Size validation

Size validation

Decode markings, compare sizes, and understand diameter, load and speed changes.

How to read a tire size How to read a tire size: decode every number and letter in P205/55R16 91V — width, aspect ratio, rim diameter, load index, speed rating. Tire type guide — P, LT, metric, radial & flotation What do the letters in a tire size mean? P, LT, metric, radial (R) and flotation tire types explained. Tire sidewall markings decoder Complete guide to every marking on a tire sidewall: size string, construction code, load index, speed rating, DOT date, M+S, 3PMSF snowflake, UTQG, max pressure, country of manufacture, and brand-specific symbols. Tire load index chart Use the tire load index chart to convert ratings 60–130 into kg and lb, then verify the vehicle placard and axle-load requirements. Tire speed rating chart Use the tire speed rating chart to convert symbols from L to Y/ZR into km/h and mph for replacement tire checks. Tire section width guide What does the first number in a tire size mean? Tire section widths from 165 to 305 mm explained with compatible sizes and rim widths. Tire aspect ratio guide What does the aspect ratio (series) number mean in a tire size? 35, 40, 45, 50, 55, 60, 65, 70 explained with sidewall heights and popular sizes. Plus sizing guide What is plus sizing? How to go from plus 0 to plus one or plus two with a larger rim and lower-profile tire. Plus-sizing fitment study Original TireFitLab study of plus/minus tire-sizing candidates computed from the same engine as the live calculator. Speedometer error guide Why changing tire diameter causes speedometer error, how to calculate it, EU/US legal limits, and how to check if your new tires will pass. Tire size conversion guide How to convert tire sizes between metric (225/45R18), P-metric (P225/60R16), LT (LT265/70R17), flotation (31×10.50R15LT), and classic inch-based (6.00-16) formats. Includes conversion formulas, worked examples, and when each format is used. Tire upsizing and downsizing guide What happens when you fit wider tires, lower-profile tires, or a larger rim: effects on wet/dry grip, ride comfort, fuel consumption, speedometer accuracy, wheel arch clearance, and tire load capacity. Low-profile tires: handling, comfort, damage risk, and aspect ratios explained Low-profile tire guide: what aspect ratio means and how it defines a low-profile tire, the handling advantages of a shorter sidewall (less flex, faster steering response, wider contact patch), the ride comfort penalties, the increased vulnerability to pothole damage and kerb damage, TPMS importance on low-profile fitments, and winter suitability of low-profile tires. Tire load capacity guide How tire load capacity works: the load index table, how inflation pressure affects load carrying ability, single vs dual fitment ratings, and why overloading is dangerous. Choosing a tire speed rating for the vehicle and real use Source-reviewed workflow for choosing tire speed symbol and load index from vehicle approval, UN R30/R142, seasonal exceptions and exact tire data. Tire speed rating exceeded: evidence and next steps Source-reviewed guide to tire speed symbols, service descriptions, UN load/speed tests, V/W/Y load interaction and post-event inspection. Tire ply rating and load range: what LT tire load ranges mean and how to choose the right one Guide to tire ply rating and load range: what ply rating originally meant (number of cotton carcass plies) and why modern tires use load range letters instead (C/D/E/F/G), how each load range corresponds to a maximum inflation pressure (C = 50 psi / 3.45 bar, D = 65 psi, E = 80 psi / 5.5 bar, F = 95 psi, G = 110 psi), how to calculate maximum load capacity for a given load range and size, LT tire vs P-metric tire load capacity comparison (LT carries more at same size — LT225/75R16 E vs P225/75R16 example), when to choose a higher load range (towing, payload, frequent full-load use), the trade-off between load range and ride quality (stiffer sidewall = harsher ride on normal roads), and how to read the load range from the tire sidewall. Tire aspect ratio and handling: evidence guide Source-reviewed guide to aspect-ratio geometry, handling evidence, plus-sizing, load rating, wheel approval and vehicle clearance. Tire section width effects: evidence and fitment guide Source-reviewed guide to section width, exact-tire evidence, rim approval, wet grip, rolling resistance, noise and clearance checks.

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Technical check: 2026-06-28
Content updated: 2026-06-28

What changed

Added pillar pages for the existing guide bundle taxonomy.