Halfords Crossfuse E-Bike speed accuracy

I have at times had a separate GPS sensor on my bike, which I have compared to mobile phone and Google maps on many occasions. What has become clear, is that the Crossfuse display reports speed over ground 2mph faster than either GPS sensor or Google maps. Now, Google maps straight lines the distance and does not take extra distance of going up or down hills (I think), so should read less mph if on a hill? The bike has a 27" frame and tyres. I have moved the sensor on the wheel to its extremities, but that did not change anything. Anyone else seen the same error and possibly has a fix? The 2mph difference is pretty constant, regardless if doing 10mph or 20mph etc. Not looked at it at faster speeds for obvious reasons.....

Annoying, as on hills it means the assistance cuts out sooner than it should.

I have moved the sensor on the wheel to its extremities, but that did not change anything.

Moving the magnet won't change anything. All that's being sensed is each rotation of the wheel and calculated against the set wheel (tyre) circumference from which it can gauge speed and distance. For that reason, to ensure each rotation is being correctly picked up, it's best to put the magnet back where it was - centrally relative to the pick-up in the sensor (should be marked on it).

What I did find is that changing tyres can/might marginally change speed. e.g. Marathon Plus tyres with an added 5mm puncture belt have a greater circumference than the lower profile tyres origionally fitted on one of my e-bikes. On one e-bike, I can adjust the wheel/tyre circumference in "10ths of an inch" to fine-tune the speed readout. On another bike I can't... all I can set there is wheel size (26", 27.5", 700c, 29" etc)

I don't know if that "exact circumference" parameter is settable within Bosch's own dealer software? Strangely, being able to set exact tyre circumference in mm seems to be a standard setting even in most cheesy £10 bike computers, but on an e-bike it seems something of a rare feature.

Moving the magnet won't change anything. All that's being sensed is each rotation of the wheel and calculated against the set wheel (tyre) circumference from which it can gauge speed and distance. For that reason, to ensure each rotation is being correctly picked up, it's best to put the magnet back where it was - centrally relative to the pick-up in the sensor (should be marked on it).

 

What I did find is that changing tyres can/might marginally change speed. e.g. Marathon Plus tyres with an added 5mm puncture belt have a greater circumference than the lower profile tyres origionally fitted on one of my e-bikes. On one e-bike, I can adjust the wheel/tyre circumference in "10ths of an inch" to fine-tune the speed readout. On another bike I can't... all I can set there is wheel size (26", 27.5", 700c, 29" etc)

 

I don't know if that "exact circumference" parameter is settable within Bosch's own dealer software? Strangely, being able to set exact tyre circumference in mm seems to be a standard setting even in most cheesy £10 bike computers, but on an e-bike it seems something of a rare feature.

Thanks for the great response, yes it does seem strange you spend thousands and there is no simple adjustment....

Here's a partial screengrab of a page from the Bosch Dealer's Software; it clearly shows they can adjust the wheel circumference in mm, and apply a correction to that measurement (?). I'd have them check those first just in case they're what's throwing your speed (and it follows, distance) reading out.

Here's a partial screengrab of a page from the Bosch Dealer's Software; it clearly shows they can adjust the wheel circumference in mm, and apply a correction to that measurement (?). I'd have them check those first just in case they're what's throwing your speed (and it follows, distance) reading out.

 

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Cheers, I have a three year plan with Halfords, even though i got the bike second hand with very few miles on it, so will ask them this week to see if they can adjust. I keep tyre pressures bang on, so I thought I had tried everything before posting. I would say apart from this issue, the bike has been a great purchase and really happy with it.