Speed sensor & King Meter KM-529 LCD for XF07 36V front hub kit

S1966W

Finding my (electric) wheels
Jul 15, 2018
12
1
53
I have recently purchased the XF07 700c front hub kit with 17Ah battery & fitted to a tandem.

The first 100 mile is under the belt & I am more than satisfied with the performance of motor hub and battery so far. The only small niggle, & it is small (but if I were following an Audax route it could be annoying) is the discrepancy with the speed & hence odometer.

The speed sensor is fitted to the rear seat stay securely & within 5mm of the spoke magnet. The red led on the sensor briefly illuminates on each passage of the magnet & the speed displayed on the KM-529 LCD display is fairly steady (i.e not erratic).

With 700c wheel size option entered into the KM-529 the displayed speed is just over 15% in excess of actual speed - i.e 15mph on the KM-529 equals about 12.6mph. I also checked over a fixed 10 mile course and the KM-529 displayed 11.7 miles. I have just entered a 24 inch wheel size option & that has brought the error down to about 2.5%. Unfortunately there is no wheelsize option for 23.4 inch which would see the meter accurate!!

Hopefully I am not coming across as a total pedant!!, but it would be interesting to note what associated wheel circumferences are tabulated against specific wheel diameters in the factory settings.

Anyhow, I remain very happy overall and the 24 inch wheel size option gives a sufficiently accurate speed/distance for my purposes, although it would be interesting to establish if anyone else encounters a similar discrepancy.

Cheers, Simon
 
Last edited:

anotherkiwi

Esteemed Pedelecer
Jan 26, 2015
7,595
5,691
The European Union
Yes they are not exact because of tyre size - there is a 27 mm difference between a 28 mm tyre and a 55 mm tyre (one inch is 25.4 mm).

The only way to have an exact speed reading is to be able to enter the exact diameter as measured on your bike. Most people who need precision use a GPS or even a dedicate odometer which can be programmed with exact wheel diameter.
 

S1966W

Finding my (electric) wheels
Jul 15, 2018
12
1
53
Yes. I can understand the tyre size issue. However, my current set up with panaracer ribmos 32mm gives an actual measured diameter of 682mm. The KM529 must be using a diameter of around 786mm........a pretty hefty tyre on that baby!! Now I am being a pedant (but that is the reality).
 

anotherkiwi

Esteemed Pedelecer
Jan 26, 2015
7,595
5,691
The European Union
My KT controller isn't that far off that is for sure! I think I have about 5% error.
 

S1966W

Finding my (electric) wheels
Jul 15, 2018
12
1
53
Just as a follow up, after completing just over 600 miles on the above mentioned configuration (24 inch wheel size entered for 700C tandem) I again noticed a pretty large discrepancy between actual speed & that displayed on the KM529.

I therefore entered a wheel size of 700C to the menu &, lo & behold, everything now tallies. The speed & hence distance now correlates with reasonably well calibrated other sensors, very strange but also rather satisfying!!
 

Woosh

Trade Member
May 19, 2012
10,558
7,497
Southend on Sea
wooshbikes.co.uk
thank you for the update.
The optimal gap between the magnet and the sensor is usually between 5mm and 10mm. Too close, the magnet can give wrong reading.
 

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