Well, be cause weight-to-power ratio is just one of many factors affecting efficiency, and motorcycle makers have had little motivation to work toward better efficiency. It's been adequate just to be noticeably better than most cars and trucks.

 

This pretty much sums it up, plus bikes are considered "toys", and usually not designed around effective fuel mileage. Most folks would like to have good mileage, but that is usually not the basis they buy on. Manufactures build what sells, and until people force the issue of mileage, it will not be an issue of design.

 

Around the first of the year one of the Dallas/Ft. Worth TV stations did a small news special on motorcycles, they stated that one of Kawasaki's Ninja's got 72 mpg.

 

The major difference is the coefficient of drag. A modern car has a very low CD, whereas a rider on a motorcycle has to deal with a lot of wind resistance.

My GSX 1400 (1.4 liter engine) gets about 38 to 40 mpg - and a top speed of about 145 mph. The main reason it can't go faster is not the motor or gearing - it's simply not able to compensate for any more wind resistance.

 

And with all the extra electronic nannies that cars have, they can run more efficiently. Relatively speaking.

 

New bikes have the same electronic "nannies" that cars have. (not including the electric stuff featured in hybrid cars), I'm talking about fuel injection, O2 sensors, electronic timing advance/redard, TPS, MAP, all of this helps to improve gas mileage. I'm willing to bet that within the next 5 years or so, bikes will be getting a lot better mileage due to the integration/perfection of all of this stuff. I've also heard a rumor that bikes will have to pass smog here in a few years (which is crap), so gas mileage will be of more importance to the manufacturers due to EPA regulations.

Drag has a lot to do with gas mileage as well, and that's why all the manufacturers of cars have been focusing on aerodynamics in the past 10 years or so. Sportbike manufacturers pay attention to drag, but not for gas mileage purposes, more for speed than anything. However, due to the fact that these sportbikes are quite slippery (they have low drag coefficients), decent gas mileage is a nice side effect (get 40-45 on my gixxer600). Cruisers have less high-performance-tuned engines, so even though their drag coefficient is higher than that of a sportbike, they tend to get better gas mileage. Weight is another key factor, but bike manufacturers don't really have to worry about that seeing as new bikes are extremely light anyways.

 

I get 55-60 mpg in my Honda Insight hybrid, 1.0 liter 3 cylinder and 49-53 mpg on my M50. The Insight is much more comfortable in the cold and rain, however the M50 is much quicker to 60 mph.

 

I was able to aquire a proto-type Subaru back in the days before they were imported over here. It was a no-nonsense car, and had a BMW motorcycle engine stuck in it. 52 mpg, front wheel drive. My uncle had a BMW motorcycle at the time, and it only got 42 mpg. Both weighed about the same, lol. So, I guess wind resistance was the factor here.

 

I'd venture that gearing had more to do with it. At speeds where cars are most efficient (45-50 mph), air resistance still isn't that large a factor. It's about gearing and usage as much as anything.

 

Even at low speeds, wind resistance is always a factor – see: soapbox racers -- albeit low initially but going up exponentially as speed increases… The gearing and CD are both significant issues for bikes… A car such as the ancient Ford Taurus had a CD of about 0.28 (roughly 28% of the drag of a flat plate of equivalent frontal area…) whereas the Busa, one of the more aerodynamic bikes is doing all it can do to achieve a CD of 0.55 – the ZX-12R was just a hair less efficient at 0.56 as I recall…

Cruisers are notoriously un-aerodynamic with all that tubing and stuff hanging out and the pressure gradients are astronomical -- a CD of 0.80-1.00 is not unusual (a 0.9 is about what an 18-wheeler box van rates at…). Surprisingly windshields and fairings often increase the efficiency of a scoot, rather than reducing because a modest windshields is less draggy than the bolt-upright rider… which only leaves gearing… usually the smaller engines are geared crazy… well off the torque peak of the engine for cruising power RPM… internal combustion, especially gas, engines seem to work at their peak volumetric efficiency when running around their torque (not horse power) peak or slightly below – many, especially smaller, scoots are geared to allow their engines to run near peak power and are way off the torque peak… big-tourers, however, are often the most efficient over the long haul (factors of nice torque allowing low RPM cruising and good aeros for a scoot). Actually big-inch crotch rockets don't score all that badly generally -- as long as the rider is wiling to stay in a modest crouch and uses some throttle discipline – but that sorta spoils the whole effect doesn’t it…

On the other hand, my carbureted mid-90s Harley often gets near 50mpg commuting and I don’t have to put up with the isolation of a cage, nor get so bored that I must listen to Tzaichovsky, NPR or talk-radio…:roll:

 

Now that's what I call a post! Bravo!

I'd argue that soap box racers strived to overcome mechanical friction more than air friction, though, at the speeds they typically operate. Bullet shaped bodies were more about coolness factor, at least at the Boy Scout level.

 

I may be wrong (I deal with stationary sources of pollution, not mobile), but I thought bikes already had to meet EPA emission standards.

 

Yes they do, but seeing as they only need to meet these regulations once (rather than every two years like a car), the manufacturers are far less concerned with those standards than a car manufacturer would be. I'm not saying that bikes don't get excellent gas mileage, because that would be either a lie or an ignorant statement on my part hahaha. I do, however believe that better gas mileage can be/will be achieved in the near future. Think about how long smog has been around in cars, and we're finally getting the hang of it (we now have 400+ bhp V8 engines that can get 19 mpg and pass smog with flying colors). This technology is just starting to be used in bikes, and even though the technology has almost been perfected, the application to motorcycles has not yet been perfected, so that's why I believe that gas mileage in bikes in the next 5 years or so will be up to par with that of automobiles (comparing engine size with power with vehicle weight). This is just an assumption, maybe an educated guess on what will happen. I'm not trying to predict the future or anything hahaha.

 

All I know is that my 3/4 ton Dodge Ram 4x4 gets 8 in the city and 11 on the highway. Compared to that, the 42 I get on my Harley and the 50 I get on my Intruder are a joy!

 

Bear in mind, if the point of this whole discussion is about motorcycles being cheaper to run than cars because of some perceived savings in the fuel department, think again.

I put pen to paper a few years ago and found that a bike is at least as expensive to operate as a car. The tires (lasting 3,000-5,000 miles and costing so much to mount and balance) pretty much seal the deal.

 

What kind of tires are you buying? I got 12,000 out of sets for my Rebel and about 10,000 from my S50. I do all my own maintenance except for the tire change. Insurance is also cheaper. The s50 is closer to the operating cost of a car, but the rebel is hands down the winner in every catagory. Something else to factor in is the fact that the more I ride my bikes the longer my cars last. I'll probably be keeping my car 20 years (had it 15 already). The fact that your $20,000 car will hang around twice as long is huge. There are alot of economic benefits to owning a motorcycle as long at it isn't used strictly for pleasure.

 

Not if European gubments get their way. They have already threatened that bikes will be required to pass smog inspections in the future, the only problem is that they are understaffed to even deal with the CARS on the road right now, so there is no way that they can get around to testing the 600,000+ bikes on the road in Switzerland alone.

 

So bikes are required to meet the new vehicle emission standards, but they aren't subjected to continued testing to assure that they have maintained that level of emissions?

Sounds like bikes need to be tested just like cars. In fact . . . if they'll test for decibel levels I'LL BUY THE GD METER.

In Memphis, they have to have their cars tested every year, but us county folks don't have to get our vehicles tested (yet). We have been an ozone non-attainment area for right at 3 years now, so that day is just around the corner.

 

So bikes are required to meet the new vehicle emission standards, but they aren't subjected to continued testing to assure that they have maintained that level of emissions?

Yes, you are correct. I don't know why it's like this, but that's the way it is. Maybe it's just the beginning of more smog laws to come.

Or maybe it's the same reason that pre 1975 (I might be a little off on that) vehicles don't have to be smogged, yet new vehicles do. Which also doesn't make sense to me, especially since in highly populated areas like San Francisco, the air going into the intake of newer cars is often dirtier than what's coming out of the tailpipe. So, yes, these vehicles should be tested to make sure that they're maintaining they're efficiency, but why aren't the Chevys with big block 454's and four-barrel carbs made back in the early 70's, the ones that are really polluting the atmosphere, required to pass any emissions tests?

Vehicles with diesel engines also aren't required to pass smog, even if they're boosting 45 psi and pouring black smoke out of their pipes.

Smog laws have the best of intentions, however they're always directed towards the wrong areas (IMHO). I don't think that requiring bikes to pass smog is necessary at all. I don't have a problem with it, as I don't plan on modifying my bike, however I'm pretty sure that the emissions coming out of our bikes is fairly low, a lot lower than that of a 70's V8 or a diesel engine.

 

The way I see it, I'm getting Porsche-performance and Prius-fuel efficiency. Not a bad tradeoff.

 

Have we considered power output vs displacement and its effect on fuel usage? Sportbike engines are producing over 3 horsepower per cubic inch and have to spin pretty high to achieve that output. My smallest, lightest bike puts the most power on the ground, and also gets the worst fuel mileage, but its really fun, so I don't mind. In my experience, a 1000-1200cc V-twin has been the most efficient for power and mileage.
MikeH, between my wife's car and my bikes, we travel 30,000 miles a year, but our 69 Camaro with 11 mpg only goes about a thousand. It wouldn't pass any smog test, but it's used very little, so does it contribute much to the junk in the air? It would be nice to put in a new drivetrain, but that's expensive for how much it is used.

 

Mike, the pre-1975 cars don't need to be tested for several reasons.

First, they weren't built with any kind of smog equipment (it wasn't a requirement when the vehicles were produced), so there are no specification to test against.

Further, the number of 30+ year old cars is small, and geting smaller every year. There is no benefit investing money to develop after-the-fact standards and tests for a dying population.

The great majority (90+%) of the vehicles on the road are less than 10 years old, so it's more effective to ensure that these are all meeting the specs.

 

<more about coolness factor, at least at the Boy Scout level...>

LOL -- Yep, I'd say in 99.9% of the cases cool shapes lead to big smiles -- always wanted to build one, but there ain't no shape that will disguise the forever corpulant... I did see a derby racer where the youngser had diligently followed a NACA laminar-flow grid, however, so at least some have given it a little thought...

 

It doesn't matter. We are gonna run out of oil anyway. :roll:

 

Yes, but ...

... what's going to happen to the Middle East when the oil wells run dry?

Right now, they are getting very, very rich pumping oil and selling it to the world. But what will happen when their wells run dry? You think it's bad NOW with Saudi terrorism, when they have MONEY, just wait until they are poor and hungry!

 

If they're smart, they'll take that money and use it on energy research. If they know the next energy sourec before the rest of the world, they can use their riches to ensure an economically viable future for many generations to come.

Since they're not smart, my money says they'll continue with religious fanaticism for as long as it holds out. Once the oil dries up, the world won't have to kiss their ass. Instead, maybe we'll all get tired of the violence and go over there and give them a good ass kicking. It's not like they aren't expecting one.

 

50 MPG on my 07 Harley Electra Glide of course I don't save much on gas compared to my Dodge Ram because I take the long way home on the bike! : )

 

<a bike is at least as expensive to operate as a car. The tires (lasting 3,000-5,000 miles and costing so much to mount and balance) pretty much seal the deal…>

Must be trying to commute on a zinger with gumballs… both of my scoots are in the 800# range and a tad heavier, gassed… rears get about 14-18K miles, would still pass inspection but don’t like seeing the air inside… and fronts typically run 20-26K… add to that, that I can run the HOV lanes on the scoot and I save $200+/- on parking each month (as well as parking just outside the office window) and the scoot is a no-brainer… I figure real-time savings of $150-200 a month... plus, I get to ride...

Granted I don’t have a hybrid, so my gas saving aren’t in that category, but either of `em still beat my econo-box Pontiac (even the gas-guzzler Kawasaki beats it by about 5mpg, and the Harley by about 15mpg…).

 

I've got to agree with Landry on this one. (Gaah, did I say that?).

I've gone through several sets of tires on my bike (1400 ccm, 550 lbs street weight), and get an average of about 8000 km (5000 miles) out of them before I'm down to the warning bars.

Tire wear depends upon a lot of factors - road surface, riding style, rubber mixture, etc. I've had Continental RoadAttacks and Metzeler RoadTec Z6's, and both of these showed the same life span.

 

My car gets better mileage than my bike, VW TDI, about 45 mpg for the bike 55 for the car. New TDI engine scheduled to come to america is estimated to achieve over 80 mpg and be the cleanest diesel ever with CO2 emissions less than most hybrids.

Pollution on the other hand is another animal altogether. Gallons of fuel used is not a direct indication of pollution levels. Plenty of two stroke engines still out there, mowing the average lawn once a week with a 2 stroke pollutes more than the average car does in a week. Up to 50% of the oil/fuel mixture is just blown out the exhaust.