OK Fellas, answer me this. I just installed 4.56s and 35s. The 4R100 has a 0.71:1 overdrive ratio. I checked on Randy's Ring and Pinion web site to use the rpm calculator to see where i should be at with this set up. The calculator says that I should be spinning at 2020 RPMs. But my truck is spinning at about 2350. Why would I be spinning over 300 RPMs more?


Also, my speedo should be correct because I got a SCT Xcalibrator II and set my Revolutions per mile at 600 which is standard for a tire of this size.

 

Disregard this question. I figured it out.

When I first got my Xcalibrator II, I installed a custom tune into my truck and adjusted for the 35s.

They sent me another tune a couple days later and when I installed that tune I wasn't given the option to adjust my tire size.

So basically, when I installed the second tune it erased the first and therefore erased the speedo calibration. Thanks and sorry for the confusion.