# Questions tagged [physics]

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### Does changing gear relation produce different speed at same applied power?

When you are starting the ride, I potentially believe ("know?") that with a smaller plate(cog with fewer teeth in the rear cassette), you obtain more velocity than with a bigger plate(cog with more ...
28k views

### How do I calculate the power required to climb a hill at a given cadence?

Suppose I ride at a cadence of 50RPM for 10 minutes with a 39x23 gear ratio on a hill with 10% grade. Is there a simple formula to calculate the power output required?
9k views

### Why are emergency inflation cartridges filled with CO2?

Why aren't they filled with ambient air using air compressors? Isn't compressing ambient air cheaper than generating CO2? If it is, then those cartridges would have two benefits: Cheaper to ...
127 views

### Understanding science of speed difference between two bikes

I have two MTBs and one is slower than the other. Bike1 has Deore derailleurs and a double chainring with 10 sprockets and Shimano hubs. Which has a great speed irrespective of the gear combination. ...
108 views

### Counter-intuitive steering in crosswinds with hands off the bars

It should not be surprising that it is difficult to ride in a straight line with both hands off the handlebars when there is a crosswind. However, I find it most unintuitive, that for example if ...
403 views

### CdA of a bike without rider

This question at aviation.se got me calculating the acceleration of a bike strapped to the outside of a plane if the straps broke. As you do. I couldn't find a figure for CdA of a bike without rider ...
190 views

### Is a bicycle wheel an indeterminate structure? [closed]

Does anyone knows whether a bicycle wheel is a statically determinate or indeterminate structure?
324 views

### Why does shifting under power affect shift quality?

I recently was attempting to shift up a hill and observed that The shifting levers on the handlebars displayed significant resistance to my pushing them. Despite several rotations of the crank, the ...
496 views

### Maximum Descending Speed

This is a hypothetical question but I'm curious. Assuming an endless, freshly paved road with no turns, what would be my maximum speed? EDIT My question is too general so to help I'm adding some ...
403 views

### Factors Involved With Tire Wobble When Riding Without Hands

I recently upgraded road bikes from a heavy one (25lbs+, 25mm) with thick tires to a very light one with skinny tires ( 16 lbs, 22mm ). One thing that changed noticeably was the loss of the ability ...
942 views

### How much does wind affect the speed of a professional cycling peloton?

It's a well known fact that due to air resistance increase of speed on a bike takes non linear increase of power, so the huge marginal increase of power needed to go faster while riding at around 40-...
656 views

### Why do deep section front wheels get pushed around in crosswinds?

If a bike with a deep front wheel or a front diskwheel were to receive crosswinds with a 90 degree yaw angle handling would not be affected since the pressure would be equally distributed among the ...
1k views

### Does a fat tire ride softer than a skinny one at the same pressure?

Fat tires are associated with good bump absorption. Is this due to their fatness, or is it due to the low pressure with which they can be used? If I pump a fatbike tire to 120 psi (yes, that would be ...
3k views

### If I attached a “pointy” pool noodle to my bike, would it make me safer even from sadistic drivers?

A few sources suggest that mounting a foam pool noodle on the back of your bike can help stop drivers from passing too closely. Such noodles are available at my dollar store, unlike spring-loaded bike ...
15k views

Someone suggested going with a 700c wheel to go faster, and after thinking about it I am wondering if a larger wheel actually does go faster. I understand that your gears will cause a wheel to rotate ...
17k views

### What makes a bike stay upright when moving?

What makes a bike stay upright when it is in motion? What is the relationship between speed and stability? Is it a linear relationship? I could ask this on the physics site however I am hoping ...
964 views

### Dynamic stability of a tricycle

I'm currently designing the "electric bike of my dream" (please do not laugh! it's for fun, nothing serious), and I came up after some though with a tricycle, where 2 rear wheels are supporting the ...
1k views

When turning sharp at high speed, does it make sense to shift the weight to reduce risk of skidding? I do not see the point of doing so. Both wheels are leaned at the same angle against the ground no ...
152 views

### Does it takes longer to cycle a route with a mountain on it comparing to the same distance without a mountain? What is the cause of that? [duplicate]

Imagine you cycle 100km. On one route there is a mountain 100meter high on an other route is not a mountain but a straight way. Usually it takes longer on the route wiht a mountain. One reason for ...
1k views

### Where does the energy loss in cycling go proportionally? [duplicate]

If you are biking on level ground with no wind, I understand that there are losses inherent in your activity which you provide effort to overcome (if you want to maintain a steady speed): Air/wind ...
640 views

### Is contact patch area governed by A=W/P

contact_patch_area = weight / tire_pressure Is this true? Wikipedia says "mostly". This guy analyzed some automobile tire manufacturer, and although the info was self-conflicting, he concludes ...
2k views

### Riding into a headwind faster than my top speed - how is it possible?

Recently we've had some pretty strong winds here -- today the weather forecast said 20mph gusting to 30mph, but a few weeks ago the gusts were supposedly over 40mph. The forecast direction was within ...
2k views

### Why do skinny tires require less pedal effort?

Everyone knows (citation needed) that (at fixed rim diameter) tyres with smaller section require less effort to move around (at least on a paved road). TL; DR. Why? A bit of context. I always ...
3k views

### What does a cyclocomputer actually measure for calculating the speed of the bike?

What does a cyclocomputer actually measure for calculating the speed of the bike? Is it the time for one revolution \$T\$ or is it the number of revolutions \$n\$ per given time \$t_0\$? If the radius of ...
335 views

### Descending without braking: where's the sweet spot?

This may get too math-heavy, but it seems that only a few variables are needed to estimate the optimum slope to descend without gaining/losing speed. I looked around, but wasn't able to find anything ...
986 views

### (racer) Standard vs compact crankset: Increased leverage for same gear ratios true?

I'm a road and mtb regional racer about to have a go at my first road endurance nationals very soon. I'd like some educated scientifically validated answer on a matter that has been on my mind ever ...
238 views

### why does the lemond revolution turbo trainer quote its volume of air resistance in meter^2 and not per second cubed?

The Lemond revolution states that it creates consistent aero resistance with its fan power from 0 newtons to 40 newtons along one axis and 0 to 160 meters/second^2 on the other axis. Since air flow is ...
11k views

It would be nice to be able to estimate the grade of a road while riding, even if the estimate is not completely accurate. With a GPS, in theory it should be possible in theory to ride a short ...
2k views

### Is a bike faster than a car for the first ten metres? [closed]

The city I live in has just installed cycle boxes in front of traffic at light controlled intersections. This has spark a lot of debate online. My experience is that I will generally, through timing ...
3k views

### Approximately where is the center of mass of a mountain bike?

Take a "standard" multipurpose bike like this one: http://www.islabikes.co.uk/bike_pages/beinn29.html (Weighing 12.2kg) I'm conducting a physics investigation, and for this I need to know the ...
2k views

### What is the effect of adding weight to a wheel vs adding it to the frame?

There are claims often made that, eg, "An ounce of weight at the rims is like adding 7 ounces of frame weight." This is "common knowledge", but a few of us are skeptical, and our crude attempts at ...