tires
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New User
Joined: Nov 2003
Posts: 16
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From: great falls montana
tires
I just traded my 97 f150 4x4 for a 04 150 4x4.Dealer put a leveling kit and 285/70-17 on it looks great.Question, stock tires were 235/75-17. Do I need to recal the computor.
Posting Guru
Joined: Jul 2004
Posts: 1,479
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Here are the specs going from stock to the 285's
Stock(235x70x17)
Sidewall = 6.9"
Radius = 15.4"
Diameter = 30.9"
Circumference = 97
Revs/mile = 653
New tires (285x70x17)
Sidewall = 7.9"
Radius = 16.4"
Diameter = 32.7"
Circumference = 102.8"
Revs/mile = 617
So in essence you are traveling faster then the speedometer is showing, so yes you need to get it recalibrated.
BTW, you just lowered you tow capacity by actually changing the overall ratio.
Stock(235x70x17)
Sidewall = 6.9"
Radius = 15.4"
Diameter = 30.9"
Circumference = 97
Revs/mile = 653
New tires (285x70x17)
Sidewall = 7.9"
Radius = 16.4"
Diameter = 32.7"
Circumference = 102.8"
Revs/mile = 617
So in essence you are traveling faster then the speedometer is showing, so yes you need to get it recalibrated.
BTW, you just lowered you tow capacity by actually changing the overall ratio.
Last edited by KevinM; Aug 24, 2007 at 09:06 AM.
