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View Full Version : CABI stats: a mysterious difference in mileage



elbows
03-16-2015, 08:34 PM
Today I rode from 39th & Veazey st NW to Van Ness Metro / UDC and then repeated the same ride back again. I rode the same route. Van Ness is downhill from 39th & Veazey so I knew that I took longer riding from Van Ness and riding with a lot of weight and in my work clothes, I knew my pace was "relaxed", but I find it strange that the mileage distance is so different. What's up with this? Now I feel like I'm going to need to stop eating the CABI calorie counts of girl scout cookies if the numbers are so unreliable.


Start
2015/03/16 12:30:05
Van Ness Metro / UDC
8 m 48 s
$0.00
End
2015/03/16 12:38:53
39th & Veazey St NW
CO2 offset
0.80 lbs
Distance
1.17 miles
Calories burned
50 cals
Gas saved
0.05 gallons

Start
2015/03/16 11:20:41
39th & Veazey St NW
6 m 10 s
$0.00
End
2015/03/16 11:26:51
Van Ness Metro / UDC
CO2 offset
0.56 lbs
Distance
0.82 miles
Calories burned
35 cals
Gas saved
0.03 gallons

jrenaut
03-16-2015, 08:41 PM
I think CaBi just guesses based on your start and end point. Check Google Maps bike directions for those two routes - it wouldn't surprise me if the mileage matched up to the default routes.

chris_s
03-16-2015, 09:56 PM
I think CaBi just guesses based on your start and end point. Check Google Maps bike directions for those two routes - it wouldn't surprise me if the mileage matched up to the default routes.

CaBi bikes do NOT have GPS in them, so it doesn't know your actual route. jrenaut is almost certainly correct on this one.

Brn Moore
03-17-2015, 04:59 AM
IIRC, buried somewhere in their FAQ, it seems that they assume you ride at a constant rate (about 8 miles an hour, I think? Maybe less? I'll have to look later), and guess that you went at that speed for the whole time the bike was out. Their estimated distance is a function of elapsed time, not station-to-station distance.

DCAKen
03-17-2015, 09:42 AM
IIRC, buried somewhere in their FAQ, it seems that they assume you ride at a constant rate (about 8 miles an hour, I think? Maybe less? I'll have to look later), and guess that you went at that speed for the whole time the bike was out. Their estimated distance is a function of elapsed time, not station-to-station distance.

In the Member Area is a link to how they calculate the various figures:


Estimated Distance Traveled: 7.456 mi/h (12 km/h) times the total trip duration of trips greater than or equal to 60 seconds and under 2 hours. Trips over 2 hours max-out at 14.9 mi (24 km).

Gas saved is an estimate using your distance traveled multiplied by 0.04149 gallons per mile (24.1 mpg).

Gas saved = [Distance traveled] * 0.04149

For carbon offset calculations, we use the goDCgo's Carbon Calculator to determine your CO2 output, using 7.456 miles per hour as an average cycling speed. Next, we determine the CO2 output of a midsized car traveling at 21mph for the same distance as your trip. Subtracting your output from the car's gives us your carbon offset.

For calories burned, we start with base equation of averages where a 180lb person traveling at 7.456 miles per hour burns 43 cals per mile. Your calories burned are equal to 43 multiplied by your miles traveled.

PotomacCyclist
03-17-2015, 11:17 AM
That formula seems close but not exactly what I found in a recent trip. I did a longer CaBi ride over the weekend, where I docked and undocked the bike at a few different stations. At one point, I undocked from a station, rode around for a while and docked back at the same exact station. That segment was 24 min. 25 sec. The distance was calculated as 3.26 miles.

If I punch in the numbers using the 7.456 mi/h estimate, I would get 3.034 miles.

It doesn't really matter to me though. If I want to know the estimated distance, I bring my Garmin GPS watch. (I have the Forerunner 220, which I can use for running or on bikeshare.) GPS isn't exact either, but it's close enough for my purposes. I look at the CaBi distance, calories burned, gas saved and CO2 offset as very rough estimates. Some people might use them as motivation for getting out there more often. If so, that's good. But I wouldn't use those numbers to track anything precise. For example, if someone is tracking calories burned and attempting to match them up with calories consumed, the CaBi numbers aren't a very reliable way to do this.

Other calorie counters are also imprecise, I think. When I load my Garmin data to the SportTracks program on my computer, I can click on the button and see an estimate of the calories burned for the session (whether it's cycling or something else). I think the program calculates the number based on my bodyweight, the speed of the session and the duration. But I still don't trust the numbers completely. It would be nice if the numbers were within 20 percent of the true figure, but if isn't, I wouldn't notice.

If I'm trying to lose some of the extra winter fat, then I know that I just have to be more consistent about exercise, and that longer workouts seem to have more of an effect on that. I also monitor myself to make sure I don't overdo it, because once you get injured, your whole fitness program goes out the window.