Gas mileage guestion?

[Hoomgar]

Also keep in mind that an engine produces it's best efficiency at it's peak torque output. the closer you are to this at whatever speed ( reasonable, of course) the more efficient the engine will run,and better mileage it will produce.

Tim found an easier way to say what I am saying. Paul, your talking about "getting" to a speed vs what I am saying is only talking about what you get "once there"

Bottom line is this, Beby's bike, my car and a lot of other gas burning vehicles get better fuel economy when "CRUISING" at higher speed than they do at certain lower ones or vastly higher speeds. Each engine has it's own economic cruising speed and traveling above or below it will produce a lower fuel economy like Beby is describing here. The lower and higher speeds referenced in each comparison will be different and depend on the vehicle and it's engine.

So although I know what you saying about the law of physics, we are not really talking about that as what we are talking about is more of a sustained reading than it is one taken while "getting there" What your talking about is fuel consumption used getting up to said speed. I am talking about fuel consumption averaged over time while cruising at a sustained speed. I assure you what I am saying is true. I am not just sharing an opinion here buddy

Point in case, Beby's bike is doing just this. My car does it. I can tell you for sure than if you cruise 100 miles in my car on the highway at 55 - 60 MPH you will get around 21 MPG. If you cruise the same exact highway all conditions the same but travel at 75 - 80 MPH you will get just shy of 25 MPG.

Law of physics be damned buddy, these are cold hard facts


Back on topic. I really think (this part is my opinion) that what is going on with Beby's bike is just this. His powerband wants to cruise at the higher speed he mentioned in order to reach peek fuel economy. Most likely a product of his twin engine and the gears ratio's he has installed in it now. I'll bet the bike is running just fine.

[syafi]

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

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

[Anonymous]

hey where the pop and popcorn..i want to sit down and enjoy this..you guys are funny to listen too...although I respect both sides....sounds like a mythbusters episode on the way!!javascript:emoticon('')

[scotty]

i just installed a counter shaft pulley on my buell. It is 3 teeth smaller than the stock 29 tooth one. I seem to be getting a hair over 51 mpg compared to just a hair under 50 as before. I got the idea from riding with those wackos in roaring river park. I was going up and down hills constantly. shifting gears till my right hand was getting cramps and i got 50 mpg on every tank full while i was there. My bike needed to lug less was my assumption.

[Clone]

You can get better milage at a higher speed within reason, it depends on like was said how hard the engine is working and the powerband of the engine. If you lug an engine, use it below its powerband, it will require a larger throttle opening, hence it will draw more fuel. If you shift gears to a higher RPM the engine will be in its powerband, the throttle opening will be smaller, it will draw less fuel.
If you change the drive line ratio by changing the sprockets, you push your powerband up to a higher speed, so below that speed the engine has to work harder, larger throttle opening=more fuel.
It is a simple test put a mark on the grip edge, check the positon of this mark in various gears at differing speeds and note the difference.
I had a Ranger that would occasionally pull a horse trailer, 2.9L FI, 5th gear at 100km/h, the pedal was on the floor and my milage would suck. 4th gear, same 100km/h, the RPM was way up, the throttle was half down, the milage was noticably better.

[dpep]

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.

[BigMattyD]

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

[redliner1973]

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? .

In the same case, does/would it make sense to make an engine that revs to 9K with a 55mph speed limit?

[Clone]

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.

[Hoomgar]

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

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

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.

[Hoomgar]

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?

You missed the part where he explains that he changed the stock sprockets Don.

[Hoomgar]

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.

This gets my vote. That's what I have been trying to say. Thanks guys

[BigMattyD]

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..

[gspaul]

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!..........

[KEITH KRAUSE]

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.