Power Meters - Zero Reset

-

 What is a Zero Reset? 

The Stages SB20 bike has power meters that support a zero reset function. 


Zero Reset tells the vertically positioned crank power meters: "Torque should now be zero Newton-meters (Nm)". This allows subsequent readings to be made from a correct starting value. It's like setting 0 lbs/kg on a bathroom scale.

Here are things that commonly affect the starting value:

1. Different pedals.

2. Temperature or humidity changes.

The Left:Right numbers you see in the Stages app are a representation of the amount of torque that will be added or subtracted from each PM reading.

Zero Reset is not Calibration

A zero reset does not "calibrate" the power meter's primary function: measurement of force as you push the pedals.   


To do minor Stages power meter calibration see:

Stages SB20 - Measuring Torque Against Factory Specifications

Comparing Power Meters with ZwiftPower


Comments

Post a Comment

Popular posts from this blog

Stages SB20 - Drive Belt Adjustments

-
Image
 STAGES SB20 DRIVE BELT ADJUSTMENT  Stages includes belt adjustment tips in their support note on fixing SB20 noises:   Flywheel Making Noise . Several people have mentioned these instructions are incomplete. I’ll try to help . I wish this process was easier. Good news: With practice, you can complete all adjustments in less than 30 minutes. TWO GOALS Adjusting the drive belt accomplishes two things: Align the belt to ride as much as possible in the centre of the drive cogs. This reduces friction and positions the front axle perpendicular to the drive belt. Don’t be too worried about this step. The SB20 manufacturing tolerances aren’t perfect. Getting the front drive wheel roughly aligned and generally perpendicular is about all we can expect to achieve. Get belt tension right. Optimal tension means quieter running and no slipping during hard efforts. For most of us, this is a trial-and-error process.You want tight but not too tight. For me, this is measured as a 1 cm deflection when p
Read more

Stages SB20 - What's Inside?

-
Image
The Stages SB20  indoor smart bike was released in 2020. Let's take a look at the electronics that enable it  on platforms like Zwift.com and TrainerDay.com. An external power supply routes power to different bike components through a series of printed circuit boards (PCBs). The bike also includes two battery powered crank-based power meters. Here's an overview the basic functions: USB Board - Wedged vertically under the phone tray. It powers 3 USB ports. Upper Board - Fastened horizontally under the phone support rail. This System On a Chip (SoC) handles wireless communication and controls the bike itself. Switch Board - This wire distribution board sits inside the aluminum handlebar stem. It routes connections for the brake level controls  and under handlebar tape "blip" shifter buttons.  Lower Board - This mainly analog circuit board is attached to the flywheel / electronic brake unit. It controls bike resistance and sends power to other PCBs. Power Meters - A
Read more

Indoor Bike Improvement #10 - SB20 Rocker Plate

-
Image
10 of 10 - Leaning one way and another Rocker plates make indoor riding more realistic. I'm not entirely convinced. Indoor bikes struggle to recreate outdoor resistance, road conditions, pedalling dynamics and acceleration. I'm not sure that side-to-side movement helps with realism. My personal take is more conservative. Two years of rocker plate riding has improved my overall comfort and helped with out-of-saddle sprints.   My Journey I began experimenting with different rocker plate designs in 2021, starting with the following requirements: ✓ Progressive side-to-side movement that offers stronger resistance as you move from the upright or vertical position. ✓ Forward-and-back movement. Many riders claim this is a critical element in real-world riding simulations. ✓ Small footprint. Commercial products are often quite large to accommodate a wide range of bikes. A custom design for my particular bike should be smaller. ✓ It should remain easy to get on and off the bike.  
Read more

Smart Bikes, Zwift and Bike Computers are all WRONG

-
Image
My SB20 smart bike comes with an app that shows power, distance, cadence, L:R balance and current virtual gear. You can also use a bike computer like a Garmin 540/840/1040  to show similar data. When you use either at the same time as  Zwift, you see different numbers.  Who is correct? Answer: They are ALL CORRECT and ALL WRONG!  How can that be?   Let's find out. Before getting started,   it's a good idea to agree on basic parameters. Note: In this discussion, I use the term  Indoor bike  for smart bikes and smart trainers along with their related apps. RESISTANCE AND POWER 1. RESISTANCE - An indoor bike creates resistance that makes it harder or easier to pedal.  2. POWER - The harder you push against the indoor bike's resistance (measured in newton metres) multiplied by how fast you pedal (RPM) defines the POWER you are producing (specified in watts per second or just watts). POWER is a measured number and is EXACTLY the same if you are riding with Zwift, using your
Read more

Stages SB20 - Measuring Torque Against Factory Specifications

-
Image
Torque Measurement I previously documented how to compare SB20 power meters with a set of calibrated pedals. It gives you a good indication of how your power meters compare in actual riding scenarios.   This test  statically measures  torque with a pair of fixed weights. It tells you if your power meters meet factory specifications . This test does not provide the full calibration that you can perform with Garmin or Favero pedals. You can't change  offset  or slope parameters to get the Stages PM measure correctly in the future. Basic Testing Procedure The basic method involves two ( big ) steps: 1. P osition the cranks horizontally to get raw measurements produced by hanging 25 lb weights from each crank. 2. Use a spreadsheet to process raw measurements and get an average reading for both cranks. Compare these readings against expected values  (t he list of expected values is shown later in this post ). The test setup looks like this: With equal weights on each side, cranks can
Read more

Batteries and SB20 Power Meters

-
Image
Today's question: How does battery level affect SB20 power meter measurement? Let's do a deep dive and find out! Replaceable Batteries The Stages SB20 power meters have replaceable batteries. An advantage: No degradation of built-in batteries as the power meters age. A disadvantage: No ability to top up batteries to 100% whenever you wish. Battery Life CR2032 button cell batteries are used in the SB20 power meters. Stages says they should last 150-200 hours . Let's verify this claim with bench tests and torque measurements. Estimating Remaining Capacity The StagesPower  app, and others like BT Inspector, report battery capacity. They use the Bluetooth Low Energy (BLE) wireless protocol to ask each power meter for a battery life estimate.   🔬It doesn't matter which app you use.  All apps report the estimate returned by the power meters. Why Battery Estimates are so Bad Many people complain that battery life estimates from the power meters show 100% most of time. The
Read more