Speed sensor : wrong auto-calculation

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  • Official comment
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    Shruti

    Hi All,

    This issue has been addressed in today's release. Thank you for bringing this to our notice!

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    Abhishek Anand

    Hey Luc.

    The wheel autocalibration on Karoo 2 is calculated automatically. It is set at 'auto-calibration' by default. I am sure you would have connected your speed sensor and set the precedence over the GPS. Besides, here is the link that would help you set the wheel circumference manually - https://support.hammerhead.io/hc/en-us/articles/360051707494--Setting-the-Wheel-Circumference-

    Meanwhile, I would like to inform you that there would be an expected percentage of error for the calculation of wheel circumference and speed. I see the difference is not huge. However, I would like to hear about your findings on the data recorded after the manual calibration.

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    Gordon Sakamoto

    I also noticed this problem. I think there is something wrong with the Auto Wheel Circumference. This is why my distance data did not match or even come close to matching my friend's distance data when comparing on Strava. Strava takes the Garmin speed sensors' data over the GPS data and uses this to compute the distance traveled. This is also why on the Karoo dashboard, the distance matches my friends distance- the dashboard uses the GPS data.

    Auto wheel circumference works fine for my Garmin 530 edge, but the Karoo 2 overestimates my wheel's circumference and therefore, overestimates my total distance traveled. You have to "revert distance" on Strava to correct it so it uses the GPS data instead. Or, you can manually enter your wheel circumference. I am going to manually enter the wheel circumference my Garmin auto calculated into the K2.

    I think that Hammerhead needs to look at the Auto Wheel Circumference and how it is computed. It is off and nowhere near accurate. Garmin calculated my wheel at 2127mm and Karoo 2 calculated 2203mm. Most online charts put my wheel at 2136mm. Over a 29.3 mile ride this added about 1.2 miles to my total distance. The GPS was accurate in calculating the distance... 

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    Luc

     

    Hi Abhishek,

    Thanks for your answer.

    I have done more tests with another bike, another wheel size, another sensor and another device (Garmin Edge).

    I did 3 times the same process:

    Unpair the sensor from both Karoo 2 and Garmin Edge, re-pair the sensor to both devices in configuration 'auto-calculation', take a ride for about 6km, then check the calculated circumference on the devices.

    Here are the results of the 3 measures:

    Garmin Edge: 2236mm - 2238mm - 2247mm
    Karoo 2: 2423mm - 2406mm - 2412mm

    According to Strava, Garmin is closer to reality than Karoo 2: GPS measured distances are correct for both device as Strava corrected ("reversed") distances are approximately the same for both devices and correspond to what the Garmin Edge measures. Also, during the ride, if I change the precedence on the Karoo 2 and put the GPS on top, I have the correct instant speed.

    I agree there is a percentage of error, but the result here is a difference of 1-2km/h on average speed for the ride.

    I know I can enter circumference manually (for me it would mean copy the value measured by Garmin to Karoo 2), but I would like to get rid of my Garmin Edge that has other problems. I'm still disappointed by the difference of measure for a device that wants to be the "World's finest cycling computer".

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    František Cimmer

    @luc:
    It looks, like the use wrong conversion inch <-> mm. For example historical length of Portutgish inch which was 27,5mm.

    Then all length of circle calculated from 28" of diameter will be around 2400mm :)

    Maybe a typo of constant in the progam ;)

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    Gordon Sakamoto

    I have been posting about this issue as well. At first, I thought it might a battery issue with the Garmin speed sensor. I replaced the battery with a brand new battery and again, it overestimated the wheel circumference and therefore the total distance of the ride. It is disappointing to say the least that the K2 can't auto calculate a wheel circumference. 

    I think someone needs to look at this problem...

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    Edward Behrens

    Ditto. I ride with my wife and my Garmin was always close but slightly behind hers. Switched to the Karoo 2 and noticed a jump in speed and distance when riding regular routes.  I’m now 5% above her, 1 mile for every 20 we ride. Performed a distance correction in Strava and all my rides on the Karoo 2 were reduced by about 5%. Definitely an issue with the Karoo 2 auto-calculate. 

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    Ali

    Hi all, this is a known problem and something that requires a fix to our accuracy. Although, when it comes to the wheel circumference reading it is triggered through GPS and we expect a 2-3% error. Let me know if you are seeing error percentage more than this.

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    František Cimmer

    @Ali:

    difference of 200mm as in last Luc post is about 7-8% error....

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    Permanently deleted user

    I'm running into this issue as well. My metrics (speed, distance, and elevation) are all inconsistent with what strava reports. have sold my edge but edge and strava were much closer to reality than k2 and strava are. 

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    Lammert

    Experiencing the same with auto calculation. Started a ride with Karoo 2 and Garmin bike computer:

    Distance on Karoo 2: 117.0 km
    Distance on Garmin: 108.8 km

    ~7% error....

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    Johnny Pugh

    I agree that Karoo’s auto wheel calibration is unacceptably inaccurate. It has been that way since they introduced it. That’s why I manually set the correct wheel circumference on all of my speed sensors.

    I begin by getting the circumference from a tire size calculator for my initial setting. I then go on a ride of at least 10 miles and upload it to Strava. Then I use Strava to correct the distance. If the Karoo’s distance and Strava distance are the same, the setting is good. If there is a significant difference then I use the following formula to get the corrected wheel circumference.

    Formula: Old Wheel Circumference X Corrected Distance / Incorrect Distance = Corrected Wheel Circumference

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    Ali

    Hi all, we are monitoring this post for all the inconsistency reports and it is true that 7% error is just unacceptable. I am trying to collect more information so any help would be greatly appreciated. We have not seen all the riders and only a small minority group of riders, and we need to isolate the case and identify any pattern.

    Could you please fill this form Auto-wheel circumference inaccuracies?

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    František Cimmer

    Hi @Ali,

    what does mean the question "What is the actual Wheel size? in mm/inches" in the form? Does it mean my actual measured (by means of old hand method) circumference of wheel?

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    Ali

    Hi Frantisek, it would be the number that you think is correct by old methods or tire size. You can refer to this chart.

    https://support.hammerhead.io/hc/en-us/articles/360003199993-Wheel-size-Reference-Chart

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    Ali

    I would request everyone to please provide us with the details on the form here

    https://docs.google.com/forms/d/e/1FAIpQLSfWU6OJBl68-5ush6netTcnWIetVvqJXdxTV2I5L7nGCVxs2w/viewform

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    Robert

    Add me to the list of people who find that the autocalibration feature on the Karoo 2 overestimates distance.  BTW 2-3% is not an acceptable error threshold.  Both Garmin and Wahoo (I use them also) have mastered this issue. 

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    Ali

    @Robert - We will get this right. Do not worry!

    Please fill the form attached above and don't forget to mention the make as well as the model of your speed sensor. Thanks!

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    Robert

    HI.  any update on this issue? 

    I use garmin speed sensors on my front axle and am always outside when i turn on my computer.  pretty standard stuff.

    are you not finding this problem yourselves?  if not, i can only assume that it is not software but that some of us have defective karoo units.

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    Akhil

    Hey Robert,

    As Ali had previously mentioned, We have been actively monitoring this issue and collecting the reports around it. We have been able to reproduce it to an extent. This has been classified as a bug, As we do approach our bug fixes and feature development based on a structured workflow to pull a bug/feature into the software pipeline.

    I do apologize for not being able to give you a timeline here but I can assure you that we will improve this in the future releases 

    Could you please fill this form for Auto-wheel circumference inaccuracies?

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    Felix Pruemmer

    Same problem here with a Wahoo Speed Sensor coupled through ANT+. Distance approximately 7-8% too far. I think it also affects the accuracy of turn announcements in situations where these come in short intervals of less then 100m. The announcements seem to lag behind.

    reverting to manual circumference by the table has reduced the margin significantly.

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    Lammert

    Any update? Is one of the developers working on a bug fix?

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    Benno Zwanenburg

    Measure it manually till this bug is fixex and distance and speed will be 100% perfect!

    And please keep in mind the tyre-pressure and weight of the rider is very important to make a good measurement! Set your tyre-pressure correct and sit on your bike with your normal outfit. Mark the tyre and the place where the tyre is on the ground and drive one turn with your wheel while sitting correct on your bike. Mark again and measure the distance of the two marks on the ground, that's your correct wheel size. It's hard to do it alone so ask someone to help you. Do it several times and take the average length.

    FYI: my MTB wheelsizes are with 3,7 bar (for road rides) 2306mm and with 1,6 bar 2263mm

    Have a nice ride with perfect distance and speed!

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    Torben Bergland

    I've consistently had the same issue. It's about 5% too high.

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    Lammert

    Benno, in my opinion you are addressing exactly why automatic calculation is needed at the start of every ride. I vary my tire pressure depending on the terrain I ride on. My weight depends on the clothes and gear that I bring, which depends on the weather type and the length and purpose of the ride. With 4 to 5 trips per week, it is impossible to measure this manually each time. I expect an accurate measurement / calibration every ride. In addition, the question is whether hammerhead really wants to compete with Wahoo and Garmin. After all, they can do it too. So lazy? No, not really. Do I expect a top bike computer as promised? Yes.

     

     

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    Brad Stoppenhagen

    I came here to report that I'm also having the same issue.  I didn't realize it until this weekend where I road a predefined route in a group.  My Karoo2 showed 133.3 miles and 16.8 mph.  The other 2 had Garmin readings of 126.7 miles /16.1 mph and 126.82 miles / 16.1 mph.  The two Garmin riders distances were close to our preride route map.

    I don't have time right now to measure my actual wheel circumference, but I ride with the computer outdoors on the road.  I'm using a Garmin speed sensor which is mounted on the rear wheel.

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    Denny Doyle

    Bstoppenhagen I would just use a standard setting from a table. For a road tire it will be pretty good. 700x23 2096, x 25  2105, x28 2136. 

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    Benno Zwanenburg

    Never! use settings from tables, measure!!! See my post above from 14 days ago.

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    Vito Squarciafico

    I don't understand why this is so difficult to fix, on a 31 mile ride my Karoo2 records 32 miles.  Other in the group I ride with get accurate readings.  The have Garmin's.  Hammerhead developers,  get off your Kester and fix it! 

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    Martin B

    @Vito I don't understand why this is so difficult to insert the circumference manually by measuring it. I'm just saying.

    I did that and now riding happy life with my accurate distances.

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