differential ratio?
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Junior User
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differential ratio?
I could use some help with the math on my rear differential, I have a 01 250SD
V10 Auto Trans.4:30 Ls and put 315/78X16 tires on my truck. so roughly what would my ratio be after this change? thanks
V10 Auto Trans.4:30 Ls and put 315/78X16 tires on my truck. so roughly what would my ratio be after this change? thanks
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Joined: Feb 2004
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From: Ormond Beach
Originally Posted by Gregsd250
I could use some help with the math on my rear differential, I have a 01 250SD
V10 Auto Trans.4:30 Ls and put 315/78X16 tires on my truck. so roughly what would my ratio be after this change? thanks
V10 Auto Trans.4:30 Ls and put 315/78X16 tires on my truck. so roughly what would my ratio be after this change? thanks
Go here - it is the calculator section. All the info you will need...
http://www.ring-pinion.com/calculato...latorsind.html
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From: Allen, Tx
I think I know what you want. Your truck came with 4.30 axle ratio and 265/75R16E tires (most likely) which are 31.64" tall. You put on 315/75R16 tires which are 34.60" tall so your new effective ratio would be 3.90 and you'd need a 4.70 to bring it back to stock. (4.88 is the closest avilable for a Ford/Sterling 10.5" axle.)
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From: Allen, Tx
To figure out the new ratio needed to bring it back to stock is:
(Original ratio x New tire diameter)/ old tire diameter = new ratio
(4.30 x 34.6) / 31.64 = 4.70
To find out what your ratio changed to after the tire swap:
old ratio - (new ratio - old ratio) = effective ratio.
4.30 - (4.70 - 4.30) = 3.90
(Original ratio x New tire diameter)/ old tire diameter = new ratio
(4.30 x 34.6) / 31.64 = 4.70
To find out what your ratio changed to after the tire swap:
old ratio - (new ratio - old ratio) = effective ratio.
4.30 - (4.70 - 4.30) = 3.90
Elder User
Joined: Nov 2003
Posts: 987
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From: Bass Lake, CA
i think this formula should be in the FAQ!!!!
it gets posted/requested ALOT!!!!
i know it has helped me a few times
it gets posted/requested ALOT!!!!
i know it has helped me a few times
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From: Back in the TX Coast
here is good link for common formulas
Good "rule of thumb" calculation is to mutiply .12 by your tire diameter.
(.12 X 38" = 4.56)
http://www.4lo.com/geartable.html
Good "rule of thumb" calculation is to mutiply .12 by your tire diameter.
(.12 X 38" = 4.56)
http://www.4lo.com/geartable.html
Last edited by Autobahn F-250 Lariat; Jul 28, 2004 at 02:33 PM.
