not tread depth or inflation.