Treadmill Accuracy question

[Gourou]

Hi guys,

I recently notice something weird with my treadmill. I did a 13 miles LSD, with 10 miles@ 6.0 mph, 1@6.2mph, 1@6.4mph and the last mile @6.6 mph.
Quick average calculation should be 6.1 mph right? NOT. I ended up with a 5.8 mph average!

When I sped up for the last 3 miles, I noticed each mile STILL took me 10:00 to complete ( it should have taken me 9:00@6.6 mph)

Last night, I decided to do some tests. I started the mill at 6mph for 1 mile. It should take 10:00, but ended up with 10:06.
I did the same thing at 8mph for 1 mile and got 7:37 instead of 7:30.

This is really bugging me. When I ran on the mill, I thought I could trust the pace I was running at and base my training on it. But what if the mill is slow??
Should I run each training faster to compensate?
Is there a way to calibrate the treadmill to get accurate pace?
Am I worrying too much about pace accuracy?

Thanks!

[LadyV]

I don't know if any measurement is 100% accurate. Even if you were running outside and measuring your pace with a GPS,it would not be 100% accurate.
If you want to go really crazy, run a mile outside with a gps on each arm (I tried that ). You will get 2 different measurements!
When I run on my teadmill, I try to run by "feel". If I program the treadmill with my targeted pace that I would use outside, it always feels easier on the TM. At first, it bothered me, but now I simply increase the pace a little bit on the TM so that it feels like I am running outside (I keep an eye on the heart rate - this tells me what my effort level is).

Learning to run by feel is very useful on race day, because you can't really rely on your GPS for your target race pace

[Kristen]

Last night, I decided to do some tests. I started the mill at 6mph for 1 mile. It should take 10:00, but ended up with 10:06.
I did the same thing at 8mph for 1 mile and got 7:37 instead of 7:30.

Steve, were you timing it from when the console already displayed 6 mph and 8 mph? Or, did you start timing as soon as you punched in the numbers and the timer started on the TM? It might be as simple as the TM needing a little extra time at slower speeds until it reaches the target speed.

[Gourou]

Last night, I decided to do some tests. I started the mill at 6mph for 1 mile. It should take 10:00, but ended up with 10:06.
I did the same thing at 8mph for 1 mile and got 7:37 instead of 7:30.

Steve, were you timing it from when the console already displayed 6 mph and 8 mph? Or, did you start timing as soon as you punched in the numbers and the timer started on the TM? It might be as simple as the TM needing a little extra time at slower speeds until it reaches the target speed.

Thanks LadyV, I guess I will have to learn to do that

Kristen, I used the timer on the mill. It can really be that it takes some time at the beginning to ramp up to the selected speed, but it still doesn't explain why it took me the same time to do a mile at 6.6 mph as it did at 6mph...??

I guess I'm ok with the treadmill not being totally accurate, but something was definately wrong with that LSD run: 13.6 miles run done at a speed greater than 6 mph in a time of 140 minutes. you do the math..something doesn't jive.

[Kristen]

Kristen, I used the timer on the mill. It can really be that it takes some time at the beginning to ramp up to the selected speed, but it still doesn't explain why it took me the same time to do a mile at 6.6 mph as it did at 6mph...??

Indeed it doesn't... I'm thinking either gremlins or beer were involved. Which was it?

In any event, I suggest going by feel as well. Here's hoping the 6.6 mph mile felt more challenging than the 6.0 mph mile... otherwise, things could get quite complicated...

[Gourou]

Kristen, I used the timer on the mill. It can really be that it takes some time at the beginning to ramp up to the selected speed, but it still doesn't explain why it took me the same time to do a mile at 6.6 mph as it did at 6mph...??

Indeed it doesn't... I'm thinking either gremlins or beer were involved. Which was it?

In any event, I suggest going by feel as well. Here's hoping the 6.6 mph mile felt more challenging than the 6.0 mph mile... otherwise, things could get quite complicated...

It was indeed Superbowl Sunday, but no beer was involved..at that time anyway!

Yes I do feel the speed increase, my guess is that the timer is going too fast, thus slowing down my average. I need to do some more tests and compare 1 minute on the treadmill vs 1 minute on my watch or garmin.

[turd ferguson]

I recently notice something weird with my treadmill. I did a 13 miles LSD, with 10 miles@ 6.0 mph, 1@6.2mph, 1@6.4mph and the last mile @6.6 mph.
Quick average calculation should be 6.1 mph right? NOT. I ended up with a 5.8 mph average!

That doesn't make any sense at all. You never went slower than 6 mph, but your average was below 6 mph.

How long was your entire run? By my math, it should have been 128 minutes 8 seconds, or 6.08 mph.

Did you have a warmup or cooldown take down your average?

[Jwolf]

If you are really taking 10:00 to go a mile at 6.6 mph, then there is indeed something wrong with the one or more of settings on the treadmill.

But I'm a a bit confused because I didn't think that a treadmill measured distance and speed separately. I thought one was dependent on the other.

This has never happened on any treadmill I've been on. I know that the calibration is different from machine to machine, so a mile on one machine at 6.6 mph might be harder than the next one at 6.6 mph. But it always takes the same amount of time. Most treadmills I've been on display the pace in min/mile after you change the speed, and the mile takes exactly that time to finish (within a few seconds to allow for belt speed change).

Your differences of 6-7 seconds in your test today seem about normal for belt speed increases. You will notice that in only the first mile of a new pace.

So I'm thinking that maybe there is something wrong with the calculation you did to get the 5.8 mph? Is it possible you wrote down the time incorrectly?

[Strider]

Your differences of 6-7 seconds in your test today seem about normal for belt speed increases. You will notice that in only the first mile of a new pace.

BINGO on that one. It does take up to 20 seconds for some machines to get up to speed, especially when you take into account the time for you to actually enter the speed from when you press START.

As far as the other, based on your speed test it seems right, there is something else in the big picture

[dgrant]

Not really possible. The treadmill doesn't measure your distance, it just calculates it using the speed multiplied by the time. It's entirely possible that the speed is off due to calibration error, but the distance traveled would be proportionately off as well. The distance and speed don't have to both be correct, but they have "match" since one is derived from the other.

The Precor treadmills at our gym accelerate at about a mph/s, so I could see a mile at 6mph taking 6:03 or 6:04 for sure, but that's different than the 13 mile run issue.

[turd ferguson]

Most treadmills I've been on display the pace in min/mile after you change the speed, and the mile takes exactly that time to finish (within a few seconds to allow for belt speed change).

Most treadmills I've been on don't account for actual belt speed change.

By that I mean that if you're going at 6 mph and you punch in a change to 10 mph using the keypad, it thinks you're going 10 mph right away even though the belt speed hasn't caught up to the display yet.

But in the end those are minor rounding errors, especially on a 13 mile run. The fact that gourou's average speed was less than the lowest recorded speed is the real weird one.

[Jwolf]

But in the end those are minor rounding errors, especially on a 13 mile run. The fact that gourou's average speed was less than the lowest recorded speed is the real weird one.

True, so there can really be only two possible conclusions:

1. Steve mistakenly thought his total time was longer than it really was on the 13-mile run.
2. There is a problem with the settings on the treadmill (i.e., the speed isn't really increasing when he is pressing the speed increase buttons). It sounds weird but it could be true-- I was once on a hotel treadmill that had a "safety" mechanism built in to make sure hotel-goers didn't run dangerously fast. The speed never went over 6.0 mph. (But since he was able to do the "test" yesterday at 8.0 mph, I doubt this is the problem, either.)

[Gourou]

Thanks for all the replies guys,

I definately need to do some more tests. I may have made an error when I wrote down the time..I doubt it.. but I can't remember for sure anymore.

I'll do some more runs and get back to you with the results.

[ian]

Not really possible. The treadmill doesn't measure your distance, it just calculates it using the speed multiplied by the time.

Not always. When a friend and I did a "treadmill marathon" last winter, we both had our fancy gym TMs set at 8.0 mph, yet his total distance was gradually opening a gap on mine (about one quarter mile lap per hour). At the time, we commented on how we wouldn't be surprised if 8.0 mph on one TM wasn't quite the same speed as 8.0 mph on another TM, but there was no obvious reason for a discrepancy in going from speed to distance, yet that is exactly what was happening.

[turd ferguson]

Not really possible. The treadmill doesn't measure your distance, it just calculates it using the speed multiplied by the time.

Not always. When a friend and I did a "treadmill marathon" last winter, we both had our fancy gym TMs set at 8.0 mph, yet his total distance was gradually opening a gap on mine (about one quarter mile lap per hour). At the time, we commented on how we wouldn't be surprised if 8.0 mph on one TM wasn't quite the same speed as 8.0 mph on another TM, but there was no obvious reason for a discrepancy in going from speed to distance, yet that is exactly what was happening.

That's opening up a new question: what exactly does a treadmill measure?

Does it measure speed and calculate distance? Or measure distance and calculate speed?

Does it measure speed by RPMs of the mechanism?

Or does it measure anything at all? Does it just have a calibration chart built-in so that if you punch in (say) 6 mph it sets the motor to 50% and infers all the numbers (speed, distance) on the console.

[Lazagna]

If you google around, you can find a method of "calibrating" your treadmill. It involves measuring the tread, marking it with a white line so you can see if go by, and then setting a speed, watching it and counting the number of times it goes by in a set time, then doing the math to figure out exactly how far it's travelled.

So, if you set it at 10km/h, and you watch it for 5 minutes, and you're actually at 10.1km/h after all the calculations, you do it again at 5km/h to see if the same 10% variance exists. If it does, then you know the TM is 10% slow. (as an example randomly pulled out of my butt)...

[jgore]

So, if you set it at 10km/h, and you watch it for 5 minutes, and you're actually at 10.1km/h after all the calculations, you do it again at 5km/h to see if the same 10% variance exists. If it does, then you know the TM is 10% slow. (as an example randomly pulled out of my butt)...

I'm not sure I agree with your math there, Laz. 10.1 km/h is 10% faster than 10 km/h.

[Lazagna]

So, if you set it at 10km/h, and you watch it for 5 minutes, and you're actually at 10.1km/h after all the calculations, you do it again at 5km/h to see if the same 10% variance exists. If it does, then you know the TM is 10% slow. (as an example randomly pulled out of my butt)...

I'm not sure I agree with your math there, Laz. 10.1 km/h is 10% faster than 10 km/h.

Like I said, I pulled it out of my butt... but hopefully everyone gets the idea...

[dgrant]

Not really possible. The treadmill doesn't measure your distance, it just calculates it using the speed multiplied by the time.

Not always. When a friend and I did a "treadmill marathon" last winter, we both had our fancy gym TMs set at 8.0 mph, yet his total distance was gradually opening a gap on mine (about one quarter mile lap per hour). At the time, we commented on how we wouldn't be surprised if 8.0 mph on one TM wasn't quite the same speed as 8.0 mph on another TM, but there was no obvious reason for a discrepancy in going from speed to distance, yet that is exactly what was happening.

But how? The treadmill doesn't actually measure the distance, right? Isn't it only measuring time, and displaying speed and distance (both defined, not measured) as functions of that same measured time? Does the treadmill motor actually have a tachometer to measure rpm (and therefore actual speed)? (Not rhetorical, I really don't know...)

[ian]

But how? The treadmill doesn't actually measure the distance, right? Isn't it only measuring time, and displaying speed and distance (both defined, not measured) as functions of that same measured time?

That's the point: I don't know, but whatever my TM was doing might also be related to Steve's original question. It doesn't make sense but it was an especially reliable observation on account of having the two TMs side-by-side (and having 3 hours of time to kill discussing it).

[dgrant]

But how? The treadmill doesn't actually measure the distance, right? Isn't it only measuring time, and displaying speed and distance (both defined, not measured) as functions of that same measured time?

That's the point: I don't know, but whatever my TM was doing might also be related to Steve's original question. It doesn't make sense but it was an especially reliable observation on account of having the two TMs side-by-side (and having 3 hours of time to kill discussing it).

I can't stop thinking about this. What about this for a hypothesis.

I keep assuming the timer used to calculate the distance (which is rpm(defined) x belt length(defined) x time(measured)) is the same as the one used to originally calibrate the motor... in which case mathematically the distance and speed have to match up. But what if, for instance, when originally calibrating the motor I use my wristwatch which perhaps differed from the treadmill's timer. Maybe 1 minute on my wristwatch equals 59.9s according to the treadmill (or whatever)?

If what I call a minute is different from the time of calibration to the time of measurement, I guess that would allow the speed to be "correct" and the distance to be "correct" without them matching up. The distance is calculated right now using the treadmill timer, but the speed (also calculated) used a different timer way back when it was manufactured/repaired. No? Hmm...

[RA.]

So, if you set it at 10km/h, and you watch it for 5 minutes, and you're actually at 10.1km/h after all the calculations, you do it again at 5km/h to see if the same 10% variance exists. If it does, then you know the TM is 10% slow. (as an example randomly pulled out of my butt)...

I'm not sure I agree with your math there, Laz. 10.1 km/h is 10% faster than 10 km/h.

Not sure I agree with your math there, Jim. 10.1km/h is 1% faster than 10km/h. 1.1km/h is 10% faster than 1 km/hr, or 11km/hr is 10% faster than 10km/hr.

[Garrett]

Not really possible. The treadmill doesn't measure your distance, it just calculates it using the speed multiplied by the time.

Not always. When a friend and I did a "treadmill marathon" last winter, we both had our fancy gym TMs set at 8.0 mph, yet his total distance was gradually opening a gap on mine (about one quarter mile lap per hour). At the time, we commented on how we wouldn't be surprised if 8.0 mph on one TM wasn't quite the same speed as 8.0 mph on another TM, but there was no obvious reason for a discrepancy in going from speed to distance, yet that is exactly what was happening.

Consider the additional forces your friend exerted on the belt to cause a faster revolution. Depending on the strength of your friend, the force of his push-off might cause a momentary acceleration of the belt greater than yours, and added up over time, an increased distance if it is measured in rpm.

[Lazagna]

So, if you set it at 10km/h, and you watch it for 5 minutes, and you're actually at 10.1km/h after all the calculations, you do it again at 5km/h to see if the same 10% variance exists. If it does, then you know the TM is 10% slow. (as an example randomly pulled out of my butt)...

I'm not sure I agree with your math there, Laz. 10.1 km/h is 10% faster than 10 km/h.

Not sure I agree with your math there, Jim. 10.1km/h is 1% faster than 10km/h. 1.1km/h is 10% faster than 1 km/hr, or 11km/hr is 10% faster than 10km/hr.

Picky people, I guess my hurried example was TOO hurried. It's really 1%, not 10% and the fact that it's faster or slower, I don't care, it's a difference to adjust for.... (not upset, I would pick on the numbers too....I'm an accountant, and I just tossed some numbers in and messed it up royally... ah well)

[RA.]

Picky people, I guess my hurried example was TOO hurried. It's really 1%, not 10% and the fact that it's faster or slower, I don't care, it's a difference to adjust for.... (not upset, I would pick on the numbers too....I'm an accountant, and I just tossed some numbers in and messed it up royally... ah well)

I was only picking on Jim since he picked on you when you already said you were using random numbers.