Driving: Save Gas by "Short Shifting"
I bought a Scan Gauge in anticipation of redoing our "We Test the Tips" article about fuel economy. I was eager to try it out so I ran a short test over the weekend with the help of my son Tony, 17.
Using my 2007 Honda Fit Sport, with a manual transmission, I decided to see what effect "short shifting" had on fuel economy. Driving a 9.3-mile loop that has many stop signs and stop lights, I decided to drive it once shifting no higher than 3,000 rpm and then again taking it up to 4,000 rpm.
As I drove I found myself wanting to rev it higher than 3,000 rpm. I realized that my normal driving style was to take it nearly to 4,000 rpm. Still, I was suprised that I could shift at 3,000 rpm without feeling that I was lugging the engine. It was happy and I felt more relaxed. Also, no one was blasting their horn at me for going to slow. The result: 32.4 mpg costing 86 cents worth of gas at about $3.00/gallon.
Tony wrote down these results, we reset the Scan Gauge and set out again. We tried our best to duplicate every other aspect of the test except the shift point. This time I took it up to 4,000 rpm. "This is more like you," my co-pilot said as I came up on the bumper of an SUV in front of us.
As I drove this loop I became aware of the boost in power between 3 and 4,000 rpm that Honda's VTEC engine afforded. I wondered if the VTEC engine was offsetting the higher engine revolutions. Still, when I pulled back up in front of my house, Tony told me that we had gotten 30.6 mpg, a 5.5 percent difference.
- Posted by
- Philip Reed January 16, 2008, 9:42 PM
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Phillip, this is very interesting. And I have a similar experience. Usually, when I drive in town I shift at 2500 rpm. Hence, I often do 40 mph and above in 5th. With my Protege, I get a fuel economy of about 27 mpg in city driving.
I avoid revving above 3000 rpm, except in the following situations:
- When I'm bored and I want to have some fun. This happens typically two or three times a month. The Protege's engine is a very rev-happy one and sounds great at high rpm.
- When merging onto a highway.
- When I have to do above 60 mph. (The Protege does 60 mph at about 2900 rpm in 5th gear.)
- When I have to overtake another car on a two-lane road.
I have a question: is there an optimum rev range for which an engine is more efficient? Or is it simple a "the lower the rpm the higher the efficiency" issue?
blackadder: the idea of doing this and getting a Scan Gauge came from a post in our forums by a Jetti TDI (diesel) owner. He said he changed the shift points and boosted the fuel mileage. I do know that high revs drink down gas but rapid acceleration to lower shift point might not. In fact, cars are sometimes more efficient at high rpm than moderate revs. So, about all I can say is that experimentation is the best way to solve this question. I suspect the answer is that yes, the lower the rpm the higher the efficiency. But the flip side to this is that the higher rpm might not be as bad as you think. In fact, I was anticipating a much bigger difference between these two driving styles.
Race car drivers also do this to improve their fuel economy when they know the window is going to be tight.
Excellent blog entry, Phil!
philip is rate, it depends on the engine
I play this game a lot too. I'm not that scientific about it, but I've been shifting below 3000 rpm in my Mazda3 and obeying all posted speed limits, and getting just about 33 mpg in mixed driving. In my wife's Yukon I try to keep it below 2,000 rpm and gain about 1mpg (17 versus 16). Not as easy to do in an automatic, you have to be pretty light on the throttle or it will hold 2nd gear. Which is nice when you need to boogie, but can frustrate the more impatient drivers behind me. Like I care - pass me if you're in a hurry. I'm not a danger on the road, I go with the flow of traffic generally and stay out of the passing lane when I'm loafing. But I accelerate gently, and don't see the point in beating everyone to the next red light where we all sit together again. Anyway, I love the complete control with the 5-speed manual in my car.
It's important to remember that even 1 mpg improvement in a vehicle that normally gets 16 mpg is significant. It doesn't seem like it but it is a 5 percent improvement.
Hard acceleration consumes more gas then gentle acceleration? Who would have thunk?
Since when is shifting at 3000rpm short shifting? I haven't driving a Honda Fit, so I can't speak for it's engine. Perhaps, it's just that short on torque. When I drove a 4cyl stick, I typically shifted before 2500 for casual, in town, acceleration.