Changing wheel diameter size on Bosch powered bikes

Nev

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May 1, 2018
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I was reading a thread on here the other day and it showed that Bosch allow bike shops to change wheel size in their software so this got me to think about a couple of things namely.
1. If the software is currently set up for 29 inch wheels and its changed to 26 inch wheels (but you don't actually change the wheels), when the motor cuts off at about 16.8 mph as indicated on the Bosch speedo, will you actually be going faster than 16.8 mph?
2. Does anyone know what speed you will actually be going when the situation of question 1 appertains?
 

soundwave

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May 23, 2015
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it can only be out buy so much so if you did that you would just get a 503 error
 
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Artstu

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Aug 2, 2009
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it can only be out buy so much so if you did that you would just get a 503 error
Unlikely, how is the bike to know it isn't running on the standard wheels?

I'd be going for 16" wheels if it has that setting.
 

soundwave

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May 23, 2015
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on my old intuvia display you could change the wheel size for i guess different size tyres but it would only go so far b4 you got a 503 error.

tho a dealer can still change the wheel size but it is not a option on new bikes with the latest firmware as it is not a option to do it yourself.
 
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WavyDavy

Finding my (electric) wheels
Apr 7, 2019
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If I have got it right it goes the other way. You need bigger wheels. You won't go so far for one rev of a 26 compared to a 29. So 16.8 on a 29 will be 15 on a 26 and 9.3 on a 16.

As I understand it you are only allowed a small variation of adjustment by Bosch to enable small corrections. Not enough to make any significant difference. I don't know the exact numbers.
 

Nealh

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With a smaller wheel size speed reading it would be under reading, if you were able to do so and could pedal at 16.8mph indicated your actual true speed would be faster.
 

Nev

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Unlikely, how is the bike to know it isn't running on the standard wheels?
Yes I agree I can't see how it would know, unless it does something like compare the speed sensed using the magnet with say the speed provided by a GPS system and I cant see Bosch going to the expense of doing that. I suspect if you are using 29 inch wheels but input into the system you are using 26 inch wheels then you would get away with it.

My guess would be though that if you inputted say 16 inch wheels then you would get the 503 error code that SW mentioned, but that would be because only certain sizes would have been written into the software as being acceptable.
 

Nev

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With a smaller wheel size speed reading it would be under reading, if you were able to do so and could pedal at 16.8mph indicated your actual true speed would be faster.
Yes this is how I understand it too, do you have any idea Nealh what the true speed would be in this situation?
 

Artstu

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Certainly there are bosch bikes on 20" wheels, perhaps they do even go in folders on 16" wheels too, although I've not seen one myself.
 

Nev

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I see WavyDavy has used a ratio of the two wheel sizes to work out the new speeds if this is correct then a reading on speedo of 16.8 mph would actually mean your doing 18.738 mph is this method correct?
 

soundwave

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May 23, 2015
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just get a badass dongle if the display reads 15mph you are going 30mph :cool:
 

Nev

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Certainly there are bosch bikes on 20" wheels, perhaps they do even go in folders on 16" wheels too, although I've not seen one myself.
Using 20 inches as you wheel size (but really using 29 inch wheels) gives a true speed of 24.36 mph when the speed is reading 16.8 mph. This all seems a little bit too easy to me, surely if it was this simple then there would not be such a big market in dongles. I must be missing something anyone know what it is?
 

soundwave

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it is why they stopped it on the gen 2 motors as the magnet on the cranks did work for the gen 1 motors
 

Artstu

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Aug 2, 2009
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Using 20 inches as you wheel size (but really using 29 inch wheels) gives a true speed of 24.36 mph when the speed is reading 16.8 mph. This all seems a little bit too easy to me, surely if it was this simple then there would not be such a big market in dongles. I must be missing something anyone know what it is?
Probably due to finding a dealer willing to do it if it is actually something they can alter. I need a firmware update due to fitting a new remote switch that won't talk to my old firmware (so I'm told) so I'll ask and see what they say.
 

Artstu

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it is why they stopped it on the gen 2 motors as the magnet on the cranks did work for the gen 1 motors
But you could buy a motor programmed for 20" wheels. Are you saying the adjustment isn't something that can be altered by a dealer now where once it was possible?
 

soundwave

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May 23, 2015
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yes a dealer can change the wheel size but with the intuvia display you could do it ur self but it is for diff sizes in tyres and if you went to far would get a 503 error.
 

ebiker99

Esteemed Pedelecer
Feb 17, 2019
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This video shows how dealers can change the wheel size on Bosch systems:

it also shows that the latest Bosch system attempts to detect whether dongles etc have been fitted, my guess is that since it knows wheel rpm, crank rpm, crank torque and motor torque it profiles these and maybe other variables to flag up anomalies via the "tamper" number.

Why would Bosch and other suppliers do this? Possibly to prevent their systems from being abused resulting in extra warranty costs and long term damages to their reputation.

Also the Bosch ebike system division is currently the most profitable of all Bosch divisions and they'll be keen to make sure that their global ebike sales aren't hit by something similar to the VW emissions "scandal". If ebikes were seen to be too easy to derestrict then stricter regulations would be enforced, eg compulsory licenses and insurance, which would impact Bosch sales. These big companies aren't stupid.
 
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Nev

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my guess is that since it knows wheel rpm, crank rpm, crank torque and motor torque it profiles these and maybe other variables to flag up anomalies via the "tamper" number.
You might well be right but I wonder how Bosch do this, here are a few examples of how difficult this would be to do.

Lets assume we have told the Bosch software that we are using a 26" wheel but in reality we have a 29" wheel fitted. Lets assume we are traveling along at 16.8 mph (indicated on the display) but in reality we are actually doing 18.7 mph.

Now our crank rpm (assume we are pedaling) will be higher in top gear at 18.7 mph than it should be for the indicated 16.8 mph, but I don't think Bosch measure what gear we are using. So the software would not know we were in top gear we could be in another gear which would now mean the rpm would not appear unusual.

A similar thing can happen with crank and motor torque, both of these will be increased when actually doing 18.7 mph instead of the indicated 16.8 mph, but Bosch are not measuring things like the slope you are on (you could be riding up a hill), they are not measuring wind direction (you could be riding into a strong wind).

Bosch engineers are obviously a lot smarter than I am, and so perhaps they have thought of ways to get around these problems, just from a point of interest it would be good to know how they do it.
 

ebiker99

Esteemed Pedelecer
Feb 17, 2019
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Now our crank rpm (assume we are pedaling) will be higher in top gear at 18.7 mph than it should be for the indicated 16.8 mph, but I don't think Bosch measure what gear we are using. So the software would not know we were in top gear we could be in another gear which would now mean the rpm would not appear unusual.
Maybe by recording the highest wheel rpm to crankwheel rpm ratio over a long time? Probably top gear would be active in this case and if the ratio changed significantly it could indicate that a dongle had been fitted?

A similar thing can happen with crank and motor torque, both of these will be increased when actually doing 18.7 mph instead of the indicated 16.8 mph, but Bosch are not measuring things like the slope you are on (you could be riding up a hill), they are not measuring wind direction (you could be riding into a strong wind).
Maybe by averaging figures over many rides?? That could possibly remove the effects of hills and head winds?

I've no idea what the algorithms are doing but clearly Bosch are taking measures to detect tampering and they must have some value to Bosch otherwise they wouldn't be there.
 

Fishy

Pedelecer
Nov 16, 2018
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on my old intuvia display you could change the wheel size for i guess different size tyres but it would only go so far b4 you got a 503 error.

tho a dealer can still change the wheel size but it is not a option on new bikes with the latest firmware as it is not a option to do it yourself.
I have a new Bosch powered bike with the Kiox display, within the settings I can change the wheel circumference to pretty much anything. So far I've only tried making it 10% smaller, and the bike rode fine with no errors, display showed motor cutting out at the usual speed, but I had no independent means of checking actual speed at the time. Gonna try this again when I can compare speed properly.
 

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