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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 Sun, February 15th, 2009, 10:42 AM
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Check the link out below...there's a couple of formulas you can use to determine the correct gear ratio and the RPM range for your tire size.

http://www.4x4offroads.com/gear-ratio-chart.html
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Old Sun, February 15th, 2009, 11:55 AM
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And, I qwould not worry much about voiding your warranty. Just make sure you program the truck back to stock EVERY time you take it to the dealer and, of course remove the Gryphon and it's mount from the dash - it's really easy!

Unless you tell the dealer you've tuned it, I doubt he'll even check for this.

- Jack
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Old Mon, February 16th, 2009, 01:16 AM
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What was the stock wheel on your truck?

Why I am wondering, the size my truck has on it is stock for 20" wheels from Ford. They are 275/55/20 they are the same height as my spare which is 18" wheel. This is what is called +2 sizing. Changing the rim size and profile of the tire. But what everyone forgets is the wheels add more weight to get going and to stopping. Now your size is 275/60/20 not much different than mine maybe 1/4" taller. I run 3.73's for gears and really no problems. While reading this thread researched stock sizes and if you started out with the 235/70/17 and 3.55 gears and did a +3 sizing from the 17" wheel then there should not be any performance loss.(During the +3 sizing if the tire runs out sidewall while maintaining total height then a +2 should be done to maintain true height) But some where along the way oversizing came into play then performance is lost and other purchases such as gears then mods. The other place the mfg plays around with gearing in the transfer case. Oh yah if your truck did start with 17's on it might want to look into bigger brakes, the rotors might be to small for 20's.

Sorry if I gave you an info overload!

If you love the wheels go with the gears and the tuner that's only if they are oversized. If it's a +2 situation go with the tuner(started with 18" stock wheels + tires. Just remember if your pulling and the tires are over sized the tranny getting an extra work out.

Lars
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