# Computer Settings



## wavz (May 30, 2007)

I'm just wondering if my computer is set right. My tires are WTB Velociraptor 26x47/52 which equals out to 26x2.00 from what I understand. I have a Sigma BC 906 computer, and it seems as if the distance I logged last ride was off. So I was wondering how you all calibrate your computers for rides to see if they are accurate? I'm new to bike computers so any suggestions would be a great help. :thumbsup: Good looking out :thumbsup: 

Wavz


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## shiggy (Dec 19, 1998)

wavz said:


> I'm just wondering if my computer is set right. My tires are WTB Velociraptor 26x47/52 which equals out to 26x2.00 from what I understand. I have a Sigma BC 906 computer, and it seems as if the distance I logged last ride was off. So I was wondering how you all calibrate your computers for rides to see if they are accurate? I'm new to bike computers so any suggestions would be a great help. :thumbsup: Good looking out :thumbsup:
> 
> Wavz


Do a rollout measurement. The manual should tell you how.


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## Speedub.Nate (Dec 31, 2003)

As Shiggy suggested, "roll your own."

The process is simple, and requires a tape measure and maybe a calculator.

Inflate your front tire to your average riding PSI.

Extend the tape measure out along a sidewalk.

Line the valve stem up with the '0' mark on the tape measure (which is more than adequate; the zip tie I used in the photo below was just for demonstration, but is potentially more accurate -- I always use the valve stem).

Put some downward pressure on the handlebar to simulate your weight, and begin rolling forward.

Two... Three... Four revolutions forward, whatever you can muster, then stop and take a reading where the valve stem is at the 6 o'clock position.

Divide the measurement by the number of wheel revolutions for your circumference. To convert to centimeters or millimeters, if your computer requires it, multiply by 2.54 or 25.4, respectively.

I usually do three roll-outs and average the results. But it's not necessary to get that anal about it -- a difference of a few millimeters won't make a noticable difference either way.


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## wavz (May 30, 2007)

Thanks for the help! I rolled my own as you both suggested and pow it is right on now! I guess the wheel sizes in the manual are just rough guidelines, because it said my settings were supposed to be 2114mm when actually they were 2032mm. Just a slight bit off  . Again thanks for your help :thumbsup: 
Wavz


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