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Cyclecomputer Calibration Chart

Calibration Chart Models Not Listed Sizes Not Listed
Rollout Test Measured Course Test ISO Tire Size Approach
Most bicycle computers use one of six different calibration systems to allow the user to tell the computer what size wheel the bicycle uses.

I have used the letters A through F to designate the six different systems in common use.

To find your calibration number, refer to the list below to find which is used by your computer. Then, use the chart to find the appropriate value for your tire size (and whether you want readings in miles or kilometers.)

If you click on the name of your cyclometer model, you will go to a specific chart for that calibration family.

If you have a computer model that's not listed, here, most likely it uses one of the 6 calibration schemes shown. Remove the batteries, wait a few minutes and reinstall them. A calibration number will usually appear. This default value will normally be for a tire in the size range of normal full-sized tires, and if you examine the chart, you should be able to figure out which calibration group to use.

Most manufacturers use the same calibration formula for all models, so if your make is listed, but not your model, try the formula listed for other models of the same brand.

In addition to the raw calibration numbers, I have on-line instructions for some models. If your computer model name is highlighted on its calibration chart, that is a link to the Calibration Procedure Instructions Page entry that applies to that model.

If you want to print out a general version of the Cyclometer Calibration Chart, click here.

These values will give a pretty good approximation, usually within 1-2%. If you have an tire size that is not listed, interpolate (split the difference) between the next larger and next smaller sizes listed.

For higher precision, refer to the sections on:

This site also has pages on:
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MakeModel Calibration:
Miles
Calibration:
Km (if different)
ActC-3 C
C-0.5 C
AdventAC500 E / 10 (Miles) C (Km)
AtechCycle Computer; KA-4, 8, 10 F
AvenirAV-1 C
5000 E
Avocet15 F
20 B
25 F
30, 31 B B + 1 (Km)
35, 40, 45, 45tt, 50 AF (Km)
BikemateBrio7 F
CatEyeAstrale F
Astrale, Astrale 8 F
ATC F
Enduro, Enduro 2, Enduro 8 C
Kosmos F
Mate C
Micro C
Mity, Mity II, Mity III, Mity 8 C
OS F
Solar E (Miles)F (Km)
Solar II F
Tomo C
Vectra C
Velo 2, Velo 4, Velo 5, Velo 7, Velo 8 C
Wireless C
Ciclomaster Most models D
CM-37 C
Diamondback AC-3 F
Echo All models F
Equus C
MaguraVelotronic 5, 7 F
Velotronic Easy D x 1.242D x 2
MongooseCompact Cycle Computer
Nashbar NA-CCF
ParamountSeries 8 F
Series 10 E (Miles) F (Km)
PLS 200 F
Planet Bike Protege 5, 8, 9 F
Polar S625X F
CS200cad F
Raleigh Pro 7 F
AS 816 Wheel Diameter (inches)
Sachs Hurét Road Monitor 1, 2 E (Miles)F (Km)
SchwinnFunction 12 F
Speed Thing A (Round to 1")
ShimanoFlight Deck 6500 F
SigmaBC 300 E/10
BC 500 E (Miles)F (Km)
BC 1100 E
SpecializedSpeed Zone C
Speed Zone Comp Tire size menu
SSB SB2006 Plus C
SB2003 Wheel diameter (inches)
Trek Radar F
Sensor F
Sonic F
Sonic 2 F
VettaCycle Computer (Original) E (Miles)F (Km)
Compact Cycle Computer F
C-5, C-06, C-10, C-15, C-16 F
C-20 A (Miles)F (Km)
C200 (Wireless), C300 F
C500 (Wireless) F
HR1000 F
RT33, RT55, RT77, RT88 F
VHR25, VHR50, V100, V100A, V100HR F

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Tire SizeISO Group A Group B Group C Group D Group E Group F
700 X 56 56-622 91.53 249 232 370 1444 2325
700 X 50 50-622 90.29 246 229 365 1424 2293
700 X 44 44-622 87.55 236 222 354 1382 2224
700 X 38 38-622 85.82 231 218 347 1355 2180
700 X 35 35-622 84.21 230 217 345 1347 2168
700 X 32 32-622 83.22 227 216 342 1339 2155
700 X 28 28-622 82.55 225 214 336 1327 2136
700 X 25 25-622 82.12 223 211 335 1308 2105
700 X 23 23-622 81.56 222 210 333 1302 2097
700 X 20 20-622 81.02 221 209 332 1296 2086
27 X 1 3/8 35-630 85.08 232 217 345 1349 2169
27 X 1 1/4 32-630 84.33 230 216 343 1343 2161
27 X 1 1/8 28-630 83.58 228 216 342 1339 2155
27 X 1 25-630 82.91 226 215 340 1333 2145
26 X 2.125 54-559 82.12 225 207 330 1286 2070
26 X 1.9 47-559 80.63 220 206 324 1276 2055
26 X 1.5 38-559 77.71 212 199 312 1234 1985
26 X 1.25 32-559 77.44 206 195 311 1213 1953
26 X 1.0 25-559 75.31 205 191 305 1189 1913
26 x 1/650C25-571 76.85 206 195 311 1213 1952
Tubular Wide 83.34 224 212 338 1316 2117
Tubular Narrow 82.12 223 210 335 1308 2105
26 X 1 3/8 35-590 81.41 222 207 330 1288 2068
24 Most 75.43 205 192 305 1191 1916
24 x 1 25-520 69.01 188 175 279 1089 1753
20 X 1.75 44-406 60.15 158 150 254 927 1491
20 X 1 1/4 28-451 63.70 173 162 257 1005 1618
18 x 1.5 40-355 75.94 207 137 218 849 1367
17 x 1 1/4 28-369 52.17 142 133 211 838 1325
16 x 1 3/8 35-349 50.47 137 128 204 797 1282
16 x 1.5 37-305 42.3 115 108 172 670 1079
Formulas: Circum.
inches
Circum.
inches
X 2.727
Circum.
cm
Radius
mm
Circum.
mm
X .621
Circum.
mm

Inconsistencies

The calibration charts are to a large extent based on instruction sheets provided with various cyclecomputers. Different manufacturers would have used different brands of tires to calibrate, so there are some areas where there is slight inconsistancy in values between one group and another.

If you requre greater accuracy than this chart provides, do a rollout test or measured distance test.

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Sizes Not Listed

The charts don't list all possible tire sizes, but do list the most popular ones. If your marked tire size falls between two sizes shown on the chart, interpolate the appropriate calibration number between those above and below.
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Models Not Listed

If you have a computer model that's not listed, here, most likely it uses one of the 6 calibration schemes shown in the chart. Remove the batteries, wait a few seconds and reinstall them. A calibration number will usually appear. This default value will normally be for a tire in the size range of normal full-sized tires, and if you examine the chart, you should be able to figure out which calibration group to use.

A little bit of experimentation should show you which button does what. Often switching from mode to mode, or entering "set" mode is accomplished by holding one of the buttons for several seconds.

If you have imformation on any newer models or others that I might have missed, please

let me know, so that I can update later editions of this listing.

Copyright © 1995, 2007 Sheldon Brown

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Roll-out Test for Super Accuracy

The values on the chart will generally give a value accurate to within one or two percent, which is more than good enough for the vast majority of cyclists, and is much more accurate than most automobile odometers. If you require more accuracy, you can do a "roll-out" test. Since the effective tire size is affected by tread thickness, tire pressure, and rider weight, the rolling circumference should be measured by rolling the bike with the rider aboard for one wheel revolution.

You may use the valve stem as a reference, starting the roll with the valve right over a perpendicular line on the floor, and ending when the valve is back at its low point one revolution later.

Another approach is to put a small dot of paint on the tire and measure the distance between the marks that the paint prints on the road. With either approach, the rider must hold the handlebars absolutely straight while an assistant balances and pushes the bike. Otherwise, the wheel may not follow a straight path.

Once you have measured the rolling circumference, use the formula indicated to find the calibration number for the cyclecomputer involved. For cyclecomputers that require a radius value, divide the measured circumference by 6.283 (2 x π) to get the radius.

Formulas:

A Circumference in inches
BCircumference in inches X 2.727
CCircumference in centimeters
DRadius in millimeters
ECircumference in millimeters / 1.6093
FCircumference in millimeters

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Using a measured course to fine-tune your setting

If you have access to a measured course, you can fine tune your settings by riding the known distance and checking the reading. Divide the actual distance by the cyclometer's mileage reading, then multiply your calibration number by the result to get a corrected calibration number.

Actual Distance
Cyclometer Reading
 X  Old Calibration Number = New Calibration Number
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Deriving tire diameter from ISO/ETRTO numbers

The I.S.O. tire size consists of a tire width and a bead seat diameter. Both of these numbers are in millimeters. For example, a 28-622 (700 x 28C) tire has a nominal width of 28 mm on a rim with a bead seat diameter of 622 mm

To get an approximate diameter (in mm) add the bead seat diameter to twice the tire width (since the tire comes into the diameter twice: 622 + (28 X 2) = 678. Multiply this by pi (3.142) to get the circumference in mm (F) 2130. Appropriate calculations will yield calibration numbers for computers in other groups.

(Thanks to Chris Ziolkowski for suggesting this.)

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I would like to thank those who helped with updates and error spotting, including: John Allen, Miha Ambroz, Badarka@aol.com, DaveM10@aol.com, Richard Drdul, Peter Epstein, John Everett, William Fallon, Rich Kim, Doug Milliken, Richard Nelson, Dave Poleshuck, Liam Relihan, Cliff Schlueter, Rich Shapiro, Emil Sit, Steven Sheffield, Adam Spiers, Rick Teichler, Jack Tingle, Kris Vlæminck and Desmond Walsh.

Feedback? Questions?

Harris
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Copyright © 1995, 2008 Sheldon Brown

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