Forerunner 235 indoor accuracy

Oct 31, 19 7:40

Post #1 of 17 (4139 views)

I just bought a Forerunner 235, upgrading from my old watch specifically for one that can track treadmill work without a foot pod as I just can't do early am runs outside for one more winter.

I used it for the first time this am for some intervals. Intervals were 5 min tempo, 5 min recovery, repeated.

I usually run my tempo at 4:15-4:35min/km depending on the intervals, and recover around 5:15-5:30min/km.

The treadmills at my gym apparently work in miles, and I was getting readings of 6:47mile/min and 8:10miles/min.

However, when I looked on Strava after, it showed my tempo pace as something like 5:15min/km, around a minute per km slower.

I don't have a ton of experience with treadmills, but I know what 5:15min/km feels like, and I was definitely moving a lot faster then that. My LSD pace is 5-5:15, which I can fall comfortably in to without a watch telling me I'm there.

I guess the treadmill could be inaccurate, or the watch, or both?? Is it normal for this function to be so off?

Long Chile was a silly place.

Re: Forerunner 235 indoor accuracy [BCtriguy1] [ In reply to ]

Oct 31, 19 7:52

Post #2 of 17 (4123 views)

I believe treadmills, footpods and wrist based pace estimation all have potential errors - some larger than others. It likely depends on the specific equipment, but I personally trust the following in order of accuracy (most accurate at top):

1- Stryd footpod
2- Garmin footpod
3- milestone pod / Zwift pod
4- treadmill
5- wrist based pace

Even after "calibrating" my watch for wrist based treadmill use I find the plots for pace to vary wildly and not show intervals very clean at all (kind of a sign of poor accuracy). My stryd fairly clearly shows any pace change which causes me to at least trust it's relative measurement. My garmin footpod is somewhere in between.

In my personal opinion, the wrist based distance and pace is only useful to log that I did a run for very roughly some time/distance (maybe within 15-20%?).

Re: Forerunner 235 indoor accuracy [BCtriguy1] [ In reply to ]

Oct 31, 19 7:55

Post #3 of 17 (4119 views)

A variation of this just hit in another thread. The gist is that there are multiple factors that make it hard to know which is right.

The treadmill's calibration - there is no telling if the gym treadmill has ever been calibrated
Your stride calibration - you need to run outside (under GPS) to let the watch auto-calibrate your stride length
Your stride & cadence changes while on a treadmill versus your stride & cadence while running outdoors (where the pod likely calibrated)
The belt's behavior of slowing during the moment you are in contact and then unloading and speeding up while you are momentarily airborne

The internal sensors in the 235 may not be as good as a foot pod for pace and distance. And, even better than a generic foot pod is a Stryd, which measures actual distance in 3-D space. So, if getting good indoor pace and distance is a priority, you might want to consider getting a Stryd to compliment the watch.

Re: Forerunner 235 indoor accuracy [BCtriguy1] [ In reply to ]

Oct 31, 19 8:05

Post #4 of 17 (4106 views)

I think you are just asking too much of your device, indoor running is just never going to be that accurate. Especially if you are using just a wrist device. Mine also measures very slow, if I do a 9 minute mile, its says like 10;15+. And when I watched the pace down, still off quite a bit. No doubt that some of the other gadgets are more accurate, but why not just use the treadmill speed, as long as it is close? I only run on commercial ones, and they all seem really close to real pace, and would never use a wrist based GPS over what they say.

Kind of like the swimming ones, they are close, but not close enough to beat an actual pool clock. Do a different stroke, or kick, or a drill, and they just don't know what to do with that info. Someday I suppose, but not sure what it is trying to fix in the first place?

Re: Forerunner 235 indoor accuracy [BCtriguy1] [ In reply to ]

Oct 31, 19 8:15

Post #5 of 17 (4096 views)

I use the 235 as well. Who really knows how accurate it is but my pace is always slower than I felt. If you are good at judging an effort by feel you can kind of calibrate the watch to yourself. It won’t be accurate on Strava but at least you will know how hard you worked. Also I feel that running with an incline really throws it off.
But as said before. Run outside under gps a few times and make sure all your user settings are set up correctly in Garmin connect first.

Last edited by: Mabes72: Oct 31, 19 8:17

Re: Forerunner 235 indoor accuracy [BCtriguy1] [ In reply to ]

Oct 31, 19 8:54

Post #6 of 17 (4068 views)

My 235 consistently says I ran 4 miles on the treadmill and the treadmill says I ran about 3.6 miles. I believe the watch because I hate the treadmill. In addition, I always set the slope to 1.0 on the treadmill.

Watch will say I'm running 8:30 pace and the treadmill pace is like 9:00.

I've never calibrated it for inside use. Don't even know how.

Re: Forerunner 235 indoor accuracy [monty] [ In reply to ]

Oct 31, 19 10:08

Post #7 of 17 (4044 views)

monty wrote:

I think you are just asking too much of your device, indoor running is just never going to be that accurate. Especially if you are using just a wrist device. Mine also measures very slow, if I do a 9 minute mile, its says like 10;15+. And when I watched the pace down, still off quite a bit. No doubt that some of the other gadgets are more accurate, but why not just use the treadmill speed, as long as it is close? I only run on commercial ones, and they all seem really close to real pace, and would never use a wrist based GPS over what they say.

Kind of like the swimming ones, they are close, but not close enough to beat an actual pool clock. Do a different stroke, or kick, or a drill, and they just don't know what to do with that info. Someday I suppose, but not sure what it is trying to fix in the first place?

It seems weird to me to offer a product that basically doesn't functionally work (if it is that far off, it is essentially useless). I'm just asking the device to do what it says it can do!

I just checked out the Stryd foot pod... $300 CDN, no thanks!

Looks like I'll just have to convince my running friends on Strava I don't actually run my intervals at below recovery pace ;-).

Long Chile was a silly place.

Re: Forerunner 235 indoor accuracy [BCtriguy1] [ In reply to ]

Oct 31, 19 10:53

Post #8 of 17 (4031 views)

It seems weird to me to offer a product that basically doesn't functionally work (if it is that far off, it is essentially useless). //

My guess that most people buy these things, to first run or ride outdoors, or in the swim OW. Running indoors is probably way down on most peoples list, and as we can see, way down on their list of things to perfect. My watch is useful for me 98% of what I use it for, that other 2% is just probably never going to be there anyway. If you bought it just to track your treadmill runs, well then yes, you got screwed...I'm happy as long as the outdoor stuff works pretty close, but still a bit slower than I actually run, suppose there is a way to calibrate that, just not sure how to as of yet...

But you are right in that if you claim a function on your device, it ought to be closer than horse shoes..

Re: Forerunner 235 indoor accuracy [monty] [ In reply to ]

Oct 31, 19 10:56

Post #9 of 17 (4029 views)

I do run outdoors quite a bit, I just wanted to switch my two weekly early am runs to indoors this winter, just to mix it up. Running in the cold, dark, rain, when it won't be light out for another 4 hours, can wear on you :). Plus, I thought it would be good to do intervals on the mill as you have so much control.

Long Chile was a silly place.

Re: Forerunner 235 indoor accuracy [BCtriguy1] [ In reply to ]

Oct 31, 19 10:59

Post #10 of 17 (4023 views)

Plus, I thought it would be good to do intervals on the mill as you have so much control. //

It is good, and you can do the intervals, the only thing that is changed, is you cannot tell the world how your workout went. I guess I'm just old fashioned that way.. (-;

Re: Forerunner 235 indoor accuracy [monty] [ In reply to ]

Oct 31, 19 11:09

Post #11 of 17 (4008 views)

If it's not on strava, it never happened ;-).

I cannot tell you how pissed I was when my watch died at km 20.5 of a half marathon last month...

Long Chile was a silly place.

Re: Forerunner 235 indoor accuracy [BCtriguy1] [ In reply to ]

Oct 31, 19 11:43

Post #12 of 17 (3992 views)

I have the Forerunner 230 and alone it is wildly inaccurate on the treadmill. I got a Garmin footpod that I leave on my shoes, and that is WAY more accurate. For its cost, I'm happy with Garmin footpod's accuracy/ease of use. When I go outside, GPS gets used instead of footpod.

Re: Forerunner 235 indoor accuracy [BCtriguy1] [ In reply to ]

Oct 31, 19 12:14

Post #13 of 17 (3978 views)

I feel your frustration. I have the 935 and it is out by about 1 min/km, so for example a 5min/km pace usually comes up around 5:55 - 6:00. Even if I increase speed to tempo and threshold over a long stretch it can't really detect an increase, except HR.

Since I upload to TrainingPeaks, a straight treadmill run can be corrected via the Calibrate and Save option, although lap times don't make sense and Strava, for some reason, will receive the original incorrect number, presumably eeking that data out to reduce Strava doping. The more I calibrate the worse the issue has become so I just try to be zen about it all.

Bricks are worse as the calibrate feature only seems to adjust for the whole bike/run distance, not just treadmill so I correct TP manually.

To get some positive affirmation it's good to go outside once in a while and see how fast those angry miles got you.

Kiwami NA Racing Team

Re: Forerunner 235 indoor accuracy [shaggyrider] [ In reply to ]

Oct 31, 19 13:23

Post #14 of 17 (3959 views)

My Fenix is doing the same thing. I had it pretty close, then went on a fairly quick outdoor run (for me) and now it is just stupid. I set my treadmill on 6.7 (8:57/mile) for my brick runs. Pretty sure it is consistent as it lines up well with my Zwift pod when running in Zwift. My watch, however, reads 12:00-13:00 min miles. This morning I ran 2.7 miles and the watch thought it was 1.92.

Whatever, Strava is not right but at least Garmin takes the calibration before loading into Connect.

Re: Forerunner 235 indoor accuracy [chooch] [ In reply to ]

Oct 31, 19 13:32

Post #15 of 17 (3956 views)

chooch wrote:

I have the Forerunner 230 and alone it is wildly inaccurate on the treadmill. I got a Garmin footpod that I leave on my shoes, and that is WAY more accurate. For its cost, I'm happy with Garmin footpod's accuracy/ease of use. When I go outside, GPS gets used instead of footpod.

Thanks for the info! For $80, that seems like a much better option. I'll try this route out.

Or just impress the shit out of my running group when I show up much faster then my training suggested :-).

Long Chile was a silly place.

Re: Forerunner 235 indoor accuracy [BCtriguy1] [ In reply to ]

Nov 1, 19 9:01

Post #16 of 17 (3886 views)

I had the same experience when i used a 230.

First used a Garmin footpod, then moved to a Stryd footpod.

Personally, now i would just find a bluetooth footpod to use with zwift (for entertainment) and the watch (for tracking).

I didn't find the stryd any more useful although it works really well for power and treadmill running.

Re: Forerunner 235 indoor accuracy [djhuff7] [ In reply to ]

Nov 1, 19 9:07

Post #17 of 17 (3879 views)

Same issue here with my Fenix 5 Plus. I don't know if it relates to other models, but Garmin has acknowledged that there's a problem after the last (or at least one of the more recent) update. There's a few threads on it on Garmin's forum where a bunch of people are experiencing the same issue. Apparently Garmin has said they are working on fixing the issue, but has no timeline for it.

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