new sigma bicycle computer

[Jay_wolf]

My acewell came with a Set of Wheel guides , the Rim is a 17 inch ,so i looked it up  and because its a Magnet epoxyed on to the rim , and the sensor is on the fork leg  it says for a 17 inch wheel, input 1357  admitedly its having its mot soon , as its SORN at the moment i havent got to test it for more than 7 mph lol

[tripleb]

That's weird.  I rolled the bike out and measured the wheel length that way.

With the 1357mm setting I couldn't get the bike past 60mph on the speedo so you might want to roll yours out for your acewell too.

[Kerry]

My acewell came with a Set of Wheel guides , the Rim is a 17 inch ,so i looked it up  and because its a Magnet epoxyed on to the rim , and the sensor is on the fork leg  it says for a 17 inch wheel, input 1357 [...]

What you're saying finally sunk into my brain.... 

Maybe it will help to visualize what happens as the wheel spins.  No matter how far from the axle you mounted the sensor...
        * at the hub
        * halfway up one of the spokes
        * at the edge of the rim
        * at the outer diameter of the tire itself
... the sensor would detect the same number of rotations for a given distance of travel.  That's because all of those "virtual mounting points" rotate at the same rate - after all, they all go around together.  (Imagine if they didn't!  )

The important thing for your computer to "know" is the road distance represented by each one of those rotations.  If you had no tire on your rim, and the rim were REALLY 17" in diameter, then 1357mm would be the correct setting:

     circumference = pi x diameter
                   = 3.14159265 x (17 inches x 25.4mm/inch)
                   = 1356.5mm    (Rounds up to 1357)

However, there are two problems with these numbers.  First, the rim is NOT actually 17 inches in diameter.  I just went out with a tape measure and eyeballed it, and it looks more like 17.5 inches.  But that's OK - I wouldn't recommend testing your computer with no tire mounted on the rim anyway. 

More importantly, there IS a tire mounted on the rim.  The "eyeballed" diameter for my 110/70-17 BT45 front tire is somewhere around 22 inches, giving the following (estimated) results:

     circumference = pi x diameter
                   = 3.14159265 x (22 inches x 25.4mm/inch)
                   = 1755.5mm

tripleb's circumference figure of 1797mm denotes an actual diameter (for his particular front tire) of 22.5 inches.  So, he's on the right track.  "Roll it out" and measure it!  (An actual circumference measurement will be more accurate than a calculation based on an "eyeballed" diameter. )

[Cal Price]

Cor........now I know why we missed Kerry so much.

[OPTheory]

Questions for those of you with sigma bicycle computers:  What kind, and how long do the batteries last in these guys?  Do I need to keep pressing a button in order for it to light up or does it automatically light up in the dark?

My speedometer is broken and rather than paying $150 to get it replaced I figured I can get one of these instead.

[Jay_wolf]

Mines Designed for a motorbike ,so it runs off the battery , and the Light is on all the time , like a stock gauge , u only see it in low light conditions

[OPTheory]

Mines Designed for a motorbike ,so it runs off the battery , and the Light is on all the time , like a stock gauge , u only see it in low light conditions

Very nice!  But then again, yours costs the equivalent of $150 vs. the $16 for a bike meter soooo...

It's also a tachometer, right?  How responsive is it to sudden changes?  Is it jumpy? Did you get one because one of your other gauges were broken?

I'm trying to find a place to buy one in the US unless anyone knows of a viable substitute.

[tripleb]

the sigma isn't permanently backlit so if you ride it at night you'd have to keep pressing a button.  but for only $30 USD its a pretty good deal.  I've only had it for a few weeks, but it works great and I love it.

[510]

Questions for those of you with sigma bicycle computers:  What kind, and how long do the batteries last in these guys?  Do I need to keep pressing a button in order for it to light up or does it automatically light up in the dark?

My speedometer is broken and rather than paying $150 to get it replaced I figured I can get one of these instead.

I honestly wouldn't recommend a bike computer as a substitute for a speedometer. It updates pretty infrequently, I think every second or so, and even the backlit models require you to press a button to keep them lit.

If you want a gauge replacement then get a computer designed for a motorcycle, like an Acewell. Or if you have even more money to burn, a Veypor.

[Jay_wolf]

No well i did it because i wanted a one off bike , but then came the Kat front end ,so it was even better ,

Its a speedo and tach ,no. the tach is spot on ,runs off the Coil ,

it has a bar on it , and a XXXXX rpm .so 7k would be X7000         and 11k  would be 11000

Im putting a Mini Tach on it anyways for when u need to Really Shift at 11.5 or what ever , im sure the acewell would do it , but i like the idea