Can anyone calculate watts without a power meter??

It is not that easy.  You need to know all the forces acting against the rider.  But if you are willing to make some assumptions, try here:

http://www.analyticcycling.com/ForcesPower_Page.html

It is very complex and not something one would be able to do without collecting a great deal of data while racing and being able to complete non-trivial calculations after obtaining said data.

Better to race using RPE or HR rather than chase a bike split or average speed.

Shane

As JK said it can be very tricky, you can certainly try analytical cyclist but take it with a grain of salt specially if you make many assumptions.

For instance, one of my athletes did his final one of his workouts for IMLP; he did a few 10 mile loops (same loop) striving for an even pacing at a determined wattage. His power average for both loops was exactly the same (he paced rather well) however for the 2nd loop he rode almost 1 mph faster. Most likely, the wind changed and he got a tail wind or maybe the 2nd loop he rode with more cars passing by providing with drafting benefits or maybe he stayed completely aero on the end loop vs the 1st where he might sat up (that didn't happen but it could affect the results), etc.

Agree that there's really no way to do it. I can ride the same route at the same average wattage and the difference can be 2 mph or more. That's with the same rider, equipment, position, weight, etc. Throw those in as variables and you don't have a chance.

Thanks guys, that is what i was figuring. I was not looking for exacts, i was just trying to guesstimate the power i put down in a race. So i thought if i weighed 215, went 13 miles and averaged 25mph it might give a ball park for avg watts I ,needed to hold that pace, weather, wind and draft non important.

i appreciate the feedback and link, i will try it for giggles and haha's

Not that it is relevant, but you can minimize some of the assumptions that you make on a flat course by timing yourself up a known grade.  IIRC, you just need a hill with a good grade that is constant and runs for a good while.  Frontal area, Cd, and wind become much less a factor (They still matter, just way less however, not very specific to a 40k tt. The calcs are online.  I think I used the one at 2peak.com

If you have a GPS you can upload your rides to Strava.com and use their free membership and it plots out your wattage.  They claim to be pretty accurate, although I don't have access to a PT to confirm their claims.  If nothing else, it's a pretty cool site.

That calculator rocks..thanks for sharing it!

Thanks Kim, that is interesting, it says that to push 25mph for 13.2 miles i am in the 350-380 watt range based on a 1% elevation change.

The reason i asked was i just did a sprint on a very technical course with not much climbing and averaged 24.45 miles per hour, i was just interested to see how much power i might have been putting down, I know it is not 100% accurate, but at least is gives me an idea of where i am, like was i pushing 250 watts, 300w etc.

it does not take into consideration the multiple accelerations that i had to do due to rights and lefts, but it gives me an idea

thanks everyone!!

Hi Rudy,

A 1% suggests that the course finished almost 700ft higher than it started. 

If it's a loop or out-and-back, the average elevation gain is 0.



(edited for type, oops)

Edited by dredwards 2010-07-22 12:38 PM

350-380 is very high.  just fyi.  i think you would have to put some wind in there maybe 2-3 mph.  i would venture to say it would be around 300w.  your accelerations would even out over the course also.

btw impressive pace and huge improvement from your last years races.  your olympics you were at 20 mph ave and jumped to almost 25 mph ave, very nice.

First off all, that's some good speed.

I went back to some workouts and at 172lbs, aero, I would probably have to push 280 watts for that speed, on one of the courses I do my workouts. If you weigh more, you would need to push more. If you are less aero, you would have to push more.

That's without an aero helmet, disc cover....bla bla...in training

Just to give you a rough order of magnitude

how much do you weight?

ahh....didn't not think about the weight

..


Edited by Rudedog55 2010-07-23 8:58 AM

race day i weighed 217lbs

does weight force you to create more or less power, i would think simple physics would require more power to keep an object in motion on a flat surface.  If it helps i also have 48" wide shoulders, so i am not the most aerodynamic person.

while i am giving details, i was using a TT bike with 2 tri spoke wheels, no aero helmet. and the course had 11 corners per lap for a total of 22 90* corners

Edited by Rudedog55 2010-07-23 9:00 AM

yes you will need more power to move a heavier object to obtain similar speed. 

i average about 23.5 mph for 10 miles and i can do it on 245 watts.  so 300w will put me at a very high ave.

I'd take the power estimates from that site with a shaker full of salt. I did a rolling out and back last night. I used both sets in the form and reversed the grade and wind numbers to represent the out and back. The calculator comes up with 120 watts out and 147 watts back. Actual numbers were 177 and 173.

The only variable in the calculator that I may have wrong is the wind. I had to fudge that to even get as close as I did. I used -4 mph going out and 4 mph coming back, but the wind was definitely stronger than that.

The wind speed and the CdA of rider and bike are such overriding factors in the amount of power required that they make the estimate pretty much impossible. I've had instances where I'm riding right beside someone else at the same speed and they're pushing 20-30 watts more than I am simply because of the difference in position.

so i guess the correct answer is  "enough" or "a good amount".... lol



anyone recommend a non-wheel mounted power meter??

i have done very very limited research and have read a little about a quarg??  or I bike pro III??

for a guy that does a couple Tri's a year and couple dozen bike races, is it even a cost that is worth incurring??

dang Rudy! You were a rockstar out there on that bike course!

Besides the quarq, the only other crank based power meter that I know of is the SRM.

Limitation to crank based is that it will live on that bike; upside is you can put any wheel set on that bike and still use power. Downside to having wheel based power is that you are limited to the wheel set, but can put it on any bike. Alternatives is to have either multiple wheel sets with power or multiple bikes with cranksets with power.

My opinion on the iBike is that in expert hands it can replicate the torque sensing meters, but it requires constant adjustment and is very difficult to set up.

Polar has a harmonic-sensing, chain stay-mounted unit, but the same caveats apply.

Also, in my opinion, the power meters are GREAT tools when combined with a plan that uses the numbers to not only track performance, but to allow you to hit numbers so that you aren't ever lying to yourself that your workout was enough, when it was not.  

Nevertheless, if you ride lots, and ride hard, and mix it up a bit, but are riding,  I dont see a power meter making the difference between MOP and FOP.  First and third maybe.  

Now if you like numbers and tracking them.  Get it.  It only lightens your wallet. It doesn't kill puppies or cause the mass clubbing of baby seals.