Differences in numbers from Garmin to WKO

[maxroadrash]

Can one of you guru persons explain this to me? I'm seeing a pretty substantial difference between both TSS and IF numbers that I'm getting from Garmin (500) and WKO+ (GC seems to match the WKO numbers pretty closely).
Here's an example. I did a 120k ride this morning, and while the power numbers and so on match up fairly
closely, WKO says TSS=341.7 IF=.796 (GC says virtually the same). Garmin says TSS=321.6 IF=.849
FTP is set the same for all of them and I was under the impression that Garmin is using the same algorithm as WKO. Data is data so what is happening?
Thanks

 

[RapDaddyo]

I don't know about the Garmin algorithm, but you can actually compute the result yourself in Excel. Just copy and paste the raw data from WKO+ (view graph in raw data mode) or you can export the file as CSV (File > Export Copy As > Power-Tap Files (*.csv). One thing to look for is missing data and any stops during the segment you are looking at. Different post-ride analysis applications deal with missing data and stops differently.

 

[An old Guy]

Perhaps your FTP is different.

 

[Alex Simmons]

Originally Posted by maxroadrash .

WKO says TSS=341.7 IF=.796 (GC says virtually the same).

Garmin says TSS=321.6 IF=.849

FTP is set the same for all of them

WKO data suggest a ride time of 5 hours 23 minutes

Garmin data suggests a ride time of 4 hours 28 minutes.

Which makes sense for your ride?

 

[maxroadrash]

WKO: Duration: 5:31:17 (5:41:04)

Golden Cheetah: Duration: 5:41:04 Time Riding: 5:03:25

Garmin:
Time: 5:30:46 Moving Time: 5:03:04 Elapsed Time: 5:41:03 Without knowing the formulae , I'm guessing WKO and GC use the 5:41:04 time and Garmin the Moving time of 5:03
So then the question becomes is there anyway to change things up so the head unit reads out what I'll get in WKO/GC?

 

[alienator]

Without knowing the formulae , I'm guessing WKO and GC use the 5:41:04 time and Garmin the Moving time of 5:03 So then the question becomes is there anyway to change things up so the head unit reads out what I'll get in WKO/GC?

Garmin moving time is calculated based on time between "pauses" on the road. If you have auto pause set up, this means that moving time won't include any time spent at speeds below the auto pause speed you have set (for instance, my auto pause is set at 3mph). It seems like WKO and GC might not take that into consideration, or maybe I'm missing something. Otherwise, the moving times should be the same. Try either turning off auto pause or setting it to zero.

 

[maxroadrash]

Thanks Alienator, I'll give that a shot

 

[Alex Simmons]

Originally Posted by maxroadrash .

Garmin says TSS=321.6 IF=.849

Originally Posted by maxroadrash .

Garmin:
Time: 5:30:46 Moving Time: 5:03:04 Elapsed Time: 5:41:03

None of those times can explain the TSS / IF value reported by your Garmin.

So something is badly wrong with the Garmin calculations.

 

[maxroadrash]

Originally Posted by Alex Simmons .


None of those times can explain the TSS / IF value reported by your Garmin.

So something is badly wrong with the Garmin calculations.

I guess I shouldn't be surprised. Last year when I got the Garmin I damn near starved to death using their idea of calories instead of Kj.
I'm going to try what Alienator said (the auto pause was set to 4.6 k) and see if it helps. I also just d/l'd their latest firmware so maybe that
will have some effect.
Thanks to all of you for your input (with the exception of he who is blocked).

 

[acoggan]

Originally Posted by maxroadrash .

I was under the impression that Garmin is using the same algorithm as WKO.

Any particular reason why? (Just curious.)

 

[maxroadrash]

Originally Posted by acoggan .


Any particular reason why? (Just curious.)

I thought I read it on their site but I read so much stuff I could easily be mistaken.

 

[BrianMacDonald]

I have always noticed about a 10% difference in the numbers, with WKO being higher. This is pretty close to what you have observed. This even happens on the trainer during 2x20 sessions where stopping, coasting, etc. are not factors. I view WKO as the 'truth' here and so I simply learned to mentally adjust the TSS reported by the Garmin if I needed to know the exact number at any time. I considered adjusting ftp in the Garmin so the numbers matched but it never really bothered me that much. It would be nice to know why they are different though.

 

[RapDaddyo]

I have built many programs that compute statistics from ride files and, while the algorithms are straightforward, real-world data require judgment and different post-ride programs can deal with those issues differently. The issues common to most power meters are blanks and zeros. Blanks occur when an observation is recorded by the power meter but there are no data (I am distinguishing a blank from a zero). I have never seen this with SRM data, but I see it regularly with PT files. Zeros in speed requires a judgment call -- include the time stopped or not. The third issue is unique to Garmin, from my experience, because the user can choose a "Smart Recording" option to reduce the file size, which results in variable duration segments. This is a nightmare, because instead of working with frequencies at fixed recording intervals you now have to convert to elapsed time, split segments, and so on. Ugh!!! I always set my Garmin for recording at the highest frequency (1sec) and never, ever use Smart Recording. Any one or a combination of these issues could cause differences in Garmin's post-ride stats versus WKO+ or other programs.

 

[BrianMacDonald]

I will wager that the smart recording feature is the culprit. I am going to turn that off this week and report back.

 

[maxroadrash]

Originally Posted by BrianMacDonald .

I will wager that the smart recording feature is the culprit. I am going to turn that off this week and report back.

I wouldn't be so sure of that. I went back and looked and I have it turned off so at least for me, that's not the issue.

 

[BrianMacDonald]

I just got back from a ride with it turned off and the difference was still there.

 

[maxroadrash]

How do you have the auto pause set?

 

[Alex Simmons]

I think in more recent firmware versions, when power is used smart recording is automatically disabled. But I could be wrong on that.

Even if the pauses are considered, the IF, duration(s) and TSS values simply don't compute, which suggests that the algorithm used is simply wrong.

 

[Sam1971]

I think in more recent firmware versions, when power is used smart recording is automatically disabled. But I could be wrong on that. Even if the pauses are considered, the IF, duration(s) and TSS values simply don't compute, which suggests that the algorithm used is simply wrong.

My Garmin reports TSS values very similar to WKO...don't know if they are exact but definitely close enough for me to not think about the TSS reported at the end of a ride on the Garmin is any different to the TSS that WKO logs. If mine works I'm guessing that the algorithm used by Garmin is OK... I'd bet that you have some setting wrong in the Garmin settings. Sam

 

[Felt_Rider]

My power data displayed between Garmin Connect and WKO+ are almost always near identical. The only time I have noticed a difference was average speed where GPS signal is weak under heavy tree canopy and Garmin Connect seems to correct the speed average and WKO does not. I have not loaded the latest firmware for the Edge 800. My data on Strava is a bit different as I recently learned it is based on Golden Cheetah or something to that effect.


On a recent ride
http://connect.garmin.com/activity/328185347
From Garmin Connect
Distance: 81 miles
Avg. Moving Speed: 16.3 mph
Moving Time: 4:59:18
Total Time: 5:09:30
Ride Total TSS: 190 (0.62 IF)

From WKO
[SIZE= 12px]Entire workout (116 watts):
Duration: 5:03:57 (5:09:32)
Work: 2075 kJ
TSS: 190.6 (intensity factor 0.62)
Norm Power: 136
VI: 1.18
Distance: 81.098 mi
Min Max Avg
Power: 0 419 116 watts
Cadence: 7 111 76 rpm
Speed: 0 36.5 15.7 mph
Pace 1:39 0:00 3:49 min/mi
Crank Torque: 0 1304 130 lb-in
Temperature: 62.6 91.4 76.3 Fahrenheit

I hope you can get the kinks worked out[/SIZE]