Speedometer Calibration 2003 SD ?
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Joined: Oct 2003
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Speedometer Calibration 2003 SD ?
I changed my tire size thinking I could go to my dealer and get the speedometer re-calibrated and be good to go.
I know it may sound silly but I went lower profile tires, I have my reasons.
My dealer told me the 2003 is gear driven at the transmission and then turns it into an electrical pulse, then sends it to the speedometer.
He also stated the gears make about 4 mph jump for each size change.
Is this truly the case or is he mistaken?
I know it may sound silly but I went lower profile tires, I have my reasons.
My dealer told me the 2003 is gear driven at the transmission and then turns it into an electrical pulse, then sends it to the speedometer.
He also stated the gears make about 4 mph jump for each size change.
Is this truly the case or is he mistaken?
Sit. Stay.
Joined: Oct 2001
Posts: 18,308
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From: Washington State
First off, welcome!
Did your dealer recalibrate your speedo for you?
What size rim & tire do you now have?
I may be mistaken for the 03s but on other SD trucks the speedometer gets its input from the speedo sensor on the rear diff. It reads the pulses from the ring gear. (simplified term)
I'm not sure what you meant by this: He also stated the gears make about 4 mph jump for each size change.
Sounds false.
Did your dealer recalibrate your speedo for you?
What size rim & tire do you now have?
I may be mistaken for the 03s but on other SD trucks the speedometer gets its input from the speedo sensor on the rear diff. It reads the pulses from the ring gear. (simplified term)
I'm not sure what you meant by this: He also stated the gears make about 4 mph jump for each size change.
Sounds false.
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OK, here goes. I changed my tire size to 245/75-16 E. I have 3:73 gears. I checked under the truck and there is a wired type plug-in on top front of the rear differential. I checked the Hypertech web site and it shows no adjustability for the diesel SD. for tire or axle ratio ability. My math shows a 3.73199% fast speedometer reading, this equals 2.8 mph at 75. This isn't a big deal but I'd like to have it close and have a GPS unit to dial it in.
Jet Performance makes an "accu-speed" for some of the vehicles. has anybody tried this one.
I'd still like to have something more like a factory calibration and keep shift points, ABS, and speedo all insink.
Any help is appreciated.
Jet Performance makes an "accu-speed" for some of the vehicles. has anybody tried this one.
I'd still like to have something more like a factory calibration and keep shift points, ABS, and speedo all insink.
Any help is appreciated.
Posting Guru
Joined: Jan 2003
Posts: 1,238
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From: Back in the TX Coast
Sno jet,
Try this site it'll have your answer for the speedo ? .
http://www.mgbexperience.com/misc/tirecalc.html
Try this site it'll have your answer for the speedo ? .
http://www.mgbexperience.com/misc/tirecalc.html
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Joined: Dec 2002
Posts: 466
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I installed a truesped and love it. you can set it to run 2 sets of tire combos at the flip of a switch. not to hard to install either.
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I think you will be happy with it. I got mine within 1 mph with a 12 channel gps on a clear day with cruise control set. Stock the ford speedo was around 2-3 off comparing to my gps when the truck was brand new, so the truespeed should hook you right up bro.
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