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

[Sarris]

Mines about 2 more MPG. As for all that theory, it's all bullshit.
:chop:

[Dirt_McGert]

Drag (wind resistance) plays a large part in fuel economy - the more drag, the more fuel you need to keep operating at a certain speed. Weight plays a large role too. However, so does engine size and engine speed (RPM.)

"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."

Hmmmmmm... It may be producing maximum power and torque at 8,500RPM, but the engine is also guzzling fuel to keep the crankshaft spinning that fast. It'd be like keeping the throttle maxed all the time in 2nd gear going 25mph on your bike or in 1st gear in your car. The engine speed wouldn't be matching road speed - you don't need that much power and torque that 1st or 2nd gear would give if you're travelling say 40mph.

[jonathan180iq]

Originally Posted by Sarris

As for all that theory, it's all bullshit.
:chop:

thanks for the clarification... :roll:

I'm holding on at a 4 MPG increase real world.

[Easy Rider]

Originally Posted by Sarris

As for all that theory, it's all bullshit.

And you are a qualified expert on which.......theory or bullshit? :??:

I suspect the latter! :roll:

[Sarris]

Originally Posted by jonathan180iq

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

Just my way of ageeing with "Theoretically Irrelevent". No personal affront intended. I'll bullshit no more....

[prof_stack]

I've taught some physics to some HS students and teachers over the (getting up there...) years. Not wanting to get into obtuse equations, which would tax my summer brain :cool: , I will just add some comments.

There should be a modest increase of MPG with the 16T sprocket. Most riders will be cruising at lower RPMs much of their time riding. Remember that the bike doesn't have less power, but that the powerband in each gear is spread out a little.

The motor will usually be a little less stressed which for many will lengthen its life (hmm, that works for people, too...).

[Badbob]

I have to agree with the BS assessment.

If you can't explain it with numbers (math) and some real scientific test results its speculation not theory.

The heat generated buy the engine is wasted energy not a measure of how much power the engine is putting out. You could look at it as wasted power. More powerful engines do generate more heat but this is because they are less efficient.

He claims his riding gear has more drag than jeans. There is no way to know this without some serious scientific testing which has probably never been done. It the same as the idea many people have that a nice smooth windshield has more drag than your chest. There are way to many variables to even make an educated guess.

BTW I got As in my high school and college physics.

[gossterd]

Since I changed to the 16T sprocket I averaged 2 MPG better. ( This average is for two tanks, with the last tank getting 90MPG )

Now if I could eliminate the valley I have to drive through to get to work..... LOL!!

[gossterd]

93.1 MPG this tank :-)
168.5 miles 1.81 gallons