Wahoo KICKR Snap Spin Down Calibration

Hello everyone,

img_5508-2
The Puppy ate my Vortex Smart Power Cord.

Curiosity got the better of me with my last test.  I was curious to see why the TACX Vortex Smart had an accuracy rating of +/- 10 percent.  After I completed the TACX Calibration Review, I had a few people ask me to do the same thing with the KICKR Snap.  As chance would have it, my new puppy ate my Vortex Smart power cord.  This gave me the opportunity to test the spin down calibration of the Wahoo KICKR Snap.  However, before we begin, we should look at what Wahoo says about doing the Spin Down Calibration for this trainer.  Wahoo covers this in their article “How to get the best results from you new KICKR Snap.”   The one difference in my testing is, I did the advanced spin down each time I changed something and wanted to measure it.

If you think this review is pretty cool, well there are ways to support the site.  You can buy a KICKR Snap by clicking here: Wahoo KICKR Snap Affiliate link.

If you want to skip all of the reading, you can watch my video below.

Baseline Power Curve

The first thing I wanted to establish is the baseline power curve for the KICKR Snap.  Every mid-range trainer will have a baseline virtual power curve.  As you can see from the image below, the KICKR Snap’s large flywheel gives it a power curve very similar to that of a Fluid based trainer.  Mag trainers have steady increases in power over speed, where fluid trainers get progressively harder as you go faster resulting in a power curve that starts bending upwards.

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The graph above is a simple scatter plot running my Stages Power Meter on the KICKR Snap.  I just convert the Garmin file into a .csv file using Golden Cheetah.  If you want to do this yourself, I talk about that in this article “Creating and Understanding Your Own Virtual Power Curve.”  Everything below the red line is where you cannot go.  You cannot get below the base line power curve.  I have some users who complain that they get stuck at 160 watts and ERG mode is supposed to keep them at 135 watts.  That is because the wheel speed is too high and must be decreased.  Most of these mid-range trainers will need some shifting to meet targets.  Everything above the red line in green, is the extra resistance that the Wahoo KICKR Snap will add on with the Electro-magnets.

Testing

I do some pretty simple testing.  Even though the testing is simple, it does take me hours to do this and compile all of the information.  I also wouldn’t consider this a scientific result.  There are still other variables to consider, like manufacturer tolerances and tire types.  I used the S-Works Turbo tire in this test.  Someone with a Conti Gator Skin may have a slightly different result.  You have to keep in mind, tire contact and friction will have an influence on these results.

Part 1, Advanced Spin Down

The first thing I did with the Wahoo KICKR Snap is go to the Wahoo Fitness App and conduct an advanced spin down.  That means two full turns on the resistance knob after the tire makes contact.  I then jumped on the Sufferfest Training Centre App and did the video workout “Ignitor”.  As you can see from the chart below, the KICKR Snap over reported power by about 15 to 20 watts.

wahoo-advanced-spin-down
First test was to check accuracy after Wahoo’s advanced spin down.

Part 2, Marking The Resistance Knob

img_5505-2For part two, I needed a way to measure how much I was turning the resistance knob.  This is the one thing Wahoo could improve on.  If they marked the knob somehow, it would be unnecessary for me to use the black marker.  So, to ensure that I was making a full turn of resistance, I broke out the black permanent marker.  You can see that I just simply marked the knob at the 12 o’clock position after I had my two full turns of resistance on.

Part 3, One Full Turn Up In Tire Contact

After I marked the resistance knob, I added one full turn of tire resistance.  This would increase friction and make the trainer report closer to my power meter.  What I found, is that one turn of resistance now had the KICKR Snap reporting near 20 watts lower than my Stages Power meter.

test2-tire-increase
As you can see from the trend line, the KICKR Snap is now about 20 watts over my Stages Power Meter.

Part 4, Advanced Spin Down With 1 Full Additional Turn

The next reasonable question was, “How does the full turn resistance affect the calibration after another advanced spin down?”  With three full turns of contact on the tire, I did another advanced spin down.  Surprisingly, that advanced spin down brought the trainer right back to its original calibration; the KICKR Snap was again reporting 20 watts higher than my Stages power meter.  This shows me that Wahoo’s advanced spin down calibration does take into effect the amount of resistance that the tire contact is creating.  That is pretty much how I thought it would work.

test-3-recal
With three full turns after tire contact, the advanced spin down still reports the same as the 2 full turns of contact.

Part 5, 1/2 Turn Resistance After Advanced Spin Down

For this last part with the Sufferfest Training Centre, I put the tire back to two full turns and checked to see if it was going to over report.  Surprisingly, the KICKR Snap doesn’t over report if you take off tire contact.  So, I couldn’t see doping this trainer on Zwift at all besides the additional 20 watts you get in the beginning.  Next, I did the advanced spin down one more time with 2 turns of resistance.  After that was complete, I added only 1/2 turn of resistance.  The image below shows that this put my KICKR Snap reporting right in line with my power meter.  The trend lines are almost right on top of each other.

12-turn-resistance
Doing and advanced spin down or normal spin down and then adding 1/2 turn in resistance seems to be key to getting my KICKR Snap right in line with my Stages Power Meter.

Part 6, Testing the 1/2 Turn Theory on Zwift

The last thing I did here was to go on Zwift and test out my theory.  I did another Advanced Spin Down Calibration with the two full turns of resistance (this was getting exhausting).  Then, I connected to Zwift and rode for 6 minutes.  The resistance felt correct in the beginning but I could tell it was drifting a bit.  Now, the trend line won’t be as accurate here.  You can see in the image below where the app was stuck on the FE-C call.  At 3:15, Zwift kept reporting 225 watts while you can see the power numbers on the Stages drop.  This is very typical of all apps, but it could easily be missed when riding around in Zwift.  It is more apparent in other Apps like The Sufferfest Training Centre and Trainer Road.  In those Apps, you are dying on intervals and desperate if it doesn’t release wattage off the interval, or you feel a bit discouraged when it doesn’t add resistance coming on an interval.

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I stopped my ride at 6 minutes, then got off the bike to add the 1/2 turn of resistance.  In the image below, you can see that the power numbers were more closely aligned, or at least moving in that direction at the end.

zwift-12-increase

Conclusion

In the end, we see again that even the best built trainers are still not as accurate as a Power Meters.  The best thing we can do is make a judgement call when we are riding our trainer.  If you feel like the resistance is too easy, then give your KICKR Snap a half turn up in resistance after you do your spin down calibration.  That worked for me.  However, your mileage may vary.  Again, tire type and inflation pressure will dictate how much resistance needs to be added.  I’m not willing to test every tire out their.  However, I am curious and if I ever found the time, I wouldn’t mind seeing what a Gator Skin tire or a tire specifically built for indoor training looked like.

The key here is to be consistent each time you get on your trainer.  I would argue that being consistent is more important than being accurate; consistency in numbers builds consistency in training.

Here is what I would do:

  1.  Do your advanced spin down first with the two turns of resistance.
  2. Mark your resistance knob to ensure you can measure how many turns or 1/2 turns you are putting on.
  3. Then add 1/2 turn of extra resistance.
  4. After you complete a workout or ride, make sure you remember how many turns you backed off to get the roller off your tire.  Then, just add that many turns when you get back on.
  5. Make sure your tire pressure is the same each time you get on your trainer.

Having a power meter makes all of this pretty irrelevant.  Most training apps are moving towards Power Match (most are already there).  Power Match allows you to read the power from your power meter and then control the trainer with that power reading.  I wouldn’t be surprised if we start seeing some companies that make indoor trainers, start to construct power meters or pair up with existing companies to package power meters with indoor trainers.

Thanks for reading everyone!  If you would like to read my review of the Wahoo KICKR Snap, you can follow the links below.

Wahoo KICKR Snap Review Part 1: The Build

Wahoo KICKR Snap Review Part2: The Ride

Aaron Johnson

Aaron Johnson

Aaron served in the military for 20 years. Multiple tours in Iraq and Afghanistan. He retired from the military after 20 years of service to take care of our three small children in 2013 as a Stay At Home Dad.

athletictechreview has 55 posts and counting.See all posts by athletictechreview

20 thoughts on “Wahoo KICKR Snap Spin Down Calibration

  • December 12, 2016 at 3:45 pm
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    I received the following last week from Wahoo tech support reference properly calibrating the Snap.
    Thanks for the call tonight. It looks like KICKR snap has become uncalibrated, please follow the steps below to calibrate the Snap properly. Please complete the following in the Wahoo Fitness app.

    1. Inflate your rear tire before every ride to 110psi
    2. Tighten the roller so it barely touches the rear tire, then tighten it by 2 full turns
    3. Do a standard spindown and if the time is greater than 15 seconds please tighten the roller by 1/4 turn
    4. Do a standard spindown and if the time less than 10 seconds please loosen the roller by 1/4 turn
    5. Repeat steps 3 and 4 until you have a standard spindown within 10 to 15 seconds
    6. Do 1 and only 1 advanced spindown to lock the calibration in. Do not do another advanced spindown unless instructed.

    Following the above procedures 3 full turns resulted in a 12.5 sec spindown.

    Reply
    • December 12, 2016 at 3:53 pm
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      Thanks for that extra info Jim. I guess my experiments were pretty close. I had no idea that Wahoo was suggesting this also. I should probably email the manufacturers when I do these, but I don’t have days to wait for responses. Some manufacturers take a while to get back to you.

      Reply
  • Pingback: Wahoo KICKR Snap Review Part 1; Build and Setup | kidsandcowbells

  • Pingback: Wahoo KICKR Snap Review Part 2; The Ride | kidsandcowbells

  • January 5, 2017 at 3:57 pm
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    Fantastic and very informative article. It’s much appreciated.

    I have been a Zwift user with a relatively dumb trainer, (KK RM with an inride module attached to measure power) it gets the job done but the KK fluid power curve can be a slog at times since it feels like you are constantly riding up a slight incline into a headwind (which is how the KK curve is designed – 1% incline)

    I have been considering switching to a true smart/active trainer, such as the Kickr Snap, for some time but was intrigued by just how “road like” the applied or reduced resistance depending on the situation would feel. Looking at your virtual power curve you plotted plot for the Snap, it appears that the standard curve seems to approximate actual power numbers I see when riding on a flat road drafting (wheel sucking!) in a group.

    This had been one of my bigger concerns when shopping for a smart trainer, that it would increase resistance for going uphill but that the sensation may be lost or less apparent when drafting and somewhat when descending (I’d love a Tacx Neo, but yeah, that’s not happening!).

    A couple of questions I do have, in your vlog, you mentioned that in your low gear, low cadence test, 39×27 at approx 65 rpm, you were able to achieve 340 – 355w. The green portion of the virtual curve shows approx 340w at right about 20 km/h. At that speed I would generally be spinning at about 110 rpm. At 65 rpm I would be doing about 12 km/h which translates to about 240w on the virtual curve – I was hoping you could clarify the green portion?

    Secondly, do you notice the resistance alter when you move from leading the group and move into a drafting position in Zwift?

    Once again thank you for a very well done review.

    Reply
    • January 5, 2017 at 7:38 pm
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      Hello Nicholas! So, the red line is the base line power curve for the KICKR Snap. That is no power, that is just the base of the trainer and you can’t get less power than that with those wheel speeds. The green area is what the trainer can add on based off my rough calculations. They are not exact, but more of a representation of what is happening with wheel speed an power. So, what I’m saying is my green line is not 100% accurate. On the 39×27 gear, running 65rpm, I was getting 340 watts as a maximum. What I’ve noticed as I’ve tested these trainers, is that the KICKR Snap is much more powerful than the other trainers I’ve tested so far. I have a TACX Bushido in my basement now that I hope to test at some point. However, there is this cool new ANT+ to Bluetooth brigding device I just got from the WASP people I need to test out also. http://npe-inc.com/products/products-cable.html

      Reply
  • January 13, 2017 at 4:37 am
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    Hi, Aaron!

    Excellent work on testing smart trainers, I’ve been watching all your videos on youtube, very informative and detailed, and you seem to be the only one who pushes these trainers to its limits on low cadence & gear combo, kudos for that!

    I’m curious on Tacx Bushido you have, what’s your opinion on how it holds against Kickr Snap? By spec sheet, Bushido simulates 15% gradients (although for a 75kg rider), while Kickr Snap goes to 12%. In my region they cost about the same, so it’s a toss between those two trainers.

    Thanks again for great videos, I’m looking forward for new reviews.

    Reply
    • January 13, 2017 at 8:57 am
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      Hello and Thanks for reading my Article. I’m very interested in the Bushido Smart. I believe it is the only trainer that can go toe to toe with the KICKR Snap. It has an additional feature to run without power, which gives it a bit of an edge. I have it in the box now. I need to finish up my performance testing on the Qubo Digital Smart B+. Then, I’ll start unboxing the Bushido Smart. Sorry for the Delay. I had to spend a couple of weeks getting the new website up and running so everything was put on pause. I’m back to writing and testing in full force now.

      Reply
    • January 17, 2017 at 8:52 am
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      Hello Simon, I used 110psi on my tyre. Nothing too fancy.

      Reply
      • January 18, 2017 at 7:32 pm
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        Cheers Aaron, I’ve just read the article again. In part 3 the Snap should of read lower not higher.. hope that helps?

        Reply
        • January 22, 2017 at 6:53 pm
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          Good catch Simon! I had read that paragraph 3 times to finally figure it out. At first I was about to explain that I was indeed correct, but when I was typing out my explanation I realized my error. Thanks for letting me know.

          Reply
  • February 4, 2017 at 10:48 am
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    Is it just me or the advance spin down option is missing in the android app?

    Reply
    • February 4, 2017 at 12:18 pm
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      Hello Ron, that would be correct I think. Also missing from Android is the ability to power match the Gen 1 KICKR with an external power meter.

      Reply
  • February 10, 2017 at 2:49 pm
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    Hi Aaron. I’m having big vibration problems with my snap. It’s my second unit that has the same problem. I’ve tried 3 different wheels and bought a new mavic wheel which is true and round. I’ve bought a wired gatorskin and conti turbo tyre but still have same problem. I’ve noticed the the roller is uneven. The vibration starts at about 13mph and gets worse the faster you pedal. I don’t leave the roller on after use. Did you experience any vibration when you did your review?

    Reply
    • February 10, 2017 at 6:57 pm
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      Hello Dave, I had a little vibration up to 35mph, but not any different than other trainers. I had one person ask me about this also and they sent me a video. I could see the roller was slightly out of alignment so I emailed Wahoo. I sold my snap so I can’t do a video on this, but there are two holes in your roller that access bolts. Those bolts are used to adjust the alignment of the roller. My suggestion is to get in there and see how easy or difficult it might be to make an adjustment. Or, you could email Wahoo and see if they have any instructions on how to do it.

      Reply
  • February 11, 2017 at 8:12 pm
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    I finally got back into Zwift. I used it two years ago during beta on my Fluid2 trainer – a terrible experience because their power curve was ~50% too low!

    Current setup is a KICKR SNAP and a ’93 Specialized Rockhopper on Specialized Fat Boy tires – 26×1.25@100psi. Difficulty set to 100% (Training for a hilly century this spring). Broke the frame on my road bike, so I’m stuck with this for a while.

    Did a London loop and noticed on the downhills that my actual speed was nowhere near my Zwift speed. Don’t have a cadence sensor currently on this bike, but I wasn’t spinning that hard. 100rpm on my setup = 32.7mph. I got up to 47 down Box Hill. I immediately thought of you post on the minimum power at speed and pulled the Zwift data into GoldenCheetah and then exported it into a CSV.

    I plotted the speed and power (from the KICKR SNAP) and the added your minimum power trendline. About 20% of my ride was below your minimum power curve. Somewhat surprising.

    All the being said. It’d be nice if you keep on providing the Baseline Power Curve for the trainers you test. Especially for the power-challenged folks as myself! Have you ever done this for the original KICKR?

    https://drive.google.com/file/d/0Bx-1yTyXFwz_c2V4b1FjcVBNb1k/view?usp=sharing (chart)

    Reply
  • March 31, 2017 at 10:05 pm
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    Cheers Aaron, thanks for the great review on the SNAP, which I also own and am trying to calibrate right now. Something Wahoo don’t make clear and really should make clear is when they say 2 turns of the blue knob – do they mean 2 complete 360 degree revolutions of the knob – or two general hand turns by wrist? I had been doing the latter not knowing if this was correct or not and with the tyres pumped to 110 psi was getting a Spindown value of about 21 seconds? I assume then from your findings that the Knob must be turned 2 full revolutions of 360 degrees – hence your marking it with black pen – then adjust a 1/4 turn from here to fine tune – does that sound about right?

    Reply
    • April 1, 2017 at 12:24 pm
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      Hello! It is two complete revolutions of the knob. That is why I took a black marker and marked my knob. They should probably build something like that on the knob for us. Then I just took 1/2 turn off the resistance and it was reporting correctly. It got me right in line with my power meter. If you are using a tire that is a bit more rugged like a GatorSkin or Armidillo, you might need to go 3/4’s of a turn. Those tire’s add a bit more resistance.

      Reply

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