Magene P515 PES Spider Powermeter

[jhearrtot]

The Magene is measuring before the drivetrain and the Saris is measuring after it. A small offset would be expected anyway, but what makes you think your trainer is more accurate?

Hey, I'm a bit of a noob when it comes to this stuff, but your question is valid and it made me think about it as well.

To clarify, I wasn't trying to say that my smart trainer is more accurate in terms of absolute power numbers. Looking back, I can see how that may have been implied in my post, so sorry for not being clearer.

I did some research and came across this article from Power Meter City regarding power meters and oval chainrings:

https://powermetercity.com/2016/07/24/power-meters-oval-chainrings/

Here's the concern: most power meters make the assumption that your pedaling velocity is constant. In other words, power meters assume that you turn the pedals at a steady speed throughout each pedal stroke revolution. The problem is that oval chainrings cause your crank velocity to change during each pedal stroke, as they limit the time spent in the dead spot and lengthen the time spent in the power phase.

Indeed, most studies conclude that because of the change in crank velocity, oval rings do influence the accuracy of power meters. More specifically, they can cause power numbers to be inflated. The more non-round the chainring is, the greater the impact on accuracy. Studies suggest you can expect an increase in power readings of anywhere from 1% to 4%.

Assuming that statement is correct, my front chainring is oval, which could explain the change in crank velocity during each pedal stroke. Since the power meter is mounted at the crank, I can see how it might report slightly higher readings compared to my smart trainer.

Again, I'm no expert, but that explanation seems reasonable to me. That said, I'm not too concerned about a small difference between the two devices unless the discrepancy becomes significant.

[toxin]

That oval chainring inaccuracy is not at all universal, as the article says, it really only applies to power meters which measure cadence once per revolution and assume the angular velocity of your pedalstroke is constant, those power meters should be considered garbage and avoided. Even if you don't use oval chainrings, the angular velocity of your pedal stroke is never constant. It spikes and dips on every revolution.

This is a long-solved problem, a proper power meter measures angular velocity continuously with a gyroscope and/or accelorometer and uses an up to date force and power measurement on every sample. Usually the sample rate is in the hundreds, maybe even thousands per second. Such fine granularity effectively eliminates any potential inaccuracy that would arise from unexpected pedalling dynamics.

Magene and pretty much every spider power meter on the market should have no problem with this. 2-3% of drivetrain loss is about what would normally be expected. Though there is the question of if the trainer is attempting to take that into account in any way or not and if yes, how much.

[jhearrtot]

That oval chainring inaccuracy is not at all universal, as the article says, it really only applies to power meters which measure cadence once per revolution and assume the angular velocity of your pedalstroke is constant, those power meters should be considered garbage and avoided. Even if you don't use oval chainrings, the angular velocity of your pedal stroke is never constant. It spikes and dips on every revolution.

This is a long-solved problem, a proper power meter measures angular velocity continuously with a gyroscope and/or accelorometer and uses an up to date force and power measurement on every sample. Usually the sample rate is in the hundreds, maybe even thousands per second. Such fine granularity effectively eliminates any potential inaccuracy that would arise from unexpected pedalling dynamics.

Magene and pretty much every spider power meter on the market should have no problem with this. 2-3% of drivetrain loss is about what would normally be expected. Though there is the question of if the trainer is attempting to take that into account in any way or not and if yes, how much.

Thanks for your valuable insights! This is enough to assure me that I don't have to worry about using a round or oval chainrings with my P515.

[Dlloyd15]

Has anyone successfully removed the "PES" logo from the crank arms? I've just received my power meter and I'm wondering if it's possible to give it that clean look.

Anyone know if there's a way to remove the logo but keep the existing finish?

[Dan S.]

Has anyone successfully removed the "PES" logo from the crank arms?

In my language (Czech), it means "a dog". You don’t want to have "a dog" writtten on your crankarms?? 

[Nopileus]

In my language (Czech), it means "a dog". You don’t want to have "a dog" writtten on your crankarms?? 

nero show approved

Don't think you can remove it without taking the entire anodizing off, seems to be laser etched.

[ZacItaly15]

i'm selling my P505 165mm magene powermeter at 190euro (Italy) brand new

[Nopileus]

Firmware 0.119 is out now, only 'optimized user experience' in the patch notes.
(screenshot machine translated from chinese app)

This should be the version gplama tested with.

Edit:
Seeing unexplainable power spikes on the first ride post update, just riding along at ~180w and it suddenly reports 700-1000w for three seconds before dropping back down.

[guille11]

Firmware 0.119 is out now, only 'optimized user experience' in the patch notes.
(screenshot machine translated from chinese app)

This should be the version gplama tested with.

Edit:
Seeing unexplainable power spikes on the first ride post update, just riding along at ~180w and it suddenly reports 700-1000w for three seconds before dropping back down.

I updated mine last weekend and data is normal so far, at least in my case.

[chaseme]

I've built up a new bike this year, using a Magene Teo crank & P515. I'm trying to decide if the power readings are inflated however. My previous bike was a left side only 4iiii power meter, and showed what I would expect for my output during any given situation. The Magene though seems to be quite a bit higher (20-50% depending). I'd love to think it's me being stronger, but I'm def not

Is there a calibration or other tuning I should look into?

[ediryppah]

I've built up a new bike this year, using a Magene Teo crank & P515. I'm trying to decide if the power readings are inflated however. My previous bike was a left side only 4iiii power meter, and showed what I would expect for my output during any given situation. The Magene though seems to be quite a bit higher (20-50% depending). I'd love to think it's me being stronger, but I'm def not

Is there a calibration or other tuning I should look into?

Without comparing to a trainer or a friends power pedals, it's really hard to say. My P515 is accurate (+/- 1% with both my old Stages left side and with my Kickr, so I'd say it's good).

[chaseme]

Without comparing to a trainer or a friends power pedals, it's really hard to say. My P515 is accurate (+/- 1% with both my old Stages left side and with my Kickr, so I'd say it's good).

My old 4iiii was a refurb unit. I'm going to go on assuming the Magene is fine, and the 4iiii was always reading low thus I'm stronger than I thought 

[bubsterboo]

I've built up a new bike this year, using a Magene Teo crank & P515. I'm trying to decide if the power readings are inflated however. My previous bike was a left side only 4iiii power meter, and showed what I would expect for my output during any given situation. The Magene though seems to be quite a bit higher (20-50% depending). I'd love to think it's me being stronger, but I'm def not

Is there a calibration or other tuning I should look into?

My first ride mine reported high at an average of about 300w. I ran the calibration in the app. Now my rides average a much more believable 200w.

[Nopileus]

I updated mine last weekend and data is normal so far, at least in my case.

My next rides data looked a lot more believable, had calibrated it a couple times before the ride,
hard to verify but chances are my mistake was not calibrating right after the update.

Unfortunately i can't get much seat time in right now due to lingering knee issues flaring up again.

[andrxjoy]

Hi, I've had the PES 515 for several months and I've never had any problems (some noise every now and then, like everyone I think...) yesterday I disassembled the PES 515 because I wanted to fit a new chain ring.....now the problem is that the double preload bolt is stuck together and by squeezing the rubber ring it no longer enters the thread of the crankset.....the only thing I can do is reassemble it without the rubber ring . What can I do?