Highway Speeds
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Senior User
Joined: Feb 2005
Posts: 468
Likes: 9
From: Alabama
Highway Speeds
66 F250 4x4 4-speed 456 axle gears
What is the best way to increase highway speeds (65-70)?
Taller tires (how tall)
regear axle gears? (410)?
Gear Splitter? (which one)
5-speed transmission
What is the best way to increase highway speeds (65-70)?
Taller tires (how tall)
regear axle gears? (410)?
Gear Splitter? (which one)
5-speed transmission
Super Moderator
Joined: Apr 2004
Posts: 34,491
Likes: 2,805
Scroll down to the second calculator. (3rd one doesn't work) and enter your info.
If you want more input, post your engine, tire size, & budget.
How much do you want to spend?
The "easiest" OD is a Gear Vendor unit, which may work for you. About $3000.
http://www.gearvendors.com/
If you want more input, post your engine, tire size, & budget.
How much do you want to spend?
The "easiest" OD is a Gear Vendor unit, which may work for you. About $3000.
http://www.gearvendors.com/
Fleet Owner
Joined: Jun 1999
Posts: 24,552
Likes: 74
From: Creedmoor, North Carolina
Originally Posted by Blackwaterforge
66 F250 4x4 4-speed 456 axle gears
What is the best way to increase highway speeds (65-70)?
Taller tires (how tall)
regear axle gears? (410)?
Gear Splitter? (which one)
5-speed transmission
What is the best way to increase highway speeds (65-70)?
Taller tires (how tall)
regear axle gears? (410)?
Gear Splitter? (which one)
5-speed transmission
John
Elder User
Joined: Aug 2004
Posts: 602
Likes: 1
From: Sacramento, CA.
235 85 16's on a 16' rim from a 94 F250. Up to 1995 have the same bolt pattern as the 65.
I run 65-75 mph just nice!! My tires are a little wide and in a tight spot (parking lot or my driveway) they just barely rub on radius arms. Could go narrower .
I run 65-75 mph just nice!! My tires are a little wide and in a tight spot (parking lot or my driveway) they just barely rub on radius arms. Could go narrower .
Postmaster
Joined: Nov 2001
Posts: 3,351
Likes: 1
From: Escondido, CA
What RPM are you running at 65-70? I have 3.89 gears with 26 inch tall tires and run about 3200 RPM at 70. Swapping over to a set of 3.00 will drop my cruising RPM but make taking off a little slower. I do have a 460 to push it along just fine though.
Thread Starter
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Senior User
Joined: Feb 2005
Posts: 468
Likes: 9
From: Alabama
I am looking at purchasing a 66 F 250 with 300 6cyl, 4-speed and 456 gears. I do not know the tire height. The gentelman said it dose good 55-60 but above that the rpm's are high and the fuel mileage low. What 5-speeds will bolt up to the 300 6cyl?
Thank You!
Thank You!
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Fleet Owner
Joined: Jun 1999
Posts: 24,552
Likes: 74
From: Creedmoor, North Carolina
When that truck came off the drawing board it was designed to run about 50 mph tops. That was when the roads were standard 55 mph speed limits and trucks at 45. A lot has changed since the time they were designed, but folk didn't drive trucks fast back then. They were work vehicles only.
John
John
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Postmaster
Joined: Nov 2001
Posts: 3,351
Likes: 1
From: Escondido, CA
390Deep, I think that is a typo because a 3 foot tire wouldn't clear the front fender to turn. I think you meant 25-26". I know you can get away with a 28" or 275/60R15 tire all the way around. That is what I did run until I found all the side walls split near the bead. I was getting ready to deploy and didn't want to come home to 4 flat tires so I put some 235's for the time being. Granted that was 3 years ago.
But back to the question at hand. Black if you swap your gears to a set of 3.50 or 3.55 I think you would see a huge difference in milage and reduce the RPM's to drive at 60-70. The 4.56 gears are great for pulling heavy loads or houses around but you quickly run out of RPM and have to shift alot when you take off from a dead stop. The I-6 has plenty of torque to move the truck with a set of 3.50 It may not be break neck speeds but you will be able to enjoy the drive.
But back to the question at hand. Black if you swap your gears to a set of 3.50 or 3.55 I think you would see a huge difference in milage and reduce the RPM's to drive at 60-70. The 4.56 gears are great for pulling heavy loads or houses around but you quickly run out of RPM and have to shift alot when you take off from a dead stop. The I-6 has plenty of torque to move the truck with a set of 3.50 It may not be break neck speeds but you will be able to enjoy the drive.
Postmaster
Joined: Nov 2001
Posts: 3,351
Likes: 1
From: Escondido, CA
So it is a 4x4 F-250. I didn't even catch that on your original post. Changing tire size would be the quickest way to to reduce your RPM. Adding an overdrive be more expensive then swapping new gears in the front and rear diff. Plus the question then becomes do you have divirced T-case?
Last edited by airharley; Mar 19, 2008 at 09:41 AM. Reason: missing info