MPH vs MPG

[Mike_in_DE]

I bought a 2022 Chevy 3500 6.6L Duramax Turbo Diesel and wanted to check the fuel economy for both towing and not towing. The numbers you'll see DO NOT include regen periods where the engine is burning excess diesel to convert soot in the DPF to ash. Also, the figures are from the truck's DIC (Digital Information Center) screen where the truck calculates the MPG via the trip gauge. Some people say those numbers aren't realistic and tend to be higher than actual. However, I checked those figures with eight stops at the pump (1400 miles in total), manually calculated the MPG and found there was good agreement between the two (within 1% on average). These were NOT fill-ups, rather, they were partials and averaged 14.5 gallons per refill.

You'll see in the table the term "equation". This is the MPG using the trendline fit on the plots I generated. It's an arbitrary curve fit but does match the data pretty well. I'm simply comparing the curve fit with the averages for the speed increments I ran.

I am pulling a 2018 Highland Ridge 5th wheel that is 32 feet long and weighs about 9000lbs loaded.

Hope this is useful to some folks!

https://ibb.co/BCWxTkp

[BackOfThePack]

Lantley wrote:
Going slower to the point of impeding traffic because your vehicle can't safely go faster is one thing but going slow and impeding traffic to save fuel is selfish and unacceptable.

Operating in a legal manner is the requirement. Greatest spacing all day is the moving target for attentiveness.

Not the stupidity of the selfish can’t space themselves to get around slower vehicles in a safe, legal manner (bunched in a pack is PROOF of stupidity). Back off and wait.

62-MPH works very well. It’s the rare vehicle can’t get around one judiciously. A matter of canceling cruise control and dropping to 55 to get the ones slowest around GONE. Use headlights ALWAYS, and consider high-mount taillights as pair to the originals you want them to see you earlier.

Stay minimum of 5-below once into a 65 or metro. Get down early. This eases others around you. They’re always racing to catch the next monkey troup.

The road chosen (design) is the indicator of average speed. Not speed limit. Traveling faster confers no right-of-way. It’s the unskilled who open a story telling us how fast they’re running. . Cars are fastest, and big trucks are below that. RV’ers staying below both have the easiest day in managing others around and avoiding their screw-ups.

Bad mirrors are an RV problem. I’d not have less than EAGLE VISION for TT, and BIG convex for pickup with “towing mirrors” (additional). Low skill RV’er can be told pretty easily by their being surprised from the rear.

Your future is coming up behind you.

The Interstate is a range of from 45-80/mph depending on state and region.

“Too fast for conditions” is primarily traffic volume. Repeated passes means one’s traveling too fast.

The only hours to cover the Interstate at a high average legal speed is from 0400-0800. After that it becomes crowded. By 1100 it’s over for anything but moving along maintaining greatest vehicle separation distance anywhere near the major metros and anything east of IH-35.

Braking & Handling are what matter with RVs. Lowest skilled experience and least stable rigs. This is what to keep foremost. T

.

[valhalla360]

4x4ord wrote:
^^^So ... being too cheep to speed up on account of spending more on fuel is selfish and unacceptable but going slow cuz you're too cheep to trade the old Ram in on a new Ford is acceptable?:)

I'd say both are wrong. If you can't get in line with the semis and keep up with them on a grade, you are under powered and should either upgrade the truck or get a smaller trailer.

[BarneyS]

This thread is about MPH vs MPG not tires. Please keep any future comments on topic to avoid thread closure. Thank you.
Barney

[Cummins12V98]

Todays first tank was about 8.5 but venturing into TX with some mountains and heading to Midland, TX with a head wind running at 75mph the mileage was around 7mpg. But getting to see our Son we have not seen for too long the extra $$$ is a drop in the bucket.

[4x4ord]

I think if I was travelling with you I'd be too cheap to keep up, and I'd still be stopping more often than you for fuel on account of the pop can sized fuel tank on the short box.

[Cummins12V98]

4x4ord wrote:
^^^So ... being too cheep to speed up on account of spending more on fuel is selfish and unacceptable but going slow cuz you're too cheep to trade the old Ram in on a new Ford is acceptable?:)

You tell me, I just did three tanks of fuel crossing AZ and into NM with no winds. One 8.5, one 7.8 and another 8.5 mpg at 75mph on I-10. OH and that is with a 13'5" tall by 8'6" wide 5er that weighs 24k with a combined weight of 34,000#. UH, no trade for me!!!

I STILL love my truck!!!

[StirCrazy]

blt2ski wrote:

ford truck guy wrote:

4x4ord wrote:
^^^So ... being too cheep to speed up on account of spending more on fuel is selfish and unacceptable but going slow cuz you're too cheep to trade the old Ram in on a new Ford is acceptable?:)

hey 4x4, need a shovel for that dig? :B

comparing stick boats to stink pots!?!?!????

i have no issues with folks in thr right lane doing the limit. dont do it in the left lane. I usually drive in the middle lane a few over if empty, sometimes left if in a hurry upwatds of 10 over.
towing, right lane generally speaking, to middle. Illegal to tow in left lanes unless passing, ir right lanes blocked dye to a wreck or equal. Then i can even use the left carpool lanes to get around said blockage.
As noted, faster you go, the more fuel you use once past an X factor of seed. my sailboat, use very little difference in fuel from 0-5.5 knots, double fuel per hour from idle to 5.5. double again from 5.5-6 knots or so, double that to hull speed of 6.6. see the same with vehicles from 0-60, drop 10-20% @ 70, more yet at 80..... not discussing at the 90 grit drives

marty

if it was only that easy, a sail boat doesnt get fast enough with the motor going to have a air resistance effect, most of it is the water resistance and the hull is optomized for that, and as they go faster more comes out of the water lowering the drag. in a truck the faster you go the more wind resistnce...

my issue isn't just the fuel, I could care less about how much it costs, I used to do 10kph over everywhere I went. my issue is more the range I can get on the tank. I know I could install a larger tank and I am going to look at that, but thats only the first issue. tires are another issue, most ST tires are rated at 65mph, yes there are some rated at higher speeds but do you know whats n your 5th or trailer? in 30 years I have had 2 blowouts the firs on 9 year old tires, the second last year though a construction zone so probably a road hazard failure. I read in amazment how many blow outs I see on the board here and wonder how much of it is due to speed? also wear and tear on the vehicle and trailer its self is increased with speed, is it enough to worry about .... I don't know. and yes I am in the right lane when I travel, unless I am passing some one going realy slow.. generaly I am at the speed limit like I said before.

[blt2ski]

ford truck guy wrote:

4x4ord wrote:
^^^So ... being too cheep to speed up on account of spending more on fuel is selfish and unacceptable but going slow cuz you're too cheep to trade the old Ram in on a new Ford is acceptable?:)

hey 4x4, need a shovel for that dig? :B

comparing stick boats to stink pots!?!?!????

i have no issues with folks in thr right lane doing the limit. dont do it in the left lane. I usually drive in the middle lane a few over if empty, sometimes left if in a hurry upwatds of 10 over.
towing, right lane generally speaking, to middle. Illegal to tow in left lanes unless passing, ir right lanes blocked dye to a wreck or equal. Then i can even use the left carpool lanes to get around said blockage.
As noted, faster you go, the more fuel you use once past an X factor of seed. my sailboat, use very little difference in fuel from 0-5.5 knots, double fuel per hour from idle to 5.5. double again from 5.5-6 knots or so, double that to hull speed of 6.6. see the same with vehicles from 0-60, drop 10-20% @ 70, more yet at 80..... not discussing at the 90 grit drives

marty

[ford_truck_guy]

4x4ord wrote:
^^^So ... being too cheep to speed up on account of spending more on fuel is selfish and unacceptable but going slow cuz you're too cheep to trade the old Ram in on a new Ford is acceptable?:)

hey 4x4, need a shovel for that dig? :B

[4x4ord]

^^^So ... being too cheep to speed up on account of spending more on fuel is selfish and unacceptable but going slow cuz you're too cheep to trade the old Ram in on a new Ford is acceptable?:)

[Cummins12V98]

Lantley wrote:
Going slower to the point of impeding traffic because your vehicle can't safely go faster is one thing but going slow and impeding traffic to save fuel is selfish and unacceptable.

100% agree!!!!

[StirCrazy]

FRFrank wrote:

StirCrazy wrote:

Grit dog wrote:

It does lend some credibility to those who claim 25mpg out of their big diesels. But what they forget to mention is they’re drivin miss daisy and p!ssing off the line of cars behind them who may actually have some where to be before their next birthday.

you know, the older I get the less I car about thoes cars.. they can pass when its safe or use the left lane to go around.. especialy with fuel prices these days haha

So you're the guy doing 50mph in the center lane on the 3 lane expressway, while 400 cars are jammed up behind you in all 3 lanes trying to jockey around you on both the left and the right?

nope, and if you read faster than that you would see I am the guy doing the speed limit which in BC is 90 or 100kph on most highways, where it is over that its a multi lane and I will be in the right lane. mind you if you even read the part you quoted you would have seen that.....

[StirCrazy]

ktmrfs wrote:

StirCrazy wrote:

valhalla360 wrote:


Now back to the subject:
- Wind often makes a huge difference. If we aren't on a schedule (and we usually aren't), I'll check the wind forecast. The difference between a 10mph tailwind and a 20mph headwind can easily be 30-50% worse MPG.
- I do a running total on our scheduling spreadsheet. The dash calculator is pretty consistent with my calculations. Where it's really useful is the instantaneous output rather than the long term average. If you see, the MPG is getting hammered by current conditions, you can take action (slow down, call it a day, etc...).
- The long term average is more of a planning number and I usually assume 10-15% less.

most of our speed limits here are 90Kph or 100 if your lucky so generaly I do the speed limit. in alberta where it is 110 it is a 2 lane road so I just stay in the right and do what I feel like doing, usaly 100 some times 90 if I am worried about fuel range.

yup so many factors, frontal area, shape of that area, how much space is between the back of the truck cab and the front of the trailer, speed, wind, and so on.. even the road surface can affect the roling resistance.

with my old short box diesel I used to get 14mpg towing my old 30 foot trailer which weighed 8000lbs loaded for camping, I went to a 12000lb 40 foot 5th wheel and my actual milage went up to 16mpg. the difference mainly was how close that front of the fifth tucked up close to the back window of the truck preventing a deag zone from forming between the truck and trailer. then I bought a new truck with a long box and that space increased by almost two feet and my milage dropped a bit, but its hard to coralate as its a different truck.

but your gallons are bigger than our gallons....

haha, just ignore the actual numbers and look at it like there was a increase or decrease. ya I get triped up by the inperial/US gal game also. I see you guys posting and think man whats wrong with there truck getting that bad milage then I remember it US gal and your towing at 80mph... wait till you try figure out L/100Km I don't even like that one..

[Lantley]

Going slower to the point of impeding traffic because your vehicle can't safely go faster is one thing but going slow and impeding traffic to save fuel is selfish and unacceptable.