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20

Physics! Landing big jumps is all about dissipating the inertia that pesky old gravity has created on your trip back to earth. The better you dissipate that inertia, the better the chance that you wont kill yourself. There are several factors in play here: The Transition of the Landing.The landing is almost always sloped downwards. Combine forward momentum ...


18

This question was recently the subject of a lengthy article in New Scientist magazine. To summarize: "Why does this bicycle steer the proper amounts at the proper times to assure self-stability?" the paper asks. "We have found no simple physical explanation." http://www.newscientist.com/article/mg21028141.700-bike-to-the-drawing-board.html This ...


15

The increased weight of the larger wheel (if indeed it does increase) will of course add weight to the bike, but additional weight adds very little rolling resistance (though it does of course affect hill climbing). It is a myth that "rotating mass slows you down". In terms of top speed there's no difference between weight on the wheel rim and weight ...


13

Get an inclinometer. They're not particularly accurate, but readout is instant and the price is right.


12

The answer is "both, depending." The majority of current bicycle cyclometers use a reed switch and timer, and measure the time between successive triggerings of the switch as a magnet passes by. An advantage of this method is its simplicity and low cost, though if the magnet is ill-positioned or if the rotational speed of the wheel is too high, the reed ...


12

Assuming you want the center of gravity of the bike alone (not with a rider), there is a very simple procedure you can perform yourself, as long as you have some bike (you could borrow one): For simplicity, strap the front wheel to the down tube of the bike, so the handlebars won't turn; You could also strap the brake levers in the "full braking" position; ...


10

Most of the Garmin Edge series GPS cycling computers can display grade. The Edge 500 and Edge 800 (not the Edge 200) have barometric altimeters to determine altitude. You can then change or add a display data field to show the current grade. Funny you ask as I just put added the grade as a display field this morning on a hilly ride. It updates the grade ...


10

The three-foot extension noodle is absolutely obnoxious and a genuine safety hazard (for starters, how is another cyclist supposed to safely pass her?). The original point of these noodles, as I've seen them, is to cut one as wide as the widest part of your bike so cars could better gauge how much distance they needed to pass you. Perspective distortion and ...


10

Bike geometry provides some degree of self-stability. The angle and rake of the fork produce a situation where the front tire will tend to turn into a lean, and so correct a tendency to fall to one side. The gyroscopic effect of the wheels by itself is likely not that strong, but the gyroscopic effect on steering works with the angle/rake of the fork to ...


9

The answer I got was 2x -- adding one ounce (or gram) to the wheel at the outer diameter (ie, the tread) is equivalent, in terms of force/energy needed to accelerate, to adding twice that amount to the bike frame. The answer was a bit involved and takes careful reading to fully understand, but the answer can also be explained with this thought experiment: ...


7

Bicycles are inherently stable because of their geometry. The geometry causes the bicycle to always turn into the direction it begins to lean, which keeps it upright. The reason is best illustrated through a concept known as counter-steering. Counter steering is how all two wheel vehicles turn. When you want to turn towards the left, you turn the handlebars ...


6

The biggest factor in bike stopping distance is the mass transfer towards the front of the vehicle when braking. On an upright bicycle, the limiting factor in how hard you can brake is the point at which the front wheel goes from slowing you to simply throwing you over the handlebars. As you brake, your center of mass shifts forward, lifting the rear wheel. ...


6

You don't quite supply enough information in your specific question (that is, "50RPM for 10 minutes with 39x23 with 10% hill") to provide a full answer in absolute terms but, if we assume you're riding a standard sized 700c bike there's enough information to make a good estimate in relative terms. First I'll give a short answer, then a rule of thumb that's ...


6

You are going at constant speed when the driving force from gravity Fg is equal to the drag (air resistance) Fd plus friction (rolling resistance) Ff: Fg = Fd + Ff When coasting down a hill, the driving force is the component of the gravitational force parallel to the road: Fg = m g sin(a) Here, a is the slope (angle with the horizontal), m is the mass ...


5

Think of a cyclocomputer as a hardwired combination of a calculator, a quartz-clock, and a dedicated CPU working with a buffer. EDIT TO A MORE PLAUSIBLE ALGORITHM: Each time the magnet closes the reed-switch, a request is sent to the clock to capture a time-stamp, a time-stamped event is sent to a buffer, and the wheel circumference is added to the current ...


5

The answer is simple but the explanation behind the answer may be instructive. The simple answer is: the x-axis label should be read as (m/s)^2, not m/s^2. The longer explanation is related to this bicycles.stackexchange answer. The power needed to ride at steady speed on a flat road under calm wind conditions is Watts = Crr * kg * g * v + 0.5 * rho * CdA ...


4

Another approach is roughly guestimate the CM, then tie 3 short cords to 3 points each roughly 120 degrees apart in a rough circle. Tie the other ends of the cords to a ring or whatever and hang so the bike is essentially on its side. Adjust the 3 cords on the ring -- looser or tighter -- until the bike hangs perfectly level. The central rope will then be ...


4

Cell phones, usually not. Some applications will attempt to massage the data using elevation information provided from third-parties, but its a crapshoot at best. A dedicated GPS with a barometric altimeter is probably your best bet. I can't really speak to their level of accuracy, but it's certainly better than other practical options. If you just want ...


4

You mentioned KINETIC ENERGY, which obviously have to go somewhere. Sometimes you have reception, and the bike comes at speed, but sometimes, like in bike trial, the bike lands "flat" on plain concrete. Sometimes, too, freeriders land on flat concrete at speed, and at least the vertical component of the drop's kinetic energy disappears. I would say there ...


4

Your question really seems to boil down to: Is using such a noodle illegal? What are possible outcomes if a driver still passes me too close? My answers to this; We don't know. This is something that most likely will be dependent on the laws of your country. So I would suggest you to find out something about "allowed transport techniques on a bicycle" ...


4

Drag increases with speed. Drag is both rolling resistance and wind resistance. A steeper slope is more gravitational pull. Terminal velocity is when the gravitational pull equals the drag. On a mild slope it will be only a few miles an hour. On a very steep slope it might be over 50 mph. A 7% slope is around 20 mph on road bike on a road.


3

Wheel size is a trade off. In some ways, you want the wheel as small as possible, in other ways you want the wheel as large as possible. There is no "right" size really, except that it's handy to have the same size as everyone else so standards have risen up. The benefit of a smaller wheel is they are cheaper (less materials to make them), they have less ...


3

Others have already discussed GPS and GPS-enabled phones, altimetric barometers, and inclinometers. Bubble inclinometers (such as the Skymounti shown elsewhere among the answers) can be affected by acclerations so to get the best readings you should be stationary. dGPS (differential GPS) is used in surveying instruments to measure grades, but these are ...


3

Its like balancing a broom on you hand, you steer to move the wheels under you. Bike manufacturers help by designing the steering geometry so that the bike will stay upright on its own, if you don't mess with it. The gyroscopic forces help but are not essential.


3

You can use the calculator at http://bikecalculator.com, which will give you a reasonable estimate if you know the average grade of the hill, the day's temperature, and the wind speed/direction (probably not so relevant on a hill). A similar calculator is here so you can compare two methods. The website http://www.cyclingpowermodels.com has a host of ...


2

Theoretically, you could only measure power with a specialized instrument, usually an electronic (and expensive) torque meter embedded in a custom crankset or rear hub. For the state-of-the-art about this, take a look at http://www8.garmin.com/train-with-garmin/power-meter.html. It will point you a lot of other links on the subject. If you want, like your ...


2

Talking about science, there are two factors here: moment of inertia - smaller and lighter cogs in a compact crankset mean smaller moment of inertia, which in turn means that you need smaller force to obtain the same acceleration. In this aspect a compact crankset gives a slight advantage. Note: this parameter is practically insignificant when it comes to ...


2

While it's true that a larger chainring will have slightly less friction and thus slightly more efficiently, it's an extremely negligible amount, that you wouldn't be able to feel. More importantly, are your crankarm lengths different on the new crankset than the old? That makes a much bigger difference. For example, if you've went from 175's to 170's, that ...


2

In almost every slope you will hit a speed "sweet spot" where the gravity pull and drag from the wind will cancel each other out, this can be at 70 km/h for a 8% slope in aero position or 15 km/h for a 2% slope on an hybrid bike.


1

It's a size versus distance thing. You are lighter and so your acceleration has a more immediate effect (and I'm sure some physicist will tell me I'm wrong on the cause...but this is how my memory stored in when I took junior high physics MANY years ago). For a short distance you should win if you can come off the line in the right gear and at the right ...



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