Fuel Economy Blows: Takin Lift Down and Moving to smaller tires: Question(s) - Ford Powerstroke Diesel Forum
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post #1 of 11 Old 05-09-2010, 01:03 PM Thread Starter
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Fuel Economy Blows: Takin Lift Down and Moving to smaller tires: Question(s)

I just purchased a 2004 Excursion Limited. Its a Southern Car and is in excellent shape with relatively low miles @ 84K. I bought the vehicle for Wife to use as her DD. We needed something big and go Diesel for the F/E seemed to be the way to go. The vehicle currently has an 8" Superlift Kit with 37" Tires. The truck looks great and we love it (after many Suburbans/Yukons), however the "problem" is my F/E blows. I got 15mpg on the 700mile trip from GA to MI. City is just above single digits. I'm not sure if we'll even get 400 miles out of the 44 gallon tank in combined driving.

I am in the process of selling the lift kit and tires. I am planning on lowering it to stock or close to stock (2in.) and going with 18" wheels and 33" tires.

Questions: what is the widest tire that I can put on with the truck at stock height, without rubbing. I am considering the following tires: 325/60/18, 305/60/18 and 295/65/18: all are about 32.5-33.4" tall.

Anyone with estimates on how much F/E will improve with the tire change? Lowering? Will the 325 width yield much different fuel economy than the 295?

If you've done this or know of someone who has done this, please post your results.

Next step: tuner for F/E improvement.

Thanks in advance.
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post #2 of 11 Old 05-09-2010, 01:31 PM
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I have 325/60/18's. They rubbed a tiny bit at full lock, but I trimmed the lower valance on the bumper and zip tied the fender wells back (I used super thick zip ties ) and now it does not rub at all

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post #3 of 11 Old 05-09-2010, 01:40 PM Thread Starter
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Quote:
Originally Posted by MacbooknMyTruck View Post
I have 325/60/18's. They rubbed a tiny bit at full lock, but I trimmed the lower valance on the bumper and zip tied the fender wells back (I used super thick zip ties ) and now it does not rub at all
Any change in F/E (vs. stock) with the move to the bigger wider tires?
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post #4 of 11 Old 05-09-2010, 01:48 PM
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I think I lost maybe 1 MPG, but that's because I only do city driving. On the highway I don't see a change, maybe .5 MPG difference.

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post #5 of 11 Old 05-09-2010, 06:54 PM
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rim choice will depend on tire size and rubbing.
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post #6 of 11 Old 05-09-2010, 07:23 PM
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You want a wheel that has 4.5" backspacing.

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post #7 of 11 Old 05-09-2010, 07:36 PM
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Quote:
Originally Posted by Earl H View Post
I just purchased a 2004 Excursion Limited. Its a Southern Car and is in excellent shape with relatively low miles @ 84K. I bought the vehicle for Wife to use as her DD. We needed something big and go Diesel for the F/E seemed to be the way to go. The vehicle currently has an 8" Superlift Kit with 37" Tires. The truck looks great and we love it (after many Suburbans/Yukons), however the "problem" is my F/E blows. I got 15mpg on the 700mile trip from GA to MI. City is just above single digits. I'm not sure if we'll even get 400 miles out of the 44 gallon tank in combined driving.

I am in the process of selling the lift kit and tires. I am planning on lowering it to stock or close to stock (2in.) and going with 18" wheels and 33" tires.

Questions: what is the widest tire that I can put on with the truck at stock height, without rubbing. I am considering the following tires: 325/60/18, 305/60/18 and 295/65/18: all are about 32.5-33.4" tall.

Anyone with estimates on how much F/E will improve with the tire change? Lowering? Will the 325 width yield much different fuel economy than the 295?

If you've done this or know of someone who has done this, please post your results.

Next step: tuner for F/E improvement.

Thanks in advance.
i have a 2005 excursion with 285/75/16 michelins. drove it from nc to pa and back to nc and got 19.8 at interstate speeds. think if i had driven 60 all the way it would have been over 20mpg.

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post #8 of 11 Old 05-09-2010, 08:05 PM
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your odometer is not reading anywhere close to what it should with 37's, are you calculating for that?

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post #9 of 11 Old 05-10-2010, 01:08 AM Thread Starter
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your odometer is not reading anywhere close to what it should with 37's, are you calculating for that?
Yes. Its about 11/12 % off.
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post #10 of 11 Old 05-29-2010, 08:51 AM
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Tire size increase and possible tranny damage?

I have an '04 Ex with stock size rims & tires but would like to lift and add larger rims etc..... I've heard that increasing tire size will change the gear ratio and tranny damage will result - bigger the tires, the more the change and quicker the damage. $3000 or so will get a gear ratio change to compensate but I'm not willing to shell outthat kind of cash.

Any experience or comments on this would be appreciated?

Thanks
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