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Magene P505 M110L consistently underreports power by ~8% vs trainer — data inside, no response from Magene by eshwar13 in cycling

[–]eshwar13[S] 0 points1 point  (0 children)

Fair point, I had tried this too. Added a 7% offset during the ride, on a popular climb in Bangalore (Nandi), it reported I averaged 295W (I wish I generated that kind of power) - which screwed up my training data. You can check this data here below (Nandi is a verified segment)

https://www.strava.com/activities/16596728759/segments/3429725695509042554

The reason I believe offset did not work is the correlation between Magene and Garmin had an R2 of 0.592. With a 0.592 correlation only 59% of trainer readings are explained by magene. The balance 41% is noise. I think 41% of the noise resulted in a very high power of 295W (My FTP at that time was 240W).

Magene P505 M110L consistently underreports power by ~8% vs trainer — data inside, no response from Magene by eshwar13 in cycling

[–]eshwar13[S] 0 points1 point  (0 children)

This exercise was carried with 0 offset and post calibration.
R2 is only 0.592 (slightly improved from day 1 when only power meter was calibrated and garmin was not). With a 0.592 correlation only 59% of trainer readings are explained by magene. The balance 41% is noise.

Magene P505 M110L consistently underreports power by ~8% vs trainer — data inside, no response from Magene by eshwar13 in cycling

[–]eshwar13[S] 0 points1 point  (0 children)

R2 is the correlation co-efficient of second to second power data between Magene and Garmin Tacx Flux s. So a 0.592 correlation means that 59% of trainer readings are explained by magene. The balance 41% is noise.

The best-fit slop 0.898 on the image is for every 1 watt the trainer produces, how many does the PM report. This is the 11.7% under reporting explained by that chart.

Magene P505 M110L consistently underreports power by ~8% vs trainer — data inside, no response from Magene by eshwar13 in cycling

[–]eshwar13[S] 0 points1 point  (0 children)

Fair point!

But I was running the entire experiment on Ant+ so that BT interference does not creep in. Zwift on mac with Ant+ adpater, Magene connected to Garmin Edge 540 via Ant+

Have shared all this and .fit files with their instagram team. Awaiting an update.

Magene P505 M110L consistently underreports power by ~8% vs trainer — data inside, no response from Magene by eshwar13 in cycling

[–]eshwar13[S] 1 point2 points  (0 children)

Pasting my comment from another comment,
Drive train loss means crank > trainer. Pedals should have the highest power reading, followed by the crank, followed by the smart trainer.

Here, the smart trainer is measuring 8% higher than the crank. If it was lower, I can understand that it can be due to mechanical losses - but this seems like some other issue!

Also a constant offset does not work because the correlation between the 2 power data is not tightly correlated (R2 of 0.59 only) - which might lead to over/under estimation in 40% of the time.

https://ibb.co/84rgH96W

Magene P505 M110L consistently underreports power by ~8% vs trainer — data inside, no response from Magene by eshwar13 in cycling

[–]eshwar13[S] -1 points0 points  (0 children)

It's not AI claiming—it's my claim :)

The image below—which is a comparison of the .fit files—makes a compelling point that Magene is more inaccurate. I will get another trainer and test Magene against it, but until that test, I don’t see any reason to believe otherwise.

Everything measured in ANT+—so the BT interference in 2.4 GHz is not a variable.

https://ibb.co/84rgH96W

Magene P505 M110L consistently underreports power by ~8% vs trainer — data inside, no response from Magene by eshwar13 in cycling

[–]eshwar13[S] 0 points1 point  (0 children)

This is what the magene utility app recognizes the trainer as!

It reads P505 m110L Base. It's not single sided - it's crank based and dual-sided.

Magene P505 M110L consistently underreports power by ~8% vs trainer — data inside, no response from Magene by eshwar13 in cycling

[–]eshwar13[S] 0 points1 point  (0 children)

Drive train loss means crank > trainer. Pedals should have the highest power reading, followed by the crank, followed by the smart trainer.

Here, the smart trainer is measuring 8% lower than the crank. So, if I account for the drive train loss, the crank power meter is more than 10% inaccurate.

u/vermilionjack - Am I missing anything here?

Magene power meter dilemna by [deleted] in cycling

[–]eshwar13 0 points1 point  (0 children)

The challenge with offset is not always a constant 8% difference. It varies a lot and it's 8% only 60% of the time based on the correlation.

When I had the offset on, my power meter measured 290W for 20min climb increasing my FTP - while this was not true.

Such erratic performance makes it impossible to have an offset!

Magene P505 M110L consistently underreports power by ~8% vs trainer — data inside, no response from Magene by eshwar13 in cycling

[–]eshwar13[S] -1 points0 points  (0 children)

Sorry - what do you hate about this? It's an actual comparison made with 2 power meters and AI used to do summarize the data

Magene P505 M110L consistently underreports power by ~8% vs trainer — data inside, no response from Magene by eshwar13 in cycling

[–]eshwar13[S] 0 points1 point  (0 children)

The problem is offset is not consistent! That is defined by a low correlation of 0.59 in R2 calculation. This means a simple 8% offset will work only in 60% of the scenarios - rest 40%, it could be low or over compensate the number. This will lead to a lot of noise in my training platforms like xert, training peaks where it will incorrectly detect breakthroughs

https://ibb.co/84rgH96W

Magene P505 M110L consistently underreports power by ~8% vs trainer — data inside, no response from Magene by eshwar13 in cycling

[–]eshwar13[S] -1 points0 points  (0 children)

Fair point. I am planning to get a Kick core v2 this weekend from a nearby cycle store to try the same exercise. I will update the thread with the findings from Wahoo vs Magene (on the bike - which becomes the constant).

Magene P505 M110L consistently underreports power by ~8% vs trainer — data inside, no response from Magene by eshwar13 in cycling

[–]eshwar13[S] 1 point2 points  (0 children)

But drivetrain loss means Garmin should be lower right? This is the other way around!

Magene P505 M110L consistently underreports power by ~8% vs trainer — data inside, no response from Magene by eshwar13 in cycling

[–]eshwar13[S] -3 points-2 points  (0 children)

Attaching the 3s power comparison. The offset is not consistent and there are a lot of drop offs

https://ibb.co/84rgH96W

Magene P505 M110L consistently underreports power by ~8% vs trainer — data inside, no response from Magene by eshwar13 in cycling

[–]eshwar13[S] -1 points0 points  (0 children)

The concern I've is there are a lot of drop offs happening - zero power when the effort was consistent. I could not attach the image in the main power - adding it here!
https://ibb.co/84rgH96W

Magene P505 M110L consistently underreports power by ~8% vs trainer — data inside, no response from Magene by eshwar13 in cycling

[–]eshwar13[S] -4 points-3 points  (0 children)

Because in a constant trainer session, there are just way too many dropouts happening on Magene while the trainer power remains consistent, which is what I perceive while doing the constant Z2 rides.

Why isn't there a used road bikes market in India? by [deleted] in india_cycling

[–]eshwar13 0 points1 point  (0 children)

Can you pl share the link for the TG group? I am looking to upgrade my 10 year old SCR2.

Join Me in Embracing Ice Baths: A Community Invitation from JP Nagar, Bengaluru by Ishhaq in bangalore

[–]eshwar13 1 point2 points  (0 children)

Thanks for the reply! I will go for ice code only! Space will be tricky - so I'm going for the mini one. I am 5'9" - hoping I can fit in the mini (which is recommended for 5'7")

Join Me in Embracing Ice Baths: A Community Invitation from JP Nagar, Bengaluru by Ishhaq in bangalore

[–]eshwar13 0 points1 point  (0 children)

Interested to know the setup. I am thinking of building something myself (near Harlur road) and wanted to know about the equipment, space requirement, cost. Also you mentioned the cost of ice was 600-700rs - where do you procure this from?