Need some advice from you the experts.
Senior Member
Joined: Feb 2000
Posts: 1,544
Likes: 0
From: Kalamazoo, MI, USA
richgonfishn: If your measurements are correct, by changing your tires to a such a larger size, you effectively reduced your 3.55:1 axle ratio to 3.05:1 (3.55x(55/64)=3.05) -- which nobody would accept as a respectable ratio for towing. 
With those tires, you'd need to upgrade your axle ratio to 4.13:1 to bring your effective axle ratio back to 3.55:1 (4.13x(55/64)=3.55).
The up-side is that if your engine has enough power, you can run 116 MPH instead of 100 MPH due to the tires upping your speed by 16% (64/55-1) without needing a 'chip'.
Your calculation of 64 vs 55 implies that your 33 inch tires replaced some 28.4" tires (55/64*33=28.4) -- is that correct?
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Y2K™
XLT SC SB 5.4L E4x4 AW-Disc, 3.73LS, Skid, 7700# HD Towing, Chrome LT-245, Steps, Captain's, 6CD, Tonneau, keyless, Toreador Red, called "Nick"
With those tires, you'd need to upgrade your axle ratio to 4.13:1 to bring your effective axle ratio back to 3.55:1 (4.13x(55/64)=3.55).
The up-side is that if your engine has enough power, you can run 116 MPH instead of 100 MPH due to the tires upping your speed by 16% (64/55-1) without needing a 'chip'.
Your calculation of 64 vs 55 implies that your 33 inch tires replaced some 28.4" tires (55/64*33=28.4) -- is that correct?
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Y2K™
XLT SC SB 5.4L E4x4 AW-Disc, 3.73LS, Skid, 7700# HD Towing, Chrome LT-245, Steps, Captain's, 6CD, Tonneau, keyless, Toreador Red, called "Nick"
Member
Joined: May 2000
Posts: 44
Likes: 0
From: Colorado Springs, CO.
richgonfishn,
Instead of changing your gears you might want to check out a supercharger. I don't know the cost of changing gears, but the supercharger is activated by throttle control. You can still cruise and not be in boost, so your fuel economy will stay the same as it is now. The Magnacharger is about $3500.00 (www.magnacharger.com). You stated a tire size of 285. Is this a 70 or 75 series, and 16 or 17 inch wheel? Here is the math: example, 285 70 16 tire size, 285 X .7 X 2 divided by 25.4 + 16 = 31.7in. If you have a 75 series you would use .75 instead of the .7.
97 F150 XLT xcab short bed
Supercharged 5.4
THE WORKS
Instead of changing your gears you might want to check out a supercharger. I don't know the cost of changing gears, but the supercharger is activated by throttle control. You can still cruise and not be in boost, so your fuel economy will stay the same as it is now. The Magnacharger is about $3500.00 (www.magnacharger.com). You stated a tire size of 285. Is this a 70 or 75 series, and 16 or 17 inch wheel? Here is the math: example, 285 70 16 tire size, 285 X .7 X 2 divided by 25.4 + 16 = 31.7in. If you have a 75 series you would use .75 instead of the .7.
97 F150 XLT xcab short bed
Supercharged 5.4
THE WORKS
Senior Member
Joined: Dec 1998
Posts: 300
Likes: 0
From: Meridian, Id.
richgonfishn, The biggest problem is thoes big tires, stock they should be 245 75R 16. You are much bigger than that. ALSO did you mention if you had a automatic? Your rear gears should be 3:55, so as you can see you have changed your gears to somethig like a 3:08. Gearing grearing!
In all, with the super chip, K&N and the exhaust (assumeing you didn't go too big of a tail pipe) you *should* pull pretty good. Its got to be thoes big tires!!!!!!!!!!!!!
You can see what truck I have and I pull a 20 ft self contained travel trailer.
Just remember.........as good as the 4.6 is it's still only 281 cubic inches.
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97 F-150 4.6 auto, 4x2, 3.55 LS, WMS Velocity tube, K&N, Dynomax Super Turbo exhaust with Echo tube.
Oh yeah, it's Oxford White with crome wheels, Legacy shell & custom grill!
In all, with the super chip, K&N and the exhaust (assumeing you didn't go too big of a tail pipe) you *should* pull pretty good. Its got to be thoes big tires!!!!!!!!!!!!!
You can see what truck I have and I pull a 20 ft self contained travel trailer.
Just remember.........as good as the 4.6 is it's still only 281 cubic inches.
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97 F-150 4.6 auto, 4x2, 3.55 LS, WMS Velocity tube, K&N, Dynomax Super Turbo exhaust with Echo tube.
Oh yeah, it's Oxford White with crome wheels, Legacy shell & custom grill!
Senior Member
Joined: Apr 2000
Posts: 102
Likes: 0
From: Dallas, Tx
Man you math wizards got me interested now.
I have 275x75 R16 with a 355 gear what type of ratio do I have and would I benefit from a 4:11 gear? I do not tow just the occasional street race, also my torque converter stall has been changed to 2500. If I do a full throttle punch on ashvault I spin from first until the second gear shift, maybe I should leave well enough alone.
All this gear talk got me going again.
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Mods:K&N Intake,
3"Flowmaster,
Transgo Shift Reprogrammer
Dyno:228.6HP, 309.8TQ
4R100 TRANS
9.5" Converter 2500 Stall
Micheline 275 75 R16
Heavy Duty RearEnd W/355
I have 275x75 R16 with a 355 gear what type of ratio do I have and would I benefit from a 4:11 gear? I do not tow just the occasional street race, also my torque converter stall has been changed to 2500. If I do a full throttle punch on ashvault I spin from first until the second gear shift, maybe I should leave well enough alone.
All this gear talk got me going again.
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Mods:K&N Intake,
3"Flowmaster,
Transgo Shift Reprogrammer
Dyno:228.6HP, 309.8TQ
4R100 TRANS
9.5" Converter 2500 Stall
Micheline 275 75 R16
Heavy Duty RearEnd W/355
Senior Member
Joined: Aug 1999
Posts: 1,628
Likes: 0
From: Clemson SC US of A