I have two bikes
a 3t gravel bike with p2m ngeco and rotor crankset 170mm. and 32mm on stock wheels gp5k tires average weight 10kg without bottles.
then a road bike
chapter2 toa with sram red quarq powermeter 170mm with fulcrum racing zero db wheels gp5k 25mm in the front and 28mm in the back.
i heard that different powermeter output different numbers is it wise to use the data from either bike interchangeably? eg do an ftp test with the chapter2 and use the gravel to do an zone2 ride.
quarq and power2max are both spider pm so they should output the same watts right?
is there a way to test this. I don’t have a trainer yet.
i do not plan to go on gravel, i just want to use the 3t as a road winter bike with the bigger tires. I think it has more grip during winter months. that is why i put gp5k on it. correct me if i am wrong. ,
Those are two well trusted brands for power meters, so the chances are they’re pretty close.
Yep. The easiest way would be to grab a set of power pedals (from a friend?) and see how they line up on both when comparing the numbers for the same intervals/efforts (two head units to record both sources).
i was actually looking forward for you to answer as I choose my Power meters based on your reviews.
This being said, I ride with SPD cleats on both bikes, I have wide feet and have custom lake shoes to avoid pain.
the only pedals spd compatible i know are the rally and i was not happy with your review. I do not think those are a good benchmark to test accuracy of other power meters, unless a new firmware update has addressed the issues you pointed in your test. but I have not seen an update so I assume no.
which power spd pedals would be good to do a benchmark?
or any other method to test if both spider PM provide the same power?
Yup, my wife literally did this same thing back a few months ago. Going from Quarq to P2M. Zero issues with alignment, as @GPLama noted, thsoe two brands are respected and generally pretty accurate. Nonetheless, because these were older units lying around the DCR Cave, I did some validations just to be sure.
Like Lama said, power pedals is a good options. I use the Garmin Rally, Favero Assioma, and Wahoo Powerlink pedals interchangeably in testing. They all have their own quirks (as I’ve been dealing with this week…), but on the whole any of those three are good for power meter accuracy testing. Also, just doing back to back tests on a smart trainer is good too. Remember as a rule to always do some hard sprints (4x or so times) when installing a new power meter, before doing any baselining. And for some older units, it’s really better to throw away the first ride’s worth of data till it settles.
I wrote a post on power meter accuracy testing a while back (and Shane has a vidoe too), either resource is still 100% the same as when we published them. The game is still the same: How to: Troubleshooting Power Meter and Trainer Accuracy Issues | DC Rainmaker
I would just use those two interchangeably and accept the number it spits out. You could compare each with DCs tool to your trainer or pedals… but just accept the number. The difference is probably more how the crank interacts with the bottom bracket or your chain.
I have a 4iiii left side meter on my MTB. I lead with my right foot, so I know the number it spits out ends up being pretty low on the shorter efforts. In the end, I just accept the number. I’m just looking at it as a pacing tool or a tool to help manage fitness and freshness.
@dcrainmaker and @GPLama answering my post… it must be xmas
thanks guys… you are the reference in all my gear purchases.
unfortunately i have no immediate access to powermeter pedals…
i try to do some testing with a borrowed indoor trainer or something.
thank you guys.
Thanks for this thread, I was just wondering the same thing. I’m looking at buying a Canyon Ultimate and all the models I’m looking at come with 4iiii power meters. I’m using Garmin Rally 200 pedals that I switch between bikes and was figuring I’d just ignore the 4iiii. Seems like a waste, but it is what it is.
I have a quarq and power2max as well. I used a smart trainer to get the difference between them, set the trainer on 200 watts or whatever and see what the meters read. Do 5 minutes, go abab just to be sure and that should do it. They were 3 watts apart. Also used a single side garmin pedal but it gave very very different numbers. I was testing hard tail vs trail bike and, fwiw, the times were too close to call a winner.