ramtradxb

I have an 06 2500 that came with 265/70-17's that I installed 325/60-20's on - a change in dia of between 3 and 4 inches, and rev's/mile of about 60 less. Took to dealer (very few even want to attempt) to get recal'd so Speedo/Odo won't be 10% off, and since the tire sizes the new CAN tool allows are very limited (and not big enough), we selected the 3.73 rear ratio instead of the true 4.10 ratio it has - which from my knowledge should change speedo/odo about ten percent. But, after going back in tool to verify it now had that ratio, took truck out and speedo/odo are still off by same amount. Why wouldn't ratio change show up in speedo/odo, and what can I do to change for larger tires. (for those of you who don't know, computer changes for '06 mean DRM and it's rev/mile input no longer talks to ECU)
???
B

MedicShawn

Try contacting J Body he is a Dodge mechanic. But for my truck you have to go into the menu where it lets you input the revs/mile or Whatever. It's called resetting the pinon factor I believe. Changing the ratio didn't work because of how the computer calculates mileage.

J BODY

Changing gears has never effected speedo input since they started using the RWAL sensor as the input for the cluster to determine vehicle speed. It's the tire size that comes into play. While I can do this with the DRBIII on sec gen trucks by going into the ABS, I have not yet played with anything on the 06. Starting in 06 diag uses the STAR scan. I would be glad to go play with one on the lot, but to say I'm buried right now is a huge understatement. I have a stack of RO's I haven't even looked at yet.

ramtradxb

FYI...As some of you know, the '06's use a totally different unit than the older years to "talk" and program (with the STAR CAN program). The new program doesn't allow rev's per mile inputs - you have a select (few) sizes of tires to enter, but they're not significantly different from the stock size. More than one dealer has said to change the pinion gear ratio, since the sensor uses that ratio when converting the input from the sensor on the rear diff to calc speed and mileage - but as you guessed, it doesn't work.
That would tell me (a lay person) that the sense is coming from the ring gear rotation then (which is what JBody may know), since pinion rotation and ratio to the ring would indeed change indicated speed and odo. So - how do we get a larger tire size than the 275/60-R20 entry which is the largest (with the least rev's) inputted? And, since there's a secondary speed indicator on one front wheel to back up the rear for ABS in case of a failure, I'm assuming a tire change affects all?
And, would I have harmed anything by changing the ratio (pinion gear) entry from 4.10 to 3.73 now? (in reality, since the tires are larger and the effect on everything from them up is a change in ratio, it would SEEM that the change to 3.73 would be a wiser move - but...?)

yelloz28

Has anyone had any luck figuring this out??

mikmaze

cheap gps unit on the dash..... done. might not work well in tunnels ( disclaimer )

Brock

Not yet.....tried over and over. so far the only thing is to find a tire on the list that gives the same overall revs per mile as your tires.... i have 295 Nittos...and someone recommended like a 255 or something to get the ratio right and rpm right or close. The 295 is close to the 285 they offer so just left it at that and is a little off.

anyone know if the upcoming Smarty or the current SUperChip actually can change tire sizes for odo as claimed? ..and how do they do it.