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2004 to 2008 F-150 and Mark-LT
4.2L, 4.6L and 5.4L equipped F-150s and Mark-LTs.


 
 
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Old Tue, January 18th, 2011, 11:26 AM
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Jackpine Jackpine is offline
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Quote:
Originally Posted by hampsterzone View Post
Thanks, my stock tires were 245/70/R17 or 240/75/R17. My stock gears are 3.73 Does this give you better info to help me. My gears go in on Wednesday.
Yes, it does - working with Bill's Gear Ratio Calculator in Pegasus, if you have 240/75R17s as OEM, your tire diameter is 31.17". Increasing the diameter to 35.17" calls for 4.20 gears to get your "effective" OEM gear ratio back. Installing 4.56 gears should essentially get you close to a 4.0 effective gear ratio, and that should be fine.

Put another way, if you currently see about 2204 RPM at 76 mph in 4th gear with the torque converter locked, I predict you'll see about 2380 RPM there with 35" tires and 4.56 gears.

- Jack
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