Setting up the BAC-601 Smart LCD Display

[Lewis Balentine]

http://goldenmotor.com/e-Bike-DIY/BAC-601%20LCD%20User%20Guide.pdf

6.2.1 SE1.Electric Vehicle Wheel Diameter Setting
28in,700c,26in,24in,22in,20in,18in,16in can be optional.
Set the wheel diameter through "UP" and "DOWM" button to ensure speed and
mileage is correct.By default the LCD display is 20in.

There is NO setting for 700c. There are various settings for each of the sizes: 10.0 to 30.0
GM needs to correct the documentation and include a table that gives the circumference used for each of the relative sizes.
Better yet would be a chart referencing common tire sizes (and the circumference).

[Bikemad]

Hi Lewis,

If you can't find the correct wheel size you may have to select one that's close and then fine tune the settings using the following:

6.2.2 SE2.Wheel Diameter Adjusting Factor Setting
Setting the wheel diameter adjusting factor can obtain the accurate speed and
mileage value through "UP" and "DOWN" button.
The default setting is 1.00 and minimum is 0.7 and maximum is 1.3. (Note:actual
wheel diameter = wheel diameter X wheel diameter adjusting factor )

The true diameter of tyres can vary tremendously as the size quoted does not allow for variety of tyre depths that are now available. You can adjust the "wheel diameter factor setting" and then double check the displayed speed using a GPS device which should be good enough for most users.

Alan
 

[Bikemad]

There is NO setting for 700c. There are various settings for each of the sizes: 10.0 to 30.0.

I have just checked mine out and it appears to be the same as stated in the original instructions with the added bonus of the 29" option:



I also had a quick look at the adjusting factor and it allows any of the standard sizes to either be increased or reduced by up to 30% in 1% increments:



Alan
 

[Lewis Balentine]

Made Me Look

Daddy used to tell me that the only thing that is constant is change. In this case I think GM may have changed the software. Mine starts at 10.0. It then increments by decimal values (i.e. 10.1, 10.2, 10.3, 10.4 .....) all the way to 30.0 (lot of button pushes to get there).

>> You can adjust the "wheel diameter factor setting" and then double check the displayed speed using a GPS device which should be good enough for most users.<<
I think that I would prefer to measure the circumference of the tire or the distance traveled for a fixed number of revolutions to derive the accurate wheel diameter.

The attached spreadsheet has a table I used when I was trying to sort out the various tire sizes. It has nominal values for diameter and circumference based on tire size (thus far they have proven fairly consistent).

[Aeberbach]

It would be interesting to see if "700" and "29" give you identical results. I found out this week that you can use MTB 29" tires on a 700c rim, they're pretty much the same only the MTB rims tend to be wider & beefier.

[Lewis Balentine]

According to what I have read a "29er" use an ETRO 60-622 rim. I believe the common "700" rims run from ETRO 18-622 to 47-622. The 622 part is the rim diameter so depending on the width of the 700 rim a '29er' should fit. You might have a bit of a problem with a skinny track rim though.

The outside circumference I have listed for a '29er' is 2326mm. I am going to be running a 700x35C tire on the Smart Pie. That has a circumference of listed 2168mm. that is about a 7.27% difference. I will use a starting diameter of 27.2 inches.  I will check that against 14 revolutions on smooth pavement (should be 99 feet 7 inches).

FYI: If the information I have for the '29er' is correct then 13 revolutions on smooth pavement should be 99 feet 2-7/16 inches.

[Lewis Balentine]

I finally got out with a tape measure and checked my guesses: 14 revolutions came out to 99 feet 9 inches. So the circumference works out to 85.50 inches with a diameter of 27.22 inches. I set the wheel size to 27.2

For anyone that may wish to use this method of calibration (i.e. do not have a GPS device) I have made up the attached spreadsheet.
Simply walk you bike along a smooth surface counting the number of wheel revolutions (hint: use the air valve as your marker).
Measure the distance and then lookup the corresponding wheel diameter.
You can change the number of revolutions as needed.