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Old 04-28-2016, 03:14 PM   #31
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Can't speak to MPG pulling a TT (mine is a Sunseeker), but I can tell you that going from 30" tires to 33" tires on your tow vehicle will tend to mess with things.

Things like speed, calculated load, throttle angle, etc. are all part of the algorithm that the computer uses to decide when to shift (up or down). Having larger than stock tires will cause the truck to think it's travelling more slowly than it actually is. The larger circumference will also change the effective final drive ratio, making it "longer". This will result in the engine and transmission having to work harder than it otherwise would to pull your TT, which will have a negative effect on your fuel consumption. Think about if you jumped on a 10 speed bike that's in a high gear...you have to work pretty hard just to get going. Once you're up to speed, it's OK, but getting there uses a lot more energy (and causes more component wear) than it would if you started in a lower gear.

Here are some options:

-Do nothing at all and enjoy it as is! Pros...your truck looks cooler than stock, and this option doesn't cost you a thing! Cons...your gas mileage won't meet your expectations (which can always be re-adjusted!), and your truck will be working harder than it should. This is really only an issue when you're towing...you're unlikely to overtax anything during your daily commute, regardless of how big your tires are.

-If you like the look of the oversized tires:
At a minimum, you should find a tuner or re-flash module to correct the speedometer. This will correct the "speed" part of the shift algorithm which will improve your shift points (the computer will be making decisions on correct information). Pros...your truck will still look cooler than stock. Cons...it won't change the fact that your drivetrain is working harder than normal, and is unlikely to have any real effect on fuel consumption.

-You can change the differential gearset ratio, which will compensate for the increased tire circumference to bring your final drive ratio back to "stock" with the larger tires. Pros...your truck will still look cooler than stock, you'll get better gas mileage since the drivetrain isn't working so hard, and (in theory) the engine and transmission will last longer. Cons...you'll still have to re-flash the computer so the truck knows how fast it's actually going, and changing the gears is expensive (especially if it's 4WD).

-If you're not "in love" with the oversized tires:
Get a set of stock sized tires and be done with it. Pros...your truck will operate as designed, which should be an improvement in gas mileage and seat of the pants power over your current condition. Cons...your truck will look like everyone elses.

You learn a lot about the effects of upsizing your tires when your toad is a Jeep Wrangler....
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Old 04-28-2016, 03:18 PM   #32
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The 2006 F150 should have the 4 speed auto transmission with either the 4.6 or 5.4 engine.

The past work truck was a 2007 F150 with the 5.4 and 3:55 axles. Towing a 3,000 lb 12X5 cargo trailer it would get in the 9-10 range. We updated the trailer to a 7,000 lb 16X7 cargo trailer and mileage was in the 6-9 range. Also found truck to be in 3rd gear more often. Gas tank was only 26 gallons.
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Old 04-28-2016, 03:22 PM   #33
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If you have 3.55s and 33" you basically dropped the rear gears to 3.25. Way too low for towing. You have a loss of power and need more gas to tow. Hence the bad MPG.
The 5.4 is kinda doggy to begin with and running basically a 3.25 rear with those 33s is why you're having trouble.
As cool as the 33s probably look I'd go back to the stock size or jump to a 4.30 gear set. If you have 4wd then that's going to be $1500-2000 for a gear swap.
I think I'd just get stock tires for that much $$$$.
I towed a lighter but similar sized Tt with an 08 F150 3.73 gears and consistently got around 10.5 towing all over Oregon and NorCal.
I too had a tranny shudder @ around 45-50mph. My F150 was all stock. I didn't notice it when towing. Just when accelerating empty and from 45-50MPH. Nothing below or over those speeds.
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Old 04-28-2016, 03:28 PM   #34
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I have a 2002 f150 screw 5.4l engine 3.55 rear. I get average between 6-10 mpg while towing. I have a cap on back of truck so I think that helps me itch drag some. My dry weight is 4470 gross is 7770. It averages around 15-18 mpg when not towing.
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Old 04-28-2016, 03:51 PM   #35
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Had a rear cap on mine also. I too think that helps some. Also my TT was only 9'9"H.
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Old 04-28-2016, 03:56 PM   #36
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Welcome to the comforts of a travel trailer.....no setup, full washroom, no sleeping on the ground. I've been towing RV trailers for 20 years, in fact had the same one for 15 years and towed it with 3 different vehicles. Astro van with 4.3L/3.73, Trailblazer 5.4L/3.73 and F150 3.5 Eco/3.73. Every one of them got the same mileage 8-10mpg. Now towing a Flagstaff 8289WS with Eco 3.5 and still get same mileage. Wind resistance kills mileage, especially with gas engines. On an empty road trip I can get over a 1000Km (over 600 miles), towing its cut in half. Want your mileage back....buy a tent.
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Old 04-28-2016, 04:37 PM   #37
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Consider the lower gas mileage a trade off for convienence over tent, and savings over hotel ing it and eating out all the time and not sleeping in your own bed.
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Old 04-28-2016, 05:39 PM   #38
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This is kind of the mindset I have - and seeing the earlier post regarding what my RPMs should be based on tire size, I am leaning toward starting with a reflash of the tire size. I did find a Superchip Tuner for 150.00 that if it doesn't work I can easily resell, so worth a shot.

I am going off the VIN in regards to me gearing being a 3:55, and it is an 06, so the TOW button I don't believe was an option with the tow package. I have to assume it is a factory tow kit since it has Ford branded parts on it, the bars that are welded to the frame for additional support, the trans cooler, and the wiring all in place for 7 plug and a brake controller that is all factory wrapped and positioned.

We have our first Mini trip next weekend, only about 90 Minutes away, but I will run some numbers for the gas starting this trip, then we have one that is 5.5 hours away at the end of May that will be a full test

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Quote:
Originally Posted by rad_jr View Post
Can't speak to MPG pulling a TT (mine is a Sunseeker), but I can tell you that going from 30" tires to 33" tires on your tow vehicle will tend to mess with things.

Things like speed, calculated load, throttle angle, etc. are all part of the algorithm that the computer uses to decide when to shift (up or down). Having larger than stock tires will cause the truck to think it's travelling more slowly than it actually is. The larger circumference will also change the effective final drive ratio, making it "longer". This will result in the engine and transmission having to work harder than it otherwise would to pull your TT, which will have a negative effect on your fuel consumption. Think about if you jumped on a 10 speed bike that's in a high gear...you have to work pretty hard just to get going. Once you're up to speed, it's OK, but getting there uses a lot more energy (and causes more component wear) than it would if you started in a lower gear.

Here are some options:

-Do nothing at all and enjoy it as is! Pros...your truck looks cooler than stock, and this option doesn't cost you a thing! Cons...your gas mileage won't meet your expectations (which can always be re-adjusted!), and your truck will be working harder than it should. This is really only an issue when you're towing...you're unlikely to overtax anything during your daily commute, regardless of how big your tires are.

-If you like the look of the oversized tires:
At a minimum, you should find a tuner or re-flash module to correct the speedometer. This will correct the "speed" part of the shift algorithm which will improve your shift points (the computer will be making decisions on correct information). Pros...your truck will still look cooler than stock. Cons...it won't change the fact that your drivetrain is working harder than normal, and is unlikely to have any real effect on fuel consumption.

-You can change the differential gearset ratio, which will compensate for the increased tire circumference to bring your final drive ratio back to "stock" with the larger tires. Pros...your truck will still look cooler than stock, you'll get better gas mileage since the drivetrain isn't working so hard, and (in theory) the engine and transmission will last longer. Cons...you'll still have to re-flash the computer so the truck knows how fast it's actually going, and changing the gears is expensive (especially if it's 4WD).

-If you're not "in love" with the oversized tires:
Get a set of stock sized tires and be done with it. Pros...your truck will operate as designed, which should be an improvement in gas mileage and seat of the pants power over your current condition. Cons...your truck will look like everyone elses.

You learn a lot about the effects of upsizing your tires when your toad is a Jeep Wrangler....
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Old 04-28-2016, 06:55 PM   #39
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When I slap the 16' Madriver Canoe and a rack on the truck, 2 bikes, a campchef stove and accessories, and a load of firewood... I might be lucky to get 4mpg

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Old 04-28-2016, 07:07 PM   #40
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Just doing some basic math, if your tires were exactly 33" OD and 30" OD, the circumference difference is exactly 10%. Therefore, if you have the 33" tires on and your speedo said you were doing 65 mph, then in fact, you would actually be doing 65 +6.5 = 71.5 mph, IF the speedo has not been adjusted. That's definitely enough to see the mileage you're seeing. Most of us tow at 62-ish, or about 15% below what you're doing.

My advice - SLOW DOWN.

If you want to try 62.5 mph, about where most of us try to keep it, your indicated speed should be 56.25 mph.
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