Understanding Fuel Economy

Overall vehicle fuel economy for a given car is determined by a ratio designed into the vehicle called the N/V ratio, where N = engine speed, and V = vehicle speed. To get the best fuel economy, you want the N/V ratio to be as close to 1 as possible. For the layperson, this is achieved by getting to the highest transmission gear (say 5th or 6th) as quickly as possible. The N / V ratio is set by the transmission gear ratio as well as the axle or differential ratio.

So, for instance the N/V ratio cruising down the highway in overdrive is typically 2000 RPM / 65 MPH for a N/V of 30.77. Now, take for example driving around town in heavy traffic in first gear, for a N / V ratio of 2000 RPM / 10 MPH = 200.0

As yet another example, if your vehicle has a "Instantaneous Fuel Economy" readout in the information center, get going 55 MPH and note what the readout is showing. Now, carefully shift the transmission into neutral and note again what it says. More than likely it will be "pegged" or much greater than the readout can display. What this essentially showing you is
a very low N/V ratio: 600 RPM (engine idling in N) / 55 MPH = 10.91 (BTW this is also a technique for saving fuel called "Hypermiling").

So in supporting what Dale has mentioned below, lower speed limits actually WASTE fuel, as your engine cannot operate in the highest gear, without "lugging" the engine, forcing the automatic transmission into a lower gear, or you to shift your manual transmission into 3rd or 4th gear, rather than the preferred fifth gear.

This is also quite clear when you purchased the vehicle, and looked at the window sticker with the EPA mileage - city mileage is ALWAYS lower than HIGHWAY mileage for this exact engineering reason.

So, the next time you're cruising down the road, check your N/V ratio and try to get it as low as possible!

Fast to Save Gas

FACT:
Your vehicle gets better gas milage on the highway, than in does in the city.

FICTION:
You get better gas milage by driving slower.

Simply put, you want to get your vehicle's transmission into it's highest gear (overdrive for most new cars) as quickly as possible, so that you can cover as many miles as possible while the engine is spinning at it's lowest speed.

Driving at low speeds, the vehicles ECU (Engine Control Unit a.k.a. the computer) working in conjuction with the TCU (Transmission Control Unit) doesn't allow the engine to "lug", or to operate a low speed in a high gear (which, by the way, you can do with a manual transmission). So, the engine is forced to use more fuel in order to maintain a higher engine speed at a lower vehicle speed, lowering fuel economy.

So, something to think about: in these days of $4/gallon gasoline, federal, state, and local governments should reconsider the speed limits on their roads, so that the country can conserve fuel!

The unspoken "High Beam Flash" rule could be history.

It's a universal, unspoken code of the road: a quick flash of the high beams to warn oncoming motorists about a looming police speed trap. But is it illegal?

read more | digg story

Lane rules make everyone safer and faster

Our friends to the north agree on the rules of the left hand lane...

read more | digg story

What is it about Subaru's?

As the saying goes, you are what you drive. Or is it, you drive what you are? Whatever the case may be, I've been noticing something lately as I've been driving around town: People that drive Subaru's don't like to drive at the speed limit.

Now, I'm not talking about those who drive the sporty Subaru's like the WRX or the Impreza - I'm talking about those Foresters, Outbacks, and even Tribecas.

I'm not saying they're speeding - Just the opposite is true. It seems they have trouble distinguishing the pedal on the right from the pedal on the left. If the speed limit is 45MPH, they'll do 40MPH and have a line full of traffic waiting for the next opportunity to pass. And in these parts, that can be awhile. I'd say that in about 90% of my non-scientific observations, whenever I'm behind a line of traffic, the person that's holding up the whole shooting match is driving a Subaru.

These folks need to realise that driving under the speed limit is just as dangerous, if not more dangerous, as driving over the speed limit. How you ask? Well, forcing people to pass on a two lane road offers many more hazards than simply driving the speed limit.

So, what is it about people that drive Subaru's?

A European Driving Lesson

A few years ago, I had the opportunity to drive on the world famous AutoBahn in Germany. Driving on the AutoBahn was the personal highlight of the trip - I mean who else has the chance to legally drive 235 kph (146 mph) on public roads?

Another interesting part of the trip was witnessing the driving etiquette on the Autobahn. The left lane is the passing lane - period. If you're in the left lane, it's to pass someone, and then you move back to the right lane - nobody really cares how fast you're going.

If you need to pass someone, get in the left lane, pass, then move back to the right lane. I was truly impressed to see that everyone followed that rule, even at speeds over 100 MPH.

Why can't Americans do the same?

Driving in the Left Hand Lane

Here I am, driving along on the interstate, minding my own business, and like most folks, moving along at something over the speed limit. I'm in the right hand lane, because I know that's where you're supposed to be. As I come up to some slower traffic, I move over to the left lane to pass them and Whammo - I get stuck behind someone 'driving' in the left hand lane.

I have to tap the brakes to take the car out of cruise, and wait. And wait. Hopefully this person is going to pull back into the RH lane. Hopefully.

Why is it that folks insist on 'driving' in the left hand lane? Don't they know that the left hand lane is the passing lane? The driving lane? Yes - that's the right hand lane - that's for driving.

Go to just about any drivers manual and you'll find it there - here's a sample from the NY State manual:

"The left lane is used for passing other vehicles...

...If conditions are right for passing, check in your mirrors and signal your lane change. Before pulling into the left lane, glance briefly over your left shoulder, through the rear side window, to make sure no vehicle is passing you or close behind you in the left lane....

...When passing, move completely into the left lane. Before returning to the right lane, signal and look at your interior rearview mirror and make sure you can see the front bumper of the vehicle you just passed. Glance quickly over your right shoulder to double-check that you can see at least several feet of pavement between your vehicle and the one you passed. Then return to the right lane."

So why do people insist on 'driving' in the passing lane? Move over to the right hand lane people!