Power calculation

I am using this site
http://bikecalculator.com/wattsUS.html
I have basic ave speed.. distance to input..
my 'problem' is that I put the last stats from a 15 mile segment of a 20 mile ride.. (the issue was .. I blew up...anyways thats digressing)
but the power calc indicated I was pushin out 340 watts..
I have to take that with a huge pinch of salt surely?
whats the accuracy with these types of generic formulas?
http://bikecalculator.com/wattsUS.html
I have basic ave speed.. distance to input..
my 'problem' is that I put the last stats from a 15 mile segment of a 20 mile ride.. (the issue was .. I blew up...anyways thats digressing)
but the power calc indicated I was pushin out 340 watts..
I have to take that with a huge pinch of salt surely?
whats the accuracy with these types of generic formulas?
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http://www.analyticcycling.com/
Then you'll realise that you need to make an awful lot of assumptions in order to estimate power. The most reasonable estimates will come from steep hillclimbs.
cheers for that...
funnily enough tho , I am getting a similar figure using one the models...
the only way I have at my disposal every so often is to use an exercise bike in a gym which has a wattage output... I will put it in my diary to do a comparision test... but it's one of those fat assed Technogym bikes where I can manage about 15 minutes before my body yelling to get off 'cos you cant adjust riding position at all.
Speed For Given PowerSpeed For These Parameters 8.51 m/s
Power 330 watts
Frontal Area 0.5 m2
Coefficient Wind Drag 0.5 Dimensionless
Air Density 1.226 kg/m3
Weight Rider & Bike 83 kg
Coefficient of Rolling 0.004 Dimensionless
Slope of Hill 0.03 decimal
The ride stat was recorded as 15.5 miles at ave speed 19.89mph
I blew into a headwind , prob over 6mph and a grinding grinding slope upwards which got me
am I going way wrong here?
Just for interest, what was your Avg over the full 20 miles, as opposed to the 15.5 mile "segment"? - (Not a point about power, just curious - if I'm being nosy, ignore).
1. 19.89 mph = 8.89 m/s
2. what bike/position were you riding? Do you really have a CdA of 0.5 x 0.5 = 0.25 m^2. That's like a CdA for a time trial rider.
3. Just checking - you were going up a 3% grade for the whole 15.5 miles at 19.89 mph?
4. Crr of 0.004. What tyres/tubes are you running? Road surface - smooth asphalt or rough road? 0.004 would be for very very good race tyres on a smooth road.
5. there was a headwind - what speed was the headwind?
6. temp, air pressure, humidity, altitude? (needed for air density calcs)
the entire ride was 21 mile and after I managed to hit the lap button after I blew, I crawled in the last 4 mile .. making the ride ave 17.9... there was an initial lap of 1 mile or so where I have to get thru lights etc in order to get to the loop where I can push hard
The power required to do that would give you a power to weight ratio capable of winning alpine stages in the TdF.
Hopefully you can shed more light .
the bike weighs in at 9kg
CdA - I just took the default value, as I am not up on that
I rode on the drops and tried to keep to using gearing from 65" to 87"
The amount of gradient 120 meters of 'climb' .. so the profile a bit lumpy but not hilly
25mm tyres.. again I took default value for lack of knowledge
road surface more or less well surfaced tarmac - this is the UK after all
Headwind . yes ..always a nigglin one. Metcheck gave it as about 6mph yesterday
Air temp was warm 20c..humidity low tho' altitude not an issue..
this is getting addictive
:?
.. for this reason, I am asking of course, I value the opinion
On flat terrain, with a CdA of 0.3m^2 and Crr of 0.005, with a direct headwind of 6mph you would average ~ 250 watts. That's ~ 3.4 W/kg.