37
votes
Why are emergency inflation cartridges filled with CO2?
CO2 charger cartridges are used for bike tire inflation because they are a common, inexpensive product that has been around since the 1950s. Their other uses include powering air guns and inflating ...
- 75.9k
26
votes
Why are emergency inflation cartridges filled with CO2?
I believe you will find these articles informative:
The hidden life of a CO2 cartridge [PDF]
The CO2 Cartridge … an Under-Appreciated Marvel of Technology! — George Fox Lang [PDF]
At room ...
- 361
25
votes
Accepted
Infeasibility of a mechanical wind-up spring KERS (Kinetic Energy Recovery System) for bicycles
Ain't gonna happen.
If you want to store energy of a 100kg cyclist+bike going at 40 km/h (plausible if you want to brake at the end of a downhill), you want to store:
0.5 * 100 * (40/3.6)^2 = 6170 J
...
- 20.5k
21
votes
Accepted
Why do front gears become harder when the cassette becomes larger but opposite for the rear ones?
What makes a combination hard is the ratio between the size of the front sprocket and the rear one (front divided by rear). The higher this ratio is, the harder the combination is.
To make the ratio ...
- 22.8k
16
votes
Do ALL non-instantaneous deceleration events transfer weight to front wheel?
There is no need for all forms of deceleration to transfer weight to the front wheel, although it is in practice usually the case due to how forces are commonly applied to a bike. The tendency of the ...
- 758
15
votes
Accepted
Healthiest bike posture for slower long rides
If you are looking for the most ergonomic riding position, you should give some kind of recumbent bicycle a serious consideration.
I don't have any references to data, and soreness is subjective. But ...
- 356
15
votes
Accepted
Would a heavy fork cause problem when climbing?
Weight anywhere makes climbing harder.
Weight over the front end is somewhat beneficial when on a steep climb, because it helps give the front wheel traction, which helps with steering and balancing.
...
- 129k
13
votes
Why do front gears become harder when the cassette becomes larger but opposite for the rear ones?
An example with numbers: Let’s say the chainring (front sprocket) has 40 teeth and your currently selected cassette sprocket in the rear has 20 sprockets.
For every turn of the chainring the chain ...
- 28.8k
12
votes
Infeasibility of a mechanical wind-up spring KERS (Kinetic Energy Recovery System) for bicycles
The idea looks nice at first glance, but the deeper you get into the details, the less attractive it becomes:
You need to be able to modulate your brakes. As such, you need some transmission between ...
11
votes
Why do front gears become harder when the cassette becomes larger but opposite for the rear ones?
Renaud's answer succinctly covers the gear ratio part of your question, so I'll address the gear shifter part.
To start from basics, bicycle chain-based transmissions "change gears" when ...
- 16.9k
10
votes
Healthiest bike posture for slower long rides
I haven't been able to find any scientific papers that focus on distance riding that don't also focus on performance (I also haven't been able to find any where the full text is available for free, ...
- 30.4k
10
votes
Accepted
How does biking speed correlate with the required effort?
The simplest physical model gives that the energy is proportional to the square of the speed but in that model maintaining a constant speed requires zero energy.
This is a slight misstatement. If you ...
- 35.2k
10
votes
Accepted
When does the braking power stop scaling with Rotor Size
"wouldn't that be fundamentally limited by the friction between the ground and the rider" - no. The most common limit is the rotational force from the torque generated between the ground/...
- 52.3k
9
votes
Does a fat tire ride softer than a skinny one at the same pressure?
After reading the answers here and becoming more curious, I found this article, which agrees with @Daniel.
to briefly summarize it, they found that at the same tire pressure the narrower tires ...
- 1,981
8
votes
Why are emergency inflation cartridges filled with CO2?
This explains part of the reason in what may be too much detail:http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch4/deviation5.html
If you're going to read any of it, read the material starting ...
8
votes
When does the braking power stop scaling with Rotor Size
While other answers are correct in their assessment of peak braking power and its limits, that's not the most significant reason for fitting bigger rotors in many cases. Sustained braking power is a ...
- 61.2k
7
votes
Why do front gears become harder when the cassette becomes larger but opposite for the rear ones?
And finally I'd like to address the third part of your question, if I understand it correctly: Why do the large chain rings in the front grow from the inside out (the outermost chain ring is the ...
- 1,747
6
votes
Accepted
CdA of a bike without rider
There are, but measurements typically will be protocol-dependent (and vary slightly between different wind tunnels).
For example:
Here is a link to a comparison done at the A2 Wind Tunnel in North ...
- 14.2k
6
votes
Accepted
Does changing gear relation produce different speed at same applied power?
Yay! Another physics question.
Restating the question: if the rider power input is constant, does the bicycle velocity change if the drive-train gear ratio is changed?
Let's assume the road surface, ...
- 75.9k
6
votes
Why do deep section front wheels get pushed around in crosswinds?
The answer to your title question is "moving air exerts a force on obstacles", and deep section front wheels have more area affected by side winds so there's more force.
In any crosswind there will ...
- 23.6k
5
votes
Accepted
How fast can a cyclist accelerate from a standing start?
The power-drag equation is well-understood if not widely-known, and is discussed in this bicycles.SE answer. In particular, the drag equation shows the component for changes in kinetic energy, viz., ...
- 14.2k
5
votes
Infeasibility of a mechanical wind-up spring KERS (Kinetic Energy Recovery System) for bicycles
Part of what makes bicycles attractive is their simplicity. The simple frame-sprockets-chain-wheel with a few ball bearings in between, plus two simplistic brakes, is making the entire system light ...
- 1,747
4
votes
Dynamic stability of a tricycle
The bicycle is a deceptively simple machine. The physics behind bicycles is actually quite complex, with multiple forces interacting to produce self-stabilizing behaviour (i.e., ghost ride a regular ...
- 30.7k
4
votes
Accepted
Does a fat tire ride softer than a skinny one at the same pressure?
To make it stupidly simple, assume that the tire has a roughly rectangular cross-section. So a 1-inch tire is 1 inch across has a width of 1 inch in contact with the pavement, while a 4-inch tire is ...
- 53.9k
4
votes
Counter-intuitive steering in crosswinds with hands off the bars
If the wind is from the left, you need to lean to the left to stop the wind blowing you over to the right; leaning left makes you turn left.
- 17k
4
votes
CdA of a bike without rider
Just to add another reference / data point, this image is from an aerodynamics course presentation by Bert Blocken of Eindhoven University of Technology. In it he references wind tunnel test results ...
- 2,455
4
votes
Why does shifting under power affect shift quality?
There may be other factors that affect "shift quality", if I understand what you meant correctly, but the most significant by far is “direction of force applied.
Basically for a gear to change the ...
- 141
4
votes
Accepted
Is a bicycle wheel an indeterminate structure?
A bicycle wheel is a complicated structure. Take a spoke in a wheel for example. The spoke is statically indeterminate because it's not mounted to the rim with some sort of bearing; instead it's ...
- 2,651
4
votes
Why do front gears become harder when the cassette becomes larger but opposite for the rear ones?
Another thing I always wondered was why the gear shifters on each side
seem to be opposite to each other as well. On a road bike, there is a
"large shifter" and a "small shifter". ...
- 548
4
votes
When does the braking power stop scaling with Rotor Size
Just as a foundational thing, brakes work by applying a torque to the wheel, which is defined as the applied force multiplied by the distance to the pivot point. The pivot in this case is the wheel ...
- 16.9k
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