Why isn't MPG even better for scooters than it is?

[KentonLynne]

This is just a question that's always bothered me so I thought I throw it our there to the forum and see what kind of ideas popup:

The automobile I drive (a Toyota Rav4 V6) gets around 25 MPG.   My Kymco People GTi300 gets around 75 MPG.     That seems great -- 3X better mileage for the scooter.  But wait;  both vehicles have advanced fuel-injected 4-valve engines and great acceleration, but the Rav4 weighs about 10X what the GTi300 does.   So why couldn't my scooter get something like 10X the mileage of the auto  --  like 250 MPG?  Are scooter (and I guess you could include motorcycle) engines just not as efficient as automobile engines?   Or does it have something to do with their differing aerodynamics?   It just seems to me that as good as the gas mileage that scooters get compared to automobiles, it should be even better, given the difference in size between them.     

[Vivo]

Yes, aerodynamics, the scoot and rider may be small but the aerodynamics might be worse than the rav-4, driving habits (no WOTs on the Rav-4), when you drive at higher speeds on the scoot that increases wind drag and increases fuel consumption. By ratio and proportion, wind drag may be less in a car due to better aerodynamics. And there's "power to weight ratio". The scooter might have a higher power to weight ratio than the rav-4, thus, the engine exerts more effort to move the scoot especially when the rider is heavier. 

You can't include a motorcycle because a 50cc, 4-stroke, manual shift motorcycle can give you more than 300 MPG!

[ts1]

Big is relative efficient. May it be a truck, ship or plane.

[axy]

This is just a question that's always bothered me so I thought I throw it our there to the forum and see what kind of ideas popup:

The automobile I drive (a Toyota Rav4 V6) gets around 25 MPG.   My Kymco People GTi300 gets around 75 MPG.     That seems great -- 3X better mileage for the scooter.  But wait;  both vehicles have advanced fuel-injected 4-valve engines and great acceleration, but the Rav4 weighs about 10X what the GTi300 does.   So why couldn't my scooter get something like 10X the mileage of the auto  --  like 250 MPG?  Are scooter (and I guess you could include motorcycle) engines just not as efficient as automobile engines?   Or does it have something to do with their differing aerodynamics?   It just seems to me that as good as the gas mileage that scooters get compared to automobiles, it should be even better, given the difference in size between them.     

Because your reasoning is flawed. You are comparing weights of vehicles disregarding the fact that engine power is different. "Size" is irrelevant.

Your Toyota might have around 130 hp and 1300 kg, and weight/power ratio is around 10. Add one driver and it falls to 11.

Your scooter has (rounded) 30 hp and 170 kg, the ratio is around 5,7. Add one driver and it PLUNGES down to 9 which is much closer to your car!

If you compare these two ratios, you will see that Toyota has roughly twice less power than your scooter and scooter has 3x better mileage, the difference  can be attributed to less energy needed to roll off etc. Also, scooter is spending more time towards the end of its powerband (let's say, 75-100 %) compared to your car, and in "bad" conditions like city driving, so it consumes more. To make a real comparison you should drive your car and scooter under the same conditions at a similar % of max rpm and draw conclusions. If you compare these numbers, 11 and 9, and the fact that your scooter consumes so little fuel, it is in fact quite appropriate consumption.

[Vivo]

yeah flawed....

bats have wings, eagles have wings,... so, bats and eagles are similar? 

[baddi]

Your MPG can be calculated as this:

(outer diameter  of wheel measured in miles) / (Gallons of fuel injected per intake stroke) x (Revolutions (unitless number) x (gearing (unitless number)).
The car has a bigger engine, and are often alot more energy efficient, which gives more power. This power is used to drive at low RPM, as a car often doesnt go past 2000 RPM, because it has the power to pull high weight at higher gearing at lower RPM.

To compare the fuel effeciencies properly you need to know these numbers for both vehicles, and then you would see that the reason why the scooter has a higher MPG is because of the lower displacement (which means less fuel to maintain lambda=1) but that the reason why it doenst have an even better milage comes from the gearing and revolutions.

The weight doesnt really have anything to do here, as the engine size are sized to have enough power (Nm) to pull the weight at a given gearing. If there is more weight, then there will be added a little more fuel, and the kW will be high enough to pull the weight to a given speed.

[Vivo]

There are a lot of factors though. We did this experiment before: 

a Toyota Corolla with a 1.3L engine and another Toyota Corolla (same year) with the 1.6L engine variant.

   At 100Kph (60 mph) the 1.3 revved at 3,200 RPM, the 1.6 at 2,600 RPM. They have different final gear ratios.

   Result? the smaller engined Toyota consumed more fuel than the bigger engined one.

[baddi]

There are a lot of factors though. We did this experiment before: 

a Toyota Corolla with a 1.3L engine and another Toyota Corolla (same year) with the 1.6L engine variant.

   At 100Kph (60 mph) the 1.3 revved at 3,200 RPM, the 1.6 at 2,600 RPM. They have different final gear ratios.

   Result? the smaller engined Toyota consumed more fuel than the bigger engined one.

That's also why i want to turbocharge my agility some day. More torque at lower RPM will allow higher gearing.
But just to get something cleared: rev = revolutions and RPM = revolutions per minute, so you really cant say, that it is revving at 3200 rpm, as it will be revving at every speed, even if it was one revolution per year. The right word would be, that it had max torque at that rpm.

[streido]

a car often doesnt go past 2000 RPM

Not in my car  

I cannot drive like an old lady, i find it impossible for any longer than it takes that cop car to pass me by or for me to pass the School zone. Soon as im in the clear and the road is clear and conditions allow i speed up again, normally change gear between 2500-3500 rpm depending on my mood and what music is on the stereo  

you really cant say, that it is revving at 3200 rpm, as it will be revving at every speed, even if it was one revolution per year. The right word would be, that it had max torque at that rpm.

In general revving is used to describe the indicated rpm speed here, not max torque. I would say it was revving at 2000rpm if the tacho said 2000rpm? Ie it was revolving (Revving) at 2000 revolutions per minute? Regardless of the torque value  

[baddi]

Not in my car 

I cannot drive like an old lady, i find it impossible for any longer than it takes that cop car to pass me by or for me to pass the School zone. Soon as im in the clear and the road is clear and conditions allow i speed up again, normally change gear between 2500-3500 rpm depending on my mood and what music is on the stereo 

In general revving is used to describe the indicated rpm speed here, not max torque. I would say it was revving at 2000rpm if the tacho said 2000rpm? Ie it was revolving at 2000 revolutions per minute? Regardless of the torque value 

So rev are revolving, not revolutions? Well that clears alot up! xD

[streido]

So rev are revolving, not revolutions? Well that clears alot up! xD

Thats how i use it anyway  Different cultures, different rules, different definitions i guess?

[baddi]

Thats how i use it anyway  Different cultures, different rules, different definitions i guess?

Well, as technical terms aren't a part of the english lessons in school, i've had to guess the meaning from the content which it had been used, and since you wouldn't put double v ("revved") in the real bend of revolving: Revolved, i had to quess that it was a noun (revolutions) made into a verb, as this is most often the cause of these false bends.

[streido]

You lost me at the word "Noun"  

This is a global site so we have everyone from everywhere on here, we all use "english" in different ways but generally we get the jist of what each other are saying.

I know your english is a hell of a lot better than my Danish tho  

.........who cares anyway. Moderators arent watching for grammer mistakes.............................. YET!  

[baddi]

You lost me at the word "Noun"  

This is a global site so we have everyone from everywhere on here, we all use "english" in different ways but generally we get the jist of what each other are saying.

I know your english is a hell of a lot better than my Danish tho  

.........who cares anyway. Moderators arent watching for grammer mistakes.............................. YET!  

True

[axy]

You can't include a motorcycle because a 50cc, 4-stroke, manual shift motorcycle can give you more than 300 MPG!

It requires some serious patience, extra time to spare and light driver to drive around on 50 cc 4 stroke bike with manual gearbox.