Need some info about Ram 2500 with the Cummins engine

Shamus M · May 31, 2013

well I just so happen have 2011 crew cab cummins ram with 4:10 gears and upgraded bfgoodrich tires from the factory sittin outside and my gps reads the same as the speedo. 4:10s is a major difference than the basic gears as far as speeds. I can get video up tomorrow . I know they didn't just do a tune special for me. If your statement were true, there would be a 20mph difference over base gears

PoorPlowboy · May 31, 2013

You're presumptuous. Just because you have 4.10s/upsized tires and an accurate speedo doesn't mean mine with 3.73s and small standard ties is accurate. You just confirmed exactly what I was saying anyway. The OEM donuts result in an inaccurate speedo. By your own assertion, you have the optional larger tires. What did I say that is so hard for you to understand?

Shamus M · May 31, 2013

PoorPlowboy said:
You're presumptuous. Just because you have 4.10s/upsized tires and an accurate speedo doesn't mean mine with 3.73s and small standard ties is accurate. You just confirmed exactly what I was saying anyway. The OEM donuts result in an inaccurate speedo. By your own assertion, you have the optional larger tires.

oh Christ, I give up. you can lead a horse to water but you cant make them drink it

PoorPlowboy · May 31, 2013

You calling me a liar isn't going to change reality. I verified it myself on my own truck. Good day.

Nooodles · May 31, 2013

PoorPlowboy said:
Not always. How many tire options? You think they reprogram the PCM for each one?

i just talked to my dad and he says that they do calibrate each one and they do them in shifts as what they are running that day. they do a run of specific spec trucks and calibrated for that run. He worked in Detroit in the line He said you are probably just being a troll looking for silly fights
louie

Peacock · May 31, 2013

They are absolutely all calibrated for the tire/gear ratio.

Code54 · May 31, 2013

That is correct - the ECM is programed for each option (remote start for example wont work without a reprogram). If they run your VIN (at least the 2012 and newer for sure) they can tell every option that came from the factory up to and including the step bars on the side. It also can be reprogramed for different factory size tires but not over anything offered by the factory. For example the Power Wagon has a larger stock tire than several other 2500's so that is the largest stock size you can program for. I run 34's and Im a few miles per hour off but not too much for me to worry about - before I upsized my speedo was right on (checked via radar several times). Now if the DEALER changed the tires and didn't reprogram it the speedo could easily be off.

vrmnthntr · May 31, 2013

Mine has 3:73 gears and came with 245/70/17 tires. Got a 265 tire and now at 50 mph I am actually going 3 mph faster than it shows.

SPYDERLK · May 31, 2013

Peacock said:
They are absolutely all calibrated for the tire/gear ratio.

Well then it is unfortunate that they are all not calbrated right. I have never seen a stock tired vehicle with a speedometer that did not read optimistic. Go up a tire size to get it to read right.
larry

Danscaper · May 31, 2013

SPYDERLK said:
Well then it is unfortunate that they are all not calbrated right. I have never seen a stock tired vehicle with a speedometer that did not read optimistic. Go up a tire size to get it to read right.
larry

unfortunate for you and the other guy. "sorry officer but I went with a different gear ratio and wheel steup from the factory so my speedo is off". Good luck buddy. Give me a break.