Wired Systems FAQs

You will find a collection of the most FAQs for the SRM system here, if your question is not answered please contact us.

Q: What is supplied when I purchase an SRM?

A: Standard SRM Systems include:

  • PowerMeter.
  • PowerControl, handlebar clip.
  • Crank arms of your choice.
  • Chainrings (standard 53,39).
  • Special sensor cable.
  • RS232 PC download cable.
  • Software, manual and charger.

Please note:

  • Track and MTB systems will be delivered without left crank.
  • Track system will be delivered without chainring.
Q: What is not supplied when I purchase a standard system?

A: Please note:

  • Track and MTB systems will be delivered without left crank.
  • Track system will be delivered without chainring.

The following are additional add ons:

  • Online software and hardware.
  • Torque Analysis.
  • Adjustable Length Cranks.
Q: Is the SRM system waterproof?

A: All SRM Systems are designed to be waterproof, under normal operating conditions, except SRM track and the SRM Science PowerMeters.

The PowerControls (red boxes) for all systems are designed to be waterproof.

What you as an owner or user can do:

  • Don't use degreasers or solvents to clean the PowerMeter or the PowerControl.
  • Never use a high pressure-washer to clean the PowerControl or PowerMeter.
  • During transport (car rack):
    • Remove the PowerControl (red box) and place in a safe place.
    • Cover the PowerMeter (crank) with a plastic bag, to help ensure Water (rain) isn't applied at 120 km/h.

Maintenance to be performed.

  • Grease the plug(s) at the bottom of the PowerControl regularly to keep water from corroding the wire contacts.
  • Check the chainring bolts for tightness as the clamping of the chainrings applies pressure to the plastic lid, sealing it against the rubber o-ring inside.
Q: What Maintenance should I perform?

A: You can improve the life of your SRM by performing the following regular maintenance:

  • Routine checking of the cable system and sensors for damage.
  • Routine checking of screws used to attach the crank to the PowerMeter.
  • Routine checking of the battery charge and memory in the PowerControl.
  • Grease the plug(s) at the bottom of the PowerControl regularly to keep water from corroding the wire contacts.
  • Check the chainring bolts for tightness as the clamping of the chainrings applies pressure to the plastic lid, sealing it against the rubber o-ring inside.

Maintenance is performed prior to daily use and the crank can be cleaned with soap and water. It is important that high-pressure hoses and acetone-based cleaners are not used on SRM system.

Q: What do the different symbols represent on the PowerControl IV?

A:

  • U = low power in Power Control Unit.
  • B = battery of the Power Metre is empty.
  • X = there is no connection to PowerMeter.
  • I = actual interval.
  • L = last interval.
Q: What is the Zero Frequency?

A: Check the zero offset regularly:

The zero offset is the amount of strain being measured by the PowerMeter itself, without any force being applied to the pedals. It changes with variations in temperature, as well as with tension on the chain rings and crank arm bolts.

If it is not set, all of the power measurements will be incorrect, Therefore you must check and set the zero offset frequently.

This should be done before setting off on a ride, by spinning the cranks backwards a few times to activate the PowerMeter, and then pressing Mode and Set at the same time. The number on the left (under MANU) is the zero offset that the PowerControl is currently using. The number in the middle (under Pro) is the zero offset that the PowerControl suggests, and can be ignored. The number on the right (under Set) is the actual zero offset at that moment, and once it stabilises you should save it by pressing the Set button again. This number should then appear under the MANU heading, showing that it has been saved.

If it changes more than 10hz, go to the Troubleshooting section of the online manual.

During your ride, you should check the zero offset whenever you are able to freewheel -- make sure you are not applying any pressure on the pedals, but keep the cranks moving in order to keep the PowerMeter activated. Follow the same steps to set the zero offset frequency.

Note:
Each training file saved by the PowerControl can have multiple zero offset frequencies, so the more often you set it the more accurate your power data will be. The zero offset frequency reported in the properties file is only the first one set during the session.

Q: What bottom brackets fit the SRM?

A: The SRM has been designed with interchangeable crank arms. If you upgrade or change your bottom bracket or wish to change crank length, this is easily achieved with the purchase of new crank arms only.

Cranks arms are available from 165mm - 180mm in 2.5mm steps.

The cranks are for:

  • 102mm Campagnolo bottom bracket set (BBS).
  • 103 Shimano BBS, new Shimano model (round axle).
  • 113mm Shimano XTR MTB axles available.
Q: How does SRM measure/record Heart rate?

A: Using a pulse transmitter (Polar) on the torso of the cyclist, the heart rate is transferred inductively to the PowerControl.

The heart-rate measurement works with a Polar non-coded heart-rate sensor.

It is possible to use coded straps only codes lower than 24 will be accepted. If a code higher than 24 is randomly selected, remove the chest strap for 30 seconds and replace, until an accepted code is selected. (not recommended).

Heart rate transmission can be affected by:

  • Electromagnetic radiation (over-head powerlines).
  • Weak polar transmitter or poor connection.
  • Strong wind.
  • Interference from other riders transmitters, close by.
  • Zero crank frequency at approx 300 Hz.

Display of the Heart rate can be updated any where from 1—10 seconds, and smoothed over anywhere from 1—10 measurement points.

Q: How does SRM measure temperature?

A: The PowerControl records the temperature from inside the PowerControls housing. Therefore its response time to changes in temperature is slowed.

While riding, the temperature is normally accurate to the external temperature but may be influenced by:

  • Remaining stationary in the sunlight.
  • Sudden temperature changes (going in or outside of your home).
Q: How is power measured?

A: Strain gauge strips are attached to the metal inside the PowerMeter, and measure the stretch of this metal as force is applied to the pedals throughout the pedal stroke. These stretch characteristics are then converted to power measurements, proportional to the pedalling force. The power is measured from the sum of tangential forces on the pedals and of the angular velocity (speed of rotation).

strainQ: What are strain gauges?

A: The most common method for measuring deformation caused by force on metals is with a strain gauge. A strain gauge's electrical resistance varies in proportion to the amount of strain in the device.


Q: How does recording at different time intervals affect power?

A: To calculate power, the SRM multiplies the average angular velocity (cadence) by the average torque during each pedal revolution,

The PowerControl samples these calculations according to the interval selected.

All completed revolutions in the interval period are averaged. For example:

  • 5 second sampling at 100 rpm - all completed revolutions are averaged i.e. power equals the average of the previous 20 pedal revolutions.
  • 0.1 second sampling - all completed revolutions are averaged, if a revolution hasn't been completed then the previous data is sampled again. All calculations are made based on time so this won’t affect the integrity of the data (averages, etc.).
graficoQ: What does the SRM slope represent?

A: The slope is the relationship of torque to frequency of the crank. (i.e. when you apply torque to the crank, a corresponding frequency will be sent to the PowerControl)

Because the relationship is directly proportional it is represented as a constant, meaning that it remains the same no matter what torque is applied. That is why the one number can be used to calculate power at any given torque. You can see from the graph the importance of setting the zero offset frequency correctly -- if it is too high or too low the rest of the power calculation will be incorrect. If the slope and the zero offset frequency are correct, the measurement of power will be very precise, as low as +/-1% error.

Q: What precautions should be taken to transport the SRM system?

A:

  • During transport (car rack):
    • Remove the PowerControl (red box) and place in a safe place.
    • Cover the PowerMeter (crank) with a plastic bag, to help ensure water (rain) is not applied at 120 km/h.
  • During air travel your SRM system, should be transported as carry-on (hand) luggage - the low pressure existent in an un-pressurised baggage compartment will effect the watertight O-ring seals.
  • For sending a system by mail or courier, ensure both the PowerControl and PowerMeter are packaged adequately to prevent mechanical damage.
Q: My zero offset value has changed. Could this be a problem?

A: It is normal for the zero offset to change. As long as the zero offset is between 100 and 600, the Powermeter will function correctly. Should the value lie above or below this, the Powermeter must be sent in to be checked.

Q: Is it difficult to mount an SRM system?

A: Not really. Remove the old crank, mount the sensor cable, mount the SRM crank, the handlebar clip for Powercontrol and you are finished.

The only problem you may have is with positioning the sensor correctly on the frame. The instruction manual explains in detail how to do this.

Q: What is the expected life span of an SRM system?

A:There is no wear and tear on the SRM system because it has no moving parts. All you need to do is change the battery in the crank occasionally. If given the proper care, the system will easily function for 10 years or more.

Q: What is the difference between the different versions of the SRM Training System Amateur, Professional and Science?

A: The degree of accuracy:

  • The Amateur version (2 strain gauge strips) has an accuracy of ± 5%.
  • The Professional version (4 strain gauge strips) has an accuracy of ± 2% (with the exception of the MTB model, due to its design it has 8 Strain gauges).
  • The Science version (8 strain gauge strips) has an accuracy of ± 0.5%.
Q: What bicycle types or other devices do SRM offer products for?

A: In principle, SRM can offer a solution for just about anything that turns. Basically, however, our solutions are still geared for road, mountain, track and cross-country bikes plus the Ergometer and the Indoor-Trainer, although we do now have for example, solutions for athletes in wheelchairs and a crank design with which sailors can measure their power on the winch.