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Old 07-01-2009, 01:16 PM
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bigdreamz2000 bigdreamz2000 is offline
Motorized Bicycle Member
Join Date: Oct 2008
Location: Michigan
Posts: 35
Default Re: lousy gas mileage

Originally Posted by brucemg51 View Post
I've checked the volume of the fuel tank. It's 32 ounces, one quart. And that only got me 14 miles. I can't say that I'm completely surprised by this. Although I never bothered to check the mileage before, when I had the stock tank on the bike, I suspected that it wasn't very good, but I had no idea it was this bad. It's hard for me to grasp the idea that the oversize sprocket would cause the bike to get half the mileage that everyone else is getting, but I can think of nothing else.
Lets try some algerbra: 4.5dia/44tooth=x/53tooth x=5.42diameter of your sprocket. Is that right? Now some geometry: The circumfrance of the 53tooth is 17.02inches vs. the 44 tooth 14.13inches.

There are 63360inches in a mile. 44tooth turned 63360/14.3 = 4484 revolutions. 53 tooth turned 63360/17.02 = 3723 revolutions. Hmmm... On a normal bicycle your crank gear is bigger than your hub, but on these it is the other way around. The circumfrence of the 13 tooth is 4.17 inches so it turns 4.08times on the 53tooth sprocket per revolution. It turns 3.38 times on the 44tooth.

13 tooth spins 15189/mile with 53tooth and 15155/mile with 44tooth. A difference of 33 revolutions per mile or 495 more times in your trip. Well that told me nothing because 500 more revolutions isn't going to zap your fuel economy that much. Must have something more to do with engine torque and RPM's per mile. My math has never been very good, but I had fun . Maybe someone could expand or get Geeky on that and enlighten us!

Last edited by bigdreamz2000; 07-01-2009 at 01:18 PM. Reason: Don't know
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