I just bought a cyclocomputer

Measure the distance travelled in one complete turn of the wheel.
Do this by sitting on the bike (which gives a more accurate measurement) with the valve stem at the very bottom near the floor (either front or rear - I use the rear). Have someone make a mark at dead bottom where the valve stem is closest to the floor and then slowely move the bike forward until that very same valve stem reaches dead bottom once again (one complete wheel revolution). Make a mark on the floor once again at this point. Measure the distance between the two marks (metric) and that number in MM is the number you put into the computer. The other method is to find your tire brand/size on the chart and enter into the computer the corresponding number, but the roll-out method is more accurate.

melanie610 said:

Hey, I just bought the Sigma Sport BC 1600 and I can't figure some stuff out. Well basically, I'm stuck at wheel size. I think I figured out how to measure (as far as what I think the manual is telling me to do) but I can't figure out what the formula is to turn that number into a four digit number that is needed to put into the computer. Also, I may not know how to program anything else, but I haven't gotten past this yet. Does anyone have this computer and can help me out? I'd really appreciate it; I want to start using it. Thanks!

WoodieKnot said:

Measure the distance travelled in one complete turn of the wheel.
Do this by sitting on the bike (which gives a more accurate measurement) with the valve stem at the very bottom near the floor (either front or rear - I use the rear). Have someone make a mark at dead bottom where the valve stem is closest to the floor and then slowely move the bike forward until that very same valve stem reaches dead bottom once again (one complete wheel revolution). Make a mark on the floor once again at this point. Measure the distance between the two marks (metric) and that number in MM is the number you put into the computer. The other method is to find your tire brand/size on the chart and enter into the computer the corresponding number, but the roll-out method is more accurate.

Well, I had done that already, but the manual gives an example of a 4-digit number and the computer allows for four digits. I calculated a 3-digit number. Am I just doing the math wrong or is there something missing or does it not need to be four digits?

What was the measurement in milimeters for one complete wheel rotation?

For me, when I measured the wheel rollout, I came up with 72 7/8 inches (72.875). You will need to convert this to millimeters. In my case the converted number was 1851.025

Take this number and divide it by 1.61 for MPH.

1851.025 / 1.61 = 1149.7 (the setting is whole numbers only, so I entered 1150)

melanie610 said:

Well, I had done that already, but the manual gives an example of a 4-digit number and the computer allows for four digits. I calculated a 3-digit number. Am I just doing the math wrong or is there something missing or does it not need to be four digits?

WoodieKnot said:

What was the measurement in milimeters for one complete wheel rotation?

For me, when I measured the wheel rollout, I came up with 72 7/8 inches (72.875). You will need to convert this to millimeters. In my case the converted number was 1851.025

Take this number and divide it by 1.61 for MPH.

1851.025 / 1.61 = 1149.7 (the setting is whole numbers only, so I entered 1150)

Nevermind, I just used the measurement on my wheel. Thanks though!

melanie610 said:

Nevermind, I just used the measurement on my wheel. Thanks though!

There is a very handy guide to cyclocomputers here:

http://sheldonbrown.com/cyclecomputers/index.html

Good Luck!