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9

The main thing you have to consider at speed is drag: The force F on you+bike (mass m) is: F = ma = mg sin Q - F_d - F_rr where a is your acceleration, g is the acceleration due to gravity and Q is the hill angle to the horizontal. F_d is the drag force which doesn't scale with mass. Try dropping a balloon and a (soccer) football of the same size and ...


6

I want to use the bicycle for the 26-30mi commute that I do everyday and if it is a racing bike it could potentially save time A trained cyclist can definitely ride farther and faster on a road bike than on a hybrid bike, based solely on wind resistance and bicycle fit. However, the speeds you list are completely unrealistic. Bike speeds are based ...


6

Guy Martin is obviously a decent cyclist, but you should note that his record-breaking ride occurred under very special conditions. For starters, he built his own frame (or rather Jason Rourke built it for him). Next, he chose exactly where the run would take place - on sand flats. And not least he was towed in order to get up towards top speed, which ...


5

There are various gearing calculators available on the web. Here is one of them: http://sheldonbrown.com/gears/ The top possible speed will depend on your gearing, wheel size, and max cadence. Of course, your ability to reach that theoretical top speed will be limited by your own strength and fitness.


5

As you might expect, the exact down slope you would need for a full answer will depend on how much drag you and your bicycle produce. If you are very aerodynamically efficient and there are few losses through the bearings and tires, the slope can be shallower. If you create a lot of drag either via aerodynamic inefficiency or mechanical and rolling ...


4

The two major "drags" on a bike, on level ground, are the rolling resistance of the tires and the wind resistance of the bike and rider. In general, up to a point, a tire with higher pressure will have lower rolling resistance, as will a tire with a smoother tread. Tire width also figures in, but mostly in terms of how it influences pressure and tread. ...


4

Some of the physics are simple. To move an object of mass m up an incline requires an amount of work proportional to the weight. This is the mass times the gravitational acceleration times the displacement W = m g d. So for the heavier bike it requires more work. It also requires more average power to lift it over the same rise in a fixed set of time. But ...


4

The Varna, which was one of the best bikes in 2003 has speed + power graphs up from their Battle Mountain runs that year. At 80kph Sam was putting out about 225 watts, but accellerating. There's also a 0.5° slope to consider. This article suggests that the bike uses about 150W at 50mph/80kph. Sam weighs about 80kg, the bike about 25kg. Let's call it 110kg ...


3

Any half decent touring or racing bike can do the speeds you noted, however, a more practical value for commuting is ~10-20 mph, on flat terrain. I'd recommend a touring bike for the purpose, rather than a racing bike for all the reasons noted previously. They have slightly wider tires and sturdier frames. The first leads to a somewhat less bumpy ride, the ...


3

Usually, when you want to commute somewhere, you have to carry things (a rack+panniers are good for this, esp. if you carry laptops), you don't want to arrive in a pool of sweat (and you need a change of clothes on hand anyway) and you want to arrive comfortably (cause you should be productive at work). These are all the opposite of what a racing bike is ...


3

It's not about energy to accelerate the bike to speed, but the energy to keep it there. For bicycles the kinetic energy is a small part of the total power output of the rider (typically under 10m/s = 36km/hour and 100kg, and e=1/2 m v² = .5 * 100 * 10² = 5000J or watt-seconds. So a casual rider putting out 250W could reach 36kph in 20 seconds, assuming no ...


2

If you're just riding around the city, stopping frequently, and even expecting your dog to run along side, a Pashley bike will go "fast enough". Step-through bikes are intended expressly for that kind of riding. The only consideration I would give to gearing is whether or not the gearing is LOW enough for the types of hills that you'll encounter. If, for ...


2

I found driod support for these kinds of sensors to be patchy at best and not yet what I consider ready for prime time. Manufacturer provided software is often crap, third party often don't support the hardware. Many claims of features and devices suppported apply to the iPhone versions only. I current use Digifit iCardio on my driod phone with Scorche ...


2

Most speedometers are accurate as long as you input/set the right wheel size! I have used very cheap ones, and they allow me to set the wheel size in milimeters, and after checking the same path with two different cars, the difference is minimal compared to what I had with the bicycle (in a 25Km ride the difference was only 10 meters compared to the cars). ...


2

I don't think accuracy is a problem, even with cheap ones. I tested my first one (cheap chinese) against Google Earth and the marks on the road (every 100 m) on a paved straight road over a 15 km ride, and the differences are minimal. Cheap models only let you specify the nominal wheel size in inches. Better ones present a list with all relevant wheel sizes ...


1

Android can just about handle multiple BTLE sensors simultaneously but there are still some low level Android bugs that make it rather unreliable. The coding for is also a good bit more complex to get working than the single sensor case. I have support in my app IpBike via a beta version of IpSensorMan At this point in time if you were getting new then an ...


1

I assume we're not talking about some low-price, no-name thing from a Walmart sale but about one from one of the more common speedometer selling companies (cyclosport, sigma, garmin, to name a few). With those, I don't think that there will be significant differences in accuracy. Also wired vs. wireless should not make a difference by itself (unless the ...


1

In a practical sense, increased weight will make you go downhill faster, for the same reason decreasing weight will make you go uphill faster See this interactive calculator. If you set the gradient to "-10", set "Power P (watts)" to 0.001 (i.e almost zero): With rider weight set to 50kg you will go about 59.54km/h With rider weight set to 75kg you will ...


1

This may be half-remembered physics coming into play here, but I've raced (substantially heavier) friends down hills where they've been on bikes which should - be all accounts - be slower than my own, yet they've won. Could momentum come into play over rougher terrain? By that, I mean if a rider carrying a heavier weight were to hit a bump, or hole etc, they ...


1

The short answer is yes. See Chris's post for the long answer. The main reason for this "answer" is to encourage great caution. As a teenager (in the previous millennium), I grew up in hilly area. There were two descents we used to do regularly - a two mile run from my friends farm to home, and a steep hill of one mile. My best time to get home was 2:11, ...


1

If there were friction it'd be the exact same (remember the hammer and feather on the moon deal). However - your net drag isn't really going to be proportional to your mass. The air resistance isn't proportional at all to your mass (although the rolling drag is). Due to this, you'll have less drag per kilogram with more weight which will cause you to go ...


1

For the first question answer is «Not». The problem is air resistance, starting from 40-45 km/h it's like a wall. For every addition to you speed you'll spend more and more power. For the second — 50 km/h (and even more) is a normal speed for descents on a road bike. This bikes is pretty controllable on such speed.


1

This page is incredibly useful for figuring this stuff out. Campy shifters with just about any front derailleur should be fine since they have micro trim. http://en.wikibooks.org/wiki/Bicycles/Maintenance_and_Repair/Gear-changing_Dimensions#REAR_SHIFTING_TABLES


1

I'm not sure if this is a "legal" answer since it involves upgrading you as well. I highly recommend getting cycling shoes if you don't have it. It's almost a direct conversion of money to performance with minimal additional effort.



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