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My classic trainer is giving inaccurate readings // I'm getting the tire slipping message

zPower is Zwift's estimated power curve with acceleration for use with a select set of classic trainers. If you have one of our supported classic trainers and an ANT+/BLE speed/cadence sensor, you can ride in Zwift without a smart trainer or power meter. Zwift will instead estimate your wattage based on your speed.

Since these calculations are based on a specific set of parameters and the power curve is estimated, it introduces more places where putting in the wrong information or using the wrong equipment can give you inaccurate power readings or trigger our "Tire Slipping" message. We'll go through what we expect in our zPower calculations here so that you can check your setup!


zPower Disclaimer

While we're confident in its accuracy if your setup matches our standards, zPower is a calculated estimate for progress benchmarks, not absolute power values. Due to the number of variables - including manufacturer design inconsistencies in equipment - it's likely that the numbers you see will differ from what we calculated zPower with. If you want exact, accurate numbers, consider a power meter or smart trainer instead. 


zPower Setup Expectations

1. Use the correct trainer: Each of our zPower calculations is based on a specific trainer. You need to use the exact trainer that you're selecting from the menu; you cannot choose something that's "close" or "the same brand" - each one is different. If your trainer is not listed and you chose the "Not Listed" trainer or roller options, you won't get accurate readings. You also need to make sure that you choose the correct resistance setting, if applicable (where L# indicates the resistance level).

2. Use the correct bike tire setting: When you pair your speed sensor, you'll see an option to select your bike tire size. Be sure to pick the tire size option from the drop-down menu that matches your own. If you don't see an exact match, pick the next closest size.

3. Inflate your tires: Your bike tires will have a recommended tire pressure indicated on them, typically 100 PSI. Double-check your tire pressure and make sure they're fully inflated; under-inflated tires will cause the same problems that incorrect tire size can cause. 

4. Tighten your trainer: Check to make sure that your trainer is sufficiently tightened. This varies from trainer to trainer, so check with your hardware manufacturer to determine the correct tension.

WARNING: Do NOT over-tighten your trainer! You can bend your wheel rim by tightening it too much. If you are continually receiving the "tire slipping" message, it's most likely for one of these other reasons.

5. Make sure your sensors aren't dropping: If your ANT+ or BLE signal gets interrupted, the lost data will throw off Zwift's calculations and affect your speed. See the ANT+ troubleshooting article or the BLE troubleshooting article.

6. Check the distance between your tire magnet and speed sensor: If your magnet is too far away from your speed sensor, the sensor may not be able to track when the magnet passes, causing inaccurate readings.

7. Replace your speed sensor batteries. If your battery is weak or dying, it might not be sending consistent or accurate speed data, similar to how ANT+ signal drops can cause problems.

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