Home » Public Forums » GMCnet » Mileage chart???
| Mileage chart??? [message #196792] |
Tue, 29 January 2013 19:36  |
kerry pinkerton
Messages: 2565
Registered: July 2012
Location: Harvest, Al
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On my recent trip, I got 10.8mpg pulling the toad. Checked everything three times because that seems so high but it's right. Actually since my speedo is 3miles low at 50, the actual mileage is 6% higher. The vast majority of the trip I ran about 55 which, I suspect, accounts for the great mileage.
So here is the question.
Has anyone actually done and documented a test at various speeds from 50 to 70mph?
Kerry Pinkerton - North Alabama
Had 5 over the years. Currently have a '06 Fleetwood Discovery 39L
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| Re: Mileage chart??? [message #196793 is a reply to message #196792] |
Tue, 29 January 2013 19:54  |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
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It takes 4 times the energy to overcome the wind drag of doubling the speed. A well tuned GMC doing 55 should get an easy 10. I suspect the toad at steady speed is hiding in the wake and not degrading the numbers that badly. Don't have any other data.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Mileage chart??? [message #196795 is a reply to message #196792] |
Tue, 29 January 2013 20:13 |
rvanwin
Messages: 325
Registered: April 2007
Location: Battlefield, MO
Karma: 6
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| Kerry Pinkerton wrote on Tue, 29 January 2013 19:36 |
On my recent trip, I got 10.8mpg pulling the toad. Checked everything three times because that seems so high but it's right. Actually since my speedo is 3miles low at 50, the actual mileage is 6% higher. The vast majority of the trip I ran about 55 which, I suspect, accounts for the great mileage.
So here is the question.
Has anyone actually done and documented a test at various speeds from 50 to 70mph?
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Kerry,
I actually did make several controlled runs measuring mpg at different speeds. My friend, George Beckman, and I initially were making controlled runs trying to tune our efi systems for fuel and spark control in order to gain the maximum efficiency tune for the system. Utilizing the EBL we were able to analyze various readouts but in the end settled on the mpg that the EBL calculated.
We set up a course that was approximately 2 miles long and would get up to speed, engage cruise control, then enter the "course". We ran both directions to minimize effects of wind and the slight ups and downs in the course. Our speed for the efficiency runs was set at 60 mph.
Later, I was doing some additional tests and for fun, I made the same controlled runs at 40, 50, 60 and 70 mph. My wife was with me recording results and wouldn't let me do a run at 80 mph.
So at 70 mph the result was 8.8 mpg, 60 = 11.2, 50 =13.7, and 40 = 15.6 respectively. So, yes, speed does make a big difference. Keep in mind, these tests were only for a short period at those set speeds on a fairly level stretch, so there is not averaging of accelerating up to speed, pulling hills, etc.
For more details, here is the presentation I made on EFI that covered some of these test runs:
< https://docs.google.com/viewer?a=v&pid=sites&srcid=ZGVmYXVsdGRvbWFpbnxnbWNtaGVmaWNyZWF0ZWRvY3VtZW50c3xneDo2MGJjZjMwYmViNDNkNTQ1 >
Chart 20 shows the results.
I also ran this course with my toad which at the time was a Jeep Wrangler that weighed in at around 3800 pounds. The run I made with the toad was not as precise as the others, but i figured the cost of towing at 60 mph was 2 mpg. I now tow a Sidekick that weighs about 2400 pounds and I figure that is costing between 1 and 1 1/2 mpg. No definitive runs have been made with and without the Sidekick.
Randy & Margie
'77 Eleganza II '403'
Battlefield, MO
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| Re: [GMCnet] Mileage chart??? [message #196796 is a reply to message #196793] |
Tue, 29 January 2013 20:15 |
GMC_LES
Messages: 569
Registered: October 2009
Location: Montreal
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Kerry are you sure you didn't have someone in the toad giving you a push?
10.8 sounds pretty good to me considering the "8-10 depending if you tow or not" rule that is so often tossed around.
I sure hope my coach does that we'll once I have it on the road.
Les Burt
Montreal
On 2013-01-29, at 8:55 PM, John R. Lebetski <gransport@aol.com> wrote:
>
>
> It takes 4 times the energy to overcome the wind drag of doubling the speed. A well tuned GMC doing 55 should get an easy 10. I suspect the toad at steady speed is hiding in the wake and not degrading the numbers that badly. Don't have any other data.
> --
> John Lebetski
> Chicago, IL
> 77 Eleganza II
> Source America First
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Les Burt
Montreal
1975 Eleganza 26ft
A work in Progress
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| Re: [GMCnet] Mileage chart??? [message #196800 is a reply to message #196792] |
Tue, 29 January 2013 20:51 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
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Kerry's trip included a stop here in Americus, from where we convoyed to
Tampa. The first 39 miles were on US-280, an essentially flat highway at a
steady 55 mph. The next 105 miles were on I-75, also quite flat, at
Kerry's preferred 60 mph on cruise control. We stopped at the Flying J
just before entering Florida and I filled up with 12.0 gallons of regular.
While I never bother to check mileage, I'm pretty sure that says 144/12=12
mpg! My usual WAG at mileage is about 6 mpg when I stay with the usual
78-79 mph I-75 traffic. Even with the usual uncertainty of whether the
tank fills were equal, the mileage was dramatically better at the SLOW
speed.
Maybe I'll take Kerry's lesson to heart. :-)
Ken H.
On Tue, Jan 29, 2013 at 8:36 PM, Kerry Pinkerton wrote:
>
>
> On my recent trip, I got 10.8mpg pulling the toad. Checked everything
> three times because that seems so high but it's right. Actually since my
> speedo is 3miles low at 50, the actual mileage is 6% higher. The vast
> majority of the trip I ran about 55 which, I suspect, accounts for the
> great mileage.
> ...
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Ken Henderson
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www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Mileage chart??? [message #196805 is a reply to message #196800] |
Tue, 29 January 2013 22:04 |
A Hamilto
Messages: 4508
Registered: April 2011
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| Ken Henderson wrote on Tue, 29 January 2013 20:51 |
...The next 105 miles were on I-75, also quite flat, at
Kerry's preferred 60 mph on cruise control. We stopped at the Flying J just before entering Florida and I filled up with 12.0 gallons of regular. While I never bother to check mileage, I'm pretty sure that says 144/12=12 mpg! My usual WAG at mileage is about 6 mpg when I stay with the usual 78-79 mph I-75 traffic.
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Although you probably do a little better than 6 MPG, let's see how dramatic the COST differences for cruising at those two speeds. Faster saves time, slower saves gas. Here's the math:
At 78 MPH (6 MPG):
3 hours 50 minutes to go 300 miles and you are out of gas. 20 minute stop for fuel, total elapsed time 4 hours 15 minutes.
Say your total trip is going to be 1000 miles. Repeat 3.3 times, 12 hours, 45 minutes to go 900 miles, and 1 hour 17 minutes for the last 100 miles. Total time 14 hours and 2 minutes. Fuel cost at $3.5 per gallon and 6 MPG is $583.33
Slowing down to 60 (12 MPG):
10 hours to go 600 miles (ok, you have to stop for other stuff, but bear with me). 20 minutes to refuel. Total elapsed time, 10 hours and 20 minutes. 6 hours and 40 minutes to go another 400 miles. Total driving time 17 hours. Fuel cost at $3.5 per gallon and 12 MPG is $291.67.
It takes three more hours of driving time to cover the same distance at 60 vs 78.
$291.67 in fuel savings translates to $97.22 per hour that you are paying to save yourself EACH of those three hours of driving time.
I would drive the extra three hours. It's like getting paid $97.22 per hour. And who wouldn't like to get paid $97.22 per hour?
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| Re: [GMCnet] Mileage chart??? [message #196813 is a reply to message #196805] |
Tue, 29 January 2013 22:34 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
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Now what -- we need Jimmy C. & the 55 mph national speed limit back? :-(
Ken H.
Americus, GA (9 miles from Plains)
On Tue, Jan 29, 2013 at 11:04 PM, A. wrote:
> ...
> $291.67 in fuel savings translates to $97.22 per hour that you are paying
> to save yourself EACH of those three hours of driving time.
>
> I would drive the extra three hours. It's like getting paid $97.22 per
> hour. And who wouldn't like to get paid $97.22 per hour?
>
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Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Mileage chart??? [message #196828 is a reply to message #196796] |
Wed, 30 January 2013 07:04 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
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I managed 12 sans toad out of Asheville to Chestnut Mountain, GA. On good gas, freeway all the way, cruise set for 55 true (about 53 indicated) and there was little traffic on a cool Spring Sunday afternoon. Wownhill all the way. Slow and boring trip. But, given my overall average since I've had it of just a bit over 9 with more toad on than off miles, I'll agree with the inverse relationship of speed vs mileage. I'm normally set at 63 - 65 indicated on cruise which is 65 - 68 true. Haven't gone far enough on the new 16" whels to make a comparison with the 16.5s.
johnny
'76 23' transmode norris
'76 palm beach
From: Les Burt <gmc.les@gmail.com>
To: "gmclist@temp.gmcnet.org" <gmclist@temp.gmcnet.org>
Sent: Tuesday, January 29, 2013 9:15 PM
Subject: Re: [GMCnet] Mileage chart???
Kerry are you sure you didn't have someone in the toad giving you a push?
10.8 sounds pretty good to me considering the "8-10 depending if you tow or not" rule that is so often tossed around.
I sure hope my coach does that we'll once I have it on the road.
Les Burt
Montreal
On 2013-01-29, at 8:55 PM, John R. Lebetski <gransport@aol.com> wrote:
>
>
> It takes 4 times the energy to overcome the wind drag of doubling the speed. A well tuned GMC doing 55 should get an easy 10. I suspect the toad at steady speed is hiding in the wake and not degrading the numbers that badly. Don't have any other data.
> --
> John Lebetski
> Chicago, IL
> 77 Eleganza II
> Source America First
> _______________________________________________
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Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] Mileage chart??? [message #196831 is a reply to message #196813] |
Wed, 30 January 2013 07:19 |
kerry pinkerton
Messages: 2565
Registered: July 2012
Location: Harvest, Al
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| Ken Henderson wrote on Tue, 29 January 2013 22:34 |
Now what -- we need Jimmy C. & the 55 mph national speed limit back?  ...
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Lord I hope not! I just wondered if anyone had gathered any real DATA.
Everyone has opinions but DATA can be converted to INFORMATION.
My son and I once took our 20'box trailer full of English Wheels out to the Las Vegas Bike Expo. Pulled it with a Ford Dually Diesel. Aerodynamics similar to a concrete block.
On the way out we ran 55...it took fricking forever to get there! Dull boring trip. On the way back we were tired and wanted to get home...drove the speed limit. Still took fricking forever and was a dull boring trip to get home. I don't remember the figures but we got much better mileage at 55 but the savings weren't enough to make me do it on the way home. Gas was a lot cheaper though.
The follow-on question is the difference between interstate travel and running down US highways with the stop and go.
I don't have any politician like ulterior motive or agenda, I'm just wondering. There are a whole bunch of really smart analytical folks on here and I'm 100% sure that someone has some data.
Kerry Pinkerton - North Alabama
Had 5 over the years. Currently have a '06 Fleetwood Discovery 39L
[Updated on: Wed, 30 January 2013 07:28] Report message to a moderator |
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| Re: [GMCnet] Mileage chart??? [message #196848 is a reply to message #196847] |
Wed, 30 January 2013 11:38 |
kelvin
Messages: 608
Registered: February 2004
Location: Eugene, OR
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On 1/30/2013 9:23 AM, A. wrote:
>> Now what -- we need Jimmy C. & the 55 mph national speed limit back? :(
>> Ken H.
>> Americus, GA (9 miles from Plains)
> Absolutely not. I just wanted folks to be aware of the numbers, instead of just having a vague notion in the back of their minds that their gas mileage is "not as good" the faster they go.
> I need to pay attention to the numbers, and there may be others out there in the same boat.
> A little more time spent driving in a day (instead of going as fast as you can) adds up to serious coins. Coins you might want to apply to more gas to go more miles.
> If you want to get more miles behind you sooner rather than later, and you have dollars to spend to save yourself that extra driving time, its your money. Just know that the figures are NOT trivial.
> As usual, YMMV.
The GMC is the only vehicle I can drive at or below the speed limit and
actually relax doing it. I'm just never in a hurry when I'm behind that
wheel. Usually travel at 62-63mph in a 65 zone. (here in Oregon it's
60mph for trucks) and if I'm not slowing someone down I'll do 53-54mph
in a 55 zone.
Put me in any other vehicle, from our Dodge minivan to my Datsun 510,
and I'm generally NOT relaxed. Always someone going too slow and
getting in my way. 75mph in a 65 zone is about right and if you're in
the left lane holding me up I get annoyed. Childish, I'm sure, but it
is what it is.
With the size and marginal brakes of a GMC I can't say I'd be
comfortable doing 75mph for long. I've done it and the rig seems quite
capable, but it sure isn't fun. And I do think about the extra fuel
being consumed at that speed.
To each his own. I'm happy to use my coach as a cruiser instead of
speedy transportation.
Kelvin
'73 23' in Eugene, OR
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| Re: [GMCnet] Mileage chart??? [message #196849 is a reply to message #196848] |
Wed, 30 January 2013 12:14 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Kelvin, I call that the"Maude and Harold" behavior. As in "Dang Maude,
look at that purdy red barn. " I sometimes do the same thing. Drive more
slowly I mean. When I drive my hot rods or the turbo pt, it is a whole
different deal. Same with motorcycles.
Jim Hupy
Salem, Or
78 Gmc Royale 403
On Jan 30, 2013 9:38 AM, "Kelvin Dietz" <kelvin@datsuns.com> wrote:
> On 1/30/2013 9:23 AM, A. wrote:
> >> Now what -- we need Jimmy C. & the 55 mph national speed limit back? :(
> >> Ken H.
> >> Americus, GA (9 miles from Plains)
> > Absolutely not. I just wanted folks to be aware of the numbers, instead
> of just having a vague notion in the back of their minds that their gas
> mileage is "not as good" the faster they go.
> > I need to pay attention to the numbers, and there may be others out
> there in the same boat.
> > A little more time spent driving in a day (instead of going as fast as
> you can) adds up to serious coins. Coins you might want to apply to more
> gas to go more miles.
> > If you want to get more miles behind you sooner rather than later, and
> you have dollars to spend to save yourself that extra driving time, its
> your money. Just know that the figures are NOT trivial.
> > As usual, YMMV.
>
> The GMC is the only vehicle I can drive at or below the speed limit and
> actually relax doing it. I'm just never in a hurry when I'm behind that
> wheel. Usually travel at 62-63mph in a 65 zone. (here in Oregon it's
> 60mph for trucks) and if I'm not slowing someone down I'll do 53-54mph
> in a 55 zone.
>
> Put me in any other vehicle, from our Dodge minivan to my Datsun 510,
> and I'm generally NOT relaxed. Always someone going too slow and
> getting in my way. 75mph in a 65 zone is about right and if you're in
> the left lane holding me up I get annoyed. Childish, I'm sure, but it
> is what it is.
>
> With the size and marginal brakes of a GMC I can't say I'd be
> comfortable doing 75mph for long. I've done it and the rig seems quite
> capable, but it sure isn't fun. And I do think about the extra fuel
> being consumed at that speed.
>
> To each his own. I'm happy to use my coach as a cruiser instead of
> speedy transportation.
>
> Kelvin
> '73 23' in Eugene, OR
>
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| Re: [GMCnet] Mileage chart??? [message #196851 is a reply to message #196849] |
Wed, 30 January 2013 12:33 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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I'm generally in something of a quandry: What I really like to do is have
the GPS plot the "shortest route" and follow those back roads, many with
"no paint on them", at less than the speed limit. Frequent stops at
interesting places and no particular schedule. SHE, on the other hand,
likes to know where we're going and when we'll get there, preferably by the
shortest, fastest route. Guess who usually wins? 'T'ain't gonna be that
way when we, hopefully, leave Bean Station in early May headed west (via
the "shortest" route).
Ken H.
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Ken Henderson
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www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Mileage chart??? [message #196860 is a reply to message #196848] |
Wed, 30 January 2013 13:42 |
jayrabe
Messages: 509
Registered: June 2009
Location: Portland, OR
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But, AFTER spending some time driving the GMC, I find I drive a lot more sanely and more slowly and safer in my regular car... :-)
> Date: Wed, 30 Jan 2013 09:38:13 -0800
> From: kelvin@datsuns.com
> To: gmclist@temp.gmcnet.org
> Subject: Re: [GMCnet] Mileage chart???
>
> The GMC is the only vehicle I can drive at or below the speed limit and
> actually relax doing it. I'm just never in a hurry when I'm behind that
> wheel. Usually travel at 62-63mph in a 65 zone. (here in Oregon it's
> 60mph for trucks) and if I'm not slowing someone down I'll do 53-54mph
> in a 55 zone.
>
> Put me in any other vehicle, from our Dodge minivan to my Datsun 510,
> and I'm generally NOT relaxed. Always someone going too slow and
> getting in my way. 75mph in a 65 zone is about right and if you're in
> the left lane holding me up I get annoyed. Childish, I'm sure, but it
> is what it is.
>
> With the size and marginal brakes of a GMC I can't say I'd be
> comfortable doing 75mph for long. I've done it and the rig seems quite
> capable, but it sure isn't fun. And I do think about the extra fuel
> being consumed at that speed.
>
> To each his own. I'm happy to use my coach as a cruiser instead of
> speedy transportation.
>
> Kelvin
> '73 23' in Eugene, OR
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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| Re: Mileage chart??? [message #196879 is a reply to message #196792] |
Wed, 30 January 2013 19:01 |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
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I have 2 vehicles I am never in I hurry in, the GMC and My Sebring Convertible. Both put me in a why hurry mood. The GMC rarely sees anything about 60
The vette is usually driven slowly, but the blasts down the entrance ramps alone negate and semblance of not being in a hurry!
Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
ask me about MicroLevel
Cell, 763-732-3419
My427v8@hotmail.com
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| Re: Mileage chart??? [message #196885 is a reply to message #196879] |
Wed, 30 January 2013 20:12 |
midlf
Messages: 2212
Registered: July 2007
Location: SE Wisc. (Palmyra)
Karma: 1
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Senior Member |
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| Keith V wrote on Wed, 30 January 2013 19:01 |
I have 2 vehicles I am never in I hurry in, the GMC and My Sebring Convertible. Both put me in a why hurry mood. The GMC rarely sees anything about 60
The Vette is usually driven slowly, but the blasts down the entrance ramps alone negate any semblance of not being in a hurry!
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I used to drive "hurry". Lately I've been running under the motto of "Life is too short to be in a hurry".
Steve Southworth
1974 Glacier TZE064V100150 (for workin on)
1975 Transmode TZE365V100394 (parts & spares)
Palmyra WI
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just hanging on for dear life at 60! Got to get that rut running under control for a more comfortable ride. On the way up from Panama City, the rear was sit a bit under spec and the ride was pretty good. Except for the stretch of I65 northbound above Birmingham. Potholes were brutal and in the dark you were on them before you could dodge them. 
