Speedometer Calibration

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bsamc2000

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I am look for information on how to calibrate the speedometer on my expy when I get my new tires next week.
I have called 3 dealers local to me and they all say you cannot change this.
Any information would be greatly appreciated.
 

walnuts4x4

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a programmer will do it in a matter of minutes.... 97-98 expys need a new gear placed into the speedo with a different tooth count, however a 99+ needs to be programmed it a programmer.... my personal choice would be the Edge CS... but hypertech, diablo ect... all do the same thing... besides speedo adjustment the programmers also improve the shift points and increase HP and MPG...
 

walnuts4x4

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also what size tires are you going up too? up to 33-35s the speedo will only be off a little bit but 37s+ will cause a greater difference in the speedo... another cheap way to see your accurate speed would be to use a GPS and compare it to your speedo
 

tonydiv

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Also remember the down side of calibrating the speedo... accurate miles on the odo.

My truck is off by 6mph at 60 (10%) meaning that I have 10% fewer miles showing on the odo than the truck has actually driven. If you're thinking of selling it in a couple of years, those miles can make you a few extra $$$.
 
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bsamc2000

bsamc2000

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I'm only going with 285/75/R16 (33.2") for now. I know the speed will only be off a little but I would still like to upate it.
So if I get something like the Edge CS and change the size there do I need to leave it installed at all times to correct the speed?
 

Thermo

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If you are only stepping up to 285's, this can be accounted for in the stock computer. The dealership just needs to get in and adjust a single value. It will cost you about $80, but it will save having to buy a new computer and setting all that up. But, like others said, you can get an aftermarket ECU and then reprogram that to exactly what you want.

There are also modules out there that you can tie into the VSS sensor (what reads the speed on the output of the tranny) and this calibrator box will alter the VSS signal and make the speedo read right too. The big problem with this box is that you have to splice wires together to make it work and the use of stuff like Raychem tubing (WCSF-070 tubing) is a must to ensure longevity. The Raychem stuff actually seals the shrink tubing to the wire insulation, making for a water tight seal. if you are worried about it failing due to being under the truck, DON'T WORRY. This is the stuff we use at my work to survive a nuclear reactor blowing up. It is good stuff.
 

Remo

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I'm running the same size tire. Unless you want a programmer for other purposes, I wouldn't bother. It is easy enough to remember to add 10%...
 

panda24619

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its not worth it. your fine. it really wont be that much of a difference. just know where those road signs that show you the speed are and drive threw it. then you know the difference.
 

Remo

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His truck is stock and has 16" wheels. If the tires are factory spec, they are 255/70/16 (which is about 30"). 285/75/16 is about 33". Add 10% to the displayed speed and you are done...

30 mph is 33
60 mph is 66
70 mph is 77....etc...etc

I think that is easy enough to remember...
 

Thermo

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I ran my truck for a few years without recalibrating the speedo. Now, I was running a little bit bigger tire (315/75R16) and the truck performed fine even though the speedo was off by 16.7%. But, after putting in the new VSS gear (my truck is a 97), I noticed that my truck shifted better, at a more appropriate point, and my mileage actually went up (dropped 4 mpg due to the bigger tires, but came back 2 mpg after the speedo change). So, there are some other benefits to getting the speedo recalibrated. I know my case is more of an extreme situation, but it goes to show what the different sides are.
 
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