Power Output by different riders

cormpat

On Saturday morning I went out for a spin with a mate & as it was just the 2 of us & we both had power meters we said we would see what our average power outputs would be for the ride. We were on the road early, on very quite roads & rode side by side for the vast majority of the time - there was very little drafting. Only occasionally to let a car past, but there was very little traffic on the road.
He was using Garmin Vector's with a Garmin 500 & I was using a Power Tap G3 & Garmin 705. We hit lap & let the devices to the rest.

Afterwards when I started looking at the data our average power outputs were completely different. His average power for the lap was 186 & mine was 210. How can there be such a difference between the 2 of us? I would be a about 3kg heavier than him, but he reckoned his bike was about 2kg heavier than mine, so this would cancel the weight difference out by & large. There was also very little climbing on the route.

However, our NP were nearly spot on for the lap. His was 215 & mine was 218. Anyone got any theories on why the differences?

Beasty

Garmin Vectors are notorious for low power readings as a result of them not being put on tight enough. There's a specific torque to be applied but most "regular" riders will not have a torque wrench that can be used (as they will need to use a crows foot spanner attachment)

Someone from my club had exactly the same issue when putting a Powertap and Garmin Vector on the same bike - the Vector was recording consistently lower power output (20w or so)

cormpat

Beasty wrote: »

Garmin Vectors are notorious for low power readings as a result of them not being put on tight enough. There's a specific torque to be applied but most "regular" riders will not have a torque wrench that can be used (as they will need to use a crows foot spanner attachment)

Someone from my club had exactly the same issue when putting a Powertap and Garmin Vector on the same bike - the Vector was recording consistently lower power output (20w or so)

Cheers Beasty, I'll ask my mate did he use a torque wrench when putting them on. I do recall him saying on the ride that he thought his power was lower than this time last year (he was using a power tap pro up until recently getting the vectors).

Beasty

One other thing to check - the default on the Vector is a 172.5mm crank length. If it's any different you need to manually enter it when setting up on the bike computer - if using 175mm for example I understand that will result in understating the power if not corrected

ZiabR

Beasty wrote: »

One other thing to check - the default on the Vector is a 172.5mm crank length. If it's any different you need to manually enter it when setting up on the bike computer - if using 175mm for example I understand that will result in understating the power if not corrected

That, I did not know. Thanks for the tip.

Lumen

Maybe he is more aero than you.

Beasty

Actually looking back at the original post and the fact the NP was quite close - did you have both Garmin computers set to either include or exclude zeros? The fact that your own average was close to the NP suggests to me your's was excluding zeros

cormpat

Beasty wrote: »

Actually looking back at the original post and the fact the NP was quite close - did you have both Garmin computers set to either include or exclude zeros? The fact that your own average was close to the NP suggests to me your's was excluding zeros

My zero averaging is set to off. Not sure on my mates, will give him a bell after work this evening re it.

1750W

As beastly said maybe he is more aero than you. Also power tap is measured at the hub and the vectors are measured at the pedals. Therefore assuming both devices were working correctly the power outputs measured at the pedals should be higher than the power outputs measured at the wheel hub.

cormpat

1750W wrote: »

As beastly said maybe he is more aero than you. Also power tap is measured at the hub and the vectors are measured at the pedals. Therefore assuming both devices were working correctly the power outputs measured at the pedals should be higher than the power outputs measured at the wheel hub.

You've misunderstood; my power was the higher average & I was using the G3; 210 watts. His was the lower number; 186 watts & using the Vectors.

1750W

cormpat wrote: »

You've misunderstood; my power was the higher average & I was using the G3; 210 watts. His was the lower number; 186 watts & using the Vectors.

yep i did misunderstand apologies

I ran my power 2 max on a garmin 800 and my powertap G3 with an edge 500 on the same ride and there was a difference of circa 20W. the power 2 max was giving the higher reading. as beasty said it could just be down to Aerodynamics.

Im not a great fan of powertap having spent 1200 euro on a G3 only for the torque tube to go in to meltdown mode a month after warranty expired.

cormpat

1750W wrote: »

Im not a great fan of powertap having spent 1200 euro on a G3 only for the torque tube to go in to meltdown mode a month after warranty expired.

Sorry to hear about your G3, what actually happened with it? I got mine on ebay for €630 for a wheel set. At that price I felt it was too good value to turn down.

1750W

Basically it needed to be recalibrated for every ride. Then if you stopped it would give crazy high power outputs I then upgraded the firmware and it stopped working completely. You got it at a good price! Hope you are using it to perfect your training rides:)

harringtonp

Cross winds/half wheeling ? Though (as Beasty pointed out) my best guess would also be torque. The following goes into it in detail

http://www.dcrainmaker.com/2013/09/garmin-vector-review.html

and is one of the reasons I veered away from them (others cost and fact that moving them from one bike to another and getting it right is not as straightforward as just moving ordinary pedals).

cormpat

harringtonp wrote: »

Cross winds/half wheeling ? Though (as Beasty pointed out) my best guess would also be torque. The following goes into it in detail

http://www.dcrainmaker.com/2013/09/garmin-vector-review.html

and is one of the reasons I veered away from them (others cost and fact that moving them from one bike to another and getting it right is not as straightforward as just moving ordinary pedals).

No, it was all to do with the zero averaging on the Garmin's. He had his turned on & mine was off. That's why both our NP were nearly spot; mine was 218 & his 215.

Thanks for all the suggestions!

Beasty

I've heard of a couple of people who've installed Garmin Vectors and found them to be recording a significantly lower power output than shown by another brand of PM

I've now tried a Vector against one of my Quarqs. I've managed to get the pedals tightenen to the correct torque and was using a Garmin 510 for the Quarq and an 810 for the Vector (getting the Vector paired was a bit of a pain - I had to remove the pedals and move them and the computed outside the Quarq transmitter range to do so). After an initial variation (the Vector recorded a significantly higher power output) I re-set the Vector pedal angles, and this evening recorded the following over a 70 minute ride
Vector - AP including 0s 174w, NP 213w
Quarq - AP including 0s 172w, NP 211w

Hence the Vector is recording about 1% higher than the Quarq, entirely within the accuracy claims of both systems

lennymc

Beasty wrote: »

I've heard of a couple of people who've installed Garmin Vectors and found them to be recording a significantly lower power output than shown by another brand of PM

I've now tried a Vector against one of my Quarqs. I've managed to get the pedals tightenen to the correct torque and was using a Garmin 510 for the Quarq and an 810 for the Vector (getting the Vector paired was a bit of a pain - I had to remove the pedals and move them and the computed outside the Quarq transmitter range to do so). After an initial variation (the Vector recorded a significantly higher power output) I re-set the Vector pedal angles, and this evening recorded the following over a 70 minute ride
Vector - AP including 0s 174w, NP 213w
Quarq - AP including 0s 172w, NP 211w

Hence the Vector is recording about 1% higher than the Quarq, entirely within the accuracy claims of both systems

id be sure to use the vector so. instant 2 watt improvement in your power!!

edit - actually - would be interested in hearing your views/review of the vector pedals

Beasty

lennymc wrote: »

edit - actually - would be interested in hearing your views/review of the vector pedals

Got them for the track bike and just put it on the roadbike for a few days to compare it against the Quarq

Have now switched it over and should be testing it on the track bike tomorrow

quozl

Are at all concerned that as they're so setup dependant that it'll be hard to know if you can trust them when setup on the track bike as you won't have another meter on for validation?

Hearing this stuff about them is pretty off-putting.

Beasty

Set-up on the track bike will be the same as on the road bike. It's quite straightforward when you know how, and so long as you can be confident about getting the pedals to the correct torque (which is the issue initially identified by DCRainmaker, who now seems happy with the Vector)

If I see any anomalies (which should be very easy to spot on an indoor velodrome ride) it will be easy enough to check again against one of my other powermeters ...

Lumen

quozl wrote: »

Hearing this stuff about them is pretty off-putting.

+1. I have a Quarq and a P2Max and they both seem to "just work". This talk of precise torque and pedal angles isn't making the Vector sound like an attractive proposition.

Beasty wrote: »

If I see any anomalies (which should be very easy to spot on an indoor velodrome ride) it will be easy enough to check again against one of my other powermeters ...

That is, quite frankly, a ridiculous state of affairs.

Beasty

Precise torque is recommended - you can set the pedal pods at whatever angle you like - it then works the angles out itself (the Garmin computer prompts this). Torque is the only real variable on set-up

hf4z6sqo7vjngi

Garmin cannot get the manufacturing right on a multisport watch so i fail to see how they would get the Vector right. Expensive bit of kit to be second guessing data its giving you.