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Discussion Starter #1 (Edited)
I'm facing two contrary objectives for a planned vehicle:
- Lifting a vehicle for better off road performance
- Keeping it as low as possible for minimum frontal area/aero load

I want to build a vehicle competent off road because I plan thousands of miles a year in 4x4 mode... but I expect potentially tens of thousands a year while towing, so even a 1/2MPG improvement will pay for itself over a few years so i'm trying to figure out how to have my cake and eat it too. If it's not wheeling it will probably be pulling a trailer though. So my first exploration is how big of a difference the lifts make/maybe I don't even need to be that worried.

If I were towing big 13.5 foot tall park model mobile homes i'm pretty sure the aero would make zero difference so people with physically large loads need not post "0mpg difference". But if i'm doing half my miles unladen flatbed, and the rest usually hauling a flatbed with fairly low and compact loads smaller than the frontal area of the truck i'm assuming it does.


MOSTLY FOR PEOPLE WHO HAVE TOWED FAIRLY AERODYNAMIC LOADS both before and after something like a lift kit, what kind of changes have you noticed? If you towed a non-aero load like an RV and still had an mpg change you can post too, but i'm assuming dozens of people will say 0 difference for their RV.

I'd like to figure out some rules of thumb, like a 6 inch lift might drop it 2mpg for instance. Or if some trucks show more decrease than others due to shape. I'm especially curious about empty flatbeds (about as aero as you can get) - I wont ask a bunch more detailed questions, but more detail is encouraged. Diesel vs gas, size/shape of load, mpg no-trailer vs mpg empty flatbed vs mpg with load, etc. I'll read it and find it all valuable. :)
 

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Mileage is hard to judge because there are so many factors people don't mention (first and foremost, speed) and people love to lie about it. Some guys get out on the highway, set the cruise at 55, reset their mileage readout on the dash, then tell everybody they "average" 24 MPG on the highway. More realistically, if you drive at real highway speed (70-75 IMO) which includes wind and hills, for a full tank of fuel, the average will probably be more like 18, especially if you had calculate it instead of using the dash readout. It also as everything to do with how you drive, hills, wind, and even the fuel blend (winter versus summer).

Just moving from a H/T tire to a A/T or M/T tire of the same size can cause a 1.5-2 MPG drop. Go up in tire size to something like a leveled truck (stock 33" to 35") and it might be another 1.5 - 2.0. Get into bigger tires like a 37" and it's going to get pretty bad fast. A modern diesel with stock everything can easily pull high teens on the highway. That same truck with a 10" lift and 37" tires is going to be more like mid to low teens.

The more you're going to tax the motor, the more the diesel is going to shine in fuel savings. Gas engines in HD trucks don't make a lot of sense to me if you actually use your HD truck as intended.
 

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Careful on your tire selection. A wider tire can eat your mileage. If you are worried about off road traction, go taller but stay skinny, this will get the mileage, but aired down will still get the foot print. A wider tire has more wind resistance and more road friction. Sticking with a 9.50 tire versus and 12.50 can easily make the 1/2 or more mileage difference.

Tread patterns can also influence mileage but it is controversial as to how much. Typically, the more aggressive the tread, the more it hurts the mileage. That said, this is a small change compared to other factors.
 

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Diesels and 35s are nothing, won't notice much of anything because most can clear 35s on a stock or 2" leveled suspension

I noticed a solid 2 mpg drop in mileage when stepping up to Load E Range 37s, from my old Load D Range 35s.....the 37 a MUCH heavier tire, but the Load E Range I feel much more comfortable using on a 9,000 pound truck
 

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I lost ~3mpg when I put a leveling kit and 325/60/r20s (up from 275/60/r20) on my F250. The tires are just an inch taller than before, but they are wider and have a much more aggressive tread pattern.
 

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What type of 4X4 driving will you be doing? How much lift do you really need?

As mentioned above tire size (width), gearing, tire/wheel weight, etc all play a role as well.
 

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Just putting 33's on my diesel excursion from 31's dropped mileage a fair bit. How much is hard to tell because the speedometer was a little optimistic before which invalidates my earlier mileage calculations.
 

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Your question is way to general with way too many factors.

But, my 05 dodge diesel dropped just over 1 mpg when I put a 1.5 inch leveling kit and a 35 BFG At's.
 

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A lot has to do with the gearing too. You can tow on 44" tires just fine as long as you have the gears to do it.
In theory, but you still lose mileage based on the weight of wheel/tire combo and increased height. You also need to make sure those 44's are rated for the weight you intend to haul.
 

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A magazine did a test a few years ago and Highway tires vs all terrains was a couple mpg difference just on the rolling resistance.
 

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hasteranger:27321977 said:
A magazine did a test a few years ago and Highway tires vs all terrains was a couple mpg difference just on the rolling resistance.
word.

your best bet would be to have wheeling and road tires as two separate sets. swap when needed.
 

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What is the truck and what kind of wheelin do you want to do with it? My 2500hd on 33" MTs with no lift goes anywhere I want to take it. Length and width tend to be the major limiting factors and a lift won't help either.

That being said going from 265/75/16 hwy tread tires to 285/70/17 mud terrains and slightly cranked torsion bars made a negligible difference in towing mpgs. Empty I have no idea because I never drive a full tank without a trailer lol
 

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I pulled an 18' flatbed, dual 3.5k axles with 235/75r15s with my k3500, 5.7 vortec.

Empty truck, 7k lbs: 13-14 mpg every tank highway, 8mpg in town
Truck + trailer, 9k lbs: 9 mpg, highway. Never measured in town because it's never hooked up through a tank of fuel
Truck+ trailer+ nissan 720: 8 mpg highway. Made a 700 mile drive with that little truck and both times I fueled it was within .25mpg.

I came to the conclusion that the weight+ rolling resistance of the trailer makes a big difference, while the actual load isn't much so long as it's in the draft of your pull truck. I saw the same thing with a 20' enclosed, 6 mpg whether the trailer was empty or stuffed completely full. Now, this is all highway driving. Slower speeds the weight will make a lot bigger impact, but I did all my measuring while cruising down the highways here at the 70mph speed limit, same tires, hand calculated. Running 235/85R16E and my speedo is within 1mph at 70 according to GPS.
 

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Discussion Starter #15
Quick note to people asking me what i'm going to do... this isn't about me, it's about you! :) Im just trying to get a feel of how YOUR mileage changed. (which so far is turning out more than I would have thought in a way) Including whether people did things like alter axle ratios or not - it's all in what YOU did and the results you got from it. If I get 100 responses i'll read them all and start to get an idea of patterns emerging I think...

Those patterns will be affecting what I choose for my own rig.
 

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Get a Cummmings and straight pipe it, you'll get 27 mpg towing 15k uphill into the wind.:flipoff2:
 

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Get a Cummmings and straight pipe it, you'll get 27 mpg towing 15k uphill into the wind.:flipoff2:
People will take that remark seriously. I said the same thing as a joke in my sig and someone on here PM'ed me asking how he can do the same :shaking:

There are different adjustments for each truck that can be made to achieve better mileage with bigger tires. Finding the most efficient RPM range, adding a tuner, and helping the air flow through and out the engine will help dramatically.

Weight and width of the tires matter more than height. Tread does impact rolling resistance so keep it to a good A/T if you're looking for mileage. A leveled truck with good suspension will take you where you want to go. I've been chasing the MPG carrot for a while now with a 24v Cummins on 35s and best I can accurately get is 19 highway with 25% city driving. That's 65-70mph, auto, 355 gears, heavy 315 toyos, edge ez, BHAF, straight pipe, and a light foot.
 

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Quick note to people asking me what i'm going to do... this isn't about me, it's about you! :) Im just trying to get a feel of how YOUR mileage changed. (which so far is turning out more than I would have thought in a way) Including whether people did things like alter axle ratios or not - it's all in what YOU did and the results you got from it. If I get 100 responses i'll read them all and start to get an idea of patterns emerging I think...

Those patterns will be affecting what I choose for my own rig.
Go suck start a shotgun noob. We are not your personal think tank for whatever project you are claiming to be working on. Get 100 responses and you will then read them? :flipoff: I hope you die today in a flaming car crash.

PS: Go fuck yourself!
 

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towing
4wd
sensibility

Choose two.

Your big gay truck will not tow well
Your sensible 4wd will not tow well

One will have you stopping at every truck stop and rest area bathroom with your daisy dukes on.
The other is light weight and equipped with a very soft and flexible suspension.
 
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