Caleb MorganBy Caleb Morgan

Updated November 2026

A wheel size chart for your Sigma bike computer tells you the tire circumference to enter so your speed and distance readings match what you actually ride. Find your tire size, look up its circumference, enter the value in the computer, and check it against a known distance. The whole process takes about ten minutes and only needs to be done once per wheel setup.

Why the Wheel Size Setting Matters

A bike computer does not measure distance directly. It counts wheel rotations from a magnet on the spoke and multiplies that count by the wheel circumference you entered. If the number is wrong, every speed, distance, and average reading will be off by the same percentage. A computer set too small will undercount distance, while one set too large will overcount it. Read the full guide on how to set the right tire circumference if you want the underlying logic before you start.

Shopping for one? See our guide: 5 Best Road Bike Shoe Size Charts (2026): Expert Picks.

Step 1: Identify Your Tire Size

Look at the sidewall of your tire. You will see a series of numbers such as 700x25c, 27×1-1/4, or 26×2.1. Write down the full size exactly as printed, because the chart uses it as the lookup key. If the sidewall is worn or unreadable, check the size stamped on the rim tape or the box the tire came in.

Step 2: Look Up the Circumference in the Chart

Find your tire size in the wheel size chart for Sigma bike computer use. Charts list circumference in millimeters, which is the unit most Sigma models expect, although some list inches as well. Use the value for your exact tire, not the rim diameter alone, since a 700c rim paired with a 28mm tire measures differently than the same rim with a 23mm tire.

Common tire size Approximate circumference (mm)
700x23c 2096
700x25c 2105
700x28c 2136
26×2.1 2068

Treat these values as reference points only. Manufacturers specify slightly different figures for each tire model, and tire pressure changes the rolling size a little. When in doubt, use the figure from your tire maker or the one on the chart that matches your exact model.

Step 3: Enter the Value and Verify It

Enter the circumference in your Sigma computer’s wheel size menu, then confirm the unit matches the number you typed. Once it is saved, verify the setting on a known route. Measure a 1-kilometer or 1-mile stretch using a map app, ride it, and compare the computer’s distance. A difference of a few percent is normal, but a larger gap means you should recheck the tire size or the figure you entered.

  1. Read the tire size from the sidewall.
  2. Find that size on the chart and note the circumference in millimeters.
  3. Enter the value in the Sigma wheel size setting.
  4. Ride a known distance and compare readings.
  5. Adjust if the gap is more than a few percent.

Common Mistakes to Avoid

  • Entering the rim size instead of the full tire circumference.
  • Using the wrong unit, such as typing inches into a millimeter field.
  • Forgetting to update the setting after switching to different tires.
  • Assuming the chart value is exact, when tire pressure and wear shift it slightly.
  • Skipping the verification ride, which is the only real check on accuracy.

A basic tire pressure gauge helps keep your rolling circumference consistent, which keeps your computer readings steadier from ride to ride. View on Amazon

A spare speed sensor magnet mount makes it easy to reposition the sensor if you change wheels or frames. View on Amazon

FAQ

Does tire pressure change the wheel size setting?

Yes, slightly. A tire inflated to a higher pressure rolls a little farther per revolution than a soft one, so readings can drift a few percent. For most riders this is minor, but it is worth checking if your distances seem consistently off.

What if my tire size is not on the chart?

Measure the tire yourself by rolling it one full revolution on a flat surface and marking start and end points, then measuring the distance in millimeters. Alternatively, check the tire manufacturer’s website for the listed circumference.

How often should I recheck the wheel size setting?

Check it whenever you change tires, switch wheels, or notice distances that do not match a map. A quick verification ride on a known route is enough to confirm the setting is still accurate.

Conclusion

Once you enter the correct tire circumference, your Sigma computer will report speed and distance you can trust. Keep the setting matched to your current tires and verify it on a known route. Taking this small step now means every ride’s data will be worth tracking.

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Caleb Morgan

About Caleb Morgan

Caleb Morgan is part of our editorial team and reviews and edits our cycling for beginners guides, checking product details against manufacturer specifications and owner feedback.