Tire size adjustment

[JPereira]

If I change to a larger tire can anyone with a Smarty or similar device make the speedo correction on my truck? Is that a function that is only locked to the VIN of the owners vehicle? I was hoping maybe someone other than a dealer could help me out when I change tires on my truck.



I have 67k on my 2004 and have never been to the dealer other than when I went to buy transmission filters and transmission/differential gaskets. (Which I did not even have to use) Would be a shame to have to start now. .



If I need to have a dealer make this change does anyone know what they typically charge?



Maybe I can use this as a good opportunity for a purchase of a smarty.



Jeff

 

[JApol]

I have had 4 things done at the dealer. Turn on daytime running lights, high idle, turn off DRL's and reset for 35" tires. I got dinged on average $45 per operation.



The smarty only updates tire size on the VIN locked vehicle.

 

[p-Bar]

They tried to ding me for 85. 00 for one item that really was under warranty, so it was waived.

 

[JPereira]

If/When I bring my truck in to have the tire size corrected. Do they automatically update the ECM to a current or most recent version? I know there are updates for the reverse/beep horn, white smoke on cold start, etc.



I do not want anything else changed as my truck runs great and gets decent mileage. Fear of Dealer changing the current program in my ECM may be reason enough to purchase a device to do this on my own. I do know a person in the parts department and may try and ask him some of the same questions I am trying to get answered here.



Thanks Jeff

 

[JLovas]

I would just use this as an excuse to get yourself a Smarty. I have a GPS unit on my pickup that I use to check my speedometer, and thus use the Smarty to adjust tire size. If I remember correctly, the smarty will change wheel size in 10th's of an inch, so if your fussy, you can get your speedometer very accurate. Plus, I really like my smarty for the power and relatively cool EGT's.

 

[p-Bar]

The only other update they would do is the back up deal. They shouldn't do anything else

 

[JApol]

Thats when my truck got flashed for the backup alarm. If I had thought about it I would have told them not to.

Remember its a safety recall so they will do it without telling you before hand

 

[JShirk]

It depends on the dealer as to how much you will be charged. Some do it for nothing, some do not. The two dealers in my area both wanted $65 to adjust my revs per mile. I found out that you can change revs per mile with a Snap On scan tool. A friend of mine has one and we changed mine with it for nothing. If you know anyone with a Snap On Scanner, I'd ask them.

 

[JPereira]

JShirk

Do you know what model scanner they had to accomplish the tire size adjustment?

I know 2 people that have Snap on scanner and they did not know this was capable. Could this be a function on newer models or maybe a specific one.

Thanks, Jeff

 

[JShirk]

Jeff,

It was a MT2500 scan tool. You have to go into the ABS menu. In there you can get to the "revs per mile" section and change the revs per mile to what you want. Hope this helps. Jim

 

[JPereira]

Thanks Jim



I will pass that info along as the 2 people I know that have Snap On scanners did not believe that was possible with their tools.



Jeff

 

[WoodJ]

I have 35in. tires on my 2005 and the dodge dealer corrected my spedometer, they charged $90. 00.

 

[JPereira]

Just wanted to update that I did have my tire size adjusted using a Snap-On scan tool. Not sure of the model as he had 2 different scan tools. It is in the ABS section and I think it was labeled "Tire Count". Speedo seems much closer to correct. I am going to use a GPS to try and get an exact measurement then I will just need to purchase a Smarty to be able to get it perfect.



Just thought it was good info to know you do not need the Dealer to ding$$ you for adjusting tire size.



Jeff

 

[kd5hge]

A buddy of mine owns a trans shop here in town. We used his MTG2500 to change the tire count. We played with the settings as described above. I have 325/60/20 tires. When we read the settings from the truck, it had the stock 245 tires, tire count was 400. At those settings the speedo was slow by 16%. We changed the tire count to 500 and now it is fast by about 16%. I know that the new tires rotate 586 times per mile. So, with that said, anyone know what the tire count actually measures? Or do I have a setting wrong somewhere else?