Consistent Calibration on a Wahoo KICKR Snap

by Jeff Whitfield on | 10 Comments

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Wahoo KICKR Snap
Wahoo KICKR Snap

The Wahoo KICKR Snap is a great entry-level smart trainer. However, it's not without its flaws. One of the things about the KICKR Snap is that, with Wahoo’s 2017 refresh, they changed how calibration works. Before, a spin-down calibration required that you get it set to where it stops between 9-16 seconds. I was confused because it appeared that was still the case. It’s not. The calibration process works a bit differently for the 2017 refresh than it did with the previous version. It’s just a bit...confusing.

I’m not the only one who was confused by this. Reading various posts on Reddit, the TrainerRoad forum, and Zwift forums, many are a little confused by the calibration process with the 2017 KICKR Snap. The replies were a mixed bag with some people swearing up and down with problems but others claiming multiple years of happiness.

Ok, so here’s why so many people get confused. If you go to the KICKR Snap instructions on Wahoo’s website, you’ll see an instruction video that claims a spin down time of 10-15 seconds is recommended. But go to a different part of the support site and you’ll see Detailed Spindown Help instructions that say something completely different. In fact they explicitly say that, for the 2017 KICKR Snap, “calibration is based on proper roller tension and tire pressure” and that you can “ignore information regarding spindown times and roller adjustment” in the video. So, yeah, lots of confusion.

What Wahoo is saying though seems to be reflected in the results I get after a calibration on both the Wahoo Fitness and the TrainerRoad app. Not only do you get a spin down time but also a temperature and offset result. This leads me to believe that as long as you’re consistent with your tire pressure and the tension applied to the back tire that the resulting calibration should give you a consistent power reading.

However, there is a method to this madness. Certain steps have to be done to maintain consistency with each ride. In fact, Wahoo has a For Best Results page with a bulleted list that outlines the basic requirements for getting consistent results.

First, use a slick tire with a hard compound and set it to the recommended pressure on the tire. In some cases, you probably have to run your tire at near max PSI levels. You could use a specially made training tire but you don’t have to. Any good road slick tire will do. I’m currently running on a 32mm wide Continental Grand Prix 5000 tire as my training tire. I could probably run it at 90 to 95 PSI but figure I’ll get better results by maxing it out at 100 PSI. The fact that they mention a hard compound tire makes me think the harder the better so higher pressure it is.

Second, tension on the tire has to be consistent as well. While Wahoo recommends two complete 360 degree turns of the tension knob, you might need to add a bit of tension if you feel slippage, especially when putting the pedal to the metal. For me that ends up being right around 2 1/2 turns. Your mileage may vary with slippage so you just need to find a good middle ground and stick with it. Whatever the result, remember it and/or mark it on the knob so that you can repeat the same tension each time. My guess is that with the right tire pressure if you set the knob exactly the same as well then spin down calibrations should be relatively consistent as well.

UPDATE 2/17/2021: I know there has been some confusion over the number of turns so here's a bit of extra information based on an update I made to my trainer tire.

Vittoria Zaffiro Pro on a Wahoo KICKR Snap
Vittoria Zaffiro Pro on a Wahoo KICKR Snap

Now, that said, there are situations where an extra turn isn't needed. That 2-turn recommendation by Wahoo is likely based on the use of dedicated trainer tires which are all pretty much a uniform size. Case point, after a tube blowout with one of my Continental Grand Prix 5000 tires that I was using as trainer tires, I decided to upgrade to a Vittoria trainer tire. Right away I noticed that 2 1/2 turns was likely too much. The reason is that the trainer tire is only 23mm wide and thus the depth of the tire isn't nearly as much as the 32mm Grand Prix 5000 tire I was using before. Looking at the picture, with the tire pressure set at 110 psi, you can see that 2 turns depresses the tire about halfway. That's more than enough to maintain good traction. Any more and I noticed that the rim can buckle a bit. So, yeah, the depression the tire makes is another good indication of the correct number of turns. Once you've got that dialed in and consistent then you're set. 

Third, a 10-minute warm-up is required before each session. The temperature results told me as much. I don’t think you have to do much either. Just get on the bike and spin lightly for a few to help warmup the unit and the back tire. This insures that you don’t have any floating in power due to temperature changes. I set the timer on my watch and just do some reading on my tablet for 10 minutes. Sure, it’s an extra 10 minutes added to training time but it’s not really a big deal in the grand scheme of things.

Lastly, a spin down calibration is required for each ride. With a combination of the right tire, tire pressure, tension, and a warm-up, the resulting offset applied to the trainer should give you a pretty consistent result each time. Not doing so might cause power readings to be off quite a bit if you’re not careful.

I think Wahoo was aware of the calibration issues with the first version of the KICKR Snap. Because there are so many variables to consider with on-wheel trainers, having some sort of offset between training sessions was likely applied to the 2017 version to improve its power readings. Things like the temperature of the unit and the spin down time are all considered, which is reflected in the final values of the calibration. I just wish they’d update the documentation to make this more clear.



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on

Thanks for this post. This is very insightful. The reason I am checking this topic is because I have a gut feeling that the Zwift power readings are off as soon as I hit an incline in Zwift. I simply get passed by a lot (really a lot) of riders, even though I up my effort. When on the downhill, I manage to catch up again. I have played around with the trainer difficulty but wonder if it has anything to do with the Kickr Snap readings. And if so, will I be able to adjust this? Fyi: I have an average build, so that is not the factor here. In one of the comments it is mentioned that it makes no difference if a spin down is performed with the Wahoo app of within Zwift. I would be interested to know if anyone has ever researched this. Your thoughts on the matter will be appreciated.

on

Thanks for your comment! All very valid thoughts and questions. While I haven't fully researched this, from my understanding based on what I have researched is that the data the KICKR sends to the device that initialized the spindown is the same regardless of which app is used. Based on that, I can't see how the Wahoo and the Zwift app would be any different.

That said, I would presume that it's better to run the spindown from the app you intend to use. Best guess is that Zwift might use the data from the spindown in some way...then again they might not do anything with the spindown data. If anything, they're adding an offset to compensate for things introduced by a change in spindown data. So, basically, doing a spindown via the Wahoo app may (or may not) cause Zwift to report bad data. Can't say that's actually the case though. Just a best guess.

Aside from that, a spindown is a spindown and the calibration data would be reported the same regardless of which app is used for it. It's all based on Wahoo's own API, which don't change really.

on

So to clarify Jeff, you are suggesting to still use the wahoo app to perform a spin down with the (2017) v2 model snap - combined with your above mentioned tyre/warm up recommendations - but focus on seeing a consistent, repeatable spin down time (between 9 - 16 seconds) each time you calibrate?

on

With the 2017 KICKR Snap and above, you don't have to worry about the spindown time...just the tire pressure and tension. If you're consistent with those then the rest is good. The reason is that Wahoo updated the calibration so that it's based on the tire pressure and roller adjustment. Basically, set the tire pressure and roller, do a 10-minute warm-up, and then run the calibration with the Wahoo app. Running the calibration is good enough and you don't have to worry at all about the spindown time. :)

Strangely enough, if you have a crank or pedal based power meter then the calibration is even less of a problem. I have a Stages power meter and find that my power readings are dead-on regardless of a calibration. I still run the calibration though mainly so that any readings off the KICKR are still consistent.

on

Thanks so much - there is not a whole lot of clarity online regarding this subject! I have been following the protocol you suggested (100psi, 3.5 turns) but I was just calibrating using the zwift app (once I had warmed up and paired my trainer) - do you think either calibration method gives a more accurate power reading? Have you compared results between your stages meter and the calibration that the wahoo vs zwift app shows? Again, any advise is much appreciated - I am after consistency but also ‘real feel’ as the trainer is my only form of data analysis (no meter on bike).

on

I don't think either oen of the spindown calibration methods (Zwift vs Wahoo app) will be all that much different. After all, both apps are basically initializing the same spindown and letting the KICKR tell it what the result is. Basically, regardless of which method, the result is the same. That said, I would imagine my Stages power meter is likely to be more accurate than what is reported by the KICKR...but not by much. With a consistent spindown routine, you should be within a +/-3% variance of what a dedicated power meter would report..which is pretty good when you consider that a KICKR Core is within a +/-2% accuracy rating. I wouldn't worry too much about it. As long as you're consistent with the setup, warm it up for 10 minutes, and then do the spindown calibration each time you should get good results. :)

on

Why 3.5 turns? Isn't the instruction to use 2? I've been using 2 1/4 to get into the 9-16 sec range. Just wondering if I've misread something.

on

Good catch, Ed! Yeah, Mike, now that Ed is bringing it up....why 3.5 turns? That does seem a bit high. I would go no more than 2.5, especially on a high pressure tire. What kind of tire are you using?

on

Hey Jeff, sorry for the late reply! I am using 3.5 turns from first contact as I noticed my tyre slipping during sprints if I used less than that - I’m pretty sure the general recommendation online (ie. dcrainmaker, gplama) is to tighten until you don’t experience this issue so that’s what I’ve been going with. Some users are reporting even more than four turns needed, some right on two. I would imagine a large range of tyre compounds/slightly variable pressures being used by people, as well as other factors eg. ambient temperature, would attribute to why there can be different roller tensions needed. The tyre I use is a standard compound (conti ultra sport 3), pumped up to 110psi.

on

You're probably right, Mike. The choice in tire will definitely have an impact on the roller tension needed. Since switching from a Continental Grand Prix 5000 to a Vittoria Zaffiro Pro, I do notice that less tension is required. 2.5 turns is all it takes. So, yeah, mileage does vary. :)