Is it possible to have a massive loss of power from something "broken" on the bike?

Back by popular demand, the general all-things Road forum!

Moderator: robbosmans

Post Reply
seaneT1
Posts: 372
Joined: Tue Jun 16, 2015 11:08 am
Location: Thessaloniki, Greece

by seaneT1

It has come to my attention recently that somewhere between the pedal stroke and the wheels moving forward, around 40 or more watts dissapear and I would like to know if it is possible that there is something wrong with the bike and what could be the cause of that ( like faulty bearings, broken frame,etc...not talking about stifness and stuff like that). I know that because I compare the data with a friend of mine (around 2 kilos more than me but 40 watts lower than me on the climbs!) with whom I train alongside and also has a powermeter. We checked the powermeters and they seem to be both ok ( we will check again just to make sure in a couple of days)

by Weenie


Visit starbike.com Online Retailer for HighEnd cycling components
Great Prices ✓    Broad Selection ✓    Worldwide Delivery ✓

www.starbike.com



Marin
Posts: 4035
Joined: Wed Jan 22, 2014 11:48 am
Location: Vienna Austria

by Marin

Yes, broken powermeter can easily do that! Yours or your friend's.

Apart from that, no.

User avatar
Fixie82
Posts: 348
Joined: Mon Mar 18, 2013 3:45 am

by Fixie82

Sorry but is this from a standing start? How do you know it disappears?

It's pretty easy to get a drop of 40w just from slightly easing off the pedals, especially if going uphill. Are you sure it's not just a delay in recording data or different measurement points?

What power meter are you using?

seaneT1
Posts: 372
Joined: Tue Jun 16, 2015 11:08 am
Location: Thessaloniki, Greece

by seaneT1

I forgot to clarify that I was talking about average power on climbs from 2 to 8 minutes...today another friend with a powermeter joined, around 10 kilos more, 40 watts lower than me on a 2 minute climb that we 3 climbed together, the other friend who is almost my weight, 70 watts lower...WTF??? so powermeter might be a little broken or the bike has a seriously problem...

User avatar
kkibbler
Posts: 905
Joined: Tue Sep 09, 2014 9:30 am

by kkibbler

You haven't answered what PMs are in use.

I doubt anything is broken on your bike that would eat up 40w that you wouldn't notice without a PM.

So either your PM is smoked or you're as aero as a fridge.

Anyway, PM tech is not infallible. For all the talk of accuracy it's precision that's more critical to measuring performance changes over time.

Marin
Posts: 4035
Joined: Wed Jan 22, 2014 11:48 am
Location: Vienna Austria

by Marin

Weigh yourself and your bike and ride a steep ascent, at least 8% or more. The use one of the many online calculators, like kreuzotter.de etc. - on steep stuff they wil give you a pretty accuracte number to compare to because aero doesn't matter much uphill.


If you lost 40w on your bike somewhere, the part consuming the power would be as hot as a 40W lightbulb - i.e. too hot to touch.

Marin
Posts: 4035
Joined: Wed Jan 22, 2014 11:48 am
Location: Vienna Austria

by Marin

Then weep because your FTP is 15% lower than you always thought ;)

964Cup
Posts: 195
Joined: Tue Dec 18, 2012 1:31 am

by 964Cup

Calibrate your power meter; or swap bikes with your friend and see how you compare using his meter.

spud
Posts: 1266
Joined: Sat Feb 07, 2009 5:52 am

by spud

about the only way I can see this happening is if the rear wheel is mashing into a brake block or chain stay. But of course, you would hear/feel that. Otherwise, no way.

seaneT1
Posts: 372
Joined: Tue Jun 16, 2015 11:08 am
Location: Thessaloniki, Greece

by seaneT1

Problem almost solved...it seems that someone can be stupid enough to miss that something is rubbing like crazy in the bottom bracket area...and that stupid individual is me! :doh:

User avatar
Miller
Posts: 2765
Joined: Thu Sep 21, 2006 8:54 pm
Location: Reading, UK

by Miller

Details on that? Losing 40W in the BB would have made the crank really hard to turn?

seaneT1
Posts: 372
Joined: Tue Jun 16, 2015 11:08 am
Location: Thessaloniki, Greece

by seaneT1

Miller wrote:Details on that? Losing 40W in the BB would have made the crank really hard to turn?


Well not really..the 40 watt difference was noted when we were going with more than 300 watts,and at that times I dont really understand what is happening,the difficulty I was feeling felt natural?... when rolling around the difference was very little so couldn't notice it (at least not I, not very good with those things :S )

Dez33
Posts: 407
Joined: Thu Jun 25, 2015 9:02 am

by Dez33

seaneT1 wrote:
Miller wrote:Details on that? Losing 40W in the BB would have made the crank really hard to turn?


Well not really..the 40 watt difference was noted when we were going with more than 300 watts,and at that times I dont really understand what is happening,the difficulty I was feeling felt natural?... when rolling around the difference was very little so couldn't notice it (at least not I, not very good with those things :S )



It's not the bottom bracket (highly unlikely 40 watts anyway) then, friction there will be constant, not relative to watts or speed. If you pedal along at 90rpm the same difference will be there doing 100 watts as 300 watts.

What brand power meter do you have? Have you calibrated it?
Last edited by Dez33 on Mon Oct 10, 2016 11:50 pm, edited 1 time in total.

bm0p700f
in the industry
Posts: 5777
Joined: Sat May 12, 2012 7:25 pm
Location: Glermsford, Suffolk U.K
Contact:

by bm0p700f

You cannot compare yourself to your friend in this way. Way to many variables that have not been accounted for in any way.

You should look at your numbers to see if there is an improvement over time or the reverse. The numbers are relative to you not anyone else. I see other riders with pm putting out huge watts in a race. What does it matter if I am keeping up. The absolute numbers only matter if you have more than one PM on different bikes and flip between often.

If something was eating up 40W you would know about it very quickly.

youngs_modulus
Posts: 668
Joined: Wed Sep 20, 2006 1:03 am
Location: Portland, OR USA

by youngs_modulus

Missing 40 watts is a real possibility and happens to me all the time. I even know what's broken on my bike: it's the rider's resolve to train like he should.

In all seriousness, there's nothing on your bike absorbing 40 watts. If it were, some part of your bike would be getting hot. Incandescent light bulbs are nearly a thing of the past, but only 5% of the energy they consume is turned into visible light. The rest is turned to heat. So think about how warm your bike would be if you had a lit 40-watt bulb in your bottom bracket.

Your BB would be warm if it were dissipating 40 watts. I agree with the other posters. There may well be a calibration with one or both of the two power meters you mentioned.

by Weenie


Visit starbike.com Online Retailer for HighEnd cycling components
Great Prices ✓    Broad Selection ✓    Worldwide Delivery ✓

www.starbike.com



Post Reply