Why does my 32mm bicycle tire inflate to 34.2mm? It's because of the rim.

Therefore, meet rubbersideup.cc. A community measured bicycle tire width database which turns nominal width into WAM (Width As Measured).

Two tire cross-sections showing how internal rim width affects measured tire width

How it works

Step 1

Mount your tire

Mount your tire and inflate it to your riding pressure.

Step 2

Measure

Use calipers to measure the widest point of the inflated tire, including tread knobs.

Step 3

Submit

Add your tire brand, model, nominal width, rim inner width, and your measurement.

Why this matters

Aerodynamics. The optimal rim-to-tire width ratio for aero performance is roughly 105% — the rim should be slightly wider than the tire. Without measured data, guessing the right combination is trial and error.

Frame clearance. A tire that measures 3 mm wider than expected can rub your fork or chainstay. Knowing actual widths prevents expensive mistakes.

Tire stretch. Tires widen slightly over the first few weeks as the casing relaxes. The maturation data here helps you understand the full picture.