Calcuting forces on a slope (cycling) -online calculators wrong?

In summary, the conversation is about calculating the forces acting on a cyclist going up a hill. The person is trying to use online calculators to get the parallel force, but is getting different results. They also mention trying to calculate the forces by doing a calibration run down the hill and taking into account other forces such as air resistance and friction. They question if they are missing something fundamental and someone responds that they may be confusing slope angle and percent grade. They also mention that air drag is velocity dependent and suggest measuring acceleration at different velocities to determine the net force. Finally, they mention that transmission loss is not included in the calculations.
  • #1
Festina
2
0
I'm trying to deduce the forces acting on a cyclist going up a hill and I need help. There's 2 questions:

Q.1

I've looked at online calculator already in existence:

http://www.analyticcycling.com/ForcesPower_Page.html
http://www.gribble.org/cycling/power_v_speed.html

What puzzles me about these calculators is when I caculate the parallel force I get numbers that are different to these calculator. but are the same as http://thecraftycanvas.com/library/...pers/incline-force-calculator-problem-solver/


e.g. for a 5º slope and a 78 kg rider+equipment: -9.81 * sin(rad5) * 78 = 66.6 N "thecraftycanvas.com" get the same result, yet Gribble and Analytic cycling get 38.2 N

Q.2

Following on from this, what I am trying to do is calculate what the force are acting on the rider by doing a calibration run down the hill, the other forces (air resistance (wind, pressure), friction) besides gravity being the difference between the force on the calibration run and a hypothetical run just with the force of gravity.

So that when the rider goes up hill in X amount of time we can calculate the how much work against gravity by itself and all the other forces rolled together (deduced from the calibration run).

Am I missing something fundamental?
 
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  • #2
Festina said:
yet Gribble and Analytic cycling get 38.2 N
You confuse slope angle and percent grade.

tan(slope angle) * 100 = percent grade

Am I missing something fundamental?
Air drag is velocity dependent. You can let him roll downhill, and measure the acceleration at different velocities. From acceleration you get the net force. Substract gravity to get air drag + rolling resistance. Transmission loss is not included.
 
Last edited:
  • #3
I did indeed A. T., thanks!
 
  • #4
Festina said:
I did indeed A. T., thanks!
I added an answer to the 2nd question.
 
  • #5


I cannot speak for the accuracy of specific online calculators, but I can provide some insights into the calculations of forces on a slope for a cyclist.

Firstly, it's important to note that the forces acting on a cyclist on a slope are complex and dynamic, and can vary depending on various factors such as the terrain, the rider's weight and equipment, and the speed at which they are cycling. Therefore, it's not surprising that different calculators may give slightly different results.

In terms of your first question, it's possible that the discrepancy in results between the calculators may be due to different assumptions or simplifications made in their calculations. For example, some calculators may only consider the force of gravity, while others may also take into account air resistance and friction. Additionally, the accuracy of the calculations may also depend on the accuracy of the input values, such as the angle of the slope and the weight of the rider and equipment.

For your second question, it's important to understand that the force of gravity is not the only force acting on a cyclist going up a hill. As you mentioned, there are also forces such as air resistance and friction that need to be taken into account. These forces may vary depending on the speed and direction of the cyclist, making it difficult to accurately calculate them without proper measurements and equipment.

In summary, while online calculators can be a useful tool for estimating forces on a cyclist on a slope, they may not always give accurate results due to the complexities of the situation. It's important to consider the assumptions and limitations of these calculators and to take into account all relevant forces when trying to deduce the forces acting on a cyclist on a slope.
 

1. Why are online calculators wrong when calculating forces on a slope while cycling?

Online calculators for calculating forces on a slope while cycling may be wrong due to a variety of factors. One common reason is that they may not take into account real-world variables such as wind resistance, surface friction, and bike weight. They also may not accurately factor in the rider's body position and pedaling technique, which can greatly affect the forces on the bike.

2. How can I accurately calculate forces on a slope while cycling?

The most accurate way to calculate forces on a slope while cycling is to use a power meter, which measures the actual power output of the cyclist. This data can then be input into a physics-based equation to calculate the forces on the bike. Alternatively, a bike computer with a built-in accelerometer can also provide more accurate data for calculating forces.

3. Are there any online calculators that are accurate for calculating forces on a slope while cycling?

There are some online calculators that may provide more accurate estimates for calculating forces on a slope while cycling, but they still may not be as accurate as using a power meter or bike computer. It is important to carefully consider the variables and assumptions used in these calculators and use them as a general guide rather than relying solely on their results.

4. Can incorrect calculations of forces on a slope while cycling affect my training or performance?

Inaccurate calculations of forces on a slope while cycling may not have a significant impact on training or performance for casual cyclists. However, for competitive or professional cyclists, accurate calculation of forces is crucial for training and optimizing performance. Using inaccurate calculations may lead to incorrect training strategies and suboptimal performance on race day.

5. What other factors should I consider besides forces when cycling on a slope?

While calculating forces on a slope is important for understanding the physical demands of cycling, it is also important to consider other factors such as nutrition, hydration, and pacing. These factors can greatly affect performance on a slope and should be taken into account along with forces when planning a training or racing strategy.

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