KEISER M3

Measure of Distance

On the M3 the distance displayed is a function only of revolutions of the flywheel. M3 distance is not determined by gear. If you turn the pedal crank 200 times the distance will display “1.0”. If you turn the pedal crank 200 times in gear 1 and then 200 times in gear 3 it will display “1.0” for both gears. The distance unit of measure is kilometers, not miles.

Let’s continue the discussion by jumping to a road bike with 700c wheels. A 700c wheel has a theoretical diameter of 700 mm, which equals a circumference of 2198 mm. In order for the bike to travel 1 km the wheel has to make 455 revolutions. If you consider 200 turns of the pedal crank and 455 revolutions of the wheel the gear multiplier equals 455/200 or 2.275.

The road bike for this discussion has a 53/39 front chain ring and a 12/13/14/15/17/19/21/23/26 rear cassette. The multipliers for these gear combinations follow:

Front Ring (teeth

Rear Cassette (teeth)

Gear Multiplier

1.50

1.70

1.86

2.04

2.05

2.29

2.30

2.52

2.60

2.79

3.00

3.12

3.25

3.53

3.79

4.08

4.42

The best fit for a 2.275 gear multiplier on the road bike is 39 teeth front ring and 17 teeth rear ring, which equals a gear multiplier of 2.29.

If you interpolate the M3 multiplier of 2.275 on a scale of 1.50 to 4.42 and superimpose it against the M3 gear range of 1 to 24, the approximate equivalent on the M3 is gear 7. The conclusion at this point is that if you pedal the M3 at 90 RPM and gear 7 and a road bike at 90 RPM at gear combination 39/17 then the distance traveled on each bike will be approximately the same.

Next we need to address distance traveled and the gear the M3 is ridden at. Let’s jump back to the road bike to start this explanation. At the “easiest” gear combination of 39/26 on the road bike the gear multiplier is 1.5 and at a constant cadence of 90 RPM the rear wheel will make 135 revolutions in one minute. At the 39/17 gear combination (gear multiplier of 2.29) and 90 RPM (optimal cadence) then in one minute the rear wheel will make 206 revolutions. At the “hardest” gear combination of 53/12 (gear multiplier of 4.42) and at a constant cadence of 90 RPM then in one minute the rear wheel will make 398 revolutions. On the road bike one will travel much further in a given unit of time at the highest gear combination at 90 RPM.

If we jump back to the M3 and keep the road bike example in mind we will say that when a person rides the M3 at gear 7 then the distance displayed is representative of what one would experience on a real road bike. If one pedals the M3 in a gear less than 7 then the distance displayed is overstated compared to what one would actually experience on a road bike. Conversely, if one pedals the M3 at a gear greater than 7 then the distance displayed is understated compared to what one would actually experience on a road bike.

Conclusion (finally):

If one rides the M3 at gear 7 then the distance displayed is representative of what one would experience on a real road bike. The distance is overstated if one pedals at less than gear 7 and the distance is understated if one pedals at greater than gear 7.

Here are some other interesting notes:

* The gear multiplier between the Keiser pedal crank and the rear flywheel is 8.75. It’s interesting to note that 1,000 revolutions of the flywheel can be accomplished in 1 minute 16 seconds of pedaling at 90 RPM. In 1 hour of pedaling at 90 RPM, such as in a typical spin class, the flywheel will make 47,281 revolutions.

* Gear 7 is the only gear where watts and cadence will be equal, regardless of the cadence.

* For the road bike comparisons, 200 turns of the pedal crank at 90 RPM in gear 39/17 equals 1 km traveled in 2.22 minutes. 1 km in 2.22 minutes equals 16.8 mph.

Page Table of Contents

* Measure of Distance

* M3 Calibration

M3 Calibration

1. Bikes do not need to be calibrated if they are used in a regular spin class. In this setting the instructor should be calling out levels of exertion, such as “On a scale of 1-10 I want you pedaling at level 6”. A given gear or wattage means something different to every person in the class so to say “I want everyone to be pedaling in gear 6” will be too easy for some, too hard for others.

2. Calibrating the bikes can take a fair amount of effort. If you want to avoid calibration but still use watt based workouts then number each bike and have a student ride the same bike number from class to class. This allows the student to use watts and to track their progress over time.

3. If you want each bike to feel the same, to be consistent, then you need to calibrate. A two-step process is offered here to calibrate multiple Keiser M3s.

a. First, you want to get each bike “in the ball park”. Lay the bike on its side with the magnet assembly facing up. Loosen the cable until there is no appreciable tension on the cable. Rotate the magnet assembly a bit; let it go, let it return to dead stop. Listen for the clunk noise that it makes when the magnet assembly hits dead stop. Practice this so you get a feel for rotating, releasing and the clunk noise. Now start tightening the cable in small increments. After each increment, rotate, release and listen for the clunk noise. Keep tightening the cable until the clunk noise changes to a “softer” clunk. You want to find the spot where the magnet assembly is just barely reaching dead stop. Now repeat this process with each of the other bikes. Of course, it’s important that you do it the same way on each of the other bikes. To finish up you need to “re-learn” the cyclometer to correspond with the new cable setting. This is best explained on page 8 of the following Keiser document:

http://manuals.keiser.com/downloads/exercise_bikes/M3_service_manual_revc.pdf

b. Second, you may need to “fine tune” each bike. To do this you will need to ride each bike briefly. For each bike set the seat height, seat front to back and handlebar height the same. When you ride the bike pick a cadence and gear and ride each bike at the same cadence and gear. With the fist pass your goal needs to be to sort the bikes into two groups, those that are hard and those that are easy. Next, focus on the hard bikes. Since you set them at just above dead stop in the previous step, the hard bikes can not be made to pedal any easier. If you have a bike that is the hardest of the hard then you need to leave this one alone and focus on the other hard bikes. You need to adjust the cable length until each of the hard bikes is equally hard. Remember to “re-learn” the cyclometer after each adjustment. Now you need to focus on the easy bikes. Each of these needs to be made to pedal harder. Adjust the easy bikes until they are equal to the hard bikes. Remember to “re-learn” the cyclometer after each adjustment. When finished each bike needs to pedal at the same level of “hardness” for a given cadence and gear.

4. Over the years I have been calibrating the 16 M3s that we have at our club. Our goal is to have each bike feel the same at a given gear, watts and RPM. I now check the bikes about every 6 months and, overall, they stay in close calibration. Of the 16 bikes I probably adjust 2 each year and in each case the given bike pedals a little easier than the others so I have to adjust it to make it feel a little harder. I attribute this adjustment, the bike getting easier, to slight shift cable stretch.

I can keep our bikes calibrated to each other but have often wondered how they feel compared to other M3s in other clubs. I recently rode some M3s in a Sioux Falls club and observed that I had to pedal in gear 10 on the Sioux Falls M3s to get the same feel as gear 3 on our bikes. Also, we received 4 new M3s recently and were surprised at how easy they pedaled right out of the box. I had to use the full range of adjustment on the new M3s to get them to have the same pedal feel as our “old” M3s.

The next level of concern regarding M3 calibration is a result of our Power classes. In our Power classes the athletes can calculate their Power to Weight Ratio and when compared against an international standard they can determine their Cat 1-5 ranking. In order to make this comparison meaningful our bikes need to be calibrated against a standard. Here’s the method I used to calibrate our M3s to a “power” standard.

One of our athletes has a Felt Tri-Bike with a Cycleops Powertap rear hub. It’s a fact that the Powertap is used worldwide and is a “must have” device for competitive cyclists training with power. Keeping in mind that this Powertap is the only device available to me at this time I went ahead with calibrating our M3s. Our athlete brought in his Felt Tri-Bike and his Kinetic Trainer. For the test we set-up his Felt and a M3 side-by-side and then he proceeded to ride his Felt at a given watts and RPM and rode the M3 at the same watts and RPM all the while comparing “pedal feel” on each bike. We went back and forth adjusting the M3 until the pedal feel on the M3 was the same as the pedal feel on the Felt, again, at the same watts and RPM.

It turns out I had to adjust our M3 to pedal “easier” than before we started the test. Later, I adjusted each of our other M3s to have the same pedal feel as the M3 used during the calibration.

Conclusion:

* Our 16 M3s are now calibrated such that at a given watts and RPM each bike will have approximately the same pedal feel as the others.

* Our M3s are calibrated against a “power” standard and now our Power to Weight Ratios and Cat 1-5 rankings are more meaningful than before.

Keiser M3