codye1

I am just starting to ride more. Someone gave me a Sigma Sport BC 1600 wired computer. I have measured the tire on the floor converted it by 25.4 also found site that gave the tire size but the 1600 still not not record the correct distance, off by a little less then a quarter of a mile within the 1 mile I rode. Any ideas are welcome.

cb400bill

Welcome to Bike Forums. We have moved your thread from our Introductions forum to our Electronics forum.

Tourist in MSN

It would help if you listed your measurement and also listed the tire size that list on the tire. If you see the number 622, is there another number next to it?

Iride01 

3.14 *(BSD + (2 * tire width) ) works surprisingly well.

Though I do a rollout for at least two revolutions of the wheel and divide by the number of revolutions. Everything converted to millimeters.

You can put a spot of ink or paint on your tire tread and look for the marks if you don't care about the surface you are marking up. Ensuring your tire is inflated to your riding pressure and you on the bike might make it even more accurate.

You can be off by a little more than 1.6 inches (42 mm) and still be 2% margin of error if this is a 700C tire.

codye1

Tire size 700 x 38 C. I rolled once 86.5".

Tourist in MSN

My 37mm wide tire that is 700c would be very close to yours, I use 2204mm in my bike computer for that tire. That is very close to the 2197mm that your tire would be.

If your distance that was measured was much shorter than the distance traveled, could be weak battery or could be the magnet was not close enough to the wheel sensor.

If the battery is new and the sensor is quite close to the wheel magnet, maybe it would be best to take the battery out of the computer and let i sit a few minutes so that the computer forgets everything. Then put it back and and start all over including entering your wheel data and trying one more time.

If it is a wired computer, sometimes a wire that is broken could provide sporadic readings.

I am assuming you have a computer that can provide both mile and km readings, make sure you set it for what you want. When I go to a foreign country, I change my setting to km so that my distance matches the maps and road signs. Once when I came home I forgot to change back to miles, took me a couple days to figure out why my readings were so screwy.

Iride01 

There is always the question of how do you know the distance you compared it to is correct.

VegasTriker

This is the first bike computer I came across that doesn't have a setting for mph vs kph but requires you to put a different setting in for the wheel circumference. There is a wheel size table in the manual listing 700C X 35 and 700C X 40 but no entry for 38. The mph setting for 700C X 35 is 1370 and for 700C X 40 is 1381. The closest estimation for your tire would be 1376. If the number you calculate using a runout is much different from this value, that is your problem with accuracy. See page 14 https://www.manualpdf.us/sigma/bc-1600/manual?p=6

Tourist in MSN

Based on Vegas Triker info, I obviously gave you incorrect advice. I appologize. Every computer I have used required the circumference to be entered and has a choice for mph or km/hr. I am guessing that your distance traveled that you assumed was incorrect when you irst tried it was the km that you traveled, not miles.

codye1

I checked the distance with my vehicle. I would not think I would be 1/4 of a mile off in 1 mile. I will leave the battery out for a longer time and put the readings mentioned above tomorrow. The magnet connections look very close maybe a 1/16" or so gap.

Iride01 

You've never stated exactly what calibration number you put in. Was it the 86.5" converted to millimeters which is 2197?

codye1

Yes 2197 is what I originally put in.

2_i 

The bike computer sensor reacts to the magnet passing by. The computer counts how many times the magnet passed and scales it with the entered circumference. Any wrong result must come from an incorrect circumference or incorrect counting. A 25% error should be easy to track. The incorrect counting would be due to a weak or incorrectly mounted magnet, but could be also to some poor connection between the sensor and the computer or malfunction of the sensor. Using an easy scaling factor on the computer, such as 2000, and passing magnet by hand by the sensor fast enough could help. Cleaning the contacts to the computer is an obvious action to take as it is cheap.

Iride01 

Have you done any more rides since this one? With any trouble shooting, it helps to have some repeatable instances of the issue. If it's an outlier of many rides, the why are we even bothering?

codye1

Thank you. 1370 came out almost perfect to the mile based on what my vehicle registered.

Tourist in MSN

1370 / 2197 = 0.6236

1 km = 0.6214 miles.

I think you fooled a computer that was designed to read out in km and km/hr to read out in miles traveled and mph instead. Interesting.

codye1

I have the option to select km or miles. I selected miles. If I fooled the computer, I did not know it. But all is good.