How to read a tire sidewall: sizes, pressures, ratings

A tire sidewall packs the key specifications into a narrow strip of rubber: nominal size, permitted inflation pressure, construction, load limit and, sometimes, a wear indicator. It looks cryptic because manufacturers mix millimetres, inches, PSI, bar and kPa.

Learning to decode those markings prevents mismatched purchases and gives a sound starting point for pressure. In Australia, where tyre sidewalls often show PSI while tools may use kPa or bar, the manufacturer’s chart and recommended range matter more than any isolated number.

Start with the size code

A common road marking is 700 × 25c. Here, 700 is a nominal outside diameter in millimetres, 25 is the nominal section width, and c means clincher. A code such as 700 × 28c identifies a wider tyre in the same broad size family.

The width is not an exact physical measurement: the fitted tyre can sit narrower or wider depending on its shape and the rim. Confirm compatibility with frame and fork clearance, and check that brake pads or the rim brake cannot contact the tyre.

Match diameter to the rim

700 is a traditional trade size, whereas the ETRTO marking 622 × 25 gives a 622 mm bead-seat diameter and a 25 mm nominal tyre width. Most 700c road wheels use 622 mm, so the names describe different parts of the same fitment.

Many 29-inch and 700c wheels share the 622 mm bead-seat diameter, while 650b and 27.5-inch wheels generally use 584 mm. Check the rim decal and manufacturer specification rather than inferring compatibility from an outside diameter or marketing label.

Treat maximum pressure as a ceiling

A label such as MAX 125 PSI (8.6 BAR) states the tyre’s maximum permitted inflation pressure, not its ideal pressure. Too little pressure risks squirm, pinch flats and poor handling; too much can compromise grip, comfort and rim safety.

Choose pressure using rider weight, luggage, rim width, tyre volume, road conditions and the maker’s range, while never exceeding the lower of the tyre and rim limits. For conversion, 100 psi is about 690 kPa and one bar equals 100 kPa.

Before choosing a test tyre, review the demo ride preparation guide so the comparison reflects your actual fit and riding position. In Adelaide’s summer heat, check pressure before departure because ambient heat can raise it beyond the morning reading.

Decode ply and construction

60 TPI means about 60 casing threads per inch, not 60 plies. SINGLE or SINGLEPLY identifies one casing layer, while DUAL or DUALPLY identifies two. Labels such as SUPER RACE, TR and LIGHT describe construction, not a universal ranking of speed or durability.

A TUBELESS READY or TLR tyre can run without an inner tube only with a compatible rim, correct tape and sealant. Reinforcement belts improve puncture resistance, while casing and tread compounds influence grip, rolling resistance and comfort.

A companion guide to triathlon cadence and economy explains how equipment choices can support efficient, comfortable endurance riding.

Check load ratings carefully

Where a MAX LOAD figure appears, it applies to one tyre unless the maker says otherwise. Include rider, bicycle, luggage and bikepacking equipment in the real load, and do not treat the printed figure as permission to carry more.

Most road riders remain well below those limits, but ratings still help compare tyres and expose unsuitable setups. On steep roads around Melbourne’s Dandenong Ranges, suitable pressure, casing and braking control matter far more than approaching the maximum-load number.

Read wear and rotation marks

Wear bars or a TREAD marking indicate when a tyre should be removed. Many makers quote 1.6 mm as a minimum tread depth, but follow the sidewall limit and condition: cuts, exposed belts, uneven wear or a separated bead justify replacement sooner.

A rotation arrow matters on directional or asymmetric treads; an arrow pointing the wrong way can reduce intended handling. On Australian country highways, glass, sticks and sharp chip-seal edges make a spare tube and multipack sensible, particularly on long routes between towns.

Triathletes combining cycling with half-distance goals can keep Tenku Half alongside their equipment research, then return to the tyre’s own pressure, load and construction limits.

Choose a setup with confidence

Choose by use, not the largest number on the sidewall. Many road riders suit themselves with 25–28 mm tyres, while 30–40 mm can add comfort and control on rough asphalt or gravel. Match tread and casing to the wheel and intended terrain.

At KompetitiveEdge, bring the bicycle and wheel measurements to a fitting or service appointment and request a pressure recommendation based on your weight and riding. Browse road tyres, tubeless options and clearance stock, then book a demo ride before committing.

Secure the right tyres for your next road, gravel or triathlon outing and speak with the team about servicing, fitting memberships and available test rides.