Drafting with scangauge

[bowtieguy]

had a chance today to draft a semi while using a scangauge. driving my wife's car(my car is not SGII compatible)gave me this opportunity. VERY interesting.

70mph avg ~29mpg no drafting. when drafting(i'm a truck driver, so i did so w/ mirror in view) again @ 70mph avg ~35mpg.

now, this is where it gets interesting. drafting, same speed, downhill(slight decline--not very hilly here), yeilded a high of 182mpg. WOW!

[brucepick]

Cool.
Thanks for the "hard numbers"!

I do draft sometimes when a good opportunity presents itself. I like drafting box trucks and buses; their back end goes lower to the ground than semis. I make sure to not get too close.

The tough part is, it usually requires some pedal work to stay appropriately close to draft the truck ahead. I make an effort to avoid going so fast that I end up with a reduced net mpg.

Hills - yeah. Once today I had to brake on a downhill because I was getting too close to the draftee up ahead.

[cfg83]

bowtieguy -

Yeah, downhill is VERY rewarding MPG wise. My imaginary perfect MPG freeway would have a Ferris Wheel scaled for cars on each end. You would get on the Ferris wheel, be rotated to the top, and would *always* be going downhill (if even only a gentle slope) the whole way. The other end of the freeway would have a Ferris Wheel for the opposite direction.

CarloSW2

[8307c4]

If you're going downhill you might consider an EONG (Engine OFF in neutral glide), that's technically unlimited mpg. I usually do this when I foresee at least 1/4 mile without the need for engine power, generally speaking a good 15-20 seconds or more, big long hills.

Please don't get too close, I HATE these people like to ride up the bumper of my trailer.
What I do then is I go EONG until it forces them to pass, I'll come to a complete stop if it came down to it.
I don't have too much an issue with folks who back off after they find themselves in it, that's one thing but it's usually some family car just plasters themselves there and won't increase their distance...

You know it's about safety, I understand it's their fault if they hit me, but please understand that if they DO hit me then it also wastes at least 2 hours of my time, that's not even counting all the bs comes after we're out of there.

Oh and not-at-fault still raises my insurance:
Policy activity increases premium.

[Rower4VT]

I had my first chance to compare drafting and not drafting on a long trip. Drafting yielded a solid 2mpg increase...which for me is significant as that is close to a 10% increase. I did notice that if I found a bus I could be further behind it and still get the drafting benefits. 28+ mpg avg for 700 miles on a car with an EPA of 23mpg-hwy rating!

[RoadWarrior]

Got 36mpg in Marvin drafting all the way on a long haul. It's hard to do sometimes though, gotta find a truck just going steady.

[s2man]

Even harder to find a truck which slows just the right amount going up hill, so you can bleed off some of your speed. Of course, when you do catch a good one, your wife will need to get off at the next exit anyway. :)

[ALS]

I have found you can space your self back about 2.5 seconds and still get the benefits of drafting. Do not do this at night or in the rain or bad weather.
The down side is you must keep all your attention on the truck ahead of you.
If you have never done this you soon find out how mentally tiring it can be even after 20 to 30 minutes. Second your front end will take the blunt of all road debris that the rear tires on the truck or bus ahead of you kicks up off the road.

[RoadWarrior]

Yup, you don't need to be right on the truck's bumper, the draft (vacuum rather) has effect out to about 3 lengths of the vehicle making it at highway speed. So therefore you can give most bigs semis a good 100ft. Bear in mind this also means that shorter vehicles won't give such a good safety space. Look out for lightly loaded and empty trucks, they'll generally be bouncing a lot on their springs. Their stopping distances are significantly better than laden trucks, so you have to be extra careful. Typically a large and laden semi should have a stopping distance in the range of 2-3 times that of a typical car. However, if you have put on thinner than stock, hard compound tires, at high pressure, your stopping distance might be longer than stock. Often you can see brake light shine of vehicles in front underneath the truck, don't rely on this, but extra clues like that may help you drive better.

Do not draft flatbed trucks even if they have a large covered load on. Their beds get a heck of a lot of debris and detritus built up on them from construction sites etc, huge hard clumps of mud, gravel and grit, get close behind one of these suckers for long and you'll get stoned to death.

[1993CivicVX]

had a chance today to draft a semi while using a scangauge. driving my wife's car(my car is not SGII compatible)gave me this opportunity. VERY interesting.

70mph avg ~29mpg no drafting. when drafting(i'm a truck driver, so i did so w/ mirror in view) again @ 70mph avg ~35mpg.

now, this is where it gets interesting. drafting, same speed, downhill(slight decline--not very hilly here), yeilded a high of 182mpg. WOW!

I don't doubt it for a second. But a question. Didn't the truck driver not like you drafting? I stopped drafting because I got varying levels of messages to "get off my tale" One truck driver even hit the brakes pretty hard. Another one put on bright white lights on the back of his truck. So I've taken the hint and stopped doing it. But I'm wondering maybe it was because I was not in their rear view? Doesn't it slow them down to drag on them (aren't they essentially pulling you when you draft Going down a hill on the Mass Pike (I-90 headed toward Boston) there is a 6 mile hill that goes into the Pioneer Valley. In a prius, you can actually charge the battery going down this hill drafting! Driving a friend's Prius, drafting behind a truck down that hill, I got the battery completely charged.

[1993CivicVX]

I have found you can space your self back about 2.5 seconds and still get the benefits of drafting. Do not do this at night or in the rain or bad weather.
The down side is you must keep all your attention on the truck ahead of you.
If you have never done this you soon find out how mentally tiring it can be even after 20 to 30 minutes. Second your front end will take the blunt of all road debris that the rear tires on the truck or bus ahead of you kicks up off the road.

Yeah, I've taken some nasty debris doing this. Once I was so close to a truck that I started exiting when he exited because I couldn't see. (Duh!) I realized what was happening before I exited, but yeah... got to pay close attention, or don't draft so damn close.

[Frankenstipe]

I saw a Mythbusters episode on this subject recently. Proved to be worthwhile as long as a safe distance and steady speed are used. Once you get too close you have to constantly adjust your speed in order to stay at a certain distance which uses up more gas. Cruise Control is your friend, I drive mostly highway miles and I always use it unless traffic is bad.

I hate it when people can't maintain a constant speed, drive in the wrong lane, don't move out of the way when someone behind them is trying to go faster then them, tailgate, pass on the right, cut people off, don't use turn signals soon enough etc etc....:mad:

Anyway I'm not big on hypermiling, although I might start soon, I got to school about 30 miles from where I live to the South and I work about 40 miles from where I live to the North so I have to fill up about 2 to 3 times a week. Even if I switch out to stock tire size and do the whole hypermiling thing I'd end up using about 1 and half tanks of gas a week, which is less than than now but the money savings isn't big enough to out weight the benefits of the wider tires. I do a lot of spirited driving when I have the time, 1 or 2 extra tanks of gas a month isn't a big issue.

[bowtieguy]

I don't doubt it for a second. But a question. Didn't the truck driver not like you drafting? I stopped drafting because I got varying levels of messages to "get off my tale" One truck driver even hit the brakes pretty hard. Another one put on bright white lights on the back of his truck. So I've taken the hint and stopped doing it. But I'm wondering maybe it was because I was not in their rear view? Doesn't it slow them down to drag on them (aren't they essentially pulling you when you draft Going down a hill on the Mass Pike (I-90 headed toward Boston) there is a 6 mile hill that goes into the Pioneer Valley. In a prius, you can actually charge the battery going down this hill drafting! Driving a friend's Prius, drafting behind a truck down that hill, I got the battery completely charged.

first let me say that i drive a truck. to answer your question, they(and i) do not get noticeably angry as long as you do stay in their line of vision. certainly everyone has seen the sticker: "if you can't see my mirrors, i can't see you."

[bowtieguy]

I saw a Mythbusters episode on this subject recently. Proved to be worthwhile as long as a safe distance and steady speed are used. Once you get too close you have to constantly adjust your speed in order to stay at a certain distance which uses up more gas. Cruise Control is your friend, I drive mostly highway miles and I always use it unless traffic is bad.

I hate it when people can't maintain a constant speed, drive in the wrong lane, don't move out of the way when someone behind them is trying to go faster then them, tailgate, pass on the right, cut people off, don't use turn signals soon enough etc etc....:mad:

Anyway I'm not big on hypermiling, although I might start soon, I got to school about 30 miles from where I live to the South and I work about 40 miles from where I live to the North so I have to fill up about 2 to 3 times a week. Even if I switch out to stock tire size and do the whole hypermiling thing I'd end up using about 1 and half tanks of gas a week, which is less than than now but the money savings isn't big enough to out weight the benefits of the wider tires. I do a lot of spirited driving when I have the time, 1 or 2 extra tanks of gas a month isn't a big issue.

yes, drafting cannot be busted IMHO 'cause it works.

BTW, you have a vehicle that could get some impressive mpg if you really want it to. research and experiment...

[Frankenstipe]

Yeah, I used to get about 40 or 41 mpg on the highway going mostly 60-70 mph, lots of on/off pedal action and downhill/uphill stuff so I'm not sure how I got so much. I'm fine with what I get now, it's not very impressive but at least I know all I have to do is swap in the stock rims and go with stock tire size and I'll be good to go.

[8307c4]

I drive a smaller truck, a full-size 3/4 ton with an open trailer.

To me it isn't that I can't see them, my problem is a tailgater first dictates how I have to drive, and I find I have as much a right to be on the road as they do. Once someone tailgates I can no longer stop as quickly without fear of them plowing into me, so now I am forced to adjust my driving.
Big deal or not, this becomes the first mild irritant.

It's not always about whether or not their car can stop faster than my truck can, most can.
But all it takes is an instant of distraction on that driver's part and PLOW!

So if the car in the rear so much as 'taps' my vehicle I have to stop, at the very least to see if any damage was done. There just went 5-10 minutes and it should be no big deal but it could be yet another mild irritant. If the damage is anything but non-existent the police has to get involved and this wastes 2 hours of my time (because that's how long it takes) and it gets worse if it has to go to a body shop.

Now I do know if someone hits me in the rear it's not my fault, but insurance-wise "policy activity increases premium" which translates to "even if I'm not at fault my insurance rates could go up." This doesn't even take into account the noticeable portion of drivers who will fight and dodge you over the claim and the who was at fault issues.

Last but not least my vehicles are older, anything much over 1-2 thousand dollars worth of damage and the InsCo writes it off as a 'totalled car' and now I'm out of a means to work.

In conclusion, tailgating is total bs :p

I have found you can space your self back about 2.5 seconds and still get the benefits of drafting.

2+ seconds I can tolerate relatively easy, that should be far enough.
And I believe you are right because the huge aero wake of a truck does a lot in the way of breaking air resistance, the effect can be felt at a fair distance.

[ihatemybike]

I started drafting trucks with Grumpy this morning. I have an old CB that I'm thinking of installing so I can ask permission to draft, not tailgate.

What do you think 8307c4? Communication with a drafter a good thing?

[Nate R]

I've been wondering the same thing. There's a driver that hauls a double UPS trailer along my route from work to home every night around the same time I get out of work. I know he almost always goes to the nearby McD first. I'm wondering if I shouldn't ask him about it. (He didn't seem to mind last week for 50 miles. Another truck OTOH made it obvious he didn't want me there.)

[Nerds laugh at me]

Yesterday,I was driving just below the speed limit. ( 60 in a 65 zone )
I started wondering if it was even worth it, because of the fact that I had a huge line of tailgating cars in my wake. ( With a semi directly behind me )
How much does tailgaiting hurt the first person in line ?

[RoadWarrior]

How much does tailgaiting hurt the first person in line ?

zip... until you stand on your brakes hard.

There would be a very very slight effect on the Cd for the better if someone was very very close.

[1cheap1]

I did not know how far the wake of a semi would be until my ac broke on my Mazda. I took my 94 Intrepid automatic. It has a scan gauge type real time mpg read out upto 100 mpg. I was very shocked at the distance from the truck that my mpg started to rise. As i slowly approached the mpg continued to rise. I thought i had to be very close to get any results. Now i know different. I could see how different type vehicles affect my mpg.

[COMP]

i love drafting :D :thumbup:

[1993CivicVX]

had a chance today to draft a semi while using a scangauge. driving my wife's car(my car is not SGII compatible)gave me this opportunity. VERY interesting.

70mph avg ~29mpg no drafting. when drafting(i'm a truck driver, so i did so w/ mirror in view) again @ 70mph avg ~35mpg.

now, this is where it gets interesting. drafting, same speed, downhill(slight decline--not very hilly here), yeilded a high of 182mpg. WOW!

When drafting you often get a sucking sensation where you are literally being pulled by the truck which is why a Prius' battery will get charged full up on a down hill when drafting and why you saw a high of 182mpg. I guess this primarily happens on downhills.

[eugeneg20]

i try to draft as much as possible, and i have not met a single trucker that showed a noticable amount of irritation, i dont have a scanguage so i dont really know my benifits

[COMP]

i try to draft as much as possible, and i have not met a single trucker that showed a noticable amount of irritation, i dont have a scanguage so i dont really know my benifits

you can tell by throttle pressure and engine tone for sure :thumbup:

[lowbridescape]

Drafting does not slow the person in front. If you got close enough (inches) your bow wave would push on the person in front. At any sane distance, the effect is below negligible. You would be pushing with sound waves. ie, you can ignore it.

If you stand on the side of the highway, you can get an idea of how trucks affect the air. They are moving LOTS of it...and it's all going in the same direction they were. Now take a car like my Escape (CD = 0.40). I was having trouble keeping at the speed limit today because I had a 10-15 mph wind coming straight down the highway in my face and I'm just not used to pushing the pedal that hard. Reducing the relative wind velocity by 5 mph by following a truck at a safe distance will make a difference. I'm going to be driving to Florida this summer. That'll be 30+ hours to practice the art.

[RoadWarrior]

Drafting does not slow the person in front. If you got close enough (inches) your bow wave would push on the person in front.

I've felt that.... cruising along... suddenly your speed picks up by 3-5mph...and you look in your rearview and read renilthgierF

[theholycow]

I've felt that.... cruising along... suddenly your speed picks up by 3-5mph...and you look in your rearview and read renilthgierF

Could be worse. You're in trouble if you read ɹǝuılʇɥƃıǝɹɟ...

[COMP]

I've felt that.... cruising along... suddenly your speed picks up by 3-5mph...and you look in your rearview and read renilthgierF

:thumbup: you can also work a side draft ,,, it can drop my truck rpm 200

[vectorg]

What are the general rules for side-drafting? There must be a point where it can actually hurt you because you will be in a wave of compressed air. If I'm back far enough, the benefit must be close to that of drafting directly behind.

Geese fly in a V formation, but is it for drafting or more for navigation and staying together as a flock?

[Jay2TheRescue]

What are the general rules for side-drafting? There must be a point where it can actually hurt you because you will be in a wave of compressed air. If I'm back far enough, the benefit must be close to that of drafting directly behind.

Geese fly in a V formation, but is it for drafting or more for navigation and staying together as a flock?
No, they're drafting in a V formation. Same with fighter planes flying in a V formation. They don't just do it because it looks cool.

-Jay

[blownb310]

You are being overtaken by a truck. When does the benefit of side drafting actually start? When you are next to the truck, or just behind it diagonally?

[Jay2TheRescue]

I notice my MPG start to rise by the time the truck has "passed" me, and my front bumper is even with the front of the trailer.

-Jay

[Mr Incredible]

My CRX is too old for a Scangauge, but the low-tech redneck version is very effective. I tied a short piece of wife's yarn to my wiper arm in front of me. It really flips around when in the open air, and starts to lazily flop around when in a slipstream.

It also matches the car's color at no extra cost.

Thanks all, for the insight into distance behind that becomes effective. Around here, though, our north/south seasonal crosswinds negate much of the behind-the-truck effectiveness on our predominantly east-west routes.

[Jay2TheRescue]

Even though I have the SG I'm thinking of adding a couple of pieces of ribbon to the front of the truck. I was thinking that one on the antenna would be pretty useless as I would not be able to easily see it while driving, but the wiper arm is a great idea. I didn't think of that.

-Jay

[blownb310]

In the old cars like my '77 Datsun B210, you have manually operated fresh air vents in the dash. With these open you can feel the difference in wind pressure entering the cabin when drafting. It's as if someone closed the vent almost all the way.

[Z man]

I find it better to stick to approx. 58-62mph and not draft a whole lot, 70mph is too fast for a box-shaped vehicle.
It's nice when there is a semi in front, back and beside me. This happens on I-81 sometimes as it is a big truck route.


Anyone have a friend that lets you draft them very close?
I've always wanted to do this on a long highway trip.

[Jay2TheRescue]

I agree. I find it hard to find a truck going a steady 55 or 60 MPH for me to draft. I thought I found one last week when I was driving on I-66. He must have been fully loaded, and had a non-turbo engine. He'd be going 55 or 60, but every time he came to a hill he slowed down to 35. I was so scared I was going to get rear-ended by someone coming up on my tail at 70+ MPH I just passed him then set the cruise @ 55 MPH. I'd be curious to see how effective drafting is in THe Beast with my new grille block and extended airdam, but haven't really had the chance.

-Jay