IMPORTANT
Video: STACPerformance YouTube channel, “How to install the optional wheel weights on the STAC
Zero”
SAFETY – WHEEL WEIGHTS
The STAC Zero is a unique trainer, and some aspects of its use require care, particularly with respect to
the wheel weights.
Usage of the wheel weights:
Use of the wheel weights to improve “road feel” is OPTIONAL. If you choose to use them, follow the
following best practices to minimize risk of damage to your bike or injury to yourself. Note that the
STAC Zero can usually be adjusted to achieve a good feel AND the targeted resistance without use of the
weights simply by spinning the wheel faster.
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The weights should be firmly pressed against the wheel fairing before tightening the spoke
clamp.
If you have a carbon-fibre rather than steel or aluminum fairing, it is NOT RECOMMENDED to
ride with the wheel weights.
Do not overtighten the spoke clamp - It is tight enough if it firmly holds a weight at 12 o’clock
position from sliding towards the hub.
Check that the weights are firmly attached by giving them a push towards the wheel hub and
trying to wiggle them. A properly seated weight should not move when pushed.
If you are unable to get the weight firmly seated against your fairing, DO NOT USE the wheel
weights or contact [email protected] for help.
No part of the weight other than the spoke clamp should protrude beyond the “cage” formed by
your spokes.
A weight should have at least 3 spokes overlapping with it when viewed from the side of the
bike – the center spoke the weight is clamped on, and spokes near the tips. If you can only get 2
or fewer spokes near the weight, DO NOT USE the wheel weights.
Your wheel MUST be balanced when the weights are attached – you can test this by rotating the
weights to the 3 o’clock and 9 o’clock positions, and verifying that the wheel stays still. If it is
unbalanced, the wheel will rotate from the 3 o’clock and 9 o’clock position.
If you have a 25-spoke wheel or other pattern that prevents the weights being placed opposite
each other, DO NOT USE the wheel weights.
If your wheel has loose or bent spokes, DO NOT USE the wheel weights.
If at any time you feel or hear a clunking, stop riding immediately and verify the weights are
properly attached.
IMPORTANT
SAFETY – TRAINER
There are some components of the STAC Zero trainer that require care when handling to avoid damage
to your equipment or injury to yourself.
Trainer
Trainer Legs – Best Practices
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When moving the trainer, carry the trainer by the threaded rods that normally hold your
skewer. Not only is this the easiest way to carry the trainer, it avoids the legs inadvertently
opening and closing
When setting up or packing up the trainer, be careful grabbing the tubes under the “armpit” of
the legs. The legs can close and pinch a finger.
When setting up the trainer, verify that the legs are fully deployed by pushing downwards at the
top of the U formed by the main trainer frame.
Magnets
The STAC Zero uses 26 extremely powerful permanent magnets to generate resistance. Magnets can
occasionally be dangerous, particularly if you’re not focused on them being there. When we are
building STAC Zeros, tools frequently get pulled out of our hands if we’re careless near the resistanceunit station.
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NEVER place a computer, phone, credit card, or other electronic device close to the magnet
array of the STAC Zero. The magnetic fields can potentially wipe electronic memory or hard
drives.
NEVER place your fingers between the magnet arrays. There are safety mechanisms to prevent
the arrays from coming into contact, but if the quickrelease is loosened the magnet arrays can
suddenly snap together and pinch.
Be very careful using metal tools near the STAC Zero.
Inspect your magnet arrays before putting a bike on the trainer. If there is any metal stuck on
them, carefully remove it.
How to Use the STAC Zero
Video: STACPerformance YouTube channel, “How to Put Your Bike on a STAC Zero”
Video: STACPerformance YouTube channel, “How to space the magnets on a STAC Zero”
1. Change your rear skewer to the included trainer skewer
2. Pull the silver spring-pin on the back of each magnet array, rotate the magnet array, and let the
spring pin slide back into its slot.
a. Warning: Some spring pins can be sticky after shipping. Do not attempt to rotate the spring
pins. Pulling hard should be sufficient to unstick them.
b. Warning: The particular spring pins we’re using have a slot that they slide into on the pin
itself. When you’re trying to re-insert them, you may need to rotate the head of the spring
pin so it can “find” its slot.
3. Unscrew the skewer-holder handles to be as wide as possible
4. Balance your bike so that one end of the rear skewer is in the skewer cup
5. Tighten up one side until your rear wheel appears to be centered in the magnet array
6. Tighten up the other side until your bike is strongly clamped in the skewer holders.
a. Warning: Be careful not to clamp it on your rear derailleur, as some rear gear-shift
mechanisms look similar to the trainer skewer.
7. Slightly loosen the quickrelease that holds the magnet arrays, then move the magnet arrays by hand
so that they’re close to your brake rim. The closer the magnets are, the more resistance the Zero
will generate.
a. Warning: If at this point the magnets clamp onto your rim, please see the troubleshooting
section: “The magnets try to clamp onto my wheel”.
8. You should now be good to ride!
a. If you need more resistance, consult the “there’s not enough resistance” troubleshooting
section.
b. If you want a smoother feel, consult the “The ‘road feel’ is poor, it feels like I’m riding
through sand” troubleshooting section.
c. If you hear any rubbing, consult the “There’s a rubbing or scraping noise while a ride”.
There should not be anything rubbing during normal use of the STAC Zero.
STAC Zero Trainer Troubleshooting
Problem: There’s not enough resistance
Cause: The magnet arrays are not generating enough resistance.
Solutions:
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Video: STACPerformance YouTube channel, “How to get more resistance out of your STAC Zero”
Shift to a higher gear. The faster your wheel is spinning, the more resistance the trainer will
generate. Increasing your speed 41% will double the amount of work you have to do.
Move the magnets closer, if possible. With the magnets very close to the rim, the STAC Zero
should be able to provide ~1000W of resistance at about 60km/h wheel speed without the
magnets contacting the rim.
Problem: The “road feel” of the trainer is poor; it feels like I’m riding through sand.
Cause: The magnets are removing kinetic energy from the wheel so quickly, that it nearly comes to a
halt during your pedal deadzone.
Solutions:
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Move the magnets further away from the wheel rim and shift to a higher gear.
Install the wheel weights on your wheel – these help maintain rotational velocity during your
pedal deadzone and improve the road feel
Use a heavier wheel
Some people use this as an opportunity to practice pedaling in circles.
Problem: There is a rubbing or scraping noise while I ride
Cause: Two objects are coming into contact that shouldn’t be coming into contact.
Solutions:
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Check to make sure nothing on your bike is rubbing on your wheel. Since the Zero is so quiet,
sometimes equipment sounds that you didn’t notice outside or on other trainers make
themselves heard, literally.
o Rear brakes will sometimes rub, but can be easily adjusted.
o The front derailleur will sometimes come into contact with your chain as you pedal.
Make sure your rear wheel’s skewer is firmly clamped in the trainer, and that the skewer is
holding the wheel on the bike firmly as well. If the wheel isn’t firmly attached to the trainer, it
can move side to side as you pedal and contact the magnets.
Using your hand, gently move your rear wheel in a full revolution, and see if at any point the
magnets contact the rim or tire. If they do, try:
o Centering the rear wheel in the middle of the magnet-caliper
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Readjusting the magnets so that they are evenly spaced from each brake track
Tightening the quick-release adjustment clamp at the base of the magnet caliper to
make sure the magnets don’t move once you’re riding again.
Making sure your wheel is trued properly and doesn’t have much runout.
Problem: The magnets try to clamp onto my wheel or seem to try to clamp towards each other.
Cause: Your wheel probably has a steel component in it. This usually is in the tire, or takes the form of a
steel insert in the wheel.
Solutions:
Video: STACPerformance YouTube channel, “How to identify steel components in your wheel”
Video: STACPerformance YouTube channel, “STAC Zero Modification to support magnetic wheels”
First, run a small magnet (like a spoke magnet from a bike computer or the STAC Zero Powermeter)
around your wheel rim, looking for spots where it can stick.
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If the magnet sticks once per wheel revolution:
o This usually means your wheel is constructed with a steel insert that was used when
joining the two ends of the aluminum strip that became your wheel.
o Solution 1: Tighten the quickrelease that holds the STAC Zero magnet calipers
o Solution 2: Follow the steps in the “modification to support magnetic wheels” video
to reduce the likelihood of your magnet arrays being able to move.
o Solution 3: Get a new wheel. For 700x23C road-bike wheels, we recommend a
mavic open pro. When in doubt, take a spoke magnet with you and run it around
the new wheel’s brake rim or fairing structure and make sure that it never sticks.
If the magnet sticks the whole way around, but not very strongly.
o This usually indicates you have a tire with a steel bead
o Solution 1: Tighten the quickrelease that holds the STAC Zero magnet calipers
o Solution 2: Follow the steps in the “modification to support magnetic wheels” video
to reduce the likelihood of your magnet arrays being able to move.
o Solution 3: Buy what is known as a “folding” tire that includes a Kevlar bead. These
won’t (or shouldn’t) include any magnetic components. The STAC Zero crew ride
Continental GP4000SII tires.
o Solution 4: Simply remove your tire and ride on the trainer without it.
Problem: When I ride, I can feel a vibration in my rear wheel
Cause: Rear wheel is out of balance
Solutions:
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If you are using the wheel weights, try removing them to see if the problem persists. If this fixes
the problem, reinstall the weights, being very careful to make sure the wheel is balanced.
o Tip: You can tell if the wheel is balanced by rotating it so the wheel weights are at the 3
o’clock and 9 o’clock positions, and the wheel should stay there. If it is unbalanced, it
will attempt to rotate one way or another.
If you are not using the wheel weights, check to see if your wheel is trued and circular.
How to Use the STAC Zero Powermeter Unit
Video: STACPerformance YouTube channel, “STAC Zero Powermeter: What do those lights mean?”
Video: STACPerformance YouTube channel, “Typical STAC Zero Powermeter debugging”
1. Make sure all 3 AA batteries are installed in the unit, and in the correct polarity.
a. Tip: It is possible for a battery to be in the unit but not making a good contact, so
uninstalling and reinstalling the batteries can occasionally solve issues where the PM does
not turn on.
b. Tip: As soon as you install the third battery, the lights on the PM pod should turn on.
2. Install the included spoke magnet on a spoke on your wheel.
3. Adjust the location on your spoke that the magnet is installed at so that it will pass near the speed
sensor arm located above the STAC Zero Powermeter pod.
4. Adjust the sensor arm so that when the magnet passes by, the red light on the STAC Zero
Powermeter pod alternates on/off. Usually this requires the sensor to be within 1cm or a ½ inch of
the magnet.
a. Tip: If the magnet taps your bike as it rotates, move the magnet to a spoke on the opposite
side of your wheel so that the magnet’s body is contained entirely within the wheel.
5. If this is the first time you’ve ridden your STAC Zero since it was last moved, give it 30 seconds of
time to determine which way is down. On PM units shipped since December 2016, the green light
will rapidly blink while this determination is happening.
6. You can now ride! If you’ve never used a wireless bike powermeter before, read below for software
tips.
How to talk to phone apps via BLE with the STAC Zero Powermeter unit
1. Make sure the unit is on and lights are blinking.
2. Make sure that no other devices in the area are already connected to the PM unit. BLE is a 1-to1 protocol, and once one device is talking to the Zero, other devices will not be able to.
3. Start up your fitness/cycling app. We have tested Zwift, Strava, Kinomap, and ipBike. Use the
app to find its sensor-pairing system. Your STAC Zero should show up as “STAC Zero” in the
device list.
a. Tip: You can use the “STAC Zero Control Panel” android app to change your Zero’s BLE
device name so it can be “Art’s STAC Zero” or “Andrew’s STAC Zero” if you own multiple
STAC Zeros.
b. Tip: The STAC Zero Powermeter auto-power-offs after 5 minutes of idle time, so if you
spend too much time fiddling with your phone, you may not be able to find it because it
turned off.
c. Tip: BLE is different from “normal” Bluetooth protocols you may have used to pair
Bluetooth speakers, headsets, or with your car. You shouldn’t need to pair it in your
phone’s typical global Bluetooth settings dialog.
STAC Zero Powermeter Troubleshooting
Video: STACPerformance YouTube channel, “Typical STAC Zero Powermeter Debugging”
Video: STACPerformance YouTube channel, “STAC Zero Powermeter: What do the lights
mean?”
Problem: The STAC Zero powermeter only ever reads 0W
Causes: The speed sensor may not be picking up your wheel magnet
Solutions:
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Make sure the unit is turned on.
Make sure that the STAC speed sensor is picking up your magnet by grabbing your wheel and
moving it back and forth so that the magnet goes by the STAC speed sensor. The red light on
the PM Pod should alternate on/off each time the spoke magnet goes by.
The STAC Zero needs about 30 seconds to determine which direction is “down” each time you
move it. Units shipped since December 2016 will rapidly blink their green light while they are
engaged in this process, and a trainer that doesn’t know which down is down may report 0W.
Problem: The STAC Zero powermeter doesn’t match my existing powermeter
Causes: Myriad
Solutions:
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Note that since powermeters use many different algorithms and sense force at differing points
in a bicycle’s drivetrain, it is unlikely that two powermeters will come to identical instantaneous
readings. However, if your STAC Zero averages more than 4% above or below your other PM,
then try the tips below.
The STAC Zero is self-calibrating. However, if you store it, it may have stored a bad calibration.
Let it sit for 30 seconds after moving it for it to determine which way is down.
Make sure that the magnet-array quickrelease or any wiring is not touching the frame of the
STAC Zero. This can result in the forces of the magnet array “skipping” the force sensor, so you
don’t get credit for the power you’re putting out.
Make sure that when the STAC Zero is at rest that nothing is resting on or pressing against the
magnet arrays. This can cause the internal calibration to be in error.
From the factory, the STAC Zero is set to a brake rim diameter of 622mm, as found in most
700x23C wheels. However, if you are riding a different wheel size, you will need to use the STAC
Zero Control Panel app to adjust the brake rim diameter to the diameter of the wheel
component you’re using to generate resistance.
Download the STAC Zero Control Panel app and connect to the trainer with the debugging
menu. This will let you capture a log file with very detailed parameters for the STAC Zero team
to investigate.