Branford Bike - Started in June, 1976 Branford Bike
129 Sagittarius Skyway, PO Box 1711, Emigrant, MT 59027 USA
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Bicycle Computer Section: Page 11

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Calibration Chart for Bicycle Computers
 
Q: Is wheel circumference that 3 or 4 digit number that I must program into my computer every time I change the batteries?
A: Yes. That 3 or 4 digit number represents the exact circumference of your wheel in centimeters (3 digit) or millimeters if it is a 4 digit number. This number MUST be entered in millimeters or centimeters; inches will NOT work.

Q: What is the relationship between circumference and diameter?
A: Circumference divided by pi(3.14) equals diameter. A wheel with a circumference of 112 cm will have a diameter of 35.6 cm. The math is: 112 cm divided by 3.14 = 35.6 cm.

Q: What wheel sizes will bike computers accept?
A: Cateye computers will generally accept wheel circumferences from 112 cm to 255 cm. Put another way, that represents wheels from 14 inches (35 cm) to 32 inches (81 cm) in diameter. Sigma Sport and Topeak computers will accept a wheel size from 1 to 50 inches ( 2.5 cm to 127 cm) in diameter. Topeak and the Sigma Sport BC600, 800, 1200, 1400 and Targa all use the more precise 4 digit, wheel setting numbers.

Q: What is the best way to measure wheel circumference?
A: The most precise method is to use a 6 foot (2 meters) piece of single strand, 16 to 20 gauge wire. Bend a small "L" on one end and then tape that end to the center of your tire's tread. Be sure to bring your tires up to the normal pressure that you ride with first. Then, lay the wire lengthwise along the outside of your tire's tread and use electrical tape to hold it in place. When you come back around to your starting point, bend another "L" in the wire. Now carefully remove the wire and precisely measure it. This measurement will be the exact circumference of your wheel.
Different width, brands and types of tires will have different circumferences. If you race on one set of wheels and train on another we recommend precisely measuring both sets. If the circumference difference is more than 5% we suggest using a computer that allows for two wheel settings. Your speed and distance readings will be more precise and make more sense.

The calibration chart below gives approximate values for the circumference of various size tires. For an exact measurement and precise readings we suggest using the method detailed above.

For the following Cateye computers use centimeters; AT-100, Mity, Mity 2, Mity 3, Enduro, Velo 1 & 2, Dual, Mate, Micro, Vectra, and Cordless.

For the Cateye HB-100, Cordless 2, Kosmos, Astrale, Solar II and ATC, use millimeters.

If you have the original Solar and are using it for miles per hour, the "Solar (mph) column is for you. If you are using an original Solar for kilometers per hour then use the Millimeters column.

The Cateye calibration chart may be used for any computer that requires a tire circumference size in centimeters or millimeters.
 
Tire Size
as stamped on the sidewall		 Approximate Circumference
in Centimeters		 Approximate Circumference
in Millimeters		 Solar (mph)
700x38c21821801355
700x35c21721681347
700x32c21621551339
700x28c21421361327
700x25c21121051308
700x23c21020961301
700x20c20920861296
27x 1 3/821721691349
27x 1 1/421621611343
27x 1 1/821621551339
27 x 121521451333
26x 2.3520820831293
26x 2.12520720701286
26x 2.120720681281
26x 2.020620551280
26x 1.920520501276
26 x 1.7520220231255
26 x 1.7520219851234
26 x 1.019119131189
26x 1.0 (559 mm)19519521213
26x 1 3/8 (650 c)20720681288
24x 117517531089
20x 1.751501491927
16x 1 3/81281282797
 
Questions and answers are courtesy of our sales staff and customers.
The Calibration Chart is courtesy of Cateye.
 
Q: How can I get more information regarding my Cateye computer?
A: Call Cateye at 1-800-522-8393. They can assist you with problems or questions. Please call us if you run into any problems.

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100% Satisfaction Guaranteed

At Branford Bike we want you to be happy and satisfied with everything you purchase from us. We understand that sometimes you will need to return a product because it was not quite what you wanted. You may return anything you purchase from us within 60 days and unused, for an immediate exchange or refund.
 
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Featuring FAQ's, Frequently Asked Questions
Computers
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