Your Avg Pwr @ 20-22mph Flat
- Thread starter allanw
- Start date
I'm really confused how there is such a wide range of power output here. I'm putting out about 140 W at this speed, I'm about 92 Kg /190lbs (at about 52x15 -- I think this is about the gear I'm using, not sure of the rear cog but its one either way of 15)allanw said:
Can someone explain why, apart from weight, there should be such a large variation in power output at a given speed.
Thanks in advance
closesupport said:
Well, my method is pretty unscientific but I think good enough for my purposes:
I don't have anything on my bike, at least not yet - the power option for my Polar scares me a bit from an installation / clutter factor.
But I do have one of these that I use a lot when I can't get out on the road: http://www.kettlerusa.com/page85.html
Assuming flat terrain and negligible wind, my regular rides are either short flat out 15mile TT's or rides by the hour. I know very well what my times, mileage and HR are during these rides.
Setting the Ergo to 140 - 150 watts closely duplicates the perceived effort, HR and covered distance for me. Physically it is about the same level of fatigue at the end as well.
I realize I am leaving out air resistance but I don't think that is huge at the speeds that we are talking about in this post.
Of course there is a good chance that I have this all wrong, and chances are someone here will let me know <g>
are you using a powertap or SRM?jon_stewart said:
i use a powertap pro and it takes about 220watts on flat road with no wind to go 21mph. i'm 6'2 175lbs. i ride a cdale road bike, typical racer setup. (32spoke open pro wheels) i did a TT with no aero gear at 24.5mph average over 8 miles of rolling main highway type roads, out and back, 10mph headwind one direction. average power was 335watts.
i have tested my powermeter, and the torque is zeroed, so it is accurate.
i don't know how at 190lbs, you can go 21mph at only 140watts. either your powermeter is off, or you had a tailwind or slight downhill.
velomanct said:
Agree these numbers sound low, just based on a couple of estimates I've seen from calculations. Your power numbers match more closely with the analytic program I've got. Big variable of course is position on the bike. For the figures you cite, the program drag coefficient requires that you would be almost in a "racing tuck" position....ie, in the drops, arms bent.
As I think more about this question it appears that it doesn't make complete sense after all.
A given bike in a given environment would require n watts to maintain a given speed, the rider's only say would be in the gear chosen (I think).
If so it'd be interesting if there was such a thing as a "spec" bike and a table of watts required in each different gear.
Or maybe I'm just confusing myself some more.
A given bike in a given environment would require n watts to maintain a given speed, the rider's only say would be in the gear chosen (I think).
If so it'd be interesting if there was such a thing as a "spec" bike and a table of watts required in each different gear.
Or maybe I'm just confusing myself some more.
DanP said:
I'm not entirely sure i follow what you're saying. however, if you ride at X watts it doesn't matter what your cadence is
ric
Hey, couldn't imagine you didn't know this page:
http://www.analyticcycling.com/ForcesPower_Page.html
There are two tools: Power given speed, and speed given power
There are also the equations that rationalize in this results.
On a flat course (this is SCIENCE), the weigth of the rider has only a very small influence on the power-speed relationship. It only affects the friction component. Uphill, theres a force going down,
proportional to your weigth tha you must overcome with your power.
Ok, so the free variables in this applet are:
Weigth (bike+rider)
Frontal Area Coef,
Type of pavement
slope
speed
So, for a 85 kg (75 rider+ 10 bike) rider, at 9.5 m/s (21 mph) the power is 163.1 Watts
for a 130 kg (rider+bike), same speed: 179.8 Watts
(for an asphalt road both)
So, I guess everyone results must be between 160 and 180 Watts
This free applet is great, I can calculate with it wich slope I must go at which speed to accomplish
my power (watts goal). I can also dream with it what would be the results uphill If i dropped 5 kg.
Enjoy the site! There's also gear-speed charts and calculators... etc...
Cheers,
Oscar
http://www.analyticcycling.com/ForcesPower_Page.html
There are two tools: Power given speed, and speed given power
There are also the equations that rationalize in this results.
On a flat course (this is SCIENCE), the weigth of the rider has only a very small influence on the power-speed relationship. It only affects the friction component. Uphill, theres a force going down,
proportional to your weigth tha you must overcome with your power.
Ok, so the free variables in this applet are:
Weigth (bike+rider)
Frontal Area Coef,
Type of pavement
slope
speed
So, for a 85 kg (75 rider+ 10 bike) rider, at 9.5 m/s (21 mph) the power is 163.1 Watts
for a 130 kg (rider+bike), same speed: 179.8 Watts
(for an asphalt road both)
So, I guess everyone results must be between 160 and 180 Watts
This free applet is great, I can calculate with it wich slope I must go at which speed to accomplish
my power (watts goal). I can also dream with it what would be the results uphill If i dropped 5 kg.
Enjoy the site! There's also gear-speed charts and calculators... etc...
Cheers,
Oscar
BlueIcarus said:
The analytic site is great... however, you can't draw the conclusion you made above (160 - 180 W), simply because the power depends on CdA and environmental conditions, which can be difficult to estimate.
ric
ric_stern/RST said:
Of course, Ric, of course. This is the same thing as my Heart Rate Meter telling me how many calories
I have burnt . No exact numbers here, just an aproximation of the expected average. Not to mention
taking into account the wind speed, modelling the rolling resistance and effective frontal area (mine is around 0.6, I'm a wide guy)... etc
I only wanted to stress that at the flats, power is near independent of the weight and put a reasonable
expected power range to rule out the 200-250 W range and below 150 W range.
On the other hand, I have made several time this test: Wanted to train at 200 Watt (by instance), so figure out with the applet which terrain and speed (or better: which speed at which slope) I must train. Go out. Measure my Heart Rate. Next days go the ergometer. Put the ergo at 200 Watts. Look at my HRM. Check and guess what? It's +- 3 bpm different from the road, so... this analytic thing is very accurate, at least for my needs.
Very interesting thread, btw
Cheers!
Oscar
BlueIcarus said:
no, this is the point i'm countering against. simply, we don't know people's CdA and at ~ 9.5 m/s 200 - 250 W is very entirely likely depending on the conditions and bike and equipment. for instance, when training on a road bike at that ~ velocity i need to produce around 220 W and i'm only averaged size (1.75 m and 68 kg), with a good bike position.
ric
ric_stern/RST said:
Ok. Didn't knew this coefficient have such a huge influence on the wattage. I supose then my road
has the average friction, my position on the bike, frame, rolling resistance and wind condition must be the ones the software is expecting, b/c at the cycloergometer with same power, it seems the same RPE and same HR. But you have measured this directly, so I have nothing more to say
BlueIcarus said:Ok. Didn't knew this coefficient have such a huge influence on the wattage. I supose then my road
has the average friction, my position on the bike, frame, rolling resistance and wind condition must be the ones the software is expecting, b/c at the cycloergometer with same power, it seems the same RPE and same HR. But you have measured this directly, so I have nothing more to say
CdA has the biggest influence on power at the flat as >90% of the energy we use to power our bikes on the flat is used to overcome air drag. At velocities of 20 km/hr and greater the majority of the work done is used to overcome air drag.
it's highly unlikely that your road position (assuming you mean you have a standard type road bike) is anywhere near the default setting on analytic cycling, as a CdA of 0.25 m^2 (the default setting is a reasonable TT position with e.g., disc wheel).
You can't compare HR from the road to the indoor trainer as environmental and topographical conditions alter it at a given work load. additionally, if you aren't using a power meter such as e.g., Power Tap or SRM, then your data is likely to be wrong.
A reasonably accurate way of estimating power output if you don't know your CdA (and you'd really have to gone to a wind tunnel to get that figure) is to ride up a steep hill, where your velocity is minimised (i.e., < 15 - 20 km/hr) and that you can ride steady up for several minutes. if you know the grade or vertical gain of the climb and distance and your bike mass, your mass, and your bike kit, then you can use analytic to gain some insight into your power.
ric
what do i need to measure power output?ric_stern/RST said:
will it tell me how many rpm?
where would i purchase somthing to the job sucessfully and or around how much.
Thanks for the info Ric.
And yes, when I want to test my power, I always do this up a hill, where power mainly depends on
total weigth, steepness, and speed.
For me this is good news. It means that I actually put out more power than I do
Talking about the HR: I work by aproximations, same thing I do running outside and on the treadmill
and the general feel is that it matchs very well. Of course with HR the human factor comes in and is not that reliable. But i don't need much accuracy
And yes, when I want to test my power, I always do this up a hill, where power mainly depends on
total weigth, steepness, and speed.
For me this is good news. It means that I actually put out more power than I do
Talking about the HR: I work by aproximations, same thing I do running outside and on the treadmill
and the general feel is that it matchs very well. Of course with HR the human factor comes in and is not that reliable. But i don't need much accuracy
