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SRM FAQ

General

How accurate is the SRM power meter?

SRM uses a 144 point calibration protocol against a known mass measured to the exact gram. With precise calibration and its auto-offset feature, the power measurement of the SRM has error of less than 1%. The cycling community has long been publishing peer reviewed research using the SRM as the bench mark for measuring power.

What is the PC8 Bundle?

The SRM PowerControl 8 is SRM’s propriety head unit. SRM’s power meters are the best you can buy, and their SRM PC8 head unit is no different. The PC8 sells for $749, however if you purchase it with your SRM power meter, you save $249 on the head unit.

Which bicycle computers are compatible with SRM power meter?

SRM power meters transmit information through the ANT+ protocol. As long as your bicycle computer uses ANT+, you will be all set. We always recommend upgrading the firmware of your head unit according to the instructions given by the manufacturer for best performance.

How does the SRM measure cadence?

SRM uses a reed switch (which is inside the power meter) and a magnet which the user mounts on the bottom bracket. This method of cadence detection has been proved to be very accurate, even at high cadences.

Where does the cadence magnet need to be positioned?

The power meter will not transmit data to your display unit without the cadence magnet being properly installed underneath your bottom bracket or on the chain-stay of your frame.

Does the SRM power meter measure left and right power balance?

No it does not. The SRM measures total power, but not left vs. right power.

Can I change chainrings without affecting the slope of my SRM power meter?

Yes, with the exception of solid TT rings. If you are changing to or from a solid TT ring, it is recommended that you have your power meter re-calibrated. Do not over-tighten chainring bolts.

Please follow the correct torque specifications.

What warranty comes with the SRM power meter?

All SRM power meters come with a limited lifetime warranty for the original owner. The warranty covers the structural and electronic components of the power meter – it does not cover the crank arms, chainrings or accessories.

Can I physically open my power meter?

We don’t recommend it because the warranty will be voided and you will be responsible for all repair costs.

 

Battery

How long does the battery last?

Depending on the model, the battery of your SRM power meter can last up to 3,000 hours, by far the longest of any power meter on the market. Please see the Specs box above on this page for more information.

How do I change the battery on my SRM power meter?

SRM power meters utilize a proprietary battery. The power meter must be sent back to the factory for a battery change.

 

Calibration

What is zero offset?

The zero offset is the frequency in Hertz that the power meter is transmitting when no torque is applied. Once torque is applied, the zero offset will rise. It is important to set your zero offset at the beginning of a ride to ensure that your power meter is tared.

What is slope?

Each power meter has a unique slope value, which is calculated during the calibration of that specific power meter. The unit used to describe slope is ‘Hz/Nm.’ For example, 20.0 Hz/Nm means that for each Newton Meter of torque applied to the power meter, the output frequency will increase by 20 Hertz.

Can I change chainrings without affecting the slope of my power meter?

Yes, with the exception of solid TT rings. If you are changing to or from a solid TT ring, it is recommended that you have your power meter re-calibrated.

Do not over-tighten chainring bolts. Please follow the correct torque specifications.

Can I change the drive-side crank arm without affecting the slope of my power meter?

It depends on your power meter.

Why is it important to have my power meter calibrated at the SRM Service Center?

Calibrations done at the SRM Service Centers are the most accurate. SRM calibrates in a controlled environment using a known force and a calibration jig. This known force is hung from the chainring thus eliminating the friction from the bottom bracket and ensuring the most accurate slope.

Can I calibrate the slope of my power meter on my own?

Yes, if you have the right equipment and calculations. This requires hanging a known force from the crank arm, pedal, or chainring. In order to ensure the most accurate calibration, you must eliminate the friction of the bottom bracket by hanging a known force from the chainrings.

 

Troubleshooting

My zero offset is too low (below 200Hz), too high (above 900Hz), or reading Zero. What is the cause?

  • Your power meter may have sustained damaged that is beyond the scope of troubleshooting.
  • Your power meter battery is low/nearly depleted.

My power and cadence readings are zero, erratic, or not accurate?

  • The cadence magnet is not in the correct position over the reed switch.
  • The slope is not entered into your display unit correctly or your power meter is not transmitting the correct slope to your display unit.
  • The zero offset needs to be set.
  • The battery is almost empty or there is damage to the power meter circuit board.

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