Monday, August 4, 2008

Gas Saving Tips: Hypermiling Part 2


OK, so now on with the show! Here's the post you've all been waiting for, detailing exactly what I did to literally double my gas mileage overnight (see copies of my gas receipts and calculations to the left). Please note that the receipt on the left reflects in-town driving only with only minimal hypermiling techniques. The receipt on the right shows the results of my recent day trip with a concerted effort into hypermiling, including the one physical modification to the vehicle that I will reveal below. Absolutely anyone can do this, although your mileage may vary (YMMV). Keep in mind that there was only 1 modification to the vehicle itself (which was free and can be performed by practically anyone); the rest of these steps are simply a way to "re-train" yourself to drive in a way to save gasoline.

Basic Hypermiling Tips

1. Air up your tires! While most people realize that an under-inflated tire can result in a loss of fuel efficiency, they don't usually understand why. Lower pressure tires have more surface area in contact with the ground, which increases friction and drag on the vehicle. While it may not seem like much, every little bit counts. Now here's the trick to take this simple step to the next level with hypermiling.

Most people air up their tires to the recommendations of the car manufacturers. What is this based on? The car manufacturer doesn't know what type or rating of tire you will put on your vehicle, so how can they make a broad-based recommendation? They base it on the way the vehicle rides and the noise level from the tires and resulting comfort level of the passengers. Does this matter as much to you as fuel efficiency? It really doesn't to me ... of course my vehicle is over 10 years old anyway (LOL), but at least it's paid for ;-). So hypermilers take this to the next level by increasing their tire pressure to reflect the MAXIMUM rating for the tire, according to the tire manufacturer. As a result, less of the tire comes in contact with the ground, resulting in less friction. There is a slight increase in road noise and also you feel the road a bit more in the steering, but nothing I would consider to be a deterring to using this. So for me, this meant airing up my tires to 44 psi.

2. Accelerate and decelerate slowly from start to finish. When taking off from a stop, don't gun it! Slow down and accelerate at a slow, even pace. Work up to where you want to be and stay there. When you see a red light or stop sign coming up, let off the gas way in advance and coast. One hypermiler recommended keeping the vehicle's RPMs under 1800, but I found on my '96 Mercury Villager with an automatic transmission that this was virtually impossible. It wouldn't shift into 3rd gear unless I took it up to about 2100 RPMs. So, I made that my goal. The entire trip I adjusted my driving to keep my RPMs under 2100. The only exceptions were when I had to go uphill, in which case I increased my RPMs just enough to maintain speed, which ended up being around 2400.

3. Always stay under the speed limit and don't go over 55 mph on the highway. While staying under the speed limit is always a good idea (it is the law, after all), most people find themselves inching above it all the time. Just try it and I think you will find it can make all the difference. When I'm on a flat surface or in town, I use cruise control to help me maintain a lawful speed just under the speed limit. Keep in mind that cruise control on most vehicles doesn't work until you reach 30 mph or so. OK, so what about limiting yourself to driving 55 on the highways? Sounds like a granny move, right? Well, it might sound that way, but it can definitely save on your gas consumption.


Take a look at this general chart from a government study. It shows that optimal fuel efficiency is reached at about 50 mph and starts dropping off above 55, with a significant drop at 60+. So what about making it there on time? Ever heard of starting early? Honestly, changing your driving habits from going 70 mph (you weren't speeding were you?) to 55 mph does take some effort. Again, I used cruise control to help me out here, as my foot tended to get a bit heavy. So how much time did I lose? Well, let's figure it out.

My total trip was 96 miles. Although my average was lower because of red lights and stop signs, city speed limits and such, let's say for the calculations that my speed was a constant 55 vs your 70. It would take you 82 minutes at 70 mph to make the trip, while it would take me 104 minutes. So you arrive 22 minutes earlier than me, or I would have to leave 22 minutes earlier to make up the difference. But, all other things being equal, would more than doubling your gas mileage make it worth it? It sure does it for me, especially with gas prices as high as they've been!

OK, there you have it! Those are three of the basic steps that I took to go from an average of 18 mpg on the road to a whopping 51 mpg! Lest you think that my trip was all highway (and I still have never gotten that type of mileage on the highway either), here is a map of my trip route. As you can see, it winds through several small towns (yes, red lights) and has ample opportunity for both city and highway driving.


View Larger Map
Finally, last but not least, I wanted to leave you with another excellent news report on how hypermiling is changing the way people drive, and driving fuel economy beyond what you could ever have imagined...

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