Magene P505 PES Base Spider Powermeter

[Sebastian]

Powermeter pedals and the Spider based powermeter both measure before drivetrain losses. Both have a claimed accuracy of 1.5%. The deviation I think I’m seeing is more though. BUT - I had the Magene on my gravel bike and the Assiomas on the road bike. First time ever that I’ve used a PM on gravel so no data to go from and it might just be that my rides off road were harder than on road. Now that I moved my Magene to the 2nd road bike, it’s actually closer to my Assiomas. But it still seems higher. Need to put the Assiomas on there and compare the readings directly but so far I just couldn’t be bothered.

[Eddy_Twerckx]

I got the P505 in the SRAM 3 bolt variant on my Red crankset. I think it’s slightly overreading compared to the Assioma pedals on my other bike. I could scale it down in the app but I need to put the Assiomas on the bike to compare them directly. Other than that the thing is bomb proof.

Oval rings by any chance? My Magene on oval rings reads higher than my Assioma. On round rings they’re within a watt. It’s easy enough to scale down once you get an offset from testing.

[nickobec]

Well, you have the drive train losses between crank and hub... Maybe that can explain. I find 2 % still VERY good.

Testing I did with the older of my Powertap G3 hubs, Sigeyi AXO spider and Favero Assioma pedals was 1% between all 3 power meters. It was steady state longer rides. Somehow the Powertap even with drive train losses (it is a efficient drive train) was really close to the crank and pedals readings.

My newer Powertap G3 hub compared to the Favero Assioma pedals was out by a little over 2%, but with a little digging, retesting and calibrating. It is close to 1% for steady state rides. However, sprints (or hard efforts) both Powertaps over estimate my power (say 5% for 1 minute all out).

[Sebastian]

Oval rings by any chance? My Magene on oval rings reads higher than my Assioma. On round rings they’re within a watt. It’s easy enough to scale down once you get an offset from testing.

Nope. Regular round rings. I’ll give it a go on the turbo in the next few days and report back what the offset is. Or maybe it was just my subjective feeling.

[Sebastian]

So I put the Assiomas on the bike. I did a ramp test and a quick workout in Zwift and recorded both the Magene P505 and the Assiomas.
The Magene consistently overreads by around 5% while the cadence is pretty much identical on both units. I did a zero calibration with both units prior to comparing them.

I adjusted the power scaling accordingly in the Magene Utility app. I'll give it another go shortly to see if I can get them to match up.

[Eddy_Twerckx]

So I put the Assiomas on the bike. I did a ramp test and a quick workout in Zwift and recorded both the Magene P505 and the Assiomas.
The Magene consistently overreads by around 5% while the cadence is pretty much identical on both units. I did a zero calibration with both units prior to comparing them.

I adjusted the power scaling accordingly in the Magene Utility app. I'll give it another go shortly to see if I can get them to match up.

Just a clarification. Is the higher reading from the Magene while you ride? Or did you do an analysis of the power data after recording? If you’re just looking at the two numbers during the ride it may be hard to get an accurate comparison based on how each unit reports the data. The best way to do it record each device to a separate head unit, or one device to Zwift and one to a head unit. Then pull each file and do a direct comparison. ZwiftPower has a free tool. DC Rainmaker has the most well known but costs money. There are some others out there.

[TidyDinosaur]

Just a clarification. Is the higher reading from the Magene while you ride? Or did you do an analysis of the power data after recording? If you’re just looking at the two numbers during the ride it may be hard to get an accurate comparison based on how each unit reports the data. The best way to do it record each device to a separate head unit, or one device to Zwift and one to a head unit. Then pull each file and do a direct comparison. ZwiftPower has a free tool. DC Rainmaker has the most well known but costs money. There are some others out there.

I've used this in the past: https://compare-the-watts.com/

[Sebastian]

Just a clarification. Is the higher reading from the Magene while you ride? Or did you do an analysis of the power data after recording? If you’re just looking at the two numbers during the ride it may be hard to get an accurate comparison based on how each unit reports the data. The best way to do it record each device to a separate head unit, or one device to Zwift and one to a head unit. Then pull each file and do a direct comparison. ZwiftPower has a free tool. DC Rainmaker has the most well known but costs money. There are some others out there.

I’ve used compare-the-watts.com and recorded both powermeters. One with Zwift and one on my Wahoo.

The average wattage for the Magene is 5.14% higher than the Assiomas according to the website.
Looking at the power curve, the deviation is pretty much consistently higher by 5%, meaning that the gap increases, the higher the wattage.
Thanks for the tip with this website by the way. I did use DC Rainmaker’s tool in the past. This is just as good.

[Sebastian]

So weirdly enough, just when I was doing my 2nd test run with the Assiomas and the Magene P505 whilst messing around with the power scaling in the Magene app, a new firmware update popped up. After installing it, the Magene PM is now recording roughly 2.5% less power (with the power scaling at the default value of 100%) compared to the Assiomas according to compare-the-watts.com
I only realized it when comparing the data sets on the website. While I was riding, I set the Magene up so it showed roughly the same values as the Assiomas and I ended up back at 100%. So I guess I'll be trying 101% next. The power scaling feature has quite an exaggerated effect. Going up and down by one percent changes the readings definitely by more than that, I found. Hopefully, I'll get them to match in the next run. Until the next firmware update rolls out, that is.

[Sebastian]

3rd run - issue solved.
I did a test run of 55min of free riding on Zwift. I set the Magene P505 to 101%.
The Assiomas and the Magene were within 0.1% of each other according to compare-the-watts.com
The curves are basically indistinguishable from each other. Also the cadence reading is identical.

Very happy with that.

[TidyDinosaur]

That's very good news. I'm looking forward to receiving mine...

[Avalius]

I think once i'll match all my unit to my wahoo kickr that I'll never update the firmware again

[Greenred]

Sounds very promising. I got the PM for USD 244 on aliexpress, a no brainer (without chainrings).
Being a little weight weenie I’m curious: has anyone thought about using a lighter crankset with the magene spider? I estimate that the standard crankset in total will probably add roughly 60- 100g over my Ultegra crankset

[TidyDinosaur]

Sounds very promising. I got the PM for USD 244 on aliexpress, a no brainer (without chainrings).
Being a little weight weenie I’m curious: has anyone thought about using a lighter crankset with the magene spider? I estimate that the standard crankset in total will probably add roughly 60- 100g over my Ultegra crankset

I don't think you can use another crank since the crank-powermeter interface is unique . That's why I ordered the separate powermeter with the 3-bolt interface instead, even if it was the same price.

[Greenred]

I don't think you can use another crank since the crank-powermeter interface is unique . That's why I ordered the separate powermeter with the 3-bolt interface instead, even if it was the same price.

Got it! With what crankset do you paid it?