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Old 01-22-2016, 08:42 AM   #2 (permalink)
adam728
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Join Date: May 2008
Location: Michigan
Posts: 161

Mazda3 - '08 Mazda 3 S
90 day: 29.65 mpg (US)

DR650SE - '13 Suzuki DR650SE
90 day: 46.16 mpg (US)

Wife's - '12 GMC Terrain SLE-2
Thanks: 2
Thanked 22 Times in 18 Posts
Quote:
Originally Posted by ProDigit View Post
We now want to calculate our MPG gains.
If with our stock riding, we got 70MPG, mainly a mix of 3/4th city and suburbs, and 1/4th highway; our new MPG should come close to:
70MPG * 15/14 * 33/28 = 88MPG
The formula is derived from:
MPGstock * New front sprocket / stock front sprocket * stock rear sprocket / new rear sprocket)

We have gained an average of 18MPG compared to stock!!
Playing with gearing is always fun, and I often think many people could benefit from it but are too afraid to play with changing it.

However, I don't understand the part I quoted above. MPG isn't a linear equation with rpm change, ie, cutting rpm in half doesn't necessarily double mpg. Just like a 8.5% change in gearing on my bike (geared down for off road) only netted about a 2% reduction in fuel economy riding the same route and habits commuting to work.
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