I will be taking my truck back to the dealer on monday. i will be having them make an attempt at setting my speedometer correct. I was told by another dealer that they can only choose from a list of sizes and the biggest that they could go was about a 34 eqiv. i have 37's measure 35.5" to be exact. anybody know what they have to do to get it to work correctly. i read on another forum they can change your pinion factor (to 4.11) and then calibrate it for 30" tires. Just looking for a direct answer i may be able to give them so they wont try to charge me for a couple of hours.

Thanks

 

on my 06 they were only able to set it to a max of 285/70/17. This is what i had so no issue for me. I do not know about the pinion ratio. they did mine for free.

 

They have a way to do it with rev's per mile. I do not have the formula on hand, but you measure the circumfrence of your tire, and then figure how many times it turns in a mile. I think 315's are 601 rev's pre mile. There have been other posts on this, do a serch. (lots of help, huh?)

 

Here it is...

measure your tire's diameter in inches
multiply it by 3.14
divide that by 63,360
divide that into 1
result will be the number of revolutions per mile

 

06 is different cant do revs per mile last I know of only a select list of DC stock sizes

 

lot of good I am. That's . Sorry I was no help!
madhat

 

I had to go in for a CEL, and asked about what they could do when I upgraded my tires on this new rig (06 2500 QC): The first thing the techs mentioned was pinion factor.

 

They did my tires I will find out what they did theres only a few sets they can use.

 

i used some calculators and heres what i have found...with the stock to my 37s i am running a 16 percent difference. if they set the pinion factor to 4.11 gears it looks to only be 3% off. if they choose a slightly smaller tire, it should work out perfect. hopefully they can change the pinion to 4.11...they should isnt it an option in the automatic?

 

Unless someone has made a "discovery" on the Star Scan, we cannot change the pinion factor at will anymore. Once again, we all have the EPA to thank....

 

Didnt the 06's come with 4.11 as an option in the automatics?

 

I put 325/70 tires on 10 days ago. It's a wide 35" tire. I got the revs/mile from the tire manufacturer web site and gave it to the dealer. They charged me about $30, and it's spot on according to the interstate speedometer check signs. I've noticed a small impovement in mpg at 70 mph, but not much difference otherwise, just lower rpm's generally.

 

You must have an 04. the 06's can no longer use the rotations per mile. they have a set list of tires to choose from. i am trying to find out if the pinion factor can be changed. if they came with 4.11 stock then i am set. i have heard of guys getting the dealer to program 37's. so it CAN be done. i am just trying to find out HOW.

 

Yes, I have an '04. But I would recommend ignoring all the negative stuff you're hearing about they can't do this or that. Just go into the dealer armed with all the details you can muster about your new tires, and see what they can do. Good luck!