Do Motorcycles need better fuel economy?

2011-10-02 12:00


Automobile makers worldwide are increasing the fuel economy of all their offerings these days. They have to. Markets and governments are making it a priority. The progress continues to narrow the advantage motorcycles have always enjoyed over cages. In fact, conservative-driving hybrid owners and small car drivers often get better mileage than many sport bike riders we know. Motorcycle owners and makers should be concerned that the famous “Gee think of the money I’ll save on gas!” justification may eventually be ineffective with parents and spouses.

It’s really not surprising that Honda Motor Co., famous for fuel-efficient cars has begun to address two wheel consumption concerns. Last year, Honda Motor Japan introduced a new “Idle stop” fuel saving technology on the PCX125, a 125cc 130-MPG scooter available in select markets. Why a scooter? Well, much of the world’s scooter riding population resides in dense, traffic-choked cities and countries. Places where stop-and-go traffic is typically more stop than go and fuel prices are a lot higher than what we in the U.S. still “enjoy”. Honda’s design is a clever but straightforward system that can automatically shut off the engine after 3 seconds of idling is detected. The system optimally pre-positions the crankshaft near bottom dead center and uses a basic decompression device to expedite ultra quick, (electric) restarts by simply reopening the throttle. Similar to the way hybrid autos can function, the idle stop concept has been around for some time but Honda’s scooter-specific application is unique.

How big a deal?
It doesn’t take rocket science to know idling an engine, even for relatively short durations wastes some fuel. But how much? Using the ECE R40 driving test standard, Honda claims a 7% MPG increase for its idle stop equipped scooters. That may actually turn out to be a conservative figure for some owners. Computerized MPG displays these days quickly demonstrate the deleterious effect of even modest idling. On cars equipped with these instant MPG read outs, one can typically watch mileage drop a tenth of a mile about every 10 seconds while stopped. The familiar EPA “city and highway” spreads become much easier to understand when fuel use at a stop is observed real time. Honda’s system reinforces how wasteful “stop and wait” driving is and addresses it almost seamlessly.

Trying it out it the hard way
Unlike selective cylinder shut off systems or other sophisticated fuel saving technologies, some idling reduction can be manually incorporated by almost anyone. On a current car or motorcycle it can be as simple as putting on seat belts, helmets and gear before starting the engine.

Out of curiosity and just to see what the future might hold for idle stop technology, Bikeland experimented with the concept on a full size Honda two-wheeler and four-wheeler on some Southern California city loops. Shutting off a motor in traffic is a little unsettling at first. Extra attention and caution is required especially at red lights. Our testing involved shutting down at about half the stoplights we encountered, around ten to twelve a day, with a seventy second average duration. Red lights that we deemed too short to deal with would, of course, still benefitted from Honda’s 3-second system, as would other slow traffic situations. We also shut the car engine off at occasional drive thrus and fittingly, while waiting in line at gas pumps. On a four cylinder CB900F our test results showed a 7-8% MPG improvement while a 2007 4WD Honda Pilot attained an even more worthwhile 12-14% increase. Full disclosure: “Your results will vary” but we don’t recommend you try.

Safety first
Even though it’s not marketed in lawyer-infested America, rest assured Honda’s idle stop scooter system is designed, vetted and tested with safety a prime consideration. A number of special sensors and warnings are incorporated. One sensor even makes sure the rider is properly seated before restarts can occur. Replicating Honda’s system manually required extra operator care and focus to timely restart the motor and launch (Honda’s automatic system adds only four tenths of a second to takeoffs) Sitting through traffic lights with the ignition off is riskier in this digitally distracted driving age. Bikeland’s tester only felt comfortable killing the motor AFTER traffic behind had fully stopped. There’s also the added concentration requirement of watching cross traffic’s signals to be ready to go on the green, especially when you’re first in line.

The technically inclined may question the mechanical downsides of extra start-ups every day. Shortened battery life is a possibility, especially if the key and headlight(s) are left on while stopped. (Honda’s system dims its headlight while stopped and uses a stronger, specially designed charging system). Those weight -saving smaller batteries used on some sport bikes may not be up to the task in city-only driving. Despite oil manufacturer’s oft-cited premise of increased cylinder wear on start up, warmed up engines should be fine. When cylinders are at operating temp and walls well lubed, you have to use really poor oil to be concerned. For air-cooled bikes there’s also a potential benefit of lower oil and engine temps at those two-minute summer traffic lights.

The future
Idle shut off systems could be on the horizon for more vehicles. Scooters and small motorcycles are logical two wheel applications given their anticipated urban use compared to Touring, Sport or Adventure bikes. Of course, emission and performance related use of fuel injection and friction reduction materials has helped improve motorcycle mileage somewhat. Based on our results and anticipated future fuel prices, we think Honda and other companies will offer fuel saving technology on more motorcycles. Surely every OEM wants their prospective buyers to have that “Gee think of the money I’ll save on gas!” justification.


For more details on Honda's Idle Stop technology, check out the links below.
world.honda.com/motorcycle-picturebook/idling-stop/
world.honda.com/motorcycle-technology/Engineidlingstop/


Source: Bikeland.org

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