So we just bought a 2014 JKU and put 4 inch lift kit on 35 inch tires and decided to get some 4.56 gears put in. I do not have my pro-cal yet so I know my speedometer is going to be off. But should my tachometer be off? Strictly basing this on my estimated speed in traffic at around 60-65 miles an hour I am between 4000-4300 RPM's. Is this normal for an a 2014 (automatic) JKU with 35 inch tires and 4.56 gears? It doesn't feel like the engine is really at 4000 RPMs when I'm driving it but I am not sure. Do I just need I just need to wait until I get the pro-cal and this will fix my issue. The only thing I can think of is that it is not shifting correctly. Thanks guys I tried searching but didnt find anyone else with this issue so now im pretty worried.

 

Re-gearing and tire size will not affect the accuracy of the tach, if that's what you are asking.

 

Thanks that's what I thought, so that brings me to the next question are those numbers correct? 60 MPH at 4k RPMs?

 

Sounds like either you need to shift into 6th gear, or they installed the wrong gears

 

Its a automatic.......

 

sorry I skimmed over that. Have you counted the number of shifts to see its in OD? Not recalibrating will screw with auto and the shift points

 

if you do not use a pro cal or other such device to reprogram the computer you will not get an accurate speed/rpm and you will end up in limp mode from every thing I have read.

 

Use the select shift feature to control the shifting, see if 1st to 2nd to 3rd feel right. Then with a gear calculator using the numbers for trans gears, rear gears and tires and a GPS you should be able to verify what gears you have. Bottom line you changed tires and gear and need to reprogram it.

 

Just a thought here. Does it do it everytime you drive? I didn't realize that when in drive, my 2014 has the option to shift up or down, like a slap shift (side to side). Are you somehow shifting it down? I did accidentally and couldn't figure out why i was revving so high.

 

What was your stock gear ratio, and what RPM was the engine turning at 60 mph in fifth gear with the stock gears? You should be able to calculate your engine RPM in fifth gear with the new gears just by doing some math.