Busting the Mythbusters’ motorcycle pollution claims

We’re big fans of Discovery Channel’s Mythbusters. Not only do they blow a lot of shit up, but the show gives viewers an exciting education in the practical applications of math and science. So, when we heard they were planning to test the environmental impact of cars and bikes, hopefully proving which form of transportation was greener, we got excited. We shouldn’t have. The episode relied on flawed methodology and inaccurate assumptions to draw a poorly informed conclusion. Here’s why, at this point in time, the environmental impact of cars can’t be shown to be less than that of motorcycles.

To recap, the episode's premise was that many people are ditching cars for bikes due to the perceived reduction in environmental impact that switch brings. To test that impact, three bikes and three cars, representing the '80s, '90s and '00s were rigged with tailpipe emissions measuring equipment, then driven around a little bit. Results showed that the bikes kicked out more nasty stuff like hydrocarbons, carbon monoxide and nitrous oxide than cars did. The conclusion was then drawn that, "At this point in time, it is not better for the environment to trade your car for a motorcycle."

What we’re going to do is look at the testing performed during the show (see the full episode here) and the claims made and illustrate why those two together paint an inaccurate picture. The empirical and measurable evidence collected during the show is flawed in these ways:

1. The bikes chosen aren’t high sellers.
The Mythbusters claim that the three used bikes chosen for the test were “some of the most popular models of the last three decades.” That’s simply not true. All three bikes chosen are Hondas. Honda only accounts for roughly 25 percent of all motorcycle sales in the US while Harley dominates with over 60 percent of the on-road market.

The “most popular” road bike from any given decade would have likely been a Harley-Davidson Sportster, not something like the Honda CB1000, which the Mythbusters chose to represent the ‘90s. That bike was only imported into America for two years in such low numbers that they’re so rare you can’t even buy a rear tire for them in the correct size anymore. Bikes like the Honda CBR1000RR are reasonably popular in sportsbike circles, but represent a drop in the bucket even within Honda, which sells far more cruisers than race replicas.

2. The bikes and cars aren’t comparable.
Cars and motorcycles have changed quite a bit since they first became popular mass produced consumer goods in the early 1900s. The four-stroke internal combustion engine has gone from a barely understood novelty to arguably the most refined engine of any kind. By the time the 1970s rolled around, pollution from cars was a big problem. Regulations started appearing in 1973 to regulate smog and, in 1975, SMOG checks became mandatory and horsepower numbers dropped. It was the Malaise Era and it sucked. Look no further than the cars produced during those years to see how drastically things were effected.

Motorcycles didn't have to deal smog checks like cars did during those years. Racing was popular. People were riding. Ask any seasoned grey-beard about motorcycling in the ‘70s and they'll tell you this was the golden era for bikes. Motorcycle development continued and bikes got fast. Really fast. First there was the Ninja, the the GSX-R, then the CBRs. Specific output rose to incredible levels. Today, a 600cc sportsbike produces over 200bhp per liter, unaided by forced induction. The most powerful road-legal car ever produced, the 1001bhp Bugatti Veyron, has four turbo chargers yet only manages 125bhp per liter. Today, a sportsbike is literally a racing machine for the road.

Motorcycle emissions regulations are currently trailing cars. Looking at the data gathered by Mythbusters, we see that a 2006 Honda CBR1000RR is roughly double that of a 1990 Honda Accord and is less than half that of a 1986 Oldsmobile Cutlass Ceira. That bike has two catalytic converters and a modern fuel injection system, but keep in mind that it's built to do nothing more than cut fast lap times around a race track.

Two of the motorcycles used for testing are street-legal racers, and the third takes its motor from one. Keep that in mind while you learn about the three cars. For their ‘80s car, the team chose a 1986 Oldsmobile Cutlass Ceira. For simplicity’s sake, lets assume that the test car was equipped with the most popular motor offered, the 2.2 liter four-cylinder. With 2,200cc, it only manages to produce seven more hp than the CBR600 for a grand total of 92. It's heavy, low-tech and about as far from a high-performance car as you can get. For the 1990s, a Honda Accord was chosen. Same story as the Olds: 125 hp from a 2.2 liter low-performance engine, zillions of units sold, utterly beige, forgettable and slow. The 2000-07 Taurus/2006-07 CBR1000RR pairing is the most ridiculous though. One is a cheap rental car, the other is basically a street legal racing machine. And they're being paired up for emissions testing to definitively decide whether cars or motorcycles are worse for the environment.

Despite popular belief that it's impossible, there are ways to fit a complete emissions package on a motorcycle. They've done it. The new Yamaha Zuma 50, one of the cheapest motorized two-wheeled vehicles, has a cat, FI and full smog controls. It's not expensive, it's not hot and it's not ugly. There is nothing inherently polluting about motorcycles. If they had the same emissions controls as cars, the stuff coming out of the pipe would absolutely be proportional to gas mileage difference.

3. Testing only proved what was already known.
Look at this slide, taken from new EPA motorcycle emissions regulations. Note the vast difference between minimum regulated standards for cars and bikes. These are essentially the same results established by the Mythbusters’ testing. So why test for results which are already legally defined and published? Motorcycles pollute more than cars because they don’t face the same regulations, plain and simple.

4. Burning less gas is its own environmental benefit.
If you’re determining the total environmental impact of a form of transportation, then more data needs to be taken into consideration than simply tailpipe emissions. The entire point of this episode seems to be that, despite using less gasoline, motorcycles emit more harmful substances. But, that argument fails to take into account the impact drilling, shipping, processing and other factors involved in the creation of that gasoline have on the environment.

We can find no quantified, immediately digestible data as to the environmental impact of producing, refining and shipping a gallon of gas, but according to UC Berkeley , doing so results in “considerable pollution.” Energy is required to remove gas from reservoirs, transport it to refineries, refine it, then ship it to users around the world. One-fifth of the energy in a barrel of oil is consumed during this process. At its source, this results in air, water and soil pollution, while accidents like the Deepwater Horizon oil spill further damage the environment. That was the largest ever in US waters, releasing 4.9 million barrels of oil into the Gulf of Mexico. Less oil production would logically result in less pollution caused by oil production and related accidents. Lower fuel consumption logically requires less oil production.

There’s also the environmental impact of our reliance on foreign oil and the subsequent political ramifications. In 2010, The Guardian estimated that the current Iraq War’s carbon footprint to-date was 250-600 million metric tons of CO2. That figure only includes carbon dioxide produced by burning fossil fuels, not that resulting from explosions or other sources. Again according to The Guardian, that’s nearly as much as a “limited” nuclear exchange.

There’s 8 million registered motorcycles in America. Figuring a conservative average of 35mpg and an ambitious annual mileage of 10,000, our total annual fuel consumption is 2,288,000,000 gallons of gasoline a year (in reality, it’ll be much less). The US produces 84,498,960,000 gallons of gasoline annually. All that pollution from gasoline production and from wars being fought over foreign oil isn’t being caused by motorcycles.

5. Lifecycle cost of vehicles not considered.
By their own admission, the Mythbusters did not take into account the environmental impact of vehicle production, stating, “We looked into cars vs. bikes and the resources they take to build. The broad category, the idea of looking at a figure like this; we can’t measure everything a factory is doing. We tend not try not to represent those figures heavily in the show. The research that we did showed that because bikes are produced in smaller numbers than cars, there are inefficiencies in the manufacturing process that make bikes as or less efficient than cars to manufacturer. That it actually takes more resources to produce motorcycles because they produce so many less of them and they lose the economies of scale.”

The problem is, production (along with tailpipe emissions) is only one of many factors to take into consideration when calculating the total life cycle environmental impact of a vehicle. There’s also the cost of infrastructure and the need to maintain that infrastructure, as well as the end-life cost of vehicle disposal. Bikes neither cause congestion, nor damage roadways. That’s why many toll roads and bridges reduce or waive fares for bikers.

One mile of single-lane highway construction consumes 12,000 tons of raw materials and has a carbon footprint of 1,200 tons of CO2. There’s no way to calculate the impact on the environment of chopping down trees and blowing up hillsides to create that mile of road. There’s 4 million miles of highway in the US, most of which is more than a single lane.

That highway construction is just one example in the infrastructure required to keep cars moving, which includes parking facilities, gas stations, bridges, tunnels, traffic lights, law enforcement, emergency response etc. In nearly all of those examples, the burden created by motorcycles is lower. Bridges, for instance, don’t have to be designed to take the weight of a bike and motorcycles don't necessitate the construction of vast, multistory parking structures.

6. The test cycle was unrealistic.
The test cycle used in the show was the same standardized one developed and used by the EPA. During the test, vehicles go the speed limit and don't sit stopped in traffic. In reality, people drive faster than 65mph and cars sit stopped in traffic. In Los Angeles, for instance, drivers spend 70 hours a year stuck in standstill traffic, each of them wasting 53 gallons of gas in the process. Regardless of how efficient and clean cars are, they're getting 0mpg while they burn gas and pump out exhaust while they're stopped. Motorcycles, on the other hand, at least in California and outside the United States, keep on going unhindered by congestion.

7. The effect of maintenance wasn’t considered.
In addition to the CBR600 and CB1000 Big One being rare and somewhat high-performance machines, it should be noted that they're old. The Cutlass Ceira and Accord are also old. As vehicles age, things like valve guide seals, catalytic converters, piston rings and emissions systems wear out, all contributing to emissions. Bad valve guide seals and worn out rings let oil escape from the motor and enter the exhaust, resulting in high HC levels. An old, used up catalytic converter lets a lot more CO, HC and NOx flow straight through. There are a plethora of creative emissions controls, many of them fragile and failure prone. The high NOx readings of the CBR600 and Cutlass Ceira could easily be caused by excess carbon buildup in the combustion chambers. Carbon buildup increases compression, which means more NOx forming heat, and keeps heat from transferring effectively to the cooling system, which means hotter combustion and more NOx.

8. If decreased fuel usage doesn’t help, then why add a fairing?
Despite achieving much higher fuel economy numbers than the cars in the test, motorcycles were still shown to emit more harmful gasses. So what, then, did the Mythbusters hope to achieve by adding a fairing? Testing showed that the bikes needed stricter emissions controls, not increased fuel efficiency.

There’s also the question of the effectiveness of the homebrew fairing created for the show.
Craig Vetter figured out that proper streamlining delivers astounding results a long time ago. Back in 1985, a motorcycle using one of his off-the-shelf fairings got 477mpg. Squeezing 70.9, or .1mpg less than the EPA estimate, out of a WR250 using a homebrew fairing sounds like a waste of time.

9. If bikes are so poisonous, then why was it safe to breath exhaust fumes?
Throughout the show, the harmful effects of the chemicals being emitted by the bikes are repeated and expanded on. But, when it came time to test the faired WR250, Jamie was able to pilot it without losing consciousness despite exhaust fumes being emitting into the fairing with him. If the tailpipe emissions from motorcycles are so bad, then why was Jamie able to tolerate them for an extended period of time?

This seems to suggest that, while the cumulative effects of many miles on motorcycles could add up to significant pollution, simply riding a single one does not create enough emissions to harm a single human being. This was a good opportunity for perspective to be applied, how do motorcycle and car emissions compare to other forms of pollution and to a human body’s ability to deal with them?

10. Testing for poisons, not pollutants.
There's a lot of things coming out of an exhaust pipe, just about all of them bad, but only one is causing global warming. CO2 is the real bad guy and there's plenty of real, actual, scientific evidence to back that up. When we look at things from this point of view, the results are completely different.


NO and NO2 specifically. These chemicals are important trace elements in the Earth's ozone layer. At ground level, where we experience NOx from cars, trucks and motorcycles, it also helps to make O3, which is toxic to humans. It can also combine with water to make nitric acid (and acid rain). Fortunately, when it ends up in the ground, the soil converts it to nitrate which is of use to growing plants. Oxides of Nitrogen are not a major cause of global warming.


According to the EPA, only 29 percent of Hydrocarbon pollution comes from on-road mobile sources, or cars, trucks and motorcycles. As only a tiny, nearly negligible portion of vehicles are actually tested, and even then, only for just a few minutes, it's impossible to even get a + or - 1% estimate as to how many of those HCs are coming from bikes.

Even still, HC are not what's ruining the planet. They contribute to ground level smog and are toxic to people, but when the source of them is cleaned up, they go away. Talk to anyone who lived in Los Angeles in the ‘60s and ‘70s and they'll tell you how unbearable the smog was. Today, it's all but gone. Hydrocarbons are not a major cause of global warming, but they have been linked to asthma.


Carbon Monoxide is toxic to humans and lethal at high levels. This is what kills people when they run a car in an enclosed garage. Still, even with all the gasoline burning vehicles we have running around, the largest producer of CO is the Earth itself. CO is not a major cause of global warming.


Carbon Dioxide is a big deal. Though it's what we exhale and what trees breathe, our industrialization of the world has steadily upped CO2 production since the 1700s. The extra CO2 produced by the production of electric power, new products, vehicles, etc throws off the Earth's carbon cycle and is the largest contributor to global warming. It's not directly toxic to humans, but if we don't do something to curb CO2 production, global climate change will continue to get worse, polar bears will die and ice caps will melt. The largest contributor of carbon dioxide in the Mythbuster's test was the modern Ford Taurus produced between 2000 and 2007.

Through these 10 points, we see the following:
- A representative sample of motorcycles was not chosen.
- The motorcycles that were used in the test are in no way comparable to the cars used.
- An unacceptable amount of unknown variables are introduced into the test by the question of maintenance.
- All testing achieved was rough verification of emission levels defined by law.
- Total environmental impact was neither tested nor factored into assumptions.
- Testing didn’t replicate real world conditions.
- A portion of the testing went on a tangent unrelated to emissions.
- Unintentionally, poisonous gasses were shown to have little effect on the short term health of humans.
- Test results were weighted towards chemicals harmful to humans, not ones harmful to the environment.

Together, all this represents a serious lapse in science. The results of the testing aren’t repeatable as too many unknown variables — maintenance, vehicle condition — enter into them. The hypothesis, that motorcycles are more damaging to the environment than cars, was sweeping, yet only tested on a single variable — tailpipe emissions. The results of that single variable testing still showed that cars are more damaging to the environment because they produce more global warming-causing CO2, yet the conclusion was weighted to diminish the importance of that data.

Because of this, we have no choice but to declare the premise, "At this point in time, it is not better for the environment to trade your car for a motorcycle,” busted. A more accurate conclusion would be that a race replica motorcycle capable of speeds approaching 200mph uses less fuel and emits less CO2 than a rental car, but does emit more NOx, HC and CO, chemicals which haven’t been shown to be major contributors to global warming. But that wouldn’t have made good television, would it?

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