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Training Tips

Zwift How-To: Calculating the Speed of Your Treadmill

on September 11, 2020

The number of people purchasing treadmills is on the rise, with new societal norms leading to altered lifestyles which find many of us spending more time at home. Zwift Running has certainly seen increased event attendance, and the May Field track is busier than ever!

But how do you know your newly-purchased treadmill is reporting the correct speed? Sure, the display might say you’re running at 10kph but is that really the case? Is the belt truly moving at the same speed as the display is reporting?

In this article, we will look at one way to accurately measure the speed of your treadmill belt. (Note, however, that the speed of the treadmill belt is not necessarily the speed at which you are running. More on that later.)

Belt Length

The first thing we need to do is measure the length of your treadmill belt. You might find this information in the user manual. However, more often than not the manual will merely give the length of the running surface, which will be less than half the length of the belt.

Use a steel tape measure. Find or mark a point on the belt from which to start and measure a meter. Mark this point and move the belt around manually to reveal more of the surface. Measure another meter and mark again.

Few treadmills will have a belt longer than 3 meters, so one more measured length should bring you back to where you began.

You should now have a measurement in meters of your entire treadmill belt length.

Counting Revolutions

Now it’s time to run. Place some brightly-colored tape on the side of the treadmill next to the belt. Place another strip of tape on the belt itself.

You will need a stopwatch - use an app on your phone or on your running watch. We are going to time 60 seconds of walking on the treadmill.

Start the treadmill and speed up to a comfortable walking pace. Let’s say 4kph for example. Make sure you can see the colored tape on the belt as it passes the colored tape on the side.

Each time the tape passes counts as one revolution of the belt. Start the stopwatch and count the number of revolutions in 60 seconds.

Time for Mathematics

Let's say that the length of the treadmill belt is 2.9 meters and we counted 23 revolutions of the belt in 60 seconds. We can now carry out a simple equation to determine the actual belt speed:

23 revs x 2.9m x 60 minutes = 4002 metres or 4.002kph

In this example, we can see that over an hour of walking with the treadmill set at 4kph we would cover almost exactly 4km. The extra 2 meters would be within an acceptable margin of error.

You can now repeat this test at different speeds to see how well your treadmill adjusts to changes of pace. If your average run speed is around 10kph then you should carry out the test at this speed.

True Treadmill Speed

Having measured the true speed of the treadmill belt, we can more accurately determine the distance and speed we are running.

In the example above the treadmill display and the true speed of the belt are closely matched. However, your treadmill may show a speed which differs somewhat from the measured belt speed. In this case, you can alter the treadmill speed to account for the separation.

True Running Speed

To confuse matters, the true speed of your treadmill belt is not necessarily your true running speed.

Each time your foot strikes the treadmill belt there is a marginal but significant slow down of the belt. When you are fully in the air, the treadmill speeds up slightly to compensate.

Your ‘true’ running speed is the speed of the treadmill belt only when your foot is in contact with it. This can be measured, but involves a more complex process using high-speed filming techniques.

Perceived Effort/Exertion

While it is correct that your true running speed is slightly slower than the treadmill belt speed, this unduly complicates matters.

When running on a treadmill we want to recreate, to an extent, our experience of running outdoors. Ideally, we want our indoor heart rate, pace, and times to closely match our outdoor heart rate, pace, and times. If we run 5k in 25 minutes outdoors, we should be doing approximately the same indoors for the same level of effort.

Perceived exertion (how you feel when you are running) appears to correlate more closely with your true treadmill speed rather than your true running speed.

Notably, the Stryd footpod reports your true running speed, which is why it often measures slower than your treadmill. This may leave you feeling like you are working harder than you might outside, for similar speeds.

Wrapping It Up

It’s useful to know your true treadmill speed and your true running speed. Hopefully, the method above will enable you to feel more confident about your pace on the treadmill and on Zwift.

But, as we have said in other articles, it’s the work you put in that really counts. It’s your effort level that will make you fitter and stronger. And it’s that willingness to step out of your comfort zone that will help you achieve your goals. See you out there!