Translation required pleeeeze

[Garfield2010]

Ok so the gym bike is a Johnson.

 

If I pedal around 31km/hour it says I am putting out around 155 Watts.

 

What will this translate too on the road should I ride alone (non drafting)

 

Basically what I want to do is be able to ride at 30km/hour on my own.

 

At what speed/watts do I need to pedal the gym bike to achieve the same?

 

I weight around 80kg's if it is applicable.

 

Thx!!

[Minion]

Have a look at the 'Power, given speed' calculator here:

http://www.analyticcycling.com/

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

[Face Plant]

using some assumptions at a power output of 155 watts you will be doing about 24 km/h

[Garfield2010]

using some assumptions at a power output of 155 watts you will be doing about 24 km/h

 

You see this is what worries me. How accurate are these readings etc really?

 

You see if I do 155 watts on the gym bike, it feels like I am doing around 28 - 29km on the road, definately not 24km!!

[Garfield2010]

Have a look at the 'Power, given speed' calculator here:

http://www.analyticcycling.com/

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

 

I did not even pass woodwork st 8 my friend. So either they have to simplify it, or I should rather give up cycling and go work for the Gov............

[Face Plant]

those readings are not accurate at all, i would assume that they are calculated using friction and using average values for things like weight, wind speed, position etc etc

[Minion]

I did not even pass woodwork st 8 my friend. So either they have to simplify it, or I should rather give up cycling and go work for the Gov............

Roughly 130W

[Garfield2010]

I guess the best would be to be to get a power meter for the bicycle....

[Face Plant]

Roughly 130W

[Minion]

I'm also a little bit weary of that value. The maths behind the analytic cycling calculator is, however, sound and their input values also appear to reasonable. I think the problem is with finding a perfectly flat piece of road e.g. upping it to 1% gradient puts the power up to 200W.

On climbs and false flats, their calculator gives roughly similar values to my power meter.

[Face Plant]

there are so many variables involved it is difficult to accurately guesstimate a value but i would hazard a guess that it would not be less than 200 watts as the power required to overcome just the friction i calculated at 74.97 watts

 

where

 

Watts to overcome friction = 0.1 x V x P

 

Where velocity V is measured in meters/second and the weight P is measured in kilograms, for a decent race bike on a smooth road, the metric Cfriction is said to be about 0.1. We can therefore calculate, that at 8.33 meters per second (30km/h) , a rider and bike weighing 90 kilos faces a frictional resistance of about 75 watts. Things like road surface and position can substantially increase the coefficient of 0.1 and on the other end of things in an aero position on a really good bike the coefficient can go down to around 0.08

[Minion]

there are so many variables involved it is difficult to accurately guesstimate a value but i would hazard a guess that it would not be less than 200 watts as the power required to overcome just the friction i calculated at 74.97 watts

 

where

 

Watts to overcome friction = 0.1 x V x P

 

Where velocity V is measured in meters/second and the weight P is measured in kilograms, for a decent race bike on a smooth road, the metric Cfriction is said to be about 0.1. We can therefore calculate, that at 8.33 meters per second (30km/h) , a rider and bike weighing 90 kilos faces a frictional resistance of about 75 watts. Things like road surface and position can substantially increase the coefficient of 0.1 and on the other end of things in an aero position on a really good bike the coefficient can go down to around 0.08

Are you sure of that friction coefficient? Your value of 0.1m/s² (or 0.01 if working in Newtons) is twice as high as the values (including experimental) I've normally seen quoted for tyre rolling resistance (i.e. 0.04m/s² for asphalt going up to 0.08m/s² for really rough paved road).

 

From all I've read, the coefficient is pretty much independent of wheel loading (i.e. position) since, provided the tyres and pressures are the same, an increase in front friction is matched by a corresponding decrease in rear friction. It has absolutely nothing to do with the quality of the bike, but is heavily affected by tyre pressure, tyre type, tube type and to some extent rim shape. It is also affected by road surface, as indicated by the values above.

Edited December 14, 2011 by Edman

[Minion]

Frontal Area 0.60 m²

Coefficient Wind Drag 0.50 dimensionless

Air Density 1.056 kg/m³

Weight 90.0 kg

Coefficient of Rolling Resistance 0.006 dimensionless

Grade 0.000 decimal

Using the above inputs into a drag model, I get a roughly 2:1 split between aero drag and rolling resistance, so roughly 90W to overcome air resistance and 45W to overcome rolling resistance.

Edited December 14, 2011 by Edman

[Joe Low]

Ok so the gym bike is a Johnson.

 

If I pedal around 31km/hour it says I am putting out around 155 Watts. What will this translate too on the road should I ride alone (non drafting)Basically what I want to do is be able to ride at 30km/hour on my own. At what speed/watts do I need to pedal the gym bike to achieve the same? I weight around 80kg's if it is applicable.

 

Thx!!

 

I think there are too many variables for you to achieve your aim this way. I would rather say work hard on the gym bike 2 - 3 times midweek, and then track your progress on the same road route each week at the weekend. Sorry if thats a Flintstones' low-tech approach.

 

Accurate power measurements v difficult to get, unless you spend the money on a proper power meter. Otherwise the measurement is only useful for comparisons for your performance on a specific machine.

[Face Plant]

Frontal Area 0.60 m²

Coefficient Wind Drag 0.50 dimensionless

Air Density 1.056 kg/m³

Weight 90.0 kg

Coefficient of Rolling Resistance 0.006 dimensionless

Grade 0.000 decimal

Using the above inputs into a drag model, I get a roughly 2:1 split between aero drag and rolling resistance, so roughly 90W to overcome air resistance and 45W to overcome rolling resistance.

taking your caluclations into consideration do you still think that 130 watts is accurate?

we can get into a mathematical discussion for hours here but the point of the matter is there are just too many variables to accurately gauge the required power output we could probably nail the friction part of the equation but the other part is the tricky part, my suggestion? a letter to santa for a powermeter

[SwissVan]

I guess the best would be to be to get a power meter for the bicycle....

 

In this particular problem knowing your HR at the desired speed and using a HRM would be much simplier and probably more accurate