TIRE SIDEWALL DECODER

Size, Load, Speed & Traction Ratings — Full Reference

Every tire sidewall is a data plate. Size code, load index, speed rating, traction certifications, and manufacture date are all molded into the rubber. Misreading any one of them means an improperly rated tire on the vehicle — know what you're looking at before you recommend a replacement.

Example: P215/65R16 95H — Position Map

Service Type

215

Section Width

Aspect Ratio

Construction

Wheel Diameter

Load Index

Speed Rating

Service Type

Identifies the tire's intended vehicle class and load design. A missing letter (just a number start) indicates a Euro-metric tire — same size math, slightly different load formula than P-metric.

P = Passenger LT = Light Truck T = Temporary Spare ST = Trailer

215

Section Width

The tire's width in millimeters, measured sidewall to sidewall at the widest point when mounted and inflated to spec. Larger number, wider tire.

195 – narrow 225 – mid 275+ – wide

Aspect Ratio

Sidewall height as a percentage of section width. A 65 means sidewall height is 65% of the 215mm width. Lower number means a shorter, stiffer sidewall — common on performance fitments.

35–45 = low profile 60–70 = standard 75+ = tall

Internal Construction

How the internal body plies are oriented. Virtually every tire sold today is radial — the letter still matters for correctly identifying older bias-ply fitments on classic and trailer applications.

R = Radial D = Diagonal/Bias B = Belted Bias

Wheel Diameter

The diameter, in inches, of the wheel the tire is designed to mount on. Must match the wheel exactly — there is no acceptable tolerance here.

Measured in inches Must match wheel bead seat

Load Index

A coded number representing the maximum weight the tire can carry at full inflation, per tire. Not a direct weight figure — look it up on the load index chart before condemning or approving a fitment change.

95 = 1,521 lbs Higher = more capacity

Speed Rating

A letter code representing the maximum sustained speed the tire is certified for at full load. Never mix speed ratings across an axle, and never fit a lower rating than OEM spec without checking manufacturer approval.

H = 130 mph V = 149 mph Never go lower than OEM

DOT

DOT Date Code (separate stamp)

Not part of the size string — found in a separate DOT stamp, usually on one sidewall only. Covered in full further down this sheet.

Service Type Prefixes — Full Reference

Prefix	Meaning	Typical Use
P	P-Metric (Passenger)	Cars, minivans, light SUVs and light-duty pickups — US load formula
(none)	Euro-Metric	Same size format without the P — different load index formula at the same size, common on Euro-brand OEM fitments
LT	Light Truck	3/4-ton and 1-ton trucks, heavier trailers — higher load capacity and inflation pressure than P-metric
T	Temporary	Compact spare tires only — speed and distance limited, never a permanent fitment
ST	Special Trailer	Trailer axles only — not rated or designed for use as a drive or steer tire
C or LT (Euro)	Commercial	Vans and light commercial vehicles — reinforced sidewall for higher load duty cycles

Tread Pattern Types

Directional

V-shaped tread designed to rotate in one direction only — marked with a rotation arrow on the sidewall. Excellent water evacuation. Cannot be cross-rotated side to side without dismounting and remounting on the opposite wheel.

Non-Directional / Symmetric

Same tread pattern across the full width, no rotation arrow, no inside/outside marking. The most flexible for rotation — can go on any wheel position in any orientation.

Asymmetric

Different tread pattern on the inside vs. outside half of the tire — marked "Outside" on the sidewall facing out. Rotates front-to-back only, never side-to-side, since the inside/outside orientation must be maintained.

Winter & Traction Ratings — What's the Actual Difference

M+S (Mud & Snow)

A self-certified designation — the manufacturer declares the tread pattern, void ratio, and tread element spacing meet a basic definition for mud and light snow traction. No independent performance test is required. Most all-season tires carry an M+S rating by default. It does not guarantee strong ice or deep-snow performance.

3-Peak Mountain Snowflake (3PMSF)

A performance-tested certification — the tire must meet a minimum traction threshold on packed snow in standardized testing versus a reference tire, verified by an independent test. This is the rating that satisfies winter tire mandates in most jurisdictions that require one. A tire can carry both M+S and 3PMSF, or M+S alone.

In short: M+S is a self-declared minimum, 3PMSF is a tested and verified severe-snow performance standard. When a customer asks if their "all-season, M+S rated" tire counts as a winter tire for a mandate or chain law, check specifically for the snowflake symbol — the M+S rating alone usually does not satisfy those requirements.

Load Index Quick Reference — Common Passenger/LT Range

852 lbs

992 lbs

1,135 lbs

1,323 lbs

1,521 lbs

100

1,764 lbs

105

2,039 lbs

110

2,337 lbs

115

2,679 lbs

120

3,086 lbs

125

3,638 lbs

130

4,189 lbs

Never downsize load index below OEM spec. Load index differs between single and dual mounting on the same tire. XL (Extra Load) reaches its rated capacity at a higher inflation pressure than SL (Standard Load, factory default).

Speed Rating Quick Reference

99 mph

112 mph

118 mph

124 mph

130 mph

149 mph

168 mph

186 mph

(Y)

Above 186 mph

Fitment rules: match all four tires to the same speed rating — never fit below the OEM rating without manufacturer approval. A higher speed rating is usually fine, as long as the size, load index and tire type still meet OEM spec and the tires on each axle match.

DOT Date Code & UTQG Ratings

DOT Date Code

The last 4 digits of the DOT stamp are the manufacture date — first 2 digits are the week of the year (01–52), last 2 are the year. "2419" = 24th week of 2019. Tires older than 6–10 years (per manufacturer guidance) should be inspected closely or replaced regardless of visible tread depth — rubber compound degrades with age even when unused.

UTQG Rating

Uniform Tire Quality Grading — three self-tested numbers/letters molded on the sidewall: Treadwear (relative wear life, higher number = longer expected life), Traction (AA/A/B/C, wet braking performance), and Temperature (A/B/C, heat resistance at speed). Useful for comparing tires within the same manufacturer's line — less reliable for cross-brand comparison since testing is self-administered.

Professional Tips & Best Practices

Check the door jamb, not just the old tire

The OEM placard on the driver's door jamb is the source of truth for size, load index, and pressure — a previous owner may have already fitted the wrong tire.

XL/Reinforced tires need higher pressure

If the vehicle came with Standard Load tires and you fit XL (Extra Load) tires, the XL tire needs a higher pressure to carry the same load — use the tire maker's load/inflation table, not the door placard. If the vehicle came with XL tires from the factory, the placard pressure is already the XL pressure.

Plus-sizing changes more than looks

Going up a wheel diameter while keeping overall tire diameter close to stock changes sidewall height, load capacity, and sometimes speedometer accuracy — recalculate the full size, don't eyeball it.

4WD/AWD systems are picky about circumference

A significant tread depth or size mismatch between axles on a full-time AWD system can damage the transfer case or center differential over time — match tread depth within spec on these platforms.

Snowflake symbol location varies

Look for the mountain/snowflake icon near the size stamp — some brands place it small and low on the sidewall where it's easy to miss during a quick inspection.

Age trumps tread on trailer and spare tires

ST trailer tires and full-size spares often age out from UV and ozone exposure long before the tread wears down — check the DOT date code even on tires that look barely used.

Critical Safety Warnings

Never mix speed ratings across an axle — the lower-rated tire becomes the limiting factor for the whole vehicle, not just that corner

Never fit a tire with a lower load index than OEM spec without verifying the reduced capacity is acceptable for the vehicle's GVWR

A temporary spare (T prefix in the size, e.g. T125/70R17) is speed and distance limited — usually 50 mph max, check the sidewall — never leave one mounted as a permanent tire. Don't confuse the T service prefix with the T speed rating (118 mph)

Directional tires mounted backward reduce wet traction and water evacuation — always check the rotation arrow before mounting

Mismatched circumference on a full-time AWD/4WD system can cause drivetrain damage — verify tread depth and size match across all four corners

An aged tire can fail catastrophically even with full tread depth remaining — always check the DOT date code during inspection, not just tread wear

For diagnostic reference only — not a substitute for OEM service data. Full terms & disclaimer: kissdiagnostics.com/legal

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