Bike Computer & Distance

[GTWilliams]

I own a Sigma 1200. I really like it but the battery finally died and I replaced it and had to relearn how to program it. I have 700x38 for my hybrid, so the setting was 1374 to convert it to MPH. I'm kind of a detail person so I tested it with two different car odometers. The bike computer was well short of a mile. e.g. 100-150 feet. To get the computer to a mile I had to fib and tell my computer the tires were a full two inches shorter than they are!! That's WAY off. Yes, I've measured from top of tire to bottom...not the wheel. I've triple checked Sigma's formula and it is correct. But I wonder if Sigma programmers dialed in the wheel size and not the tire...not following their own directions. I have not taken the bike to a running track yet to check distance.

But is the computer wrong? Have you really checked your bike's odometer? Was it close? Any other problems w/ Sigma? Any ideas?

Todd

 

[PeterF]

I own a Sigma 1200. I really like it but the battery finally died and I replaced it and had to relearn how to program it. I have 700x38 for my hybrid, so the setting was 1374 to convert it to MPH. I'm kind of a detail person so I tested it with two different car odometers. The bike computer was well short of a mile. e.g. 100-150 feet. To get the computer to a mile I had to fib and tell my computer the tires were a full two inches shorter than they are!! That's WAY off. Yes, I've measured from top of tire to bottom...not the wheel. I've triple checked Sigma's formula and it is correct. But I wonder if Sigma programmers dialed in the wheel size and not the tire...not following their own directions. I have not taken the bike to a running track yet to check distance.

But is the computer wrong? Have you really checked your bike's odometer? Was it close? Any other problems w/ Sigma? Any ideas?

Todd

My 1200 was way off when I used Sigma's settings for 700 x 23 tires. Whenever I went for long rides with my club, my computer always showed the distance to be longer than everyone else's. I measured the wheel (marking a line on the floor and measuring one full revolution) and it was way off from the factory recommendations. The 1200 is a nice computer, but you are better off relying on your own measurements when calibrating it.

 

[GTWilliams]

I made the original post. Funny ending...It ends up my 2002 Yukon says 9.6 miles for every 10 travelled. I blew the dust off a GPS I never use, found a straight road and went to work. If I enter in the wheelsize Sigma recommends, I end up going 1.02 miles for 1.00 on the GPS. In other words...perfect.

I was going to tweak to perfection when I realized:
A) I don't ride perfectally straight and...
B) I had to go slightly up and down hill. The GPS might think I rode in a more linear fashion (through the hill).

I guess my point is if you have a Sigma, trust the formula! And check your car odometer while your at it. If you have a GPS, find the straightes AND flattest road you can. Also, most all running trackes are in meters so don't test his way!!

Todd