Watts higher on gym bike than at home

My most recent TR workout was the first one in the gym since Feb 2020 when Covid hit. My gym has Stages bikes with Gen 3 lefty power meters. When covid hit I got a dumb trainer for my mtb which also has a gen 3 lefty stages power meter. I got a separate wheel with a slick tire for mtb at home sessions on the dumb trainer.

The workout I did would push my threshold limits at home but in the gym it felt much easier. I ended up increasing intensity by 7% for the last interval. At home I would have failed with this intensity increase.

The temp in the gym is higher than at home.

The geo of the bikes is a bit different but I am more leaned forward at home so in better position to activate glutes.

Why at the watts in the gym higher/easier? I am thinking either the PMs aren’t measuring the same or it is psychological…maybe the gym atmosphere just puts me in a different headspace.

Any experience with this?

Also, makes me wonder about a TR feature request where ramp test, ftp and PLs are assigned to a default user profile but workouts done on a different setup (separate profile) are recalibrated by a user set adjustment so they don’t mess up the adaptation recommendations of AT relating to the default profile…


Probably this.

Has the Stages at the gym ever been calibrated?

I always calibrate (zero reset) the bikes in the gym: Performing a zero reset on the Stages Indoor Cycling console : Stages Indoor Cycling

I calibrate (zero reset) the PM at the gym and at home before each ride.

I did another workout at the gym this morning and I have another idea about the difference: gearing. The Stages bike at the gym has very fine resistance adjustment knob. My bike at home has effectively two useful gears for TR workouts…lower gear that takes me through warmups up until about 85% of FTP. Anything above that I need to do in my highest gear. I am a low-cadence MTB-er so at thresshold and VO2max I am spinning faster than I’d like to on the dumb trainer. This is probably a big contribution to why the gym bike feels easier.

I don’t want to buy a smart trainer. I don’t have any fine resistance adjustments on the trails so that’s how I need to train…

All power meters vary in measurement from each other by a few %, as do ones of the same model / brand, and some vary more than others day to day or over the course of the ride. Some claim Stages PM’s read “high”, while something like a P2M reads “low”. The high or low is only relative to what one would get in the lab or trying to compare to other people. Other than that, pay it no regard, your numbers are your numbers.

This is why power meters only really work when you use the same one, and the numbers only matter to you. There is a lot of margin of error when trying to compare numbers to other people, or between different power meters of your own.

Do two FTP tests - one on each power meter. Then you’ll know how much to adjust when you ride the gym bike.

Can’t you use all the gears on your bike? I have a smart trainer and I mostly use the gears to change resistance.

Dumb trainer doesn’t have a lot of resistance, so anything other than highest 2 gears is useless…

Related to this, what exact trainer do you have at home?

I get the impression it may be one with a low wattage resistance unit, and I would guess a small flywheel too. Essentially, I think flywheel speed (“inertia” and the related feel / loading on your body) could well be a notable difference between your two training situations.

  • Spin bikes traditionally have a very large and fast moving flywheel. It potentially leads to a different feel compared to some lower level standard (dumb) trainers with small flywheel.

Hi Chad, I have the CycleOps Fluid2 (original version with black knob). It’s leaking oil which probably doesn’t help the resistance either…

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Yeah, leaking will lead to lower peak resistance for sure. Probably gets to excessive heat as well, which might drop resistance even more. Even at it’s freshest, that flywheel is good (and better than many trainers), but it falls well short of the flywheel on a spin bike. So, just another variable that is playing in the mix and may address some of the delta you see.

Those stages bikes are +/- 25% from one unit to the next in my experience. They seem pretty consistent against itself. Someone posted the zero process, and that’s probably the way to go.

If you’re going to a pretty punchy effort, the direct read power meter may be higher than a smart trainer because of the way it reads the data as the trainers just read the flywheel rpms and make assumptions.

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I’ve ridden a lot of Stages SC3 bikes in our gym, and I always zero reset the power meter before recording. By doing that I’ve found power between bikes is very consistent, on the order of +/- 3% (roughly 5-10watts on a 250W ftp).

Some 40/20s intervals in the gym using Zwift to record power/cadence from Stages SC3:

If I could find one locally, I’d buy a well maintained used SC3 and sell my Kickr.

I’d suspect the zero-ing would do the trick. I agree those spin bikes are great and a good value used. The only problem is finding one with the PM as described in a used ad.