The latest in our series of video road tests is America's leading electric motorcycle: the Zero S, from California's Zero Motorcycles. Seventy-five miles per hour and 60 miles between charges are the big numbers here - but how does that translate to real life use? Also, since electricity costs so much less than petrol, can an electric motorcycle be viewed as an economical option? And what about the environment? When the carbon cost of electricity generation is taken into account, how green are electric vehicles? These questions and more, answered after the jump!

Now to the tricky bit - is the Zero S value for money, and how much better for the environment is it than an equivalent petrol bike?

Let's line it up against the Kawasaki KLX250F, a road-oriented single cylinder dirtbike of about the same weight and performance.

There's some pretty huge variables here, obviously, but we've done our best to come up with unbiased figures.

We figure the formula for cost of ownership goes something like this: Total cost of ownership = (purchase price) + (miles per energy unit X price per energy unit X miles) + (servicing costs).

We'll use 65,000 miles as our distance rating, because that's how long the Zero S will run before its battery takes a noticeable drop in performance and needs replacing.

So here we go:

Purchase Price

The Zero S costs US$10,000, not counting federal and state subsidies. The Kawasaki costs $5000. The Zero has a lot of catching up to do!

Energy Costs

Let's start with the Kawasaki. It gets 60 miles per gallon, making it reasonably efficient for a road/trail bike. Taking an average US fuel price of US$3.10 per gallon, the Kawasaki will cost you US$3358 in fuel over 65,000 miles.

Now, to the Zero. On the standard EPA UDDS driving cycle, the Zero S will travel 43 miles on a full battery charge of 3.9 kilowatt-hours (kWh). Now, electricity rates vary as widely as gas prices, but the 2010 average price per kWh in the US is 11.58 cents. So each battery charge on the Zero S costs about US$0.45 - and 65,000 miles will cost you about US$680.23 all up.

Servicing costs

Electric motors don't need servicing. There's no oil to change, valves to adjust, carbs to play with or anything else. The Zero is a zero-maintenance vehicle beyond tyres, suspension and chains, which we'll leave out as the Kawasaki needs the same things.

The Kawasaki on the other hand, needs quite a lot of mechanical attention. Over 65,000 miles, the logbook requires you to bring it in for 6 minor services (at about $100 each) and 7 major services at somewhere around $220. So your servicing costs for the Kawasaki will be about US$2140 - not to mention the time you spend going back and forth to the mechanic's or doing the work yourself.

Totals and caveats

So, over 65,000 miles, the Zero is going to cost you roughly US$10,680.23 - and the Kawasaki US$10,498.

That's not much of a difference... but then, it took 65,000km of riding to get there. You'd need to commute 20 miles each way, every day for around 5 years to get to this mileage. So it takes a while for the Zero to pay itself off.

Of course, we've used US figures for our energy costs - and American petrol is massively cheaper than just about anywhere else in the Western world. In the UK, for example, petrol costs 2.5 times more - and electricity only 1.6 times more - so the equation looks significantly better for the Zero bike.

And there's some pretty significant subsidies being offered by certain government departments in the USA, which bring the initial purchase cost down by as much as $1000 - so it's worth taking those into account.

But the main thing to take from this exercise is that the Zero isn't as unaffordable as it looks, provided you rack up a lot of miles on it to take advantage of energy and servicing savings.

And what about environmental performance?

How about environmental performance? After all, while the electric bike has zero local emissions, the reality is that most electricity currently comes from fossil fuel sources. So let's check that out:

According to the Carbon Fund, the average electricity source generates 1.297 pounds of carbon dioxide per kilowatt hour. The Zero averages about 3.9 kilowatt hours per 43 miles, so over 65,000 miles, the Zero will be responsible for about 7,646 pounds of atmospheric CO2 emissions.

That sounds like a lot - until you apply the same logic to a petrol bike. We don't have specific local emission figures for the Kawasaki - but if we're going to be looking back at the power plant for the electric bike, then we have to take the oil extraction and refinery emissions into account for the petrol bike too.

The average motorcycle emits a well-to-wheels figure of 0.355 pounds per mile - and over a distance of 65,000 miles that comes out at more then 23,000 pounds of CO2.

So the Zero is roughly three times better for the environment even if you don't plug it into a totally green power source.

Conclusions

Although they're well established in cities like Shanghai, electric bikes are still very much getting started in Western countries, where we tend to demand more power and performance from our two-wheeled toys.

The Zero S is designed to be a muscle commuter for the Western rider, delivering the environmental credentials of en electric but packing as much petrolheaded fun as possible into your daily commute. I'd say it does a great job. It's not going to work for everyone and it's no good for heading out of town, but early adopters are going to have a ball riding one of these things.