3

I have an exercise bike with a computer and it looks like 100 revolutions of the pedals is 430 meters, this seems like a lot.

I was wondering if there is a good number for converting pedal revolutions to meters.

I figured that without gearing the average bike wheel is 26" (0.66 M) and so the circumference of the wheel is

0.66 * PI = 2.07 M

In this instance one rev is basically 2 meters. The bike's computer seems to think one rev is 4.3 meters.

I really don't know where they get these numbers from and I am trying to make more accurate measurement of my exercise but the computer on the bike shows made up distance figures, calories etc...

1
  • 2
    Even on an un-geared bicycle, I think you would find that one revolution of the pedals isn't the same as one revolution of the tire. That could only be true if the gear on the pedals were exactly the same size as the gear on the wheel, which in my experience the gear on the wheel is always significantly smaller than the gear on the pedals, especially on an "un-geared" bike. Jul 2 '12 at 15:47
3

It depends on what the force is that you are applying to the pedals, and the resistance that the bike is giving you. For a regular bicycle, it's a function of what gear you are in and the tire size. 4.3 meters per pedal revolution isn't in the realm of silly.

The best thing that you want to find on an exercise ergometer is one that measures in watts. Because of various inefficiencies in the human system, watts can be pretty much converted straight over to calories. To find out calories, take your average watts, multiply by time in seconds, then divide by 1000.

So, if you average 150 watts for 1 hour, you would get (150*3600) / 1000, or ~ 540 calories.

1

You are looking for accurate distance measurement. Almost all stationary bikes, either traditional or spinners (more like an outdoor upright bicycle, but with an awkward method of determining resistance -- which would be a combo of elevation and wind resistance) will tell you distance. The calculation is probably very particular to your model of bike or recumbent cyle.

If you wish to measure everything yourself, it's going to be very difficult unless you take your bike apart, revealing the size of the pulley wheel, which is often restrained by a very small wheel that is actually a brake, and all are connected to computer wires that go straight to the bike console.

The bike connects wires to all of this and if you're lucky, they go to a male port which will allow you to plug it into the upcoming (2017) Wahoo "retrofit" device which will upload to an app, and you can then import the data into your favorite fitness app. This will likely give riders more accurate information. Or that's the idea, anyway. But do be careful: I have a 9-10 year old stationary bike that still works well. I don't want break anything.

But, if what you mainly want is a speed sensor, they are available from Garmin, Polar, Wahoo, and many others. They generally need cadence information to work most accurately. Cadence sensors are cheap and can attach to your shoe! Very easy. The speed sensor needs your wheel circumference because cadence is not the same thing as speed - a speed sensor, in concert with other information, will literally tell you your distance - how far you've traveled..It may be in your manual and if not, you can take one of the plastic shields off your traditional exercise bike and try to attach it. It probably won't fit. You might be able to attach it to the front spinner wheel, but that won't be easy because it's so thin: you need a hub, as on an outdoor bike. This combo will give you fairly accurate distance information. Most bikes have a console that does this for you, but the accuracy of dedicated sensors is much better. That's well-known. I have to use the bike console for mph, and I am unsatisfied with its accuracy. Also, w/out a wattage meter, calorie count is usually way off: I let my app tell me. It's based on something called "Corrected Mets" and it's generally considered accurate.

The trouble is that all these sensors may be expensive for most people at home, as are aftermarket wattage meters. Gyms will have all of this technology, but not the convenience of having your own equipment.

Getting a single revolution is a difficult task for any indoor bike, and not even a lot of fun on an outdoor bike. But if you need this information, you can pull it out.

Much luck!

0

A stationary bike can only give you an rough estimate of how far you might have gone on a real bike for a similar effort. This includes assumptions regarding your weight, gear length, wheel size, how aerodynamic you might be, etc ... It also can't account for wind resistance (which increases as the square of your speed when you actually move), road gradient, drive train efficiency.

A standard road bike using 700c wheels, 25c tyres, and a compact crankset (50:34 chain rings, 11:28 sprockets) has a development range of between 2.6m and 9.6m per crank revolution. You can calculate those using bike calculator. So your 2m are actually at the low end of a road bike range.

A better indication of your effort, which stay more consistent between real bikes and stationary trainer is power. Most modern stationary bike can provide reasonably accurate power number based on how fast you are spinning their resistance unit. This blog give you an indication of how you can convert average power into calorie expenditure using a simple formulae energy (kcal) = avg power (W) X duration (hours) X 3.6.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.