f250 PSD
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Senior User
Joined: Apr 2005
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From: south GA
f250 PSD
i am looking in to getting a ford f250 PSD 4x4 here soon and i was wondering if yall could give me the good and the bad stuff about the f250 PSD and if yall could tell me what kind of gas milelage would i get if it had a 8inch lift and big tires
Postmaster
Joined: Jan 2005
Posts: 2,753
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From: Phenix City, AL
Hey BC, 8" lift, so you are probably looking at least 37 - 38" tires. YEAH, YOU NEED TO REGEAR! Try using the calculator in my sig for the tire conversion. It should put you back in the ball park for your new tires.
Postmaster
Joined: Jan 2005
Posts: 2,753
Likes: 3
From: Phenix City, AL
Okay, I'll do a little math today.
What you're doing does this:
(old tires / new tires) x current gears = effective gear ratio
(31.5 / 37) x 3.73 = EGR
.851 x 3.73 = 3.17 EGR (NOT GOOD)
What you need to do is this:
(new tires / old tires) x current gears = gears you need to maintain original power and performance
(37 / 31.5) x 3.73 = Gears You Need
1.175 x 3.73 = 4.38
4.30's or 4.56's would put you where you need to be. I would go with 4.56's to compensate for the added weight of tires and the increased wind resistance. I'm running 4.56's with 36's and this is about perfect for the driving I do.
What you're doing does this:
(old tires / new tires) x current gears = effective gear ratio
(31.5 / 37) x 3.73 = EGR
.851 x 3.73 = 3.17 EGR (NOT GOOD)
What you need to do is this:
(new tires / old tires) x current gears = gears you need to maintain original power and performance
(37 / 31.5) x 3.73 = Gears You Need
1.175 x 3.73 = 4.38
4.30's or 4.56's would put you where you need to be. I would go with 4.56's to compensate for the added weight of tires and the increased wind resistance. I'm running 4.56's with 36's and this is about perfect for the driving I do.
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Postmaster
Joined: Jan 2005
Posts: 2,753
Likes: 3
From: Phenix City, AL
My mileage actually went up. The V10 is a little different animal. It actually gets it's best MPG during day to day driving with an effective gear ratio around 4.10. With the 4.56's, this puts me around a 4.00. The V10, when you are cruising on the highway needs to be turning around 2250 - 2500 RPM's to be in a power range that keeps the tranny from hunting gears. Any less than this and it lugs and shifts and hunts on small hills aor under a light load.
But to give you a simple answer, my MPG actually went up about 1 MPG in day to day and 1.5 - 2 on the highway.
That's why I don't get when guys don't want to regear after doing all the other stuff. I mean, don't EVER excpect to make up the difference in fuel costs to off set the gear change, but the level of performance is so much better. Not to mention your tranny life.
For the sake of putting the cost into perspective, my setup w/ install, ran about $3200. That is gears, lockers, compressor, master install kits, new seals, and labor. You won't make that up in fuel mileage for a long time.
But to give you a simple answer, my MPG actually went up about 1 MPG in day to day and 1.5 - 2 on the highway.
That's why I don't get when guys don't want to regear after doing all the other stuff. I mean, don't EVER excpect to make up the difference in fuel costs to off set the gear change, but the level of performance is so much better. Not to mention your tranny life.
For the sake of putting the cost into perspective, my setup w/ install, ran about $3200. That is gears, lockers, compressor, master install kits, new seals, and labor. You won't make that up in fuel mileage for a long time.
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