Speed sensor : wrong auto-calculation
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Speed sensor : wrong auto-calculation
When using auto-calculation with a speed sensor, wheel circumference is over estimated on Karoo 2.
I tried the following test: connected the same speed sensor to both my Garmin Fenix and my Karoo 2.
Both are configured with auto-calculation of wheel circumference. My wheel is 700x35c, announced circumference is 2168mm, measured by myself: 2197mm.
After my ride, estimated circumference was:
Garmin Fenix : 2183mm, almost what I measured.
Karoo 2 : 2249mm, way to high.
Here are the stats of my ride, started and stopped at the same time on both devices :
Garmin Fenix: 31,87km, 1:22:20, 23,2km/h
Karoo 2 : 33,27km, 1:22:52, 24,2km/h
How is such a difference possible, how does the Karoo 2 evaluates the wheel circumference ?
Thanks for your help,
Luc
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Official comment
Hi All,
This issue has been addressed in today's release. Thank you for bringing this to our notice!
Comment actions -
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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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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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 - 2412mmAccording 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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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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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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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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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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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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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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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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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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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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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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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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@Vito HH support already wrote:
https://support.hammerhead.io/hc/en-us/community/posts/1260800782169/comments/1260802818730
https://support.hammerhead.io/hc/en-us/community/posts/1260800782169/comments/1260802978249
Here are the steps to manually set the wheel circumference on your Karoo: https://support.hammerhead.io/hc/en-us/articles/360048580233-Setting-the-Wheel-Circumference
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