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BKool and P1s pedals 20 watts difference
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Hi there
For me and my girlfriend the indoor season started 3 months ago, which means BKool all Winther.
Both of us uses Powertap P1s and have been using them since preseason on the BKool. Back then the watt difference was around 5 watts (5W higher on P1s)
3 months ago when we started using our BKool it measures 20+ Watts less than both mine and my GFs p1s, eventhough we kalibrate the P1s before every ride.
Any ideas what the cause could be?

Thanks
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Re: BKool and P1s pedals 20 watts difference [Buchreitz] [ In reply to ]
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I have Bkool and find it reads on average about 10% lower than my P2M (which matches my Powertap pretty closely so assume it's fairly accurate)

I don't think the Bkool is particular accurate or consistent as that 10% seems to vary quite a lot, even within the same workout. I suspect the design of the Bkool is part of the reason for this. I'm around the 100kg mark so put a lot of pressure on the tyre/roller compared to someone lighter, similar to over tightening other turbo trainers.

I also think riding aero or sat up makes a difference as this weights/unweights the back tyre to some extent too. IIIRC DC Rainmaker raised the issue of standing in his review when they first came out but I never stand so can't comment on that specifically but would expect it to be an issue as that shifts even more weight off the rear tyre.

Depending what software you're using, power matching would solve the issue or I use the Bkool figures when on the Bkool so have a Bkool FTP & a real FTP and set sessions accordingly.
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Re: BKool and P1s pedals 20 watts difference [Buchreitz] [ In reply to ]
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All smart trainers will experience some calibration drift with time. If the trainer is moved a lot or experiences big temperature changes the drift can be significant which is why all the higher end trainers have re-calibration functions. The values you are seeing are within the range of what I would expect and I would just stick to the P1s.

As a side not I just came across the Bkool Smart Air Pro. It looks like they have found a way around Kurt Kinetic's patent on the Rock and Roll and I am fan of the design. If it works I wouldn't be surprised if it sets down a new trend in trainer design. That said it doesn't look to me as if any of the units shown o line are real working and digging further I can see BKool has been flouting not working prototypes for a couple years.
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Re: BKool and P1s pedals 20 watts difference [Buchreitz] [ In reply to ]
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Buchreitz wrote:
Hi there

For me and my girlfriend the indoor season started 3 months ago, which means BKool all Winther.
Both of us uses Powertap P1s and have been using them since preseason on the BKool. Back then the watt difference was around 5 watts (5W higher on P1s)
3 months ago when we started using our BKool it measures 20+ Watts less than both mine and my GFs p1s, eventhough we kalibrate the P1s before every ride.
Any ideas what the cause could be?

Thanks


Some part of that difference is that you are measuring at two very different points. One, at the pedals where you are getting direct power input and two, at the rear wheel where you have lost power in transmission. I don't have the numbers off the top of my head, but power at the crank (like with a SRM) is always a few percent higher than at the hub (like a Power Tap hub) because of the losses in the drive train. I'd guess that measuring at the tire interface loses a bit more. 20 watts might be on the high side though depending on what kind of power you're putting out. At 300 watts on the pedals that would be 6-7% lower at the tire. You should also look at the % accuracy claimed for the pedals and the trainer and see if those error bars close the difference.

Okay, looking at DC Rain Maker's review, the accuracy of the BKool trainer is +/-10%. That's a lot.

https://www.dcrainmaker.com/2012/12/bkool-wireless-ant-trainer-in-depth-review.html


I guess you get what you pay for... On the other hand as long as it's consistent it will still be a valuable tool as long as you take that 20 watts into account.



Kevin

http://kevinmetcalfe.dreamhosters.com
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