Mythbusters: Is a bike greener than a car?

[Ken Fry]

QUOTE=darcane;261151]The premise seems to be testing whether cars or bikes produce lower emissions (I presume this is a question because bikes have better mpg but less pollution controls). Looks like they put it to an "ultimate" test by streamlining a bike.[/QUOTE]

Mythbusters can be fun to watch once in a great while, but their science is often deeply flawed, and half the stuff they do can be answered without the theater and within a minute on the web.

Bikes emit far more criteria emissions than cars, because they are allowed to do so. (There are not as many bikes; it's harder to clean up a high-specific-output-engine; some of the manufacturers are small and would be burdened; etc.) Ironically, the fastest bikes now owe part of their speed to technologies that came from the implementation of emission controls in cars.

It used to be true to say "A Jet Ski emits more pollution in and hour of operation that a Volvo emits in an entire year." The differences in emission standards are narrowing, but a 50cc scooter is allowed to emit on the order of 10 - 50 times as much (measured in grams per mile) as a 7 series BMW. All cars have to meet one regulation; bikes have three levels, with bigger bikes required to emit less (even though they obviously burn more fuel).

So if you streamline a bike to get 150 mpg, The bike will still emit more criteria emissions than any car... even the very biggest, heaviest gas guzzlers.

However, CO2 is now considered a "pollutant" but is not regulated. In this sense, a 150 mpg motorcycle emits one third the CO2 of a Prius. (CO2 is not only conveniently tied to MPG, it is actually the thing measured in EPA dyno tests to indicate fuel burned.) (I used to use a pipette when I ran motorcycle dynos in the dark ages.) CO2 is probably more important these days. The criteria emissions are easy to deal with -- they are all but eliminated in cars (and bikes could be equally clean if we wanted to make them so). But CO2 is nearly impossible to deal with -- none of the sequestration methods seem to be likely to work well.

So today, knowing what we do, it is probably better to get 150 mpg in a streamlined bike than to get 50 mpg in a Prius with one person in it. Doesn't really mater what the criteria emissions are, unless bikes get to be a significant part of the whole.

The Montracer gets 53 mpg at a constant 75 mph, and emits fra more criteria emissions than a Prius in the process. This is about equivalent to 53 mpg in an EPA highway fuel test cycle. So getting 150 mpg in a streamlined motorcycle is more than a no-brainer -- and some claims are not measured in accordance with the EPA test cycle.

Having built a tiny enclosed motorcycle, I can say it is not easy to get over 100 (real) mpg in anything that most people will want to ride.

BSFC remains a challenge, as the Monotracer shows. If you have produced a bike that requires only 10 hp to maintain 75, then a 100 hp bike engine is far too large, and engine operating efficiency might be 8%. Make the engine 10 hp, and then acceleration is rotten (and top speed is 75) -- but you've bumped the engine efficiency back up to 25%.

No free lunches today.

[Frank Lee]

Originally Posted by roflwaffle

There are, but sooner or later they're trumped by rubber use. A bike usually goes through something like three to six times more rubber than a car. IIRC it's something like an extra ~150-300 lbs per 100k miles, which is equivalent to the same weight in plastic or about three times that weight in steel.

For a bike that goes through tires in a reasonable amount of time, say ~15k-20k per set, the comparison isn't too bad because it only reaches the embodied energy of the car after a few hundred thousand miles, but a sport bike that goes through those tires in half the time or less will add the energy equivalent of a half ton of steel every ~100k or so.

I've never had a bike rust out and have to be scrapped.

Bike tires contain far less materials than car tires, in average sizes.

Since I don't have a crotch rocket, my bikes' tire life isn't that dismal.

[sendler]

The premise of the discussion is which is greener. Not which emits less criteria. Fuel consumption must now be ranked much higher in the criteria as we will soon (a few more generations) run out. Then it won't matter how clean things are as there won't be any personal ownership of internal combustion engines.

[ProDarwin]

This is somewhat related and interesting repost:

Emissions Test: Car vs. Truck vs. Leaf Blower

Cliffs: 0.03L leaf blower is way dirtier than 6.2L 411hp truck.

On the subject of bike ownership cost... I sold my last bike like 2 years ago, but even at 50mpg, it was arguably more expensive and more hassle to operate than a 30mpg car. It could eat a rear tire in no time flat, eat brake pads, and is very maintenance intensive.
Chain clean + lube every 400 miles.
Solid lifters that need to be adjusted.
$50-100 gloves wearing out after only 10k miles.
Helmet visor replacements.
More expensive and more frequent oil changes.
Fork rebuilds every 2 years or so.
Etc.

Mine was definitely not greener than a car as it had zero emissions controls.

[sendler]

I'm looking at about 9,000 miles out of a rear tire for my CBR250R. 27,000 for the front? It still looks brand new with 6,000 miles on them. Even 50mpg should be seen as much greener than 30 despite NOx levels. And now finally, there are motorcycles that are affordable and aspire to achieve much higher mpg.

[Ken Fry]

Originally Posted by sendler

Even 50mpg should be seen as much greener than 30 despite NOx levels. And now finally, there are motorcycles that are affordable and aspire to achieve much higher mpg.

I agree that now, resource depletion and CO2 emissions are more important than NOx, etc.

And I likewise agree that it is great to see bikes like yours. In fact, it was the mention of your bike here that made me look into the 250 and its variants, and announce (in jest) to my wife that I was going to buy one like yours, the $12,000 racer and the $28,000 racer. To get the $28,000 down to essentially half the weight of yours must have required quite a bit of unobtanium. I raced when two-stroke Yamahas ruled, so I looked up their power levels, expecting them to be lower -- but surprisingly they were actually a little more powerful, with 50 some hp from a TZ1.

We raced a 350 four Honda for a couple seasons, and could, in endurance races, soundly trounce everything on the track: 500s 750's and 1000cc bikes. The only things we could routinely pass on straightaways were the "tricked out" American V twins. For me, nothing beats a small bike.

[user removed]

It would be interesting to see what a 2011 CBR250R produces as far as tailpipe emissions. It has FI and a cat, not sure about the O2 sensor but I would assume it is a feedback system. Compared to a CV type carburetor I would bet the emissions are comparable to a car, not another bike without the same system. If they are comparable as a percentage, then they would be much lower in volume.

regards
Mech

[user removed]

I just checked and the CBR does have an 02 sensor. It has a check engine light, just like OBD cars so it would be fairly safe to assume it produces the same emissions as a percentage of exhaust volume, which would be considerably lower than just about any car on the road.

regards
Mech

[sendler]

Does anyone know where I can borrow a portable emissions logger or recommend a suitable motorcycle dyno to check the stock emissions of the CBR. The cat is fairly large for a motorcycle and the O2 sensor runs in closed loop.

[GRU]

Originally Posted by ProDarwin

This is somewhat related and interesting repost:

Emissions Test: Car vs. Truck vs. Leaf Blower

Cliffs: 0.03L leaf blower is way dirtier than 6.2L 411hp truck.

On the subject of bike ownership cost... I sold my last bike like 2 years ago, but even at 50mpg, it was arguably more expensive and more hassle to operate than a 30mpg car. It could eat a rear tire in no time flat, eat brake pads, and is very maintenance intensive.
Chain clean + lube every 400 miles.
Solid lifters that need to be adjusted.
$50-100 gloves wearing out after only 10k miles.
Helmet visor replacements.
More expensive and more frequent oil changes.
Fork rebuilds every 2 years or so.
Etc.

Mine was definitely not greener than a car as it had zero emissions controls.

You're talking about regular maintenance on your bike. How about your car, it doesn't cost to maintain?
I've had bikes for 10 years and i could easily get 10000 miles on a set of tires, unless you're buying soft racing tires.
Gloves every 10k miles? c'mon now