Reprogramming for Larger Tires
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Mountain Pass
Joined: Jan 2007
Posts: 104
Likes: 15
Sorry for not responding...I was at the 4 Wide NHRA Drags this weekend...WOW!!!!!
g
Now back to the topic...shouldn't the shift points change?? What I have essentially done is changed the trucks gearing to a 3.31, correct???
If I change the rear gear to a lower (numerically higher) gear then the truck would respond correctly to proper shift points and correct speedo readings, so if I get the computer to think its a higher gear (numerically lower) then I would be doing the same thing.
Not really trying to overthink it, and I doubt I will drop $200 just so my gauges read right, but just throwing it out there for conversation.
gNow back to the topic...shouldn't the shift points change?? What I have essentially done is changed the trucks gearing to a 3.31, correct???
If I change the rear gear to a lower (numerically higher) gear then the truck would respond correctly to proper shift points and correct speedo readings, so if I get the computer to think its a higher gear (numerically lower) then I would be doing the same thing.
Not really trying to overthink it, and I doubt I will drop $200 just so my gauges read right, but just throwing it out there for conversation.
Lead Driver
Joined: Jun 2007
Posts: 6,757
Likes: 5
From: Corvallis, OR
Tires and gears can't be considered the same overall ratio. The PCM measures speed at the wheel, so changing tires makes no difference to it whatsoever, except that your speedometer will be off. Shift points are adjusted SLIGHTLY for larger tires to account for the higher load they produce. Changing gears though, will really throw off your shift points if you don't recalibrate the PCM for them because shifts are controlled by wheel speed and load, and you now have changed a multiplier between the transmission and wheel speed.
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Mountain Pass
Joined: Jan 2007
Posts: 104
Likes: 15
Tires and gears can't be considered the same overall ratio. The PCM measures speed at the wheel, so changing tires makes no difference to it whatsoever, except that your speedometer will be off. Shift points are adjusted SLIGHTLY for larger tires to account for the higher load they produce. Changing gears though, will really throw off your shift points if you don't recalibrate the PCM for them because shifts are controlled by wheel speed and load, and you now have changed a multiplier between the transmission and wheel speed.
Just kinda frustrated that Ford can't reprogram it, but Hypertech can. I will probably just leave it alone and drive it as is. I did that with my F-350 and it showed 189000 on it, but it really SHOULD have said 202+.
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VH_Girl
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May 15, 2011 10:33 AM
