P2M Power Spider and turbo trainer - low W and high MPH

Equipment
1

Installed a P2M on my 1x Allez Sprint yesterday and did a shake down outside. Power numbers were about what I expected them to be, nothing seems odd. Which leads us to today…

Trying to do a ramp test since I have a new unit of measure. Previous virtual was 238w, but I’ve done 6 weeks of SS training since then and the workouts were getting a lot easier towards the end, so I know my virtual should increase. Trying a ramp test with the P2M, I threw the chain shifting into the 10cog but I was only at 250w (measured) but doing 27mph on the trainer. Something seems grossly off as I know to go 27mph on the road is going to require a lot more than 250w and it sure felt like a lot more.

So can’t really figure out what is going on here. Either I’m way weaker than I thought, the dumb trainer with the P2M is not putting enough resistance into the bike (not enough flywheel mass / wheel pressure) which means I am looking to shift into the 10 cog (48T chainring) at only 250w, or the power meter isn’t reading high enough (doubt it).

Any thoughts other than tightening the wheel down more?

2

Trainer speeds have nothing to do with outdoor speeds. Don’t use this as a reference point.

1 Like
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@mcalista nailed it. That speed is just the flywheel speed. It doesn’t take into account any wind resistance, gradient, tire rolling resistance, aerodynamics of the wheels and bike, etc. You could find a similar result putting a speed sensor on your rear wheel, lifting your bike off the ground and spinning the cranks by hand.

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Right, I figured that, but I’m going to run out of gear is the issue. My guess is to increase the load on the rear tire to increase resistance?

5

Yeah, you may have to adjust resistance of the dumb trainer. And if you’re not already using the small ring up front, give that a try too. That will bring the flywheel speed down and potentially help with this probelm.

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It’s a SRAM Road Force 1x. 48T up front 10-32 cassette.

Will crank it down some and try later on.

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are you using a electronic trainer ?

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I am not. Just a classic Cyclops Magneto