# What is a good power output?

Discussion in 'Power Training' started by woj, Mar 30, 2003.

1. ### velomanct New Member

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yeh, that doesn't make a lot of sense. how can a 1km/hr increase cost 100watts?

2. ### maarten New Member

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The answer is actually quite easy. There are 2 big components. A 10% power increase doesn't result in a 10% speed increase(but considerabely less. Due to how air resistance increases by increasing speed(as michuel mentions already).

And then the big one the start, they are both standing but this negative effect is spread out over 1 hour in the one case where in the other its only for 4minutes.
A kilo rider for example will be about 4 seconds slower in his first lap where if you look at the power graph his first lap has the highest average power output. For pursuit and hour the start is less explosive but say the getting to speed cost you 4 or 6 or maybe 8(I don't have eaxct data but this should be not too far off) seconds in the first 500meter if you compare it with a 500meter at the same power at speed.

This time loss will make you average drop. And simple mats 4 or 8 sec on 4 minutes and a couple of seconds means roughly 1,5% to 3% of loss where for the hour its 0,1 to 0,2%. a big difference.
Getting to speed is a waste of time and power that has a far bigger effect on the average for a pursuit

There will also energy system working explanations but I ll leave these out due too complexit and not sufficient personal knowledge.

3. ### ric_stern/RST New Member

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Maarten is spot on - hadn't had a chance to answer this yet. in other words the steady state velocity of the 4-km pursuit (i.e., if you ignore the acceleration phase) requires a lot less power than originally quoted.

ric

4. ### Michuel New Member

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Yes the slow start is the cause but I think it's the consequential higher speed in the following laps which contributes most to the disproportionate effect on wattage. Boardman's pursuit splits were:- first 1K 1m8s, nest 3K at a constant average of 1m0.7s. This contributes >73% to total watts as the speed relative to hour speed is (1.064 / 1.001) in km/min terms which meets the cubic expression pushing up wattage disproportionately to speed:
(1.064 / 1.001)^(~3).

The first lap peaks in wattage up to maybe around 1200W in about 12secs with staring effort before speed increases but this in itself has a much smaller effect on total watts than the next 4 minutes.

The per kg watt estimates match up for the hour record : 69kg*6.6W = 455W while most estimates are around 446W for record.

For the pursuit 69kg*7.7W = 531W. I think Boardman has reported 515kg for max power output which I believe is highest 1 min wattage in a ramp test Anybody any data on this?

5. ### ric_stern/RST New Member

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apologies, i used the wrong data for this his mass was 68 kg and power to mass was 6.5 W/kg (442 W) and 7.6 W/kg (520 W)

The effect of the first lap acceleration adds ~ 10% to the overall power output requirement.

Boardmans, peak power has been vastly overestimated above, and significantly underestimated for his MAP. I don't believe these figures are in the public domain, so i won't bring them up.

Ric

6. ### 9606 New Member

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Resistance is proportional to velocity^3, but is not watts proportional to velocity^4?

7. ### Michuel New Member

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On the road/track watts is proportional to velocity^(~2.5->2.8). For example on track Watts is probably proportional to Velocity^(~2.6) excluding other variables, standardising conditions.

8. ### acoggan Member

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Re. the original question: to help address these sorts of queries, I've put together some tables that can be found here:

www.cyclingpeakssoftware.com/profile.html

Re. the discussion of Boardman's pursuit and hour record performances: these are, in fact, what I based the maximums for the 5 min and 20 min performances upon. To be more specific: Peter Keen has estimated that Boardman averaged 442 W during his ultimate hour record. Knowing that value, it is possible to estimate his CdA, from which you can calculate his *steady-state* power during the pursuit. To that I added a correction for the acceleration phase (based on his stored kinetic energy at the end of the race, plus some other considerations), then finally used critical power analysis to derive 5 and 20 min values from these 4 min 11 s and 60 min performances. Whew!

9. ### acoggan Member

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Close. Wind resistance is proportional to speed^2, so power required to overcome wind resistance is proportional to speed^3. As Michuel points out, though, if you simply model things empirically using an equation of the form power = speed^X, you find that X is somewhat less than 3, due to the influence of e.g., rolling resistance (which scales with speed^1).

10. ### Michuel New Member

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It’s a very useful table and reflects the decay in watts for the few checks I’ve been able to make for strong riders from TT times. And it shows the strong relationship between loss in power and time. The only questions I’ve had are:

Is it worthwhile to extend the range to 60 minutes? Or are the 5minute and 20minute checks accurate predictors of 60 minutes. There looks like a 13% decline from 5 to 20 minutes. The limited checks in wattage I’ve done from 20min to 60minute show a further 4% decline (just for a single rider I selected apart from Boardman who seems to show no power loss). I was expecting a larger decline.

Do stronger have a reduced loss in power over time than weaker riders? In general the table shows the lower the 5sec power the bigger the percentage discrepancy between 5 or 20 min power and 5 or 60 sec power, ie Boardman shows a shallower power loss than a 4th cat. I appreciate that the 5,60, 300 and 3200sec columns are independent and different slopes between the rows may be drawn as you advise but there seems some robustness just across the rows in showing decay.

11. ### acoggan Member

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'Hour power' would be a slightly better indicator of power at LT than 20 min power, since the longer the effort the smaller the 'contamination' from anaerobic capacity. OTOH, people often do sustained 20 min efforts in training, but only the true masochists go all-out for an hour. <g> So, it's a trade-off. The one thing I would say is that there's probably not much to be gained by including both 20 min and 60 min data in the table...the purpose is to provide a measure of a rider's relative strengths and weaknesses, based on four durations principally reflecting *different* physiological characteristics. By comparison, the extent to which your power does or does not decline more or less than average as time is extended from 20 min to 60 min (or longer) is a more subtle issue, and one that I don't think is easily or appropriately addressed using a table such the one I put together.

As for the relative decline across time as a function of the rider's ability, in general you would expect that the best road cyclists would tend to show the least decline between 5 and 20 min (and beyond), since that is a function of their LT (really, their critical power), and LT is the most important physiological determinant of endurance exercise performance. OTOH, you would, on average, expect an *inverse* relationship between the two left-most columns (i.e., 5 s and 1 min) and the two right-most columns (i.e., 5 min and 20 min), since the physiological traits (e.g., fiber type) contributing to very high short-term power would tend to be opposite those contributing to very high sustained power. IOW, the table should not be read as indicating that all riders of a given performance level/category show exactly the same rate of decline as indicated by the averages.

BTW, the top of the 5 s chart is based on Sean Eadie's known performance, whereas Arnaud Tournant's data was the source of the top of the 1 min column.

12. ### Kellysauto New Member

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I weigh 90 kg and on my time trial bike I have both a srm and rear powertap disc wheel so I use both meters. On a 40k flat course I willl maintain 340 watts with a average speed of 25.5 mph on a short 10k course I will maintain 355-385 watts with a average speed 27.0 mph, on take off I may spike as high as 1200 watts with a cadence of 160 for a few seconds however this usually hurts my time more than it helps because my legs tire quicky and I have to recover.
At spin class I can maintain over 400 watts for 1 hour, however I have to be in a class that is cool, 62 degrees with a big fan in directly front of me and even then I will lose weight due to sweat, this is done with a faster cadence 110-120, I cannot pedal nearly this fast during a time trial.

I am 6'4" I started with 180 cranks, then I switched to 175 and this year I have bought a set of 172.5, 170 and 165 cranks, I'm thinking that with shorter cranks I can spin faster and make more watts, does anyone have any suggestions?

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14. ### markspend01 New Member

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Hey Guys well i think that good power output is above 500 watts.Thanks!!

15. ### dkrenik Member

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Over what duration? You need to supply context.

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