Bosch Kiox wheel circumference limit
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William - Bosch Team
Well-Known Member
Hello,
Wheel circumference is set at the factory by the OEM. The adjustment that you can make in Kiox, and/or that the dealer can make with the Bosch software allows up to a 5% variation, and is purely "cosmetic," aka it will change displayed speed, but not actual speed.
Different OEMs measure for circumference in different ways, but the correct value will generally involve a virtual or carefully calculated circumference to account for average tire deflection, etc. The correct value will be less than the actual circumference of your tire at rest, unweighted.
The correction range is limited to 5% because needing to go beyond that likely indicates an improper circumference value from the factory, and the OEM will need to assist your dealer in correcting.
If possible, talk with your local Bosch Certified bicycle shop about getting this checked out.
Wheel circumference is set at the factory by the OEM. The adjustment that you can make in Kiox, and/or that the dealer can make with the Bosch software allows up to a 5% variation, and is purely "cosmetic," aka it will change displayed speed, but not actual speed.
Different OEMs measure for circumference in different ways, but the correct value will generally involve a virtual or carefully calculated circumference to account for average tire deflection, etc. The correct value will be less than the actual circumference of your tire at rest, unweighted.
The correction range is limited to 5% because needing to go beyond that likely indicates an improper circumference value from the factory, and the OEM will need to assist your dealer in correcting.
If possible, talk with your local Bosch Certified bicycle shop about getting this checked out.
William - I understand the wheel circumference won’t impact actual speed, but in my case won’t calculated speed and distance be underestimated? What if any benefit is there in underestimating distance and speed? Don’t you want to know how fast and far you are actually going? Sorry, William, but it’s possible I may have misunderstood your response. Thanks in advance.
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William - Bosch Team
Well-Known Member
The Drive Unit measures/controls speed based on the factory-programmed wheel circumference. We designed the 5% variation, or "wheel size correction" feature to allow dealers/riders to adjust the displayed speed to account for a change in tire size, closer matching to a riding partner's bike, or any other situation where it is perceived that the displayed speed may be incorrect. People like numbers to match, but most measurements, including automobiles, are just good approximations.
This works with GPS discrepancies as well, as a properly calibrated "mechanical" speed sensor on a bicycle is more accurate than most consumer-grade GPS. Since GPS speed display can't really be adjusted, the 5% variance on the Bosch System can help make those numbers match.
When you got a measured roll-out value of 2194mm, were your tires within proper PSI range, and were you sitting on the bike for proper tire deflection/sag?
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fooferdoggie
Well-Known Member
bosch seems to always read slower the your going. what I did is I changed the wheel size till my average ride was close to the same as my garmin gave me.
The issue is I can’t increase the circumference beyond 2124 mm. It’s not a huge deal but seems odd I can’t enter the correct number. I get I‘m not trying to dock with the International Space Station but not sure why there is this constraint. Again, I can live with it if it can’t be fixed.
William - Bosch Team
Well-Known Member
I'm not sure what your wheel circumference is set at from the factory, but if the value you are attempting to use is more than 5% different, the system will not allow it. The constraint is there because the need to go beyond it likely indicates another issue, whether factory programming mishap, someone installed drastically wrong tire size, or something else.
If you feel the value is too far off from what it should be, your local Bosch Certified dealer can work with the manufacturer of your eBike to get it corrected. The shop should also be able to look at the diagnostic report and see what is going on in terms of circumference values and where they should be. It may be that the circumference was set wrong at the OEM factory, or tire spec was changed mid-production, or it could be something else.
This sort of thing happens sometimes, and Bosch/the OEM has a process for getting it corrected, but it will require taking it to a Certified Dealer.
What model eBike do you have? Guessing Trek based on what looks like a Bontrager logo in your image and the custom Kiox mount? If you can share some model info, and possibly a photo, I can check with my team and see if anyone has a report from the same model that shows the proper wheel circumference. I'll help you figure out what I can remotely, but the shop will still be your best bet in the long run, especially if action is needed to change values.
FYI, I won't be able to respond again until Monday.
If you feel the value is too far off from what it should be, your local Bosch Certified dealer can work with the manufacturer of your eBike to get it corrected. The shop should also be able to look at the diagnostic report and see what is going on in terms of circumference values and where they should be. It may be that the circumference was set wrong at the OEM factory, or tire spec was changed mid-production, or it could be something else.
This sort of thing happens sometimes, and Bosch/the OEM has a process for getting it corrected, but it will require taking it to a Certified Dealer.
What model eBike do you have? Guessing Trek based on what looks like a Bontrager logo in your image and the custom Kiox mount? If you can share some model info, and possibly a photo, I can check with my team and see if anyone has a report from the same model that shows the proper wheel circumference. I'll help you figure out what I can remotely, but the shop will still be your best bet in the long run, especially if action is needed to change values.
FYI, I won't be able to respond again until Monday.
fooferdoggie
Well-Known Member
can a dealer change it since you can buy the kits? I am sure they had to set my kiox when they installed it.
William - Bosch Team
Well-Known Member
The dealer can use the Bosch software to adjust the 5% "cosmetic" allowance if needed, but nothing more. If there is an issue and the factory-set circumference value needs to be changed, the dealer will have to do a remote diagnostic session with the OEM, where the dealer connects your eBike to their software in the shop, and the OEM connects remotely to the shops software.
Displays, including Kiox, just read the factory-set circumference value from the DU where it is programmed. When they installed your Kiox, it autmatically read all of the DU info, and should have been good to go.
fooferdoggie
Well-Known Member
ok so its not in the kiox its self good to know.
Hi William - Sorry I didn’t respond earlier. The bike is a Trek Domane+ HP7; I’ve also shared a photo of the bike. It’s outfitted with 700x35 Schwalbe G-One Speed tires, which came with the bike. Thanks for your help here.
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Alaskan
Well-Known Member
I had the same issue with my Trek Allant+9.9S It took a while to fix as they local techs did not have access to change that value range. It had to be done when the right guy back at corporate tech support was available to connect in to my motor remotely and move the window slightly upward. What with covid we had to wait a week or so but it got done and now the bike and the GPS are within a percent or two....close eough,
Thanks for that reply and confirmation.
William - Bosch Team
Well-Known Member
Do you recall what the circumference value was set at from the factory, before you made the adjustment?
I may have misunderstood something here, but in your first post you mentioned having a 27.5" tire. This more recent post calls out the 700 x 35 Schwalbe, which is consistent with Trek's website. I'm guessing this is just a typo, but can you confirm your tire sidewall says 700 x 35?
BTW, beautiful picture! Where is this? Looks like an incredible ride.
I don’t recall exact value set at factory but think it was about 75”, or 15% below actual value. Yes, it’s a Schwalbe 700x35 G-One Speed tire. Turns out the outside TIRE diameter is almost exactly 27.5”. The picture was from a ride last Saturday on the backside of West Maui - yes, it’s a beautiful ride.
