# how many watts= MPH?



## deadleg

So I weigh about 150, 5' 6", standard road bike. On a flat road, no wind, approximately how many watts to go 20 MPH? 25 MPH?
I am just curious, too cheap for a power meter at this time. I amstarting training for a time trial.


----------



## asgelle

deadleg said:


> So I weigh about 150, 5' 6", standard road bike. On a flat road, no wind, approximately how many watts to go 20 MPH? 25 MPH?
> I am just curious, too cheap for a power meter at this time. I amstarting training for a time trial.


Analytic Cycling, Interactive Methods for Estimating Cycling Performance Parameters. Tom Compton


----------



## Kerry Irons

*Some numbers*



deadleg said:


> So I weigh about 150, 5' 6", standard road bike. On a flat road, no wind, approximately how many watts to go 20 MPH? 25 MPH? I am just curious, too cheap for a power meter at this time. I am starting training for a time trial.


As asgelle noted, analyticcycling.com is your source for quality power calculations. Of course you can only estimate your drag numbers, but for a general reference, you're at about 170 watts at 20 mph, and 300 watts at 25 mph.


----------



## dmong2

As a rider who recently started training with power...there is no substitute. You can actually ride faster right away because you are able to use your effort so much more efficiently. You can't comprehend how much energy is wasted by accelerating too hard too fast or using too much effort up a short hill. Riding at a prescribed watt allows no waste. 

As far as trying to recreate that with MPH, I don't think it's possible. I used to believe it was, but I don't any more. 

20 mph at 170 watts...too hard to say, too many variables. It sounds plausible, but if you are off just a tad (RPE) it can translate to big differences in watts. 

Best alternative? Find someone you can ride with who has a powermeter. Ride next to them at a prescribed watt for 20 minutes or so and try to assign perceived exertion. I think that might actually be more accurate than using speed, because there is no flat, windless roads.


----------



## pretender

dmong2 said:


> You can't comprehend how much energy is wasted by accelerating too hard too fast or using too much effort up a short hill. Riding at a prescribed watt allows no waste.


Riding at constant wattage is highly inefficient.


----------



## spade2you

dmong2 said:


> Best alternative? Find someone you can ride with who has a powermeter. Ride next to them at a prescribed watt for 20 minutes or so and try to assign perceived exertion. I think that might actually be more accurate than using speed, because there is no flat, windless roads.


Provided you weigh the same weight and have the same aerodynamic drag. A friend of mine's cruising power is significantly higher than mine at the same speed to the point where his zone 2 is high zone 3 to low zone 4 for me.


----------



## Poncharelli

~25 mph at 260W is what I calculated from analytic cycling, for my weight on flat road. (damn conversion factors)

I guess I'm a human parachute; as I suspected. 260W at 20min, I usually get around ~23mph. 

Or may be because every little tiny uphill/headwind doesn't get made up in the downhill/tailwind. The algorithm uses zero wind and flat road, which never really exists.


----------



## asgelle

The algorithm uses zero wind and flat road, which never really exists.[/QUOTE]

Correction: you chose to use no wind and flat road. Analyticcycling can handle any wind speed and direction and road slope. In fact, the default is a 3% grade.
Wind on Rider


----------



## johnlink

pretender said:


> Riding at constant wattage is highly inefficient.


Would you elaborate? Highly inefficient for what? Training? Racing?


----------



## pretender

johnlink said:


> Would you elaborate? Highly inefficient for what? Training? Racing?


There are two "naive" pacing strategies (let's think about a 40K time trial, just for sake of argument). The first naive strategy is constant speed, the second is constant power. On a straight flat course with no wind, the two strategies are exactly the same.

Add hills or wind or sharp turns, and the two strategies become very different. The optimal strategy is neither of the naive strategies, but somewhere in between the two.


----------



## asgelle

pretender said:


> There are two "naive" pacing strategies (let's think about a 40K time trial, just for sake of argument). The first naive strategy is constant speed, the second is constant power. On a straight flat course with no wind, the two strategies are exactly the same.
> 
> Add hills or wind or sharp turns, and the two strategies become very different. The optimal strategy is neither of the naive strategies, but somewhere in between the two.


Except this thread is dealing with training not racing. Is there any reason to believe a constant power training strategy is less efficient (whatever that means) than a variable one?


----------



## johnlink

pretender said:


> There are two "naive" pacing strategies


I presume you are considering racing rather than training. Please correct me if I'm mistaken.


> (let's think about a 40K time trial, just for sake of argument). The first naive strategy is constant speed, the second is constant power. On a straight flat course with no wind, the two strategies are exactly the same.
> 
> Add hills or wind or sharp turns, and the two strategies become very different. The optimal strategy is neither of the naive strategies, but somewhere in between the two.


Has anyone ever solved the optimal racing strategy as a control theory problem? I would expect it to take into account the physiological behavior of the rider (e.g., recovery time after cracking) as well as the non-linear effect of air resistance.


----------



## asgelle

johnlink said:


> I presume you are considering racing rather than training. Please correct me if I'm mistaken.
> 
> Has anyone ever solved the optimal racing strategy as a control theory problem? I would expect it to take into account the physiological behavior of the rider (e.g., recovery time after cracking) as well as the non-linear effect of air resistance.


http://www.google.com/url?sa=t&sour...IcAHc6bzgS6CO7TyQ&sig2=CEBIL4O4JpFaRiokJ5s5Gw

Among many others


----------



## johnlink

asgelle said:


> http://www.google.com/url?sa=t&sour...IcAHc6bzgS6CO7TyQ&sig2=CEBIL4O4JpFaRiokJ5s5Gw
> 
> Among many others


Having read the table of contents, WOW! I can't wait to read this paper, Thank you, asgelle.


----------



## Poncharelli

asgelle said:


> The algorithm uses zero wind and flat road, which never really exists
> 
> Correction: you chose to use no wind and flat road. Analyticcycling can handle any wind speed and direction and road slope. In fact, the default is a 3% grade.
> Wind on Rider


I believe I was messed up in several ways actually. When using analytic cycling, it sort of assuming an instantaneous event. 

Where I was looking at my average power over 20 minutes, and correlating it to an average speed. Which will probably always result with a lower average speed due to wind, grade changes, turnaround, corners, etc.

I looked at instantaneous values on the graph of power vs. speed in Poweragent, and the conclusion is still the same: I'm a human parachute. I still don't get the speed using their default coeff. and frontal area.


----------



## Alex_Simmons/RST

johnlink said:


> Has anyone ever solved the optimal racing strategy as a control theory problem? I would expect it to take into account the physiological behavior of the rider (e.g., recovery time after cracking) as well as the non-linear effect of air resistance.


Yes, and since I wrote that discussion paper linked earlier and developed the model, there have been online websites that seek to do similar. 

I was not the first - I know Andy Coggan at least had done similar before me with a segmented model approach using the equations of motion for a cyclist and Normalised Power as a global (physiological) pacing contraint, and Rick Ashburn who had done similar for Ironman analysis and his colleague Chris Whyte who suggested using TSS as a global constraint in IM racing, although I'm pretty sure I was the first to combine this approach with Virtual Elevation to account for course specific environmental variations for post-hoc analysis.

I will add though, that for many courses of moderately variable gradient, even power pacing is still a very good choice. It's not totally optimal but it's not a bad strategy by any stretch. We never actually ride that way, but for many, they would do well to moderate closer to that than how many actually ride (which is often too hard on some climbs but especially going too hard in the opening minutes).

In any case, a discussion on race pacing is OT, so will leave it there.


----------



## Alex_Simmons/RST

Poncharelli said:


> I believe I was messed up in several ways actually. When using analytic cycling, it sort of assuming an instantaneous event.
> 
> Where I was looking at my average power over 20 minutes, and correlating it to an average speed. Which will probably always result with a lower average speed due to wind, grade changes, turnaround, corners, etc.
> 
> I looked at instantaneous values on the graph of power vs. speed in Poweragent, and the conclusion is still the same: I'm a human parachute. I still don't get the speed using their default coeff. and frontal area.


If you are using a power meter, then you have the tool to determine your own CdA & Crr values. Then experiment to seek ways of improving them.

For most TTs, you are seeking to increase the ratio of sustainable power to CdA (W/m^2).


----------

