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| *Vultures Knob>>>Mountain Bike |
As a ratio, how much faster is a road bike than a mountain bike? |
Let's simplify this one; I realize that there are different grades of bikes, different tires, different frames, etc. But if I average a certain speed on an average mountain bike on a paved surface with typical knobby tires, can I expect to go twice as fast on an average road bike with typical smooth tires? Or 1 1/2 times as fast? What's a good ballpark figure? 200 watts will do around 17.8 mph on a MTB and 21.2 mph on the road bike (drops). About 19% faster . Slightly higher with less power and a bit lower with more. Here is an on-line calculator. Have a play around with it. You can see the effect of changing your wheels too. http://www.kreuzotter.de/english/espeed.... Look sorry about the distraction here but I'm sure if you play around will the calculator, you will find that if you ride a mountain bike at 15-20 mph around 19% increase in speed will be attained on the road bike. Sounds like a lot but it is only in the order of 3-4mph. P.s. Force is porportional to speed squared i.e. twice the speed four times the force Power is proportional to speed cubed i.e. twice the speed ,Eight times the power (you have less time to apply the force) PPs Gee I like these ones. Thanks for the opportunity power for rolling resistance = total mass x gravity x coefficient of rolling resistance x speed. (This part is linear i.e.twice the speed twice the rolling resistance) Power for wind resistance =.5 x coefficient of wind resistance x density(kg/msqr) of air x frontal area (m sqr)x speed(m/s) x speed(m/s) x speed(m/s) (This part, the major portion, is porportional to speed cubed) Both rolling resistance and wind resistance contribute to total power consumption Since most of the improvement From mountain bike to road bike is from reducing frontal area and drag coefficient it is almost a straight percentage improvement. "Note that the power needed to push an object through a fluid increases as the cube of the velocity. A car cruising on a highway at 50 mph (80 km/h) may require only 10 horsepower (7.5 kW) to overcome air drag, but that same car at 100 mph (160 km/h) requires 80 hp (60 kW). With a doubling of speed the drag (force) quadruples per the formula. Exerting four times the force over a fixed distance produces four times as much work. At twice the speed the work (resulting in displacement over a fixed distance) is done twice as fast. Since power is the rate of doing work, four times a work in half the time requires eight times the power. (Cut and paste from )http://en.wikipedia.org/wiki/wind_resist... Put simply power = force x speed This is the way my world works. Simple physics Flywheel effect and momentum only contribute during acceleration. Oh and 2 squared =4 and 2 cubed = 8 Hope someone finds this educational. And welcome to my planet. Source(s): http://en.wikipedia.org/wiki/wind_resist... And pretty much anywhere else you care to search the fomula for wind drag. I have never ridden a mountain bike but when I went from a hybrid to a road bike I increased my speed by 2 miles an hour. I don't think twice as fast would be possible unless you were really slow on the mountain bike. Road cyclists typically avg between 16 - 20 mph. You could probably avg 10-18 on a mountain bike but it's about conditioning too, what kind of shape you are in. Endurance/distance cycling is different the mountain biking but the other day I was going along a paved trail doin about 18 on my road bike & a dude on a mountain bike zipped past on the single track alongside me. So I don't think there is any particular formula to calculate how much faster you can go. My guess would be you could go about 4-5 mph faster. You're asking about your power output vs work done. To rephrase your question: Given the same power output on the same course, how much faster is a road bike than a MTB? Still a tough one to answer, but not nearly as big a difference as it sounds like you're hoping/suspecting. If you are putting out enough energy to move your MTB at 20 MPH, then the same amount of effort might get you 22 MPH on the road bike. That's just a guess though. There are way to many variables involved to give a straight answer on this. For example, Riding a bike is subject to a physics phenomenon known as the 'square law effect'. It doesn't take twice the power to go twice as fast, it takes the _square_ of the power. If 10 watts gets you 10 mph, it takes 100 watts to go 20 MPH; 10,000 watts to go 40 MPH. For the sake of example then, lets say this ten watts gets you 10mph on the mtb and 12 mph on the road bike. Then, 100 watts will get you 20 MPH on the MTB and 24 MPH on the road. Throw in other critical factors like your body weight, your position on either bike, let's just say that you will go faster on a road bike that is properly set-up than a mtb given the same power output, and leave it at that. How much faster is something you'll have to figure out on your own. Hi, I ride both Road and MTB. This is just my experience, but when I climb my Road bike on the same (paved) hill that I ride on my Mountain Bike on, I can climb that hill in half the time on my Road bike than on my MTB bike. I can feel the drag of my tires, the compression of my front /rear shocks and the xtra weight of my Mountain Bike when I pedal. I jump on my Road bike and it is like night and day difference. On the other hand I was climbing my Road bike on the same paved hill and my buddy on her 25lb. XC Mountian Bike passed me and pulled away from me! I am your average rider, but she is a very well conditioned racer. It depends on your conditioning, but the average person riding a Road bike is probably 1/3 faster on hills and the flats that an average person on a Mountain bike. IMO Ballpark? How about 30% faster. If you take all the important, necessary variables out of the calculations, you're only going to get an estimate and any figure is worthless. Put it this way- I usually average about 10-12mph on my mountain bike, and 15-17mph on the road bike. Again, your mileage may (and will) vary. uh, not too sure which time space dimension glennP went to school in, but it ain't the one this planet resides in. "force is porportional to speed squared i.e. twice the speed four times the force" This makes no sense mathmetically. You're saying first that F=SS, then 4F=2S. These two equations do not reconcile. Not only that, but your 'example' (i.e.) shows the relationship as linear. It is not. The same goes for your power theory. You're saying first that P=SSS, then 2S=8P. That dog don't hunt. Besides, the idea that need to cube the power in order to double the speed is completely ridiculous, unless you're riding under water. You can't really answer this question in terms of force anyways. Force has no time component. Power is defined as the force applied times the displacement, over time. This gets complicated since you need to extrapolate vector forces of gravity with drag caused by rolling resistance and wind resistance. This is why all of these studies are done in terms of power in units of watts which accounts for how fast something gets done. Using the link you provided, changing nothing but speed, and using all other default parameters, 10mph requires 38 watts, 20 mph = 172 watts, and 40 mph = 1115 watts. Clearly, this is NOT a linear relationship. Something is still amiss tho. The exponential relationship of the three values should be linear - but they are not according to the numbers on the page, though this may due to some other factors involving flywheel effect or momentum. |
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