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Old 05-02-2008, 10:21 AM   #1
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Arrow To draft or slow down?

I drive 130 miles round trip to work everyday, 2/3 is on the turnpike. I typically cruise at 75mph but I have dramatically changed my driving style this week. I have been cruising at around 62mph instead. I have noticed almost a 15% increase in economy. One thing that concerns me is that at this speed EVERYONE passes me, even tractor trailers. I am just waiting for one to not be paying attention.

Most trucks seem to cruise in the 67-72mph range. If I can find one that is around 65-67mph and draft behind it, do you think I will have the same amount of fuel economy?

While I know it's not safest thing to do, I believe that it IS safer (at least in my mind) for me to be behind a single truck instead multiple trucks coming up fast behind me.

Does anyone know for sure, or should I just test and find out?

I have a 99 civic hb auto, fyi.

Thanks!
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Old 05-02-2008, 10:27 AM   #2
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Quote:
Originally Posted by racertim View Post
I drive 130 miles round trip to work everyday, 2/3 is on the turnpike. I typically cruise at 75mph but I have dramatically changed my driving style this week. I have been cruising at around 62mph instead. I have noticed almost a 15% increase in economy. One thing that concerns me is that at this speed EVERYONE passes me, even tractor trailers. I am just waiting for one to not be paying attention.

Most trucks seem to cruise in the 67-72mph range. If I can find one that is around 65-67mph and draft behind it, do you think I will have the same amount of fuel economy?

While I know it's not safest thing to do, I believe that it IS safer (at least in my mind) for me to be behind a single truck instead multiple trucks coming up fast behind me.

Does anyone know for sure, or should I just test and find out?

I have a 99 civic hb auto, fyi.

Thanks!

I'm interested to see the response. I live in the DC metro area and have a similar issue when driving on the highway. P&D driving is a bit of a challenge because of this.

Part of the solution is probably aero modifications to reduce drag.
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Old 05-02-2008, 10:31 AM   #3
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Before drafting a truck, look to see how the trailer is bouncing on the suspension, if it's jiggling about a lot, it's likely unloaded and deadheading... find a different truck... look for one with a slow periodicity on the suspension bouncing... that one is well loaded... it has 4x your stopping distance and will maintain a steady speed, and is less likely to be changing lanes all the time... but it will be slow to follow up grades. Try to follow at a distance that lets you see the brake lights on the tractor unit, underneath the truck... this means that should a line fall off on the trailer, you'll still see it's braking... you're also usually far enough back to catch signs of "shine" of the brakelights of the vehicle in front of it off the road surface.
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Old 05-02-2008, 10:34 AM   #4
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RoadWarrior: So your suggestion is.....
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Old 05-02-2008, 10:35 AM   #5
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I don't remember the exact numbers, but in my Odyssey, 70mph with a 3-second draft was slightly better than 65mph in the open.
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Old 05-02-2008, 10:40 AM   #6
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PaleMelanesian: Are you consistently getting 60mpg? Tell me about your ride.
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Old 05-02-2008, 10:44 AM   #7
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That's my civic, manual. My best highway drive was 75 mpg over 150 miles. High Speed Pulse & Glide in a 40-60 mph range, adjusting to the terrain. Near the crest of a hill, 40, in the bottom of the valley, 60. I have a grill block, and my tires are at 60 psi, and I use a Scangauge.

I've done the same drive using P&G behind a truck at 70mph, and got 55mpg.
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Old 05-02-2008, 10:47 AM   #8
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Scangauge does what exactly?

I like seeing 60mpg without any really crazy modifications.
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Old 05-02-2008, 10:51 AM   #9
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Scangauge tells you everything the car and engine are doing, at any moment. It also tells you instant and average gas mileage. Scangauge.com has all the details.

There's also an ongoing group buy at CleanMPG for cheaper. I'm over there more than here. Try reading the articles they have. It's all written down there. I just take all the ideas and run with them.
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Old 05-02-2008, 10:54 AM   #10
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Quote:
Originally Posted by racertim View Post
RoadWarrior: So your suggestion is.....
Heh, forgot that bit, I usually find that drafting uses much less fuel at any speed up to about 75mph... beyond that, you seem to be having to get too close for comfort at that speed, and seem to get thrown around more by wake vortices, meaning you have to keep stomping the gas to catch up again.

The trucks that are moving quick though are more likely to be the unloaded ones, which are difficult to follow, due to having shorter stopping distances, more likely to be changing lanes, and their trailers have a tendency to wander around a bit, dumping you out of the draft when they go from one side of the lane to the other. So generally finding one of the ones going steady in the right hand lane is better.

So drafting something big anywhere in the 60-70 range is great for F-E. Might seem to have progressively less effect the better aero your vehicle has, but weight seems to play a bit of a part, since, in my Escort Wagon, I seem to be able to gain 20mph from a truck without moving my foot, whereas in the minivan it's more like 5 or 10... this is when you pull out into draft... like from the entrance ramp or changing lanes.
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