Speedometer Correction--- Disgusted

[1972JohnBoy]

I have an 06 truck, put 35s on and tried 4 different Dodge dealers here around home to fix my speedo errror and the 1st told me he could only put in the stock tire sizes. He asked $35 to "get it as close as he could''. I thougt I knew it could be done from the reading I had done here and on TDR so I searched this topic and read through many questions and answers about this to confirm what I thought. So I call 2 more dealers, different from the first four I tried previously, this morning, the 1st has no idea and the 2nd gave me the only stock tire can we do deal until I asked if they have the drbIII scan tool and told him I knew this can be done from reading on this site, he then relented and said yes it can be but you have to work some math formulas and blah blah and I said you need the rev. per mile of the tire and he said $90 and he could get it close but not perfect. What is the deal with these people? #@$%! I am stymied. None of the service people I have talked to seem to give a #%! about even trying to really help you solve a problem. I wouldn't mind paying $90 to get it done but I would expect some confident experience from the guy doing it to get it right. I am simply bumfuzzeled!!:-{}

 

[fox]

I think it can be done with a Smarty.

 

[CDonaldson]

The dealerships can only adjust your tire size up to 285's - thats what comes on the Powerwagons. That will bring you close, bya few mph's, but still NOT accurate as you desire.



I have a Smarty Jr, I used it to adjust for my 35's which are 34. 5 actually, spot on after the adjustment. Checks out to a GPS and also the State Police Radar.





CD

 

[J Baxter]

Go to this link.

https://www.turbodieselregister.com...edometer-correction-different-tire-sizes.html

you will need to figure out your own tire revolutions per mile.
It took me three tries to get it just right.
I went from what ever my stock tire was and 355 gears to 37" tires and 410 gears.
The dimension of my 37s used to get it just right is actually 36. 5, this is tire bulge and the fact that the tires are a little under 37"

You can find many ways of calculating the rotations per mile, this is how I did it.
Find the circumference of your tire, the distance all the way around the outside.
Pie or 3. 14 x your diameter = circumference.
mine was 3. 14 x 36. 5 = 114. 61 inches around the outside of the tire.
There are 63360 inches in a mile 63360 divided by 114. 61 = 552 Revs per mile.

I walked into the dealer with the print out from the link above, and my Revs per mile written on the page with the correct screen as well as my gear ratio and they were so thankful for me teaching them something, two of the mechanics made copies of the directions so they could do their own trucks. They wrote up a work ticket then voided it and wanted to go on a test drive with me. When I went back to have them tweak it I just yelled at one of the mechanics who I now know and they came out with the programmer and did it for me while talking about how they had done their own trucks.

So Thanks to D Daubenspeck for putting this together.

 

[J Baxter]

The dealerships can only adjust your tire size up to 285's - thats what comes on the Powerwagons. That will bring you close, bya few mph's, but still NOT accurate as you desire.



I have a Smarty Jr, I used it to adjust for my 35's which are 34. 5 actually, spot on after the adjustment. Checks out to a GPS and also the State Police Radar.





CD

you can put in other tire sizes, but not by selecting a stock size, look at the other post I just put up.

the dealer has to go past the stock tire sizes on the programmer and then click on "other" it then asks for Revolutions per mile.

 

[Regcabguy]

Find someone in your area with a Smarty. They'll need to load a program temporarily into your ecm and then adjust for tire correction. Once you nail that down(GPS needed) unload the program and the tire correction will remain with an '06-'07 5. 9.

 

[DOUGMartin]

Good to know guys. My wife picked up my truck after I had 35's put on it and didnt tell me they said they couldnt fix the speedo. One night on the way home from work a cop was nice enough to pull me over and tell me I was WAY over speed.

 

[sag2]

I have an 06 truck, put 35s on and tried 4 different Dodge dealers here around home to fix my speedo errror and the 1st told me he could only put in the stock tire sizes. He asked $35 to "get it as close as he could''. I thougt I knew it could be done from the reading I had done here and on TDR so I searched this topic and read through many questions and answers about this to confirm what I thought. So I call 2 more dealers, different from the first four I tried previously, this morning, the 1st has no idea and the 2nd gave me the only stock tire can we do deal until I asked if they have the drbIII scan tool and told him I knew this can be done from reading on this site, he then relented and said yes it can be but you have to work some math formulas and blah blah and I said you need the rev. per mile of the tire and he said $90 and he could get it close but not perfect. What is the deal with these people? #@$%! I am stymied. None of the service people I have talked to seem to give a #%! about even trying to really help you solve a problem. I wouldn't mind paying $90 to get it done but I would expect some confident experience from the guy doing it to get it right. I am simply bumfuzzeled!!:-{}

What's with these people is your truck is an 06 and uses CAN BUS to communicate. The DRBIII only works on trucks up to 2005, and you could choose "other" using the DRBIII to program non stock tire sizes. Your truck uses StarScan/StarMobile/wi-Tech and there is no provision to update from the stock tire sizes.

Don't blame the dealer, he can't make the tool do things it wasn't programmed to do.

I won't even get into why the factory doesn't want dealers changing tire sizes, but most of it is the result of emissions regulations that require the vehicle to be certified as a package. The aftermarket does not have to play by the same rules as the OEM's, so that's why Smarty and others have programming available.

 

[seafish]

Find someone in your area with a Smarty. They'll need to load a program temporarily into your ecm and then adjust for tire correction. Once you nail that down(GPS needed) unload the program and the tire correction will remain with an '06-'07 5. 9.

Hey Dave, do ya happen to know if the 2005 will hold the correction, and if not, why??

 

[cojhl2]

Rotations per mile

The easiest way to do that is to mark the tire at BDC then roll the PU until the tire rotates 10 revs or so. Then use J Baxter's calc process to get rotations per mile. You will also need to know your axle ratio or count drive shaft rotations while you are rolling the PU.

 

[EricBu12]

I have 265 75 17 stock, it read 1 mph fast than actual. . I put on my 245 70R 19. 5" Towing tires. . now it reads 1 mph Slow. . Think I'll leave it alone

 

[1972JohnBoy]

Thank you all for sharing your experience and knowledge. I am thankful for this site for thoso two things and the good people that are willing to spend some of their time and help those of us that are going through our learning curve. I guess I will try to find someone with a Smarty and go that route. I would buy one but I am waiting on the Edge Juice CTS which is supposed to be available for Dodge Trucks this summer. I called the Edge people last month to ask why they sell them for GM and Ford and not Dodge and thats what I was told. I asked about new features, speedometer correction included and he wouldn't say for sure but sort of hinted that that capability might be in this one. I like this because of the multiple guage feature and just one monitor to mount instead of several guages. I know from here and DTR that the Smarty is the most popular programmer and I don't recall ever reading anything negative about it. Thanks again to all, John

 

[roadking]

Find someone in your area with a Smarty. They'll need to load a program temporarily into your ecm and then adjust for tire correction. Once you nail that down(GPS needed) unload the program and the tire correction will remain with an '06-'07 5. 9.

when i remove the program it brings all back to stock . but i have 315's w/progran it works and speed is rite

 

[juicedcummins]

The only way to properly set the speedo is with a gps. I adjusted my smarty to make the speedo the same as my gps.

If you go by the revs per mile etc the manufacture states it will still be off.

You hear all the mileage claims over and over but most mean squat because the speedo is not accurate.

 

[brods]

Hey Dave, do ya happen to know if the 2005 will hold the correction, and if not, why??

No, I wish it did. As for why not, you have to ask the Smarty people.

 

[CDonaldson]

The 2006's were the first trucks that you couldn't go to the 'other' category and enter tire/speedo numbers by revs per mile because of the CANBUS.



My 2006 holds the correction, guess it must somehow write somewhere like firmware?? Maybe similar to how a flash is held in memory modification??



Smarty does the trick. I am sure other programmers will also, what I don't know is if the other programmers 'leave' that setting when you off-load the programmer,butthe Smarty does.





CD