I appreciate all of the comments on the previous post which discussed what those kcals were.  Let’s continue with another number often found on our indoor bike computer (and other fitness equipment) - TRIP or Distance Covered.

Looking at your total distance number at the end of a cycling class can often provoke 2 very different responses: “Oh, that’s cool” and “No Stinkin’ Way!”.  Someone who doesn’t do much riding outdoors may not have a perspective on (1) how fast they would actually be riding and (2) how far they could go in, say, an hour. This rider may see a TRIP number of 20.0 — 22.0 and think “oh, that’s cool”.  Another rider who is accustomed to tracking their distance when riding out doors may view 26.0 to 28.0 (miles) after a steady hard class and say (out loud) “No Stinkin’ Way”.

What’s going on here?

As I coach, you keep hearing me talk about all of these “factors”.  I seem to have factors for everything from cadence to training zones to power output to riding aero on an indoor bike and the list goes on.  Well, smirk if you want, but the Tom Scotto FACTOR-Y is going to churn out a few more. Indoor bikes and fitness equipment that calculate distance are often only looking at a single measurement.  For the indoor bike this would be the rotations of the flywheel (heavy wheel providing inertia/momentum).  The bike computer simply adds up the number of rotations of the flywheel (not the legs or pedals) and determines the distance as how far the wheel’s circumference has traveled. Since there are no internal or external gears like on an outdoor bike, one rotation of the pedals ALWAYS equals the same amount of rotations of the flywheel.  What are some of the other factors?  How much resistance the rider is using can play a significant role.  Is the person pushing a lot of resistance which could indicate a “fast” actual speed or spinning at high cadence with little resistance translating to a slower actual road speed?  Is the rider going uphill or downhill?  What about wind resistance (no, not the fans)?

Here is an example from one of my riding experiences and the factors:

A number of members from my team would travel to Turkey every year for a couple of weeks to train in the mountains in warmer temperatures.  One day, after having our traditional cup of Çay (Turkish tea), we headed toward one of the bigger climbs in the Taurus mountain range.  It took us about 30 minutes to ride to the base of the mountain road where the climbing began.  We climbed for 3 hours, transversing close to 70 switchbacks (sharp winding turns in the mountain road).  We descended on a shorter back road for 45 minutes and arrived back at the cafe.  One of the locals sitting at an outside table asked us how far we had traveled.  I confidently looked at my bike computer and was disappointed to read only 48 miles.  We were out for over 4 hours and only covered less than 12 miles per hour.  In this case, my computer was not incorrect because it included ALL of the factors involved in my ride (the foremost being going “slow” uphill).

Simple Math?

Bringing it back to our indoor bikes, due to the factors that the bikes are NOT considering, the number we see displaying as our TRIP distance will rarely ever be accurate. So what is it? Each manufacturer may calculate this differently, but here is the formula for the Keiser bikes:

- 200 revolutions on the Keiser M3 = 1.0 (TRIP)
- Flywheel is 49 inches in circumference
- 1 revolution on crankarm = 8.75 turns of flywheel
- 49 x 8.75 x 200 / 12 = 7145.8 feet
- 1.0 on our computer = the rear flywheel traveling 1.35 Miles

Remember, the above calculations do not include the “factors” so we are still ONLY measuring how far the circumference of the flywheel is traveling.  So what is the TRIP number good for?  Since it is directly linked to our cadence (the more pedal rotations the higher the TRIP), one can observe if their overall cadence was higher or lower for a given ride or effort.  Although the Keiser bikes already provide an average cadence number, the TRIP can tell you how many rotations you pedaled during the class (divide your trip by 200).

So, as instructors, it is important that we understand how these number work and what they represent.  This will enable us to give sound guidance to our riders so they can view their efforts with a touch of reality.  This will better prepare them (and not discourage them) if and when they venture outside.

Originally posted 2011-03-10 07:00:15.

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