Why do so many motorcycles get 35-40ish mpg?

[bpreynolds]

Silly, Sunday morning question. 

Something I've noticed over my years of riding and my obsessive motorcycle meandering, is that big bore motorcycles encompassing a vast array of power profiles, all still seem to get roughly the same 33-40ish mpg?  Yes, yes, I know I'm making a big generalization here, but it just seems odd to me that this window seems IMHO to include the preponderance of large motorcycles out there, all the way down the line from 160hp bikes to 90hp bikes.  It's almost like that is the profile that manufacturers/engineers are aiming for when designing bikes.  Just an observation on my part that could be influenced by the significant amount of caffeine I have consumed this morning 

[HDGoose]

Or why my 79 and 85 got better fuel mileage than the newer bikes can.

[elvisboy77]

The newer bikes are optimized for power and low emissions, not fuel efficiency.  You can get a Yamaza Zuma 50 that gets 110 MPG on 87 octane gas, but top speed is 35 mph and it takes a while to get there.  I own one and love it, but it is no speed demon.

[Wayne Orwig]

Wind resistance for one.
If it is air cooled, the motor is almost never at the right temperature.

That said, my Centauro would get that 35 or so MPG. But I once followed a friend on a two day ride. He is a slow rider. I got 55 MPG doing that.

[rocker59]

High Performance engines and terrible aerodynamics/huge drag coefficents hurt motorcycles' fuel economy.

Plus, I don't really think fuel economy is something most of the moto makers design for.

Car makers have to factor in fuel economy because of CAFE standards and the Gas Guzzler Tax.

[fotoguzzi]

My Buell gets 49mpg and has a claimed HP of 103.. my Madass gets 80-100 and can go 55MPH.

[Aaron D.]

I think the trend is changing. Our Scouts get consistently over 50 MPG even at 75+ MPH. The Scout has a TMAP sensor so the fueling is likely better controlled.

But our Jackal gets mid 40's, and I know a lot of folks don't do that well, so either they are riding at higher revs, or have mods that I don't.

My Sport 1100 gets low to mid 40s unless I am cranking.

[tiger_one]

My 1190 gets 44mpg, pretty easy, but if you hammer it, your mileage will drop to 39 or so.  Guess I am an easy rider when it comes to mpg.

The Super Tenere got 42-44 mpg running 65mph, if you ran 75 or 80mph then around 36mpg, if pinned (126mph) then 20ish mpg.

Multistrada 1200 2010 model got 42 mpg, ran out of gas with the 5 gallon tank, in about 203 miles!

The 2012 Tenni Griso got 44 mpg, running 70mph or less, but was using modified map.

[Triple Jim]

My Kawasaki H2 gets about 30, my Mille about 50, and my Yamaha DT100 about 60.  So from my point of view, all motorcycles get less than or more than 35-40 mpg.   

[roofus]

Further to comments made above about aerodynamics:

I remember seeing a television program a few years ago where somebody encased a motorcycle in a plexiglass "bubble" and did mileage tests.

It was a sort of complete fairing. They got excellent gas mileage and they concluded that the biggest barrier to motorcycles getting great mileage was wind resistance and turbulence.

[BMWDavid]

As others have said a lot of it is aerodynamics. I think Craig Vetter of Vetter fairing fame proved this many years ago.

My '14 FJR consistently gets 48 mpg while the best I can do with my V11 is 41 mpg. So perhaps in that comparison the FJR's fairing maybe helps with the aero and the lean mapping maybe?

[Gary]

Hmmm.. My NC700x gets 68 mpg. That's loaded with panniers and top case. Riding it sedately I have gotten over 70, but I don't often ride it that way.

[toaster404]

Air resistance is about the same for similar bikes, so the work being done is about the same. Riding about the same gives similar mileage, I expect.  Another difference includes engine furniture.  About the same on all. Tough to move beyond that without some specific design or different riding.   

Might mainly be frontal area.  I get somewhat better mileage without fairings and such, which really surprised me.

Speed and rate of energy input also has something to do with it.  I tend to get great mileage on the Blue Ridge Parkway traveling at lower speed.  Probably efficient engine use going up hill, and then coasting down (or close to coasting) uses very little gas. 

On the other hand, it isn't fair.  Big Harley gets 50.  If I have any fun at all, the 1400 gets 36.  Clearly not fair!!!!!!

I keep thinking there's a great deal more that can be done with lowering air resistance on bikes, but I don't really know what that would be.  Not my field. But some subtle stuff can really do the job.  Vortex generators on trucks, for example.  I am tempted to trick out my Lincoln with vortex generators!!   That really does highlight the problem.  My V8 Lincoln LS at not very shy of 4000 lbs averages (not peak!) 24.8 mpg on trips with lots of Interstate mainly using cruise control at 70 mph.  My Guzzi 1400 seems to be getting slightly under 40 mpg on the same type of trip, but weighs less than 1/4 of that including me!!!!  Really not fair. 

The engine efficiency issue is likely very important.  Look at the great mileage scooters get by keeping the rpm at an efficient point. 

Really, a motor-generator bike with swing load battery would be awesome.  Put the nano-whatever magic drive motors in the wheels, have a super efficient engine run the generator, battery and current control in a slab low down.  What a bike that would be!!!

Then there's always this option: http://www.gizmag.com/revatu-steam-powered-custom-motorcycle-black-pearl/37135/

We've been looking at the NCX / CTXs so when we both go we get decent average mileage!!

[Wayne Orwig]

Hmmm.. My NC700x gets 68 mpg. That's loaded with panniers and top case. Riding it sedately I have gotten over 70, but I don't often ride it that way.

Streamlined plastic (no big billboard windshield).
Water cooled so it warms up fast.

You are going to make me want that Honda, and I dislike Hondas.   


 

[Silver Goose]

Speed costs, how fast do you want to go? Motorcycle fuel mileage only matters if that is why you bought it for. Want mileage,buy a 50cc. made in china scooter.
 
Most of us buy motorcycle for the thrill and performance, one comment was about the HD getting 50MPG, true, at what RPM? How much HP does your bike produce at cruising speed ( better mileage, lower power). 

If you really need better gas mileage then you have a few choices: Buy a Prius or push the bike uphill with the engine off and coast down the back side.

If you fear running out of gas carry spare, I do, when riding my small tank Stelvio in to the outback.

I going for another cup of coffee.

[Orange Guzzi]

I have a the exception.  My Kawasaki ZR1100 Zephyr gets a consisted 23 mpg.  City or highway. The bike has 2 sparkplugs per cylinder and can burn all the fuel that is pumped thru them.   My 2003 M.G. gets a consisted 38 mpg.   The engine performance between the two 1100 cc bikes is unique to each.   

[bpreynolds]

Speed costs, how fast do you want to go? Motorcycle fuel mileage only matters if that is why you bought it for. Want mileage,buy a 50cc. made in china scooter.
 
Most of us buy motorcycle for the thrill and performance.

I think this was built into my inital question and I disagree to a point.  MPG numbers can and is often a factor with buyers - maybe not to you - but to others definitely at least a thought.  But in a way, why should mpg be a factor when - and we are back to my original post - a 170hp Multistrada gets roughly the same or sometimes better mpg numbers as my 75ishhp Stone?  So the argument that we pay in mpg on motorcycles for performance has some merit OUTSIDE of motorcycles, say in comparison to cars, but why within the motorcycle world does it happen to be that a large portion of bikes from very different performance envelopes still get about the same 35-42ish mpg?

[Testarossa]

Engine speed is an important factor. Internal friction rises with the square of rpm, so a small engine generating 30hp at 8000 rmp wastes four times as much heat as a larger engine generating 30hp at 4000 rpm. Thus my aircooled Comanche with a 540 ci engine, turning 2600 rpm, got 18 mpg at 170 mph, which is better than my van, which gets 17 mpg at 65 mph. Of course the van is heavier.

Aerodynamics is a complex issue. Aero drag does rise as the square of airspeed, but the base drag numbers are based both on frontal area and "parasite" drag, which is a combination of surface friction and the turbulence (wasted energy) generated by all the little crap disturbing the airstream -- spokes, mirrors, signals, frame tubes, cables, radiator/oil cooler, fenders, cylinders (and their fins), pegs, screens and of course the rider and gear. It all adds up and even a bike without a real fairing can benefit from plastic bodywork that hides the engine, frame and cables from the wind, and conditions air passing through a radiator. All of this explains why dustbin and dolphin fairings work so well. A barn-door touring fairing may or may not help gas mileage because, while it makes a nice bubble for the rider, it may pull a big turbulent wake behind him. A really aerodynamic bike would taper the shape of the rider and aft bodywork down to about half the cross-sectional area of the front fairing (Kamm's rule).

For what it's worth, my T gets 45mpg around town, 50 on the highway and cruising the mountain twisties. The '70 Triumph gets 67 popping along at 60mph/4000rpm. The Suzuki VX800 averaged 50. Don't remember what the other motorcycles got (gas was cheap and I didn't keep track), but the Kymco 49cc 2-stroke gets 100. It's a buzzy little engine but peaks at 30mph and the scoot is aerodynamically small and clean -- the fairing shields the rider's lower body and all of the frame/cables/engine dirtiness. If you crouch low the speed edges up to 35, even 38mph -- a really good lesson in aero principles. John Britten had a really good handle on this:



BTW, when skiing across the flats, I go faster and farther by tucking one knee behind the other and shielding arms and poles behind my back, thus pushing one big cylinder through the air rather than four smaller cylinders. In this position I easily keep up (at speeds below 40) with skiers who drop into an uncomfortable but racer-cool tuck.

[LowRyter]

My Bandit gets less than 30.  My Sport gets about 33 and my EV used to get 40+ but since the TPS replacement gets 35-40 (unsure).

so it goes. 

[Perazzimx14]

My 70's era 850cc Guzzi's get 55mpg + anything I have owner with FI got at least 15 mpg less. Maybe carbs aren't so bad??

[lucydad]

Please burn as much gasoline as possible.

Your local oil company geophysicist appreciates your support.

Otherwise the Saudis and Iranians will be your only producers in a few years.

[Testarossa]

Otherwise the Saudis and Iranians will be your only producers in a few years.

See?  Free markets work!

Sometimes not to our advantage.

[Penderic]

I am almost sure that it is another conspiracy by the big oil companies to keep all these guys employed at our expense! The nerve.

[elvisboy77]

I think this was built into my inital question and I disagree to a point.  MPG numbers can and is often a factor with buyers - maybe not to you - but to others definitely at least a thought.  But in a way, why should mpg be a factor when - and we are back to my original post - a 170hp Multistrada gets roughly the same or sometimes better mpg numbers as my 75ishhp Stone?  So the argument that we pay in mpg on motorcycles for performance has some merit OUTSIDE of motorcycles, say in comparison to cars, but why within the motorcycle world does it happen to be that a large portion of bikes from very different performance envelopes still get about the same 35-42ish mpg?

I have to agree wit BPReynolds, there does not seem to be any Obvious rhyme or reason to fuel economy....although I can say that driving style matters.  I just got back from a beach weekend and my V6 2015 mustang got 31 MPG....til I got off the 55 mph back roads and started flailing down I-95/I-40.  Then it dropped to 26 or so I think.

[Rough Edge racing]

My Buell gets 49mpg and has a claimed HP of 103.. my Madass gets 80-100 and can go 55MPH.

 My 83 HP Buell burns about 2-1/2 gallons in an hour of  felony speed back road riding.. A Prius is for fuel mileage, bikes are sport..