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Gas mileage guestion?

  • Thread starter Thread starter beby99
  • Start date Start date
I would go with the carb circuit theory. Assuming you are in top gear at both speeds it requires more energy to overcome 75mph wind drag than 65mph wind drag. Keep in mind that the drag increases exponentially not linearly with speed. And wind drag is the big factor. You could get some hellacious mileage figures riding in a vacuum. :) Motorcycles are much "dirtier" than cars aerodynamically.

Aside from any physics involved, does it make sense that a motorcycle company would market a product, particuarly a 650 twin, that operates best at 75 mph in a country where the maximum speed limit was 55 mph?

The test results are strange I have to admit. Try repeating the test controlling for surface winds. If you have a 10 mph headwind your drag will be the same as if you are riding 10 mph faster; for a tailwind, 10 mph slower. Check the local weather and notice which way the leaves and flags are blowing when you ride.

To test the carb theory you could do plug checks after a 75 mph run and after a 65 mph run to see if you can detect any difference in shading. And just for grins you could try doing a 55mph run to see what those results add to the pattern.
 
I vote for hoomgar's theory on this subject.

While it is true that it takes more overall power to ride at, say, 65 mph than 55 mph, fuel economy is not purely proportional to the power needed to maintain a certain speed.

The fuel economy is a measure of how efficiently the engine burns fuel and how efficiently the transmission delivers that power to the wheels.

An engine runs most efficiently at a certain rpm. Go above or below that, and fuel economy will decrease.

For example, try accelerating in a gear that is too high for the speed you are traveling and the engine "bogs," that is, you can open the throttle wide, and you get minimal response. Not an efficient way to run an engine.

If you switch gears to put the engine in its best power area, the engine uses less fuel and is more efficient in accelerating to a new speed.

Conversely, if you are revving the engine too high, you are wasting fuel. Once you are in the top gear, you are limited by the gear ratio you have. You need to run the engine at the rpm that will give max efficiency, which is usually a little less than what gives best power. If graphs are available for these engines, it would be a lot easier to tell what speed is best for your particular vehicle.

Also, each particular vehicle will have different frictional losses in the drivetrain and wheels, and a different amount of wind resistance. Those fricional losses vary with speed. At certain speeds, probably over 60 mph, or so, wind drag predominates and limits fuel economy, as much more engine power is needed to overcome the wind drag.

That's why, for our bikes that are bulky and not streamlined, high speeds will ruin fuel economy more than it might on a sleek sports car.

The trick is to find what works best for you.

Matt
 
dpep said:
Aside from any physics involved, does it make sense that a motorcycle company would market a product, particuarly a 650 twin, that operates best at 75 mph in a country where the maximum speed limit was 55 mph? .
Click to expand...

In the same case, does/would it make sense to make an engine that revs to 9K with a 55mph speed limit?
 
Remember he changed the drive train ratios when he changed the sprocket. Maybe his bike was originally at its best around 55 or 60, now it could be at its best at 75.
 
syafi said:
This really confuse me,

I have GS450L make 1988

Is this mean I can get better milage cruising at 80mph ( 9k rpm )
compared to cruising at 40-45mph ( 4.5k rpm )

I make 100mile trip every 2-3 days going to get my new stocks for my online shop. the road is quite clear but i thought 9k rpm will kill the bike :D

tell me more where i can see the power curves, I cant find it with my search ability for my GS450L 1988
Click to expand...

You have to find what speed your bike runs optimum at. Every one is unique. But there is certainly a speed that will be most economic for you. On that bike I would guess it is around 50 MPH but that is a guess. You have to find it yourself.
 
dpep said:
Aside from any physics involved, does it make sense that a motorcycle company would market a product, particuarly a 650 twin, that operates best at 75 mph in a country where the maximum speed limit was 55 mph?
Click to expand...

You missed the part where he explains that he changed the stock sprockets Don.
 
Clone said:
Remember he changed the drive train ratios when he changed the sprocket. Maybe his bike was originally at its best around 55 or 60, now it could be at its best at 75.
Click to expand...

This gets my vote. That's what I have been trying to say. Thanks guys :)
 
P.S. If it is because you changed the gear ratios, if you return it to stock, and the engine is running at max fuel economy RPM at the lower speed (55-60 mph,) you should have better fuel economy at that speed than you did at 65-75 mph with the current gears.

You will have substantially decreased wind resistance at the same time the engine is operating in its most efficient range.

Matt

The great thing about riding a motorcycle is that you can directly feel the effect increased speed is having on the wind resistance. On my bike, there is no windshield or fairing, and 60 or 65 is the maximum comfortable speed. Above that speed, the wind is awful..
 
Mark (Hoomgar) I guess we will have to agree to disagree on this one, but a good discusion all round on this subject.
Must be why I keep coming back to the GSR!.......... :D :D :D
 
Yup. Everyone stands by their opinion.
The more open a throttle is, the more fuel it uses compared to less throttle, all conditions remaining equal.
Now if a bike is running a faster speed, uphill, but in it's powerband, you'll possibly be at less throttle position than if you're going slower and lugging it, which will create the need to open the throttle more and lessen the mileage despite going slower. Correct/sensible gear choice matters.
But on basically level ground, steady speeds, and the correct/sensible gear choice, the faster you go (more throttle obviously) the more fuel flowing through the motor. No way around that.
 
Well, thanks for making me even more confused. :? I do appreciate all
the comments on this which gives me some ideas to maximize my bikes
performance....Should also note that I have a windshield, saddlebags,
luggage rack with bag. I'm sure wind currents will cause different results
at different speeds. Here's my bike's specs if interested and thanks again:

gr650%20specs.jpg
 
beby99 said:
Well, thanks for making me even more confused. :? I do appreciate all
the comments on this which gives me some ideas to maximize my bikes
performance....Should also note that I have a windshield, saddlebags,
luggage rack with bag. I'm sure wind currents will cause different results
at different speeds.
Click to expand...

Yeah sorry Bret :? Sometimes you can say the same thing 5 times 5 different ways and still not be understood. But it's all good. I just want "YOU" to know that the point I was making to "YOU" was not my opinion. It's just how things work. Period. More throttle equals more fuel equals lower fuel economy.

If you are still interested in knowing what it is all you need to do is go with the throttle marking idea mentioned earlier in this thread. Mark your throttle position when cruising at the speed where you know your getting your max economy and then do a test at the other speed where you know you are not and see what the throttle position is there. You should see that it is using more throttle at that speed. If so, you have your answer, know that it is your new gear ratios and can relax that your bike is fine. If it is not the case, then there may actually be an issue with your bike. My opinion in the matter is that the latter is probably not the case. I am betting your bike is fine.

I was hoping to help you, not start a debate. I hate debates. It is not one of the things I like about the GSR.

Rock on buddy 8)
 
Bret ,I hope all the idea's put forward here can be of some use to,there was no intent to confuse, sorry my friend if it ended up that way.
A big part of the GSR is that it is a mixing pot of idea's and knowledge that help's, and often entertain's.
Good luck with your bike.
 
Adding to the confusion- increasing MPG

Adding to the confusion- increasing MPG

It sounds like people in the link did not think about RPM's verses MPG (It is not just MPH vs MPG).
To think of it in the extreme case, if you tried to hypothetically do 60MPH in first gear (DON'T do this, you could damage many things on some bikes) you will not get as good gas mileage as if you are in a higher gear (say fifth that is intended to go 60 MPH).

There was a similiar thread a few months ago and someone said putting a fairing on helps MPG alot. Also, easy on twisting the throttle and one person said they skip 2nd and 4th gears when accelerating slowly. I put a fairing on and tried the other things and even though I have not yet done the calculations I think they were correct. I'll post the results once I fill the first tank back up. I tried to look for the old thread but could not find it.

Have other people found secrets to increase MPG's?
 
beby99 said:
I know...I know....this is why I'm having trouble with this....both
you guys make sense too me....will try a few adjustments and
see's what happens.
Click to expand...
Just ride the damn thing!!!! Dont worry about gas mileage.your getting way better gas mileage than most cars out there anyway~!!!!!!!!Just ride it as much as you can and you will save gas!!!!!ENJOY\!!!!!!
 
I went for a ride of 175 miles today on the 1150. Got back to town and stopped for gas before heading to the house. Gas milage with various speeds between 55 and 80 mph was only 51 mpg. What can I do to improve this?

Earl :-) :-)
 
earlfor said:
I went for a ride of 175 miles today on the 1150. Got back to town and stopped for gas before heading to the house. Gas milage with various speeds between 55 and 80 mph was only 51 mpg. What can I do to improve this?

Earl :-) :-)
Click to expand...

Send Me Your Bike and Get a Moped!\\:D/
 
earlfor said:
I went for a ride of 175 miles today on the 1150. Got back to town and stopped for gas before heading to the house. Gas milage with various speeds between 55 and 80 mph was only 51 mpg. What can I do to improve this?

Earl :-) :-)
Click to expand...
Come to Missouri and I will trade you my 650 for yours!!LOL!!!
 
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