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.
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.