Watts and speed so far out

Hi I’m new to Zwift and using as Phisio as recently had knee surgery and torn ligaments.
I’m using a kettler Racer S bike and it cannot connect directly to Zwift so I’m using a Wahoo Bluetooth speed and cadence sensor and have put the wheel size on the app to 20inch as that is the lowest setting. I am only riding flat at the moment and for around 10 minutes my problem is kettler bike watts is setting on 90 watts but Zwift is registering around 235 watts so first ride I was riding at apparently 30+ mph is there anyway to adjust this to be more accurate? As I can’t seem to change it

Thanks mark

You need to enter the actual size of tire that you have on the bike that is mounted to the trainer. I highly doubt you are using a 20in tire (it’s a kids bike size tire), so that is the reason you are seeing the abnormally high speed and watts.

Thanks Paul
My problem is the sensor mounts to the hub and the trainer is like a spin bike it doesn’t actually have a proper wheel as such

The only way you are going to get any accurate speed and power within Zwift for the is to put pedal base power meter on it (or crank arm if you can find one that will fit).

You could try different wheel sizes to see if you can get a more accurate reading withing Zwift.

Yes just mess with wheel size until it’s close. That will be the easiest and get you riding the quickest.


Ok thanks wheel size 20 inch gives the closest but is probably 8 mph faster and setting on 700c is about 17mph faster

Also the resistance setting on the spinning bike will make a difference.

so the question is; how many races have you done to destroy all the mere mortals?

No one as Like I said at the start I’m riding flat custom course for Phisio for no more than 10 minutes

Thanks for your input

Thanks I did think that but because of the recent surgery I need to keep the resistance lower.

hi all, I am having the same issue as Mark, I do have a Kettler Racer S and put a Speed Sensor and a Cadence Sensor of Garmin to be able to use it with the Zwift app. The 20in tire he mentions is correct actually, because the Diameter of the Kettler Racer S wheel is about 450mm, so it is really small, substantially smaller than a racing bike.

I would really like to know if there is anybody in a similar situation and found a solution to this. If the key is a power meter crank arm so be it, but it would be really helpful to know for sure as the power meter is an expensive investment so it better works.

But the issue with wrong speed i do have as well with the Garmin Edge where it shows very weird speed figures, so it is really a mess to find an accurate way…
I guess I will have to invest rather in a Wahoo trainer or Tacx before adding more staff into the kettler racer…

thanks for any help and suggestions

Well, I also use a Kettler Racer S 2018 BLE and I have got the App from Uwe Böhm.
It really works fantastic with that app.
You have to invest a one time fee of 25 EUR and it works Unlimited.

Best regards

Hi There Hans,
Do you have a link to donwload it ?
Thank you in advance,

Hi marcomoneytime,

well, I can’t send you the Link (not allowed in the forum), but best way will be to contact Uwe personally, because you have to make a request directly at uwe.boehm@web.de.
he is very helpful in all areas.

Best regards

P.S. tell me, if you need help getting started with it :wink: