Bikeerg watts compared to power meter pedals watts

[zij]

Hi All.

I've been cycling with the Bikeerg for about 3 years and getting stronger/faster/more watts - but comparing outdoor riding (with a power meter arm) and indoor Bikeerging, I seem to be able to do a fair bit more watts outdoors for the same heart rate effort.

I believe the Bikeerg measures watts from the flywheel rather than the pedals..

My outdoor bike has a power meter arm, so can't put that on the Bikeerg, but wondering if anyone has power meter pedals they have fitted or can fit onto a Bikeerg and see how the watts compare?

At low watts I would guess there is less watts discrepancy, but if anyone able to compare at 300+ watts that would be really helpful!

Ideally, something like "300w on the Bikeerg shows 320w on the pedals" etc..

Thanks in advance!

[jamesg]

I seem to be able to do a fair bit more watts outdoors for the same heart rate effort.

There are several factors that might affect accuracy.

Work described by pedals will include mechanical losses in transmission that are not seen when observing flywheel behaviour.

Outdoors on moving bike cooling is better than stationary.

Strain gauges are subject to a series of drift, temperature and calibration errors, from zero to slope to linearity; while a fan braked erg produces impulses at about 100Hz.

[Carl Watts]

For some strange reason people think those pedals are more accurate than a dedicated indoor bike set-up.

Does the BikeErg quote an accuracy in the spec ? Do the pedals quote an accuracy ?

My Wattbike is like 2% and I would need to move to a WattBike Atom to get to 1%. Pedals are nowhere near this in terms of accuracy.

I love the RowErg but I'm going to be honest here, no way I would go for a BikeErg sorry.

[dabatey]

For some strange reason people think those pedals are more accurate than a dedicated indoor bike set-up.

Does the BikeErg quote an accuracy in the spec ? Do the pedals quote an accuracy ?

My Wattbike is like 2% and I would need to move to a WattBike Atom to get to 1%. Pedals are nowhere near this in terms of accuracy.

I love the RowErg but I'm going to be honest here, no way I would go for a BikeErg sorry.

Most modern power meter pedals are 1-2% accurate just as most smart trainers etc. Single sided pedals are more likely to give a false(but repeatable) reading due to possible left/right leg imbalances but dual reading pedals will be pretty much spot on. Google 'DC Rainmaker' and have a look at reviews.

A quick google about bike erg shows that C2 claims 2% accuracy at the flywheel, and anecdotal evidence (from another thread here)shows about 20W loss in the drivetrain compared to around 5-10W in the (well maintained) drivetrain of a smart-trainer/smart-bike. (So OP you would seem to be roughly correct in that the difference between outdoors and bikerg is about 20W).

So pedals are better than a smart-trainer/bike which in turn are better than a bike-erg for showing the power actually produced by yourself.

Cycling weekly does a fair review of the bikerg mentioning it's power measurement. https://www.cyclingweekly.com/reviews/b ... erg-review

[zij]

So pedals are better than a smart-trainer/bike which in turn are better than a bike-erg for showing the power actually produced by yourself.

Cycling weekly does a fair review of the bikerg mentioning it's power measurement. https://www.cyclingweekly.com/reviews/b ... erg-review

From the link, it says:

On a less positive note, taking power reading at the flywheel means that some watts are lost, when compared with more direct measurements - for instance at the crank or pedal. Attaching a pair of power meter pedals, you will see a +15 - 20% difference which is a big factor to take into consideration if you are intending to race online.

So I read that text as "the watts measured at the flywheel under reports the watts compared to power meter pedals and if you were to attach a pair of power meter pedals and do 200 watts on the PM5 (measured at Flywheel) it could show 230-240 watts on the power meter pedals..

Have I read that right?

[dabatey]

I would say roughly yes. Remember though that a lot of folks (not all) tend to have higher power numbers outdoors vs indoors even on the same power-meter pedals (due to the likes of cooling/ bike movement/ standing more) so you might be comparing apples with oranges if you are trying to match indoor and outdoor power.