Much higher power readout on hill compared to flat

I have at least 10-15% power “bonus” on hills compared to flats or workout mode. Some stats: in workout mode I can manage about 210-215 FTP with a big effort. On Alpe du Zwift I can easily hold over 230 for the whole hour, and today I got an FTP score of 233 from my last 20 minutes when I ramped up the effort, still had something left at the end. My slider is set to 50% but that shouldn’t influence how long I can hold a specific power level. There must be some issue about how the power readings are processed. I’ve seen other posts with similar although less pronounced effects, although some of them have reported the opposite effect, i.e. lower power on hills.

I have a Tacx Flow Smart which I calibrate every time but that only ensures the wheel tension is within range, doesn’t influence power measurement.

I would bet this affects many more people. It would be good to resolve it, I’d quite like to know my real FTP!

It may be a bit of psychology. When I started virtual riding, I found it easy to put out high watts on climbs - because the stimulated resistance required high watts to get moving let alone moving at even a modest speed. But on the flat, the resistance to work against isn’t there unless you create it by getting up to a high speed and forcing yourself to hold yourself at that speed.

Air resistance (which is being modelled on the flat) isn’t linear, so even a slight reduction in speed causes a large reduction in the power required to hold that slightly lower speed - whereas on a climb gravity is constant.

The challenge is forcing yourself to hold that higher wattage, and hold it and hold it. Find the watts that you know you can hold for a long period on a climb. Then when training on the flat, watch the watts display and try riding to hold that higher level you know you can do. Its hard because your body notices (and likes) even the slight ease, but you can learn to force the higher wattage.

I suspect that it’s probably a mental thing too. I have a similar issue myself - I find it easier to push my power on a climb rather than the flat.

Try doing your FTP test up Alpe du Zwift, if you haven’t already.

Could be due to low wheel speed. You can check this while doing a workout: try with high vs low gear at the same power and see if your perceived exertion changes.

Thanks, yeah, I thought it might be psychological, but realistically there’s no way. My best recent FTP on the flat was 214W from a very hard short race. Yesterday I got 233W from the last 20 minutes of the Alpe du Zwift KOM race, i.e. managed nearly 250W for 20 minutes having already pedalled nearly an hour. In a recent workout on ERG mode I was knackered after 250W for three minutes!

It’s definitely something in the processing of the power values. I’m going to try with different slider settings.

I would still call psychology on that one.

I recently tried a sub 1h AdZ and I thought I’d do the 1h FTP at the same time. I finished in little under 55 minutes but really struggled maintaining the power for the remainder of the hour. And I wasn’t all work out, if the segment would have gone on uphill for another five minutes, I don’t think there would have been a problem

233W is a fair bit short of 250W. And what were the cadences involved?

Like others here, I still think it’s psychological. The mind is a very powerful thing.

233 was the FTP @ 95% of the 20 minute effort (245). OK a bit short of 250 but it felt comfortable at the end of the Alpe, whereas holding over 220 for just a 20 minutes effort on the flat is hard work. I tend to keep around 85rpm under most conditions.

I’m going to try to borrow a power meter, it seems the only way to prove it!

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