Magic number for calibration of Bell Dashboard 150 with CCS computer

[Badgerdogmomma]

Because I want an odometer on my CCS, I bought a Bell Dashboard 150 cycling computer. I want to have it calibrated with my CCS' computer so that they show the same speed, and are recording the same number of miles. With my other bikes, I have always done a roll-out measurement to get the right number to set the computer up. With my CCS, a roll-out measurement was not practical for a variety of reasons.
I think that the default setting for 700c on the Bell is 2124, and the default setting on the CCS computer is 2225.
At first, I tried the default, which was obviously too small. Then I checked the CCS' computer and saw that it was set a 2225, so I tried that on the Bell, and it was to big. I spent several rides changing the number several times a ride, and then riding more miles to find the Goldilocks number, and I think I have it.
(Drum roll, please)
The magic number for my bike is:
2197
This is with the stock tires aired up to just under max pressure.
Hope this might save someone some time or frustration.

 

[Bruce Arnold]

I also experimented with this. With the Marathon Pluses, a setting of 2237 on the CCS computer returns a distance equal to the GPS tracker on my smartphone

 

[Badgerdogmomma]

I also experimented with this. With the Marathon Pluses, a setting of 2237 on the CCS computer returns a distance equal to the GPS tracker on my smartphone

Interesting. I haven't compared my smartphone readings yet. If they are too far off, I may want to change the CCS and Bell later. When they did not agree, it was distracting and annoying. Now that they are the same, I am much happier, haha.
In the past I have read that the computers set with a roll-out measurement are actually more accurate than a gps. I do know that on a ride of more than about 7 mi on any of my other 3 bikes that were set up with a roll-out measurement, that my smartphone app says that I have ridden a little farther than the computer on the bikes. That doesn't bother me, though, because I can't see it happening during the ride, and if it is longer ride, I can congratulate myself on the extra distance traveled. ; )