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I have a Garmin Vector Power meter (one-side) and I use plain Tac-X rollers with no technical bits on them. My speed and power come from sensors on the bike.

My power output seems low relative to my perceived effort compared to when riding on the road. I'm knackered between 200-300W and dying if I push towards 400W. On the road I am relatively comfortable at 200W and on a push I can go to 400W for say a short steep climb. When I slow down, I am still pretty tired spinning at 150W output on the rollers.

I don't doubt the accuracy of my power meter(or rather I don't doubt that the power meter works indoors as it does outdoors), so why does it feel so different?

Thanks

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    Can you check the resistance settings on your rollers? There may be a hand-knob, or a screw/bolt. The resistance may be friction, or possibly magnetic. I wonder if the setting is too hard. For example tacx.com/product/blue-twist
    – Criggie ♦
    Mar 22, 2020 at 10:50
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    I second @Criggie's recommendation to just double check this. I was pretty recently at an indoor training class, and I inadvertently had the rollers' resistance setting on maximum. Normally, they leave the resistance off entirely on that roller model. I agree that my perceived effort was a lot higher than my actual power.
    – Weiwen Ng
    Mar 23, 2020 at 14:02
  • I will check, but as far as I am aware there is no setting on these rollers.
    – doc
    Mar 23, 2020 at 16:42

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Perceived effort isn't determined only by power output. That is, power output is certainly one of the things that affects perceived effort but there are others. There are (at least) two other possibilities:

First, you may be overheating during indoor riding, so the perceived exertion is high compared to riding outdoors. In that case, a large fan can help you maintain convective cooling and reduce your perceived exertion.

Second, crank inertial load on rollers is quite different to that on the road. You can think of crank inertial load (CIL) as related to how much momentum is maintained with each pedal stroke. Outdoors on real roads CIL is high while on a trainer or on rollers CIL is relatively low: that means when you're on real roads you can coast or pedal softly and maintain speed while when on rollers as soon as you let up the wheel speed drops. Some riders are more sensitive to low CIL than others; some riders are initially sensitive but with training get used to it. If you're relatively new to roller riding, your muscles may not be attuned to having to spin at high cadence and low torque, so your heart rate and perceived exertion may be higher than when riding on the road. Some trainers have a large flywheel, so although the CIL may be less than on the road, they will have higher CIL than rollers.

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    The CIL is really key to how a bike/trainer feels in my experience. Anything that doesn't have some serious CIL simply does not feel like a bike at all. And a high CIL provides a mental bit of reward for your effort: When you've been going fast, you feel that you've been going fast for a few seconds after. The higher the CIL, the stronger this reward, and the more willing your legs are to work for their reward. Still, nothing, absolutely nothing can beat a real bike on a quiet, smooth road through a nice countryside...
    – cmaster - reinstate monica
    Mar 23, 2020 at 6:34
  • Thanks for you answer - this makes a lot of sense. In fact, if I stop pedaling, my wheels will very quickly come to a stop, which is obviously very different to being in the road.
    – doc
    Mar 23, 2020 at 8:06

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