Zwift Power vs IRL

Been on Zwift for a couple months on a Wahoo Kickr Bike (v1). This is my 1st time with something that measure power. It measures power at the hub.

Wednesday morning, did a 15km ride in the virtual world. Wahoo said 180W average. Group C ride

Ran some errands in Waterloo, and then realized how nice it was outside… Took my bike (Gravel) on the road for a short 17km ride down the paved section of Boomer. Bike currently has 35mm Panaracer Gravel King slicks on it.

Average HR and Cadence are almost the same, but the the cycling computer or Strava thinks I’m putting out only 108W on average… I think both rides were about the same intensity going by HR…

Watcha think? Time for Power Meter for the in real life bike?

My two cents – the Strava estimates aren’t very accurate. They can look at speed and terrain (based on maps) but they don’t have any way to account for things like headwinds (or tailwinds) and beyond fairly slow speeds, overcoming aerodynamic drag is where most of your power goes on flat ground.

I also have a trainer that measures watts and have no idea if the number is accurate, but as long as it’s consistent I can at least compare progress. On the road/gravel, I usually just take note of Strava PRs on various segments I ride a lot – or who I can manage to hang with on a group ride – as a very casual measure of progress!

Power meters are great for training and improving fitness. It will be your best metric for comparison or to see how hard the ride actually was.
Heart rate is okay, but it depends on multiple factors and can vary quite a lot (fueling, fatigue, mindset etc).
Your goal for training is to raise your ftp or other power zones, your smart training is great as it will be consistent.
A crank arm or pedal power meter will let you extend your training outdoors.
Comparing a smart trainer with a crank arm power meter I tend to find a small variance which can come down to power averaging by the head unit and/or drivetrain efficiency loses.


Agreed. I got a crank mounted one directly from 4iiii and was able to get one mounted on a gently used crank and then send my original crank back for $$ which made it a better deal all around. With a proper head unit you gather all the data you might want for training as well as managing efforts on the road. A great piece of kit.

I’ve got SRAM Apex crank on my outdoor bike.

Do you think this would work? Apex AXS Crankarm Power Meter Upgrade | PM-APX-ASSY-D1 | SRAM

As another option, more expensive but more versatile, I have power meter pedals. I have an older set of Garmin Vector 3’s on my road bike and recently got a new set of the Garmin Rally pedals for my gravel/cross bikes. You can swap them between bikes which is great

I believe that is the wrong crank arm. I think you need the GXP. I believe your spindle is on the chainring side.
Let me search for a compatible one. You will need to know your crank arm length.

Probably going to be best to bring it to your LBS, GXP power meters are hard to find. The vector 3 pedals that Amy mentioned may be about the same price and can be moved to a new bike easily.

thx for the feedback…

I’ll just likely ride by HR/speed for now outdoors, unless i find a super deal on the Garmin Rally pedals.

stages makes a gxp compatible (carbon) power crank arm, they occasionally pop up in the used market.

or if you can find a force or red nds gxp arm, 4iiii can add the sensor to it (what i use)

*edit: believe it should be apex gxp compatible, but never tried!

thx. i emailed 4iiiiii’s yesterday with my pics and compatibility.

You might also want to check the comparability with your frame. The single arm crank arms typically have a bulge on the back which can hit or rub against the chain stay if the clearance is tight.

I run an older 4iiii on my aspero and the clearance is just a mm or 2. I actually got a bit of grit in between and scratched the frame but some frames are even closer.

4iii’s answered my email… no go for the apex crank arm…

I would 100% vote for the rally pedals. I’ve had a lot of crank arms, they are great but bike specific. I’ve had my pedals on MTBs, tandem, cargo bike, gravel. I’ve abused them and submerged them on one silly ride with @KevRidesGravel.

My only annoyance is that they don’t like large winter time temperature swings when bikes are stored inside. Although I recently updated the filmware, so I’m cautiously optimistic that will mitigate some of those wonky readings.

Another option for power meter pedals it get the Assioma shi ones that are a Shimano spindle. You can then use them on either road SPD-SL pedals or certain SPD pedals.

I have been rocking those for years and they are very accurate and reliable. Sadly you have to get the dual sided ones but they are cheaper than the Garmin ones and frequently on sale.

Apparently you can use the standard Assioma pedals (not the shi ones) which are available single sided and hence cheaper but you are restricted to only certain SPD pedals:

I’m also voting for power pedals in general. (I’ve got the Garmin Rally dual sided)

I started with a stages power meter (on sale) a bunch of years ago. That very quickly turned into a second one, and then a third one, for three different bikes.
Then after yet another new bike, I finally smartened up and realized the extra cost of the pedals would quickly be offset by the number of bikes I could use them on. These pedals are routinely going between four bikes now: good gravel bike, winter gravel bike, mountain bike, and fatbike.


i’m going to keep an eye out on the rally xc200. They had them on the Cdn Tire website last yr as online only, but right now not available to order.

I’ve got a bunch of cdn tire money to use up that will bring the price down significantly…

Will update here when they are available to order again.

Favero is coming out with their own spd power pedals, seems like a solid unit and better price than garmin pedals… also no need to fuss around with the assioma hack and have a wider q-factor.

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I’d like to be in for those if they r available for this spring

the assioma mx pro pedals are out of stock. signed up for notification when they come back in stock…(says 2 months)