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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 Fri, January 21st, 2011, 11:33 AM
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Jackpine Jackpine is offline
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Bill SHOULD include your new Gear Ratio (GR) and Tire Size (TS) in your tunes. But, the TS is a bit of a WAG. Personally, I think you can refine the TS using a speed readout on the GPS and compare it with a speed readout on the Gryphon (not the dash speedo - which always reads faster due to mechanical errors).

If you stabilize the speed on the highway (70-75 mph is a good speed) and find a TS that gets them to match, you're golden. I've found my GPS speed stabilizes within less than 3 seconds at a constant speed.

Longshot, I'm going to "quibble" with your suggestion of 2770mm, it seems too large. A tire diameter of 35" has a circumference of 2793mm. Reducing that by 3% for squish give me 2709mm.

But, regardless - pick one of those values as a starting point. If your Gryphon speed indication is too fast, reduce the TS. Increase the TS if the Gryphon speed is too slow.

And, I'm sorry but I'm not coming up with any thoughts about your odometer.

- Jack
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