MPG, Fuel Economy, - the definitive resource

[Davydd]

Actually if you stay off the freeways you can plan a route shorter in distance but not necessarily shorter in time. Distance not time determines fuel savings.

[Photog]

So, in the rest of the forum, there have been threads discussing all sorts of things, and someone inevitably jumps in and asks about fuel economy issues, usually in some electronics upgrade or storage thread. Then folks start talking about fuel economy.

Now we have a whole section devoted to all considerations of fuel economy, and it all comes down to two things?
1) Drive slower
2) Shortest route

What about tire pressure, tire size, RPM range, fuel grade, extra weight, trailers, temperatures, humidity, air-dam under bumper, specific class B, specific motor, RV brand, Chevy-vs-ford,...? Maybe all those things are insignificant, compared to speed and distance.

If so, we now have three threads we can send folks to, when they start mucking up a good "Refrigerator Install" thread, asking fuel economy questions.

Any thoughts??

[Mike]

Somewhere on here I had a discussion about tire size, going larger diameter, to reduce rotations
per mile, and to try increase mileage, but I'm darned if I can remember where it is.
Feel free to resurrect it if you can locate it.
I sent some emails and did a bit of research, probably prior to last Spring when I got the new
set of standard sized tires. I believe the costs of switching to a slightly larger tire size wasn't
recoverable over a reasonable amount of distance and time. Nor was it recommended or safe.

[Photog]

Originally Posted by Mike

Somewhere on here I had a discussion about tire size, going larger diameter, to reduce rotations
per mile, and to try increase mileage, but I'm darned if I can remember where it is.
Feel free to resurrect it if you can locate it.

I think I found it. I did a search for "tire size MPG".
viewtopic.php?f=9&t=1258

Originally Posted by Mike

I sent some emails and did a bit of research, probably prior to last Spring when I got the new
set of standard sized tires. I believe the costs of switching to a slightly larger tire size wasn't
recoverable over a reasonable amount of distance and time. Nor was it recommended or safe.

Were the larger tires that much more expensive than the stock size?

Did you notice any MPG improvement, when you switched to Michelin tires?

[Mike]

Originally Posted by Photog

I think I found it. I did a search for "tire size MPG".
viewtopic.php?f=9&t=1258

Were the larger tires that much more expensive than the stock size?

Did you notice any MPG improvement, when you switched to Michelin tires?

I sent letters to local GM Dealers, as well as GM Canada, describing what I wanted to do.
The main issue was having to not just buy the larger tires, but also the appropriate larger rims, and I believe
there were some other concerns regarding turning clearance inside the wheel wells. When I looked at the info
I'd gotten back, the mpg increase would be marginal, I don't recall exactly how much, but it was less than a 3% improvement.
I decided to go with Michelin AT/2 (more aggressive tread pattern than MS2 series) with OEM specs. I like them, they
ride nice, I try to keep them at 80 psi rear and around 65 psi front, for improved stability and mpg reasons. I think they
help, although again, no idea by how much.

[booster]

Trying to guess if you will get better, same, or worse mileage from a tire size change is pretty much a lesson in futility, unless you have seen very similar combos before.

The energy needed to move the van down the road doesn't change, only the wheel and drivetrain rpm. How the mileage comes out depends on where in the efficiency curve of the engine and drive train you are. If it were just a matter of big gears/low rpm, you would see much different gear ratios in things. If your rpm drops enough that your torque multiplication isn't enough, you need more throttle, which may put you at a different place on the fuel map, change spark advance, change cam valve timing, cause it to come out of lockup, downshift etc. If any of these things happens, even a small % of the time, you can lose mileage. When they make the monster top gear 6 speeds, they count on the transmission to only use those gears when at very low engine outputs, downhill, or whatever. The other gears take up the rest of the situations, and are closer to what you see on the 4 speeds. I haven't talked to anybody that has the new Chevy 6 speed and compared to the 4 speed, but I would guess on a 9600# Roadtrek, it is out of 6th gear a lot of the time. I would it expect it to get a bit better mileage than the 4 speed, but not huge differences.

Bigger tires, in general, also have higher rolling resistance, so that can cost you.

I can't tell you how many friends have done the "how much further they move per wheel revolution" calculation, and then expected that much improvement in mileage. Let's say they were all pretty disappointed.

[Photog]

Mike,
I noticed the 235/85R16 was mentioned. It is 1" larger diameter (3.3%), or 1/2" taller sidewall. 31.5" tire that fits the same wheel size as stock.

I would not think this would rub in the fender well. It would be more narrow, which might be a good for MPG.

With ours being lifted, I am looking at a 33" tire. We may need to have the axle re-geared to 4.56:1 (currently 4.11:1). If we can fit the 33" tires, I will do a number of MPG and mountain driving test, before considering the re-gear. If it all works out well, we may not install 4X4.

Booster,
I agree with you. From my research, good mileage comes from driving at an RPM somewhat below maximum torque. I'm not sure how far below max-torque. So, the final gear ratio (tranny/axle/tire) needs to be correct to have the engine in the optimum RPM range, at the desired highway speed.

The 1 ton vans may not be setup at factory, to run in the optimum RPM range, since there are other performance factors to be considered. Lower gear rations make it easier for the engine to haul around a heavier load, as it pushes the RPM range up closer to max-torque, at cruising speed.

[shezonit]

About 20 yrs ago, bought a '77 hightop van,Dodge 360 camper. It got 14-16 mpg. Sold it for Asia travels.
About 10 yrs ago, bought a '77 hightop Chevy 350 camper. It got 10-11mpg. Tried everything-- bigger alloy wheels/Michelin tires, various carb/ air filter mods, even an overdrive transmission...... It still gets 10-11.
About 2 years ago, got a '96 Ford 351 EFI. It carries a lot more weighty equipment, and gets 14-16mpg. I attribute this to the EFI, what seems a great transmission, and a lower profile roof design.
The PO of the Ford told me he got 18mpg.... he was from Canada-- lower speed limits-- it makes sense. If I made myself drive this van 55mpg for a whole tank, I'd probably get 18,too.
So, the lesson here is you can spend a heap of $$, and not see any improvement. The ONLY thing that improves the mpg in any of these vans is..... drum roll........ go slower.
Meanwhile, keep tire inflation correct, don't drive with full water tank(s). My dad told me drive like there is a raw egg between your foot and the gas pedal...... easy does it.

[Mike]

Originally Posted by shezonit

The PO of the Ford told me he got 18mpg.... he was from Canada-- lower speed limits-- it makes sense. If I made myself drive this van 55mpg for a whole tank, I'd probably get 18,too.

Possibly bigger gallon, too?
1 Us gal = 3.8 L versus
1 Imperial (Canadian) gallon is around 4.5 L. = More gas per gallon.
I can get around 20 mpCg on a flat road, on cruise, at around 100 kph (62.5 mph), with no wind or hills.

[Photog]

Originally Posted by Mike

Possibly bigger gallon, too?
1 Us gal = 3.8 L versus
1 Imperial (Canadian) gallon is around 4.5 L. = More gas per gallon.
I can get around 20 mpCg on a flat road, on cruise, at around 100 kph (62.5 mph), with no wind or hills.

Now that just makes things confusing.
Don't the Canadians measure fuel economy buy the number of liters per 100km? (I know, more confusion. ).

[shezonit]

Originally Posted by Mike

Possibly bigger gallon, too?
1 Us gal = 3.8 L versus
1 Imperial (Canadian) gallon is around 4.5 L. = More gas per gallon.
I can get around 20 mpCg on a flat road, on cruise, at around 100 kph (62.5 mph), with no wind or hills.

Could be-- although the PO had the van in Arizona for awhile. But it would be a way of "inflating " the mpg without telling a fib. So, you're saying a US gallon is 84% of a Canadian gallon? And if Canadians ( love ya) use liters, then why are there even "gallons"? Why not "4 Liter" increments instead of ---- 4.5?
When I drove it home, totally empty except gas and 1/2 tank of fresh water, from AZ to MT, I drove Hwy 93, through flats and mountains in Idaho and Montana - I was sorta afraid of it , so kept it at about 65ish, and I got 16+. So, I don't know about ever getting much better, with it now loaded for travel, and I tend to run it closer to 70 now. Although with gas at $4., I may be slowing down.......

[Mike]

Originally Posted by shezonit

So, you're saying a US gallon is 84% of a Canadian gallon? And if Canadians ( love ya) use liters, then why are there even "gallons"? Why not "4 Liter" increments instead of ---- 4.5?

Yes, about 84%.
Because like you, we are descended from Brits, and have to deal with a thing called an Imperial gallon,
which is 4.5 litres, and still exists. If we were all measuring fluid volume in litres, there'd be no issues
about converting. We'd all use miles per litre. ( btw, 16mpUSg = 4.2 mpl = $0.21/mile, at a gas price of $3.50/USgal )
So, now it's my turn. Why is an American gallon smaller than a Brit gallon (3.8 versus 4.5 litres)?
Most Canadians are at the least paper trained, we rarely fib, and we make excellent pets.

[skcyclist]

Originally Posted by markopolo

I'll mention for what it is worth that MPG seems to have more than just an economic effect.

My Class C gets 8 mpg and that does not encourage me to drive it. We went larger for comfort but are less likely to use it. We are more "frequent trips of less duration" people than I thought when we bought the "drive and stay month Class C".

Anyone want to to buy my C?

Hi, Steve here, the newbie with 1994 Ford Coachmen w 351 Ford engine. Checking in after my first road trip from Carpinteria to Lone Pine to highway 120, through Yosemite, to Watsonville and return. Around town, idling and running generator; mileage as low as 10 MPG. On the highway, 15+. Even got 15+ on the stretch over the Tioga Pass. Extremely pleased with the MPG, mostly driving 60-65 MPH. Learned the cruise control makes RV go up or down 1 MPH per tap on control. Discovered that I took too much stuff. RV is like a woman's purse (pardon the sexist remark): put too much in and you can't find anything. The fold out bed in the middle of van, not too handy, but I can easily adapt and live with it. Also learned to move at half speed or less inside the van to avoid banging head and other body parts into things. Think before you move is a good plan. The RV battery is not being charged by the motor. I have to fix that. The generator "lopes" after it warms up. Also have to fix that. Everything else works fine, though I haven't tested the space heater or the toilet. The shower/bath is for midgets, but it can be done and is way better than nothing. Overall, I am very pleased with the unit. The Ford drives nice and is economical. For 10.5K, a very good deal. You can't have compactness, driveability and economy without some trade off. Dog and I had a great time Hoping to go to Bend, Oregon for cycling nationals end of August.

[g1g]

Many years ago I added water induction on my car. I'll say it did add at least 2 mpg. I haven't tried it since computer control though. As for how I did it I attached a T in the vaccum line that pulls vaccume from all cylinders. The one I used was at the base of the carberator. Attached to the T I added a hose that I installed an aquarium valve. On another leg I put the hose into a gallon jug of water. I would adjust the aquarium valve to draw how much water I wanted it to pull and also to suck additional air in another valve. With both those valves I achieved the 2mpg consistant to at times I did get more than 5 mpg compared to mt benchmark of prior to adding it. There may be other factors but I believe I can without any doubt say I improed it 2 mpg

[Catlover]

New to this site-we're in the thinking stage of getting a used B. Which class B gets the best mileage highway and in town? I am leaning toward the Sprinter b/c the diesels get better mileage ( so I've read). I like the style of the Sprinters but have not seen the inside of one in person, or any B for that matter. This week-end we're going to St Louis to an RV van dealer that seems to have lots of new and used models. So we have lots of questions but the first is about MPG.
Thanks!

[Photog]

I think the diesel gets better fuel economy. Maybe even enough to overcome the higher price of diesel fuel.

The Sprinter-based Class-B can be built with single or dual rear wheels. They are typically taller and wider inside, with more storage space.

There are a few folks on this forum that have these, and have good photos of their interiors. Do a search for "Sprinter", to find them.

[booster]

Originally Posted by Photog

I think the diesel gets better fuel economy. Maybe even enough to overcome the higher price of diesel fuel.

The Sprinter-based Class-B can be built with single or duel rear wheels. They are typically taller and wider inside, with more storage space.

There are a few folks on this forum that have these, and have good photos of their interiors. Do a search for "Sprinter", to find them.

I agree, except that many (most?) of the Sprinters don't have a lot of storage space for their size, at least when compared to Roadtrek Chevy based units. They have very open floor plans, and large bathrooms, which leave less space for stuff. The 190 Roadtreks, with temp bathrooms use the space the best in our opinion, but they are not wide open like many of the other brands. A big advantage for the dually versions is the elimination of carrying a spare, if you so choose.

[Mike]

Originally Posted by Photog

I think the diesel gets better fuel economy. Maybe even enough to overcome the higher price of diesel fuel.

The Sprinter-based Class-B can be built with single or duel rear wheels. They are typically taller and wider inside, with more storage space.

There are a few folks on this forum that have these, and have good photos of their interiors. Do a search for "Sprinter", to find them.

By "wider inside" do you mean more open floor plan?
I though they were taller but narrower overall.
The ones I saw at the London RV show had all the Roadtrek models including the new one on the
Nissan truck chassis. The dealer was from the London area, but I can't recall the name. Said there were only about 10 of them in the province. I didn't ask about mileage, sorry.

[Photog]

Some of the storage is more useful than the other. Our C190V would make better use of the storage space, if the power couch/bed were simplified, and non-motorized. Booster did a great modification to his bed, and opened up the area under the bed. The outside storage compartment would be easier to use, if the door-opening were larger.

From Roadtrek: Storage capacity

Chevy 190: 62 cu. ft., 80 w/options

Chevy 210: 74 cu. ft., 81 w/options

Sprinter RS: 55 cu. ft., 81 w/options

I assume the "options" are the cabinets that replace the extra seats.

[Mike]

I have the older outside storage configuration with swing up hinged doors. Those newer ones may not
be more convenient, but the slide out style drawer looks better than mine. Not sure what else could be done, the vans aren't meant to be full of beds, galleys, and bathrooms, they were supposed to be full of cargo.
Except switch to a travel trailer. Just imagine the wide open (storage) spaces.......