2015 R/T - Gear Ratio Change - What Needs To Be Re-Calibrated? 3.06 to 3.92.

[2therock]

A 2015 R/T - Just had a Gear Ratio Change from 3.06 to 3.92 - What Needs To Be Re-Calibrated?

What happens if nothing it changed?

Thanks

[2therock]

Bump?

[THXDEAR426]

If I recall correctly, the 2016's and newer take the speed from the front wheels and not the rear. You should just be able to swap and go without any programming needed.

[2therock]

I hope you are correct. Some how with all the different parameters involved in both the ecm and pcm just for shift points, who knows.
We are looking into it on another forum and the vehicle owner who made a swap is experiencing odd trans behavior one being weird down shifting.
This is why I ask. Thanks

[THXDEAR426]

I also have done some reading on another forum i belong to and it seems that the newer cars don't seem to care what the rear gears are...which is totally cool. Best of luck and hope you don't have any issues.

[Jay@HAP]

you should use the scanner to change the gear ratio, if not you will get an incorrrect trans gear ratio and it will throw it into limp mode. I just did a 15 Jeep that had deeper gears and big tires and it would go limp till I changed the ratio and tire size.

[Blue Bee]

you should use the scanner to change the gear ratio, if not you will get an incorrrect trans gear ratio and it will throw it into limp mode. I just did a 15 Jeep that had deeper gears and big tires and it would go limp till I changed the ratio and tire size.

But you are also talking the difference between a NAG and an 8-speed car Jay, I haven't done any 8-speed rear gear ratio changes so I can't say what will need to be done. Shift speeds are based on output RPM so really they shouldn't need to be changed, as output RPM and engine RPM will correlate no matter what's in the rear.

[JoshCP527]

8 speed stuff does not require the change..... I have heard of some odd stuff when major gear changes happen but on the two cats it was just a change to 3.0 something. They have floated around that going to say the 3.9 some thing would hurt the trans in lower gear changes do to not staying in the gears long... it was not very informative but was mentioned it happened to some. This is very vague but with the two cats we did the regular swap on we did not change a thing other then the regular stuff to up shift rpm that would work the same on the stock rear gear ratio.