Speedometer recalibration

[David Muench]

Does anyone have any information on the abilities for the dealer to recalibrate the speedometer in the 3rd gens? Perhaps someone with the service manual?



I've heard the dealer can recalibrate it, but I am trying to find out to what degree. . Can you enter an arbitrary measurement, such as tire diameter or revolutions per mile, or do you have to choose from a preset list of settings? If so, what are the available choices?



Trying to do a little planning for when my 315/70-17's show up this week. .



Thanks. .

 

[4xquadrod]

I went to a 5 star dealer and they said I would have to look in the after market arena. They did not have the means to mess with it. I haven't found one yet.

 

[jdh63]

Speedo Recal

David,



I ran into this problem with my 98 when I put 33's on it. Dealer could only calibrate the speedo to the factory offered tire sizes. I ended up buying a calibration device from Dakota digital that splices between the speed sensor and the PCM. It uses a series of selectable dip switches to correct for the error and can be changed for any tire size. If you have the factory service manual it is pretty easy to install.

 

[BigCarl64]

4xquadrod,



Any chance you could post some pictures of your truck. I am thinking of bigger tires and lift on a new 2003 and would love to see how it looks.



Thanks!

 

[krabman]

Scroll down a little to the post about wheels or something like that and there is a link to the other site with pictures of two differnt trucks with those tires. Mine are coming in on Wednesday and I was wondering about the speedo myself.

 

[sag2]

Just played a bit with the scan tool after reading this post. I went to Anti-lock brakes, Set Pinion factor, and there is something new this year. There is a selection for 10. 5-11. 5 diff with UNKNOWN tires. It then lets you set the tire size in rev's/mile from 636-690. Don't have my book at work with me that has the conversion table. I will post it when I get it.

 

[David Muench]

Sounds like a Superlift TruSpeed will be the way to go then.



My tires are in my local fedex warehouse (already! Ordered Friday), so I called to have them held and was told I could pick them up any time. . I went over there to get them and apparently "any time" means "any time but today". . So tomorrow I get the tires, and Wednesday they get put on. I'll post some pictures once they're on.

 

[David Muench]

Originally posted by sag2

Just played a bit with the scan tool after reading this post. I went to Anti-lock brakes, Set Pinion factor, and there is something new this year. There is a selection for 10. 5-11. 5 diff with UNKNOWN tires. It then lets you set the tire size in rev's/mile from 636-690. Don't have my book at work with me that has the conversion table. I will post it when I get it.

Ah nuts. The 315/70-17 is 601 revs/mile. Nuts nuts nuts.



Is there any chance you can enter something less than 636?

 

[krabman]

I just ordered the true speed also. Used a little windage on my last truck, this time I figure Ill do it right.

 

[David Muench]

What kind of price did you get? I just looked them up and I am seeing $170-185. They must be out of their minds. .

 

[jdh63]

Speedo Recal

The device from Dakota digital is called the SGI-5 and lists for $79. 95. You can check it out at www.dakotadigital.com

 

[krabman]

Mine was 190 with shipping. The Dakota Digital thing is not for use on vehicles with anti lock braking.

 

[jdh63]

OOOPS

Krabman,



You're right! They didn't mention that when I bought the last one 4 years ago but it sure states that now on the web page.

 

[Prairie Dog]

David, Do you know what the rev's per mile are for the 285/70R17?

Thanks,

Scotty

 

[sag2]

Found my formula. Measure the circumference (chalk a mark on the tire and ground, roll the tire one turn until the chalk mark is again on the ground. Measure the distance the tire rolled, and that is the circumference. ) of the tire. Revs per mile is 5280 (feet in mile) times 12 inches = 63,360 (inches per mile. ) divided by the circumference.



Example-your tire measures 102 inches



63,360 divided by 102=621 rev's per mile

 

[DIESELMAN]

Or you can use the very simple formula



5280 / (((((SW*(AR/100)*2)/25. 4)+R)*3. 14)/12)



Where



SW = Section width in millimeters

AR = Aspect Ratio as a whole number

R = Rim Size in inches



A 265-70R17 would be.....



5280 / (((((265*(70/100)*2)/25. 4)+17)*3. 14)/12) = 638 Revs per Mile



This is very close to correct excluding whether the manufacturer actually measures the tire right and how close the aspect ratio is to true.

 

[Prairie Dog]

Thanks for the data guys, it kinda sounds like the calibration is only for very fine adjustment with stock size tires. Some of those folks at Dodge don't seem to know much about what their customers do with trucks do they? Would it have killed them to be a little more user friendly?

 

[krabman]

A tech at Rickson told me a couple years ago the ability was removed from their software with an update for that very purpose. They didnt want a lawer to point out that their dealerships were calibrating speedo's for larger tires, this was kinda like saying "ok, you can put larger tires on your truck"

 

[David Muench]

Originally posted by Prairie Dog

David, Do you know what the rev's per mile are for the 285/70R17?

Thanks,

Scotty

BFG doesn't have a listing for the 285/70R17 yet, so you'll have to do the math below. . They do list their 265/70R17 as 654 revs/mile though.

 

[David Muench]

Now that more people have the 315's installed, what are you all doing for speedo correction? Did you get the Truspeed installed krabman?



Still weighing my options. .