Kickr Snap 2017 reading 30-50W lower than Stages power meter


(Gidon Reid) #1

I have the newer Kickr Snap. Even after spindown using the Wahoo app (and tried spindown in Zwift too), and the hidden advanced calibration, readings off my Kickr Snap 2017 are significantly lower than off the Stages power meter. I’ve been riding with power long enough to know the numbers are way off even without looking at my Stages power values (at least 30W-50W).

My spindown time is around 27 seconds which seems a little long. With the Snap v1 this value was meant to be between 10 and 15s but with the v2 I think it’s only an issue if the value is less than 10s and more than 45s.

Using only ANT+.

 


(Steve Ellis) #2

Have you used the Wahoo mobile app to connect to the Snap and ensure that the Snap firmware is up to date?


(Gidon Reid) #3

Yes all up to date.


(C hris Strub) #4

Tighten the knob another full turn.  Redo your spin down.  Need to try and get in between 10 to 15 seconds.  If under 10, loosen knob.  Still over 15, tight 1/4 turn at a time.  Check tire psi, adjust to 110 psi.  Make sure your tire is warmed up.  10 mins should be enough to warm up tire.


(Gidon Reid) #5

Thanks. I have tried all that - makes very little difference to spin down time.

Wahoo support said time is ok. I’ve noticed they don’t suggest the 10-15s time with the V2 snaps.

I need to do some more testing but looks like it’s the time reported in game (free ride) that shows the difference. In ERG mode it’s pretty close.


(Dan Dube) #6

i have the snap 2017, too – i had a similar problem when i started using it. i used the wahoo utility (not zwift) and tightening the knob to get the spin down to be 14 seconds. i also pump the tire to 110 psi before every single ride. (note that i do all this fiddling after i warmed the tire up for 10 mins of riding)

for me, this fixed it – but the key was getting the spindown (according to the wahoo utility) to be < 15 seconds, and then i also do re-calibrates in zwift after all of this, too.

one other silly thing i did was to mark the knob at “just touching” the tire so that i was clearly/obviously turning it at least two full turns. every subsequent setup is way faster with this mark on the knob.


(Gidon Reid) #7

Many thanks for the replies. I will try again tonight and report back. Wahoo support I didn’t find very helpful - I thought it odd the time was a bit high. I will see if it makes any difference. One thing support said was it wasn’t the time for spindown, but the variation that was the issue.

I’m also going to put on my Powertap G3 wheel for a third power measurement! 

I’ll probably use Power Match in Zwift, but it doesn’t very well in ERG mode. And also bought the Snap so I could put other bikes on it too - so want to know it’s accurate!


(Matt Thornton) #8

I’d be interested to hear how you get on with this. I’ve been having similar problems with my Kickr Snap recently. At the moment my numbers are down by approx. 30%.

Of course it’s entirely possible it’s the rider that’s at fault here… but I’d rather not consider that!


(Gidon Reid) #9

OK I’ve looked into this and even have graphs if anyone’s interested! (they’ll be going into a review I’m doing of the unit).

I put the Powertap wheel on and measure power off the Snap, Stages and Powertap simultaneously. Since the Powertap and Snap measure at the hub effectively I would expect them to read a little lower than the Stages. And also the Stages is doubling the left leg measurement, so some possible inaccuracies there.

The Stages reads about 15W higher than the Powertap - perhaps I’m a little left leg dominant. I doubt there’s that much drive train loss.

The issue with calibration seems to be the tyre used. I use Conti GP4000 tyres which are a very supple rubber, and I also use the 25mm variant. I tried some other tyres, both in 23mm: an old Specialized Mondo and a Conti Gatorskin.

With the 25mm GP4000 my spindown even at 120PSI was 26s with 2 turns of the knob from contact. With the 23mm tyres (with a higher contact pressure due to the smaller contact area), at 110PSI 2 turns gave me around 16.5 seconds, and another quarter turn gave me 15.5s.

In this article (and speaking with their support):
https://support.wahoofitness.com/hc/en-us/articles/115000510244-KICKR-SNAP-Troubleshooting

Wahoo state that with the 2nd gen Snap (2017), only spindowns under 10s and over 45s are of concern. But as suggested above even with the newer Snap, I’ve also found that if the spindown is significantly over 15s, power readings will be around 15-20W lower than a calibrated power meter, and in my case on average 35W lower than a Stages power meter.

To get my GP4000 to 16s took 3.5 turns of the blue knob. Which feels too much to me, and seems to put unnecessary strain on the unit and wheel. And also makes the ride less smooth. I’d also be worried about stripping the thread on the standard.

So thank you for the suggestions above.

In summary, having spent far too long looking into this, I’d recommend:

  1. Use a 23mm tyre at 110PSI (or perhaps a harder compound 25mm tyre?)
  2. Despite Wahoo’s recommendations, it appears you still need to get spindowns to somewhere close to 15s to get accurate results.

I’m fortunate enough to have a second wheel I will use with the Snap. And I’ve ordered a Conti 23mm trainer tyre to use with it now. And with my sons bike (the main reason I got the Snap was so I could use other bikes too!), the cheap 23mm hard tyres get a spindown of 12 seconds :).

Sorry, a bit long winded!

 


(C hris Strub) #10

I am not by any means a big watts per kg guy.  I keep my weight as it should be.  I tighten the knob almost 3 full turns.  I keep the psi at 110 when I remember and I run it with full sim.

Except last night.  I did not calibrate.  (You don’t really need to do this every time you ride unless you change something, like loosen the knob or remove the bike) 

So, I suspect it was a little loose.  I just was not in the mood for Watopia 6, but I knew I had to do it, to keep it going.

I turned off full elevation sim and it ran as a smart dumb trainer.  I also suspect it was not as tight as it should be.  My power was higher than normal. I was able to climb the hills without shifting my gears.  I could easily maintain close to 3 wpk. (More like 2.7, lol) 

I knew in my heart it was not real.  I did not care. 

I can only imagine the Strava forums lighting up in the comings months.  

“I have been a 3.5 wpk guy all winter and now that I am outside your telling my my avg is 2.0?  Strava, your estimates are way off, please fix”

That will be too funny.  


(Steven D) #11

It looks like you got some great suggestions from other members of the community, Gidon. It looks like they were helpful. Ride On!