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99 & up 7.3L Power Stroke Engine and Drivetrain Discussion of the 99 & up 7.3L Power Stroke diesel engine and drivetrain in the 1999-Up Super Duty trucks and Excursions. No gas engine discussion allowed except on transmissions and drivetrain that pertain to all models. Please confine discussion of topics in this forum to those items that are specific to the 7.3L Power Stroke engine.

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Old 01-11-2008, 02:10 PM   #1 (permalink)
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Will taller tires give better mpg?

My truck with 4.10 rear end is great for pulling my 11,400 lb toyhauler at 55mph. But when I'm not pulling a trailer and want to go 70mph, the rpms seem too high to get good mpg. If I got taller tires, would that give me better mpg at 70mph?
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2005 Nomad Rampage toyhauler made by Skyline. 11,500lb gvwr.
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Old 01-11-2008, 02:32 PM   #2 (permalink)
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Re: Will taller tires give better mpg?

It's doubtful, but within reason you could. How much? Who knows. If you run 255/85r16s on your DRW, you might pick up something over the 235/85rr16 stockers. The wider tires usually kill mileage due to the additional rolling resistance at the pavement.
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Old 01-11-2008, 02:53 PM   #3 (permalink)
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Re: Will taller tires give better mpg?

not going to make a whole lot of diff maybe .5 mpg or so your problem is trying to go 70 with 4.10 gears it just dont work like you said 4.10s are great for pullin but if you want miles your gonna have to change gears I run 3.73s in mine its kinda the best of both worlds you get good pullin power plus a lot lower rpms at 70 mph equals more mpgs
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Old 01-11-2008, 03:15 PM   #4 (permalink)
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Re: Will taller tires give better mpg?

Your sig says, "completely stock"...easy flowing air-in and air-out will probably help more than different size tires.
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Old 01-11-2008, 03:54 PM   #5 (permalink)
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Re: Will taller tires give better mpg?

i went from stock 265s to 285s and my mileage went down slightly. YMMV.
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Old 01-11-2008, 04:04 PM   #6 (permalink)
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Re: Will taller tires give better mpg?

Jack,

check yur PM's
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Old 01-11-2008, 04:23 PM   #7 (permalink)
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Re: Will taller tires give better mpg?

Your sig says, "completely stock"...easy flowing air-in and air-out will probably help more than different size tires.

Firehunter,

How much mpg could I pick up if I installed the AIS and larger exhaust?
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Old 01-11-2008, 07:50 PM   #8 (permalink)
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Re: Will taller tires give better mpg?

well I went from 285/75-16 to a 255/70-22.5. That's a 33" to a 36" tall tire. I gained about 2mpg across the board. I can still tow my backhoe and really heavy trailer no problem. I'd be willing to say that a taller tire will help you. The question is, how tall are you willing to go?
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Old 01-11-2008, 08:00 PM   #9 (permalink)
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Re: Will taller tires give better mpg?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dstuartw</div><div class="ubbcode-body"> If I got taller tires, would that give me better mpg at 70mph? </div></div>

Theoretically, yes. In the real world, no.

If you could go taller without going wider, then that should give the truck longer legs without more tire contact patch. But more contact patch causes significantly worse MPG, and nobody makes a taller easily-available truck tire that's not wider.

One possibility is "military tires" in a tall skinny size such as 9.00R16. They are 36" diameter and only a scooch wider than LT235/85R16. With 577 revs/mile, they would change your effective rear axle ratio to 3.61. Probably too long of legs for your current max load of around 20k to 21k GCW. But I've never seen any of those rated for higher than 62 MPH. So going 70 MPH on those tires is a no no. http://militarytires.com/

As others mentioned, re-gearing to a 3.73 rear axle ratio would give you 10 percent longer legs. And the truck will easily tow up to 20,000 pounds GCW. But if you're one of those that overloads your tow vehicle by grossing more than 20k on the road, then you probably don't want the 3.73 rear end.

Another possible fix is an auxiliary tranny - Gear Vendors or U.S.Gear makes them. A 20 percent "double overdrive" is common, and your truck would "feel like" it had a 3.28 rear end when in double overdrive. Long legs indeed. But not enough power to pull a hair out of a gnat's hiney, so don't even think about towing more than a rowboat in double OD.

Plus, the auxiliary trannies cost over $3,000. You can buy a lot of diesel for $3,000. They're most useful for folks with really short legs, such as F-550 towing machines with 4.88 rear end. With a GV for unloaded cruising, they would "feel like" they had a 3.90 rear end when in double OD. Not much better than your 4.10, but a heck of a lot better than their 4.88. [img]/forums/images/%%GRAEMLIN_URL%%/smile.gif[/img]
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Old 01-11-2008, 08:10 PM   #10 (permalink)
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Re: Will taller tires give better mpg?

You've only owned your truck for 6,000 miles. You might want to go and change out all your old fluids and replace them with synthetic. Check your air filter and brakes. A good wash and wax will help with wind resistance. And make sure your air pressures are up to normal. Get some guages. Get a chip from Jody at DP-Tuner and maybe a couple postions for stock, towing, and fuel economy. As long as you keep your foot out of the pedal the custom tuning of the chip will net you more MPG than trying to cheat your way with an empty load on larger tires than hurting the mileage while towing.
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Old 01-11-2008, 11:57 PM   #11 (permalink)
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Re: Will taller tires give better mpg?

I went from stock to 355-85 r-16 and got better mileage. Not much but better. A substantial drop in rpms going above 70.
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Old 01-12-2008, 12:50 AM   #12 (permalink)
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Re: Will taller tires give better mpg?

When I went to taller tires I lost milage. Alot of the time when poeple install taller tires on their vehicle they dont relize they are altering the speedometer reading. The speedo will actually read slower so when you hand calculate your milage you need to know how far off it is because your odometer will show less miles, making it seem worse than it is.
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Old 01-12-2008, 11:35 AM   #13 (permalink)
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Re: Will taller tires give better mpg?

That's the beauty of my TrueSpeed and a GPS unit in the truck at all times. My mileage is almost dead on. And if I notice it starting to drift, I reach down and grab the screwdriver and adjust it back again. And SmokeyWren is right. If you can find a tire that is narrower it will help. I lost about 4" of overall contact width with what I did. I'm sure it helped.
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Old 01-14-2008, 04:34 PM   #14 (permalink)
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Re: Will taller tires give better mpg?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: PwrStrokinDually</div><div class="ubbcode-body">You've only owned your truck for 6,000 miles. You might want to go and change out all your old fluids and replace them with synthetic. Check your air filter and brakes. A good wash and wax will help with wind resistance. And make sure your air pressures are up to normal. Get some guages. Get a chip from Jody at DP-Tuner and maybe a couple postions for stock, towing, and fuel economy. As long as you keep your foot out of the pedal the custom tuning of the chip will net you more MPG than trying to cheat your way with an empty load on larger tires than hurting the mileage while towing. </div></div>

Thank you everyone for all of the great information about MPG related to tire size. I'm still undecided about what to do with the tire size, since some people found an improvement in mileage with increased tire size, and some people thought that it wouldn't help or would be worse.

I guess I will keep the tires as they are for now.

Thanks, PwrStrokinDually, for the suggestion that synthetics would help with MPG. That is certainly an easy thing to do; so I will start there and see how much that helps. Which synthetics would give me the best MPG?
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Old 01-14-2008, 04:56 PM   #15 (permalink)
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Re: Will taller tires give better mpg?

Amsoil, Redline, and Royal Purple are a few popular synthetics. There are others, but some prefer the mentioned over others.
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APC Projectors (HID 10k), clear corners, clear cab lights, clear dually side markers, Amp-Research retractable side-steps, power rear-slider, Snug-Top canopy, billet grill, and chrome truck nutz!


Fully built motor w/ B-codes, GT42R, and Terminator w/ remote IPR HPOS.

Auto Enginuity Pro-Bundle equipped if you need assistance locally.
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