Power differences between two people
brede
Posts: 4
First post here, so thanks for any help ahead of time.
I've been riding with my father a couple of times and we've noticed a interesting trend on every ride. He always seems to have a 20-40 watt higher average power than I do. We get this while riding side by side. Here are some details that I feel are important.
We both are as near as makes no difference the same height, both 6 foot. If anything, I'm a bit taller.
He is about 5-7 lbs heavier than I am
He is riding a Venge with 35 mm rims, and I ride a roubaix with 60mm rims.
We both have ceramic BB bearings, I have ceramic wheel bearings and he does not.
I have DA, and he has ultegra
I work in a bike shop and both bikes have had regular service. However, I am unsure if he has the correct spacers on for the crankset (FSA k-force)
He has garmin vector pedals, and I have a stages. Both are left only.
Without fail, we always seem to have a fairly large difference in both average power and normalized power. I'm always at least 20 watts less, sometimes more, than he is.
We are unsure if this type of difference is normal, if there is something wrong, either mechanically or with the power meters, or if in fact there is that large of a difference.
I appreciate any thoughts or input. He certainly would like to be able to find 20 more watts if possible. Thanks everyone.
I've been riding with my father a couple of times and we've noticed a interesting trend on every ride. He always seems to have a 20-40 watt higher average power than I do. We get this while riding side by side. Here are some details that I feel are important.
We both are as near as makes no difference the same height, both 6 foot. If anything, I'm a bit taller.
He is about 5-7 lbs heavier than I am
He is riding a Venge with 35 mm rims, and I ride a roubaix with 60mm rims.
We both have ceramic BB bearings, I have ceramic wheel bearings and he does not.
I have DA, and he has ultegra
I work in a bike shop and both bikes have had regular service. However, I am unsure if he has the correct spacers on for the crankset (FSA k-force)
He has garmin vector pedals, and I have a stages. Both are left only.
Without fail, we always seem to have a fairly large difference in both average power and normalized power. I'm always at least 20 watts less, sometimes more, than he is.
We are unsure if this type of difference is normal, if there is something wrong, either mechanically or with the power meters, or if in fact there is that large of a difference.
I appreciate any thoughts or input. He certainly would like to be able to find 20 more watts if possible. Thanks everyone.
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On about 4% avg grade, 7 lbs is probably worth about 5-7 watts. In the flats/descents the aero of the 60mm wheelset and/or a helmet might account for another 5 to 10 watts.
20 doesn't sound too far off for 7 lbs weight and 30mm of wheel depth.
40w? Yeah, difference in meters maybe. It's all about consistence, not only brute accuracy. You don't train against a buddy's power meter, but your own.0 -
Take head on shots of you both and see if he's wider or higher than you. It's not the bearings.0
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Have you swapped bikes to see what happens? if its possible use your power meter on his? Do one ride with this power meter and one with yours.
As cougie said, it could be down to position on the bike. Even though your bike is "less aero", if he is sitting up more than you, arms straighter, higher stem position, never using the drops etc?0 -
brede wrote:He has garmin vector pedals, and I have a stages.
Bingo.0 -
brede wrote:
He has garmin vector pedals, and I have a stages. Both are left only.
Sell them and buy a decent powermeterI'm sorry you don't believe in miracles0 -
Im surprised its only 20 watts to be honest. Even if both PM's were spot on, thats quite close especially between 2 riders.0
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Why not put the vector on the stages and run dual headunits? See how they compare0
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20 to 40w difference on left leg power meters ...
you know the left leg power meters just double whatever power the left leg is putting out ...
So in reality you've got a 10-20w power difference ...
and - assuming both Stages and Garmin are calibrated equally - which I doubt - then basically, your Dad has a stronger left leg than you - or he's just using it more than you're using yours ...
Try getting him to pedal just with his right leg - unclip the left - then see what the power difference is .. then you try it...
yes - of course, some of this could be down to aerodynamic profile - but really, we don't need to look any further ..0 -
Gotta love the responses:
We don't know:
- what power levels we're talking about 120W or 420W
- we don't know what tyres they're running or inflated to what pressure
- we don't know their relative riding positions
- we don't know the differences in clothing they're wearing
- we don't know how hilly their rides are
ALL of which make a significant difference in this.
But, yeah, let's blame the PMs. Too funny.ROAD < Scott Foil HMX Di2, Volagi Liscio Di2, Jamis Renegade Elite Di2, Cube Reaction Race > ROUGH0 -
meanredspider wrote:We don't know:
- what power levels we're talking about 120W or 420W
- we don't know what tyres they're running or inflated to what pressure
- we don't know their relative riding positions
- we don't know the differences in clothing they're wearing
- we don't know how hilly their rides are
ALL of which make a significant difference in this.
But, yeah, let's blame the PMs. Too funny.
Basically all of this (but also difference in two single-sided powermeters) plus:
- We don't know who is the more efficient rider over the terrain
- We don't know each rider's left/right power balance
Also what were you expecting? To have exactly the same wattage?0 -
Wouldn't power readings then drop to zero?Slowbike wrote:Try getting him to pedal just with his right leg - unclip the left - then see what the power difference is .. then you try it...
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Swap the bikes and find out whether it's the kit or the meatbags0
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Vectors are duel sided...they have a single sided option though.0
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:idea:MiddleRinger wrote:
Wouldn't power readings then drop to zero?Slowbike wrote:Try getting him to pedal just with his right leg - unclip the left - then see what the power difference is .. then you try it...0 -
philthy3 wrote:
I'm happy with mine ... it agrees with my Turbo too ... battery runs fine, doesn't drop out - and with all the limitations of a single sided pm - does what it supposed to do....0 -
It's a tricky answer given that you are both using different bikes and different powermeters, so impossible to isolate what the difference could be. In terms of the powermeters themselves, pedal based systems measure force as the cranks rotate, and calculate power based on magnitude and direction of the applied force, and the angular velocity of the crank. I'm not sure on how the different models do this, but assuming there is some kind of calculation algorhythm in the software that converts all this into a power figure. It may be the case that they use a slightly different method as the two systems work in different ways, and therefore come up with different figures. The method of calculating average/normalised power could also vary. There is also the inbuilt error as accuracy is usually about +/- 2% anyway, so could account for a few watts there. Installation could be an issue as a quick Google suggests that you need to use the correct (quite hefty) torque for installation or figures can be out.
Interesting short article with a bit about comparisons here: http://road.cc/content/review/98411-stages-power-meter
And that is just on the method of measuring external force, without getting onto the rider physiology, cadence, setup, bike, and aerodynamics... I'd not worry too much about the comparison of figures, and just enjoy riding with your Dad0 -
In fact, a better question would be why would you expect there to not be a difference? Disregarding bikes and powermeters, all you're saying is it takes your father more power to ride at the same speed as you, which is a fair indicator you are a bit fitter, and possibly not altogether surprising assuming he's a good few years older and a little bit heavier. If I rode side by side with a pro of similar stature, then I would need to produce more power than them to ride at the same speed as I'm not as fit and have much less impressive muscular and cardiovascular system.0
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Tom M wrote:In fact, a better question would be why would you expect there to not be a difference? Disregarding bikes and powermeters, all you're saying is it takes your father more power to ride at the same speed as you, which is a fair indicator you are a bit fitter, and possibly not altogether surprising assuming he's a good few years older and a little bit heavier. If I rode side by side with a pro of similar stature, then I would need to produce more power than them to ride at the same speed as I'm not as fit and have much less impressive muscular and cardiovascular system.
Nope...
The Power required to move an object through the air on a set of wheels is not defined by the power source - other than it's weight and aerodynamic properties.0 -
Most likely a mixture of the different brands of power meter, body position, rider weight, bike aerodynamics, bike weight in that order.
If you're really interesting in seeing specifically where the difference comes from:
1) Do the same short loop twice alongside one another, swapping power meters in between. Should tell you difference in power meters.
2) If that doesn't account look at position head on. As your dad is older, he may well be less flexible and spends more time with his hands on the tops, or just has his bars set higher. This could well account for 20w.
You can then do whole set of tests swapping equipment between bikes and adjusting positions; but most probably you'll find the difference in step 1 and 2. You can look at Chung elevation model to differentiate quite small changes in drag due to equipment and position all using free software. But it does take time and some scientific rigor. This may be of interest to you, but I understand that for many recreational cyclists it would be a step too far.0 -
Power required to do X speed has nothing to do with fitness. It's just physics. Power to do x speed is mad up of aerodynamic drag, drive train efficiency. rolling resistance, and any work done against gravity.Slowbike wrote:Tom M wrote:In fact, a better question would be why would you expect there to not be a difference? Disregarding bikes and powermeters, all you're saying is it takes your father more power to ride at the same speed as you, which is a fair indicator you are a bit fitter, and possibly not altogether surprising assuming he's a good few years older and a little bit heavier. If I rode side by side with a pro of similar stature, then I would need to produce more power than them to ride at the same speed as I'm not as fit and have much less impressive muscular and cardiovascular system.
Nope...
The Power required to move an object through the air on a set of wheels is not defined by the power source - other than it's weight and aerodynamic properties.
Lots of people who are 'less fit' still go faster than others, simply due to being more aerodynamic.0 -
Different power meters measure power at different parts of the pedal rotation. So maybe you and your father are pedaling with a slightly different technique?0
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Tom M wrote:In fact, a better question would be why would you expect there to not be a difference? Disregarding bikes and powermeters, all you're saying is it takes your father more power to ride at the same speed as you, which is a fair indicator you are a bit fitter, and possibly not altogether surprising assuming he's a good few years older and a little bit heavier. If I rode side by side with a pro of similar stature, then I would need to produce more power than them to ride at the same speed as I'm not as fit and have much less impressive muscular and cardiovascular system.
Sounds more like heart rate. A fitter person can do more with similar heart rates.0 -
I'm still amused by the PM piece of this. DC Rainmaker (possibly the authority on PM accuracy and comparison) says than even the crappiest PMs actually make a good stab at average power. So, rather than take into account everything we know about power consumption differences, our prejudices are driving us to question the meters. Says more about the posters than anything.ROAD < Scott Foil HMX Di2, Volagi Liscio Di2, Jamis Renegade Elite Di2, Cube Reaction Race > ROUGH0
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meanredspider wrote:So, rather than take into account everything we know about power consumption differences, our prejudices are driving us to question the meters. Says more about the posters than anything.
I don't really think there's any particular 'prejudice' against PMs here as such. Simply that the technical differences between two separate systems (and maybe their setup) could well be the primary cause. It's not an argument 'against' power meters, just an expression that they could well be the cause of the discrepancy, that's all.
Nobody is saying 'powermeters are shite - don't buy one'....0 -
Lots of interesting replies here. Couple of things I'll clear up.
Our terrain is pretty flat, maybe 400 feet of gain over 30 ish miles.
These are mostly comfortable cruising rides, with average powers around 200 watts.
He actually has clip on aero bars and spends a good amount of time in them, so his frontal profiles should be a good deal less than mine.
We have wanted to switch bikes, just haven't had the time. Will be interesting to see the results. Hopefully soon.
I will put his pedals on my bike and see what the two power meters give me, however I would be very surprised if they are 20-40 watts different.
I do believe it to be more a function of two left leg only PM measuring two different people, I think the person above that said he is just a bit more left leg dominate than me is prob correct.
Thanks guys.0 -
Does your Dad ride on the front most of the time? Even with aero bars, he would be having to work harder than you if that was the case. Maybe you are outing yourself as a dodgy wheelsucker?!0
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Imposter wrote:meanredspider wrote:So, rather than take into account everything we know about power consumption differences, our prejudices are driving us to question the meters. Says more about the posters than anything.
I don't really think there's any particular 'prejudice' against PMs here as such. Simply that the technical differences between two separate systems (and maybe their setup) could well be the primary cause. It's not an argument 'against' power meters, just an expression that they could well be the cause of the discrepancy, that's all.
Nobody is saying 'powermeters are shite - don't buy one'....
No - but there's plenty of prejudice against single-sided PMs and Stages in particular. I don't doubt that there's a contribution from the PMs, but I'm sure that's only part of storyROAD < Scott Foil HMX Di2, Volagi Liscio Di2, Jamis Renegade Elite Di2, Cube Reaction Race > ROUGH0 -
The Internet of Thingies demand that you slag off Stages, it's da rules, cos it's on the internet.
My Stages gets used more than my Vectors which are on the race bike.
I've never had an issue with it.. in fact just realised that the last battery change in it was March.0
