Watts output smart trainers vs. classic trainers

Hi all:

Should I expect a drastic reduction in watts output using a smart trainer? I started Zwift using a TravelTrac Comp Fluid classic trainer. My FTP test had me pegged at 260, and I’ve been riding consistently at 200-300 W for training and races. Using my new BKool Smart Pro 2 I can barely crank out 200W unless I am REALLY hitting it hard.

In terms of speed/cadence the BKool smart trainer gives me results comparable to my outdoor riding – usually averaging 17-18 mph on a 20 mile ride. But I swear the watts output seems WAY off compared to the classic trainer. I can see 10-15% difference but almost a 50+% difference seems unlikely.

Races using the smart trainer are a joke, I am left at the starting gate unless I  go into the red big time…then finishing is not a given.

What am I missing? Are the BKool numbers off? [NB - I put in a suport ticket to BKool, but they are not too responsive] Do I do a new FTP test with the smart trainer to get my numbers in line with its output?

Any guidance appreciated

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This sounds very typical of someone going from zPower (estimated power) to a smart trainer/power meter. There have been many people saying how accurate they have their zPower setup and then they move to a smart trainer/power meter and their FTP drops 50-100 watts.

I would suggest doing another FTP test with the new trainer.

Thanks Paul…I kind of thought so. I knew the classic trainer was not accurate, but hell not THAT inaccurate. 

I was hoping you’d tell me that BKool was off and that I really could crush 430 W in a sprint.

Just to be clear, my training zones will change with a new FTP test? I can change the FTP in my other tracking programs so I don’t feel like I’m back to square one.

I guess I won’t get DQ’d in Cat D races for awhile for too high a w/kg.

To be clear the I am not assuming the BKool is not off, I’m just saying it’s more accurate than zPower.

Yes, your training zones will change once you get a new FTP.

Is it true that the BKool Smart Pro doesn’t need any calibration? Given the number of variables with wheel-on trainers, I’m surprised: My Wahoo Kickr Snap is very finicky about how tight it’s clamped to the tire, warmup, and spindown calibration. If any of these are out, the Snap can give wildly inaccurate power data.

Definitely interested in this as I have the same trainer; note this trainer does not clamp the wheel to the flywheel via the axle, it just rests there with your weight bearing down. I believe the power reading is pretty accurate given my previous experiences with bkool’s software. (Moving to zwift this season as a change - giving up the great video rides on bkool for the better interactive abilities.) Erratic cadence readings seem to be a problem on group rides though.

@Mathew Bittleston as Simon.ausage Pugh said, the fact that the BKool trainer is not clamped to the wheel, there is no spin down calibration. 

Riding the BKool “feels” right in that I get the feedback from grade changes both plus and minus (though I was faced with a  10% grade and felt slippage galore). The effort to make climbs and push descents feel very road-like. I am just surprised that the watts output numbers are so much lower than ZPower…and actually much lower than other smart trainers. Hard to believe that I would go from a 240W threshold output to having 240W feel like a major sprint effort.

First world problems, sure. I like to participate in races and with the BKool trainer I feel like I’m riding a tricycle against drag motorcycles…the BKool simulator rides are very pleasant, but nearly as fun as the Zwift races.