So I just got this bike computer hardware installed and it looks like everything is working fine. Now I'm trying to figure out what wheel size to use and here's the problem. Number one (#1), the manual sucks. Number two (#2), my wheel size is 26" X 1.95" which I thought was a really common size but it's not listed in the manual or on Sheldon Brown's conversion chart.

When you enter wheel sizes into the bike computer, it has a decimal point after the first digit which confuses me. What is the actual unit of measure on this puppy? And now, here's the main problem.

The values in Sigma's manual that came with the unit are DIFFERENT than the Sheldon Brown website, and neither one of them shows any decimal points. So, which one is right or wrong? I guess I have to average the two closest sizes and use that for 26" X 1.95" ?

I have two of the things and they are the most confusing computer I've ever used.

I'm doing better the less I touch it.

What's wrong with 2101 or 2102? It's only like a few ten thousandth of a difference, I doubt you'll notice.

-spence

For a 26" X 1.9" size, Sheldon Brown shows 2055 but the Sigma manual shows 2089. Then, when you go to actually enter it in the computer, the display has a decimal point which I don't understand.

Should I use 2055 or 2089, and do I need to convert it to something else because of that decimal point on the computer display?

Thanks.

2055 or 2089 would be in millimeters; maybe your computer uses centimeters, so you would input 205.5 or 208.9, thus the decimal point.

These values are different by about 1.5%; do you need better accuracy than that? If not, just pick one, or use the average. If you want better accuracy, you can do a rollout test - lay a tape measure on the ground, line up your valve stem with the end of the tape, roll your bike along the tape until the stem is again at the bottom, and read the tape at that point. If your tape is in inches, multiply by 2.54 to get centimeters.

https://www.bikeforums.net/commuting/557173-sigma-1200-wheel-size-chart-question.html

Ha, been there, done that.

As sakonnetclip says, Sigma 1606L is the "most confusing computer".

Had similar problem with 700x38c tires -- Sigma manual says nothing about them. When I contacted Sigma, they emailed me the same table that is in their user guide, w/o the data for 700x38c tires. Sheldon Brown's number for the 700x38c tires is 2180. For some reason I put there 2219. So I'm off by 1.7% -- 15 miles (with 221.9 number in my Sigma computer) is actually 14.73 miles according to number in the Sheldon Brown's table. Not a significant difference and I don't want to "play" with the setup to knock out other settings by accident.

Why is that decimal point there? Maybe it's in cm instead of mm.

See the attachment. Seems to me they explain the computer setup in simpler way than their manual.

Mine is last generation, but I found if I'm going to use miles per hour, I have to use the "non-millimeter" chart to find the standard entry. Before I did this, my speeds were like 19 mph on my touring bike when pedaling in Zone 1 - no way, given my Cat 7 fitness. Speed readings returned to a plausible range when I went back and used the inches table.

Yes, the manual sucks, but if you have a manual that fits your model, why do you use Sheldon's? It has to be out of date by now. Has somebody been maintaining and updating Sheldon's pages? The man can't do it himself, anymore, sadly.

My sigma 1606L is in meters, ie 2.055 or 2.089. I always use the roll out test, it's quick and ez and super accurate (especially if you put some weight on the bike as you roll it, but that's splitting hairs).

Is there any way to make it show miles per hour in .1 increments instead of .5 ?