16 Tooth Front Sprocket vs. MPG?

[jonathan180iq]

Here's something to thoughtfully chew on. This is in response to a few posts on another forum about how sprockets affect gas mileage. Now, in reality, I've personally seen an increase. This is not to say however that I haven't simply changed my driving habits.

Let me know what you think.

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Theoretically Irrelevant

The physics folks in here will be able to give you a much better description of this...

Think of it as heat = power. You need a certain amount of fuel to generate a certain amount of heat which results in a certain amount of power. An engine/motorcycle has an efficiency curve which is a combination of the engine's efficiency at a particular RPM compared to the coefficient of drag at a particular speed.

All this to say that your fuel efficiency in general is more directly related to your speed/drag than RPM. It's unlikely you'll see a great change in MPG by altering top gear RPM. You still need xx.xHP to go xxMPH.

I have two N250s which get vastly different MPG. One is a stock bike, small windshield, 15x45 gearing, single side exhaust. I usually ride locally with jeans and no saddlebags, and it typically gets 66-68 MPG. My other bike has a very large touring windscreen, a Givi trunk/hard bag, high handlebars, tall gas tank, dual exhaust, and I often ride in my riding pants which have large shin pads which catch more air than jeans. It has 15x44 gearing and gets low 50's for MPG. The difference in these two bikes is most certainly drag, and the fact it's much easier to cruise at 80MPH behind the big windscreen. (i.e. I spend more time at 75+ on the rally bike)

One last thought, the N250 produces maximum torque at about 8,500 RPM. Someone may want to clarify, but I believe this is the most efficient operating speed of the motor. If you gear your bike to cruise at 8,500 RPM you'd be maximizing your fuel efficiency to a certain degree. Note - with the 15x44 and GT501s I'm at about 77MPH (GPS) at 8.5k.

-Duke