I have an 86 cj7 with 35 inch tires, 258 engine, T5 tranny, and a dana 300 with a twin stick shifter. Right now I have 3.25 gears and I would like to change them to 4.56 or 4.88. I still need to go around 60mph but I don't want the engine to be at red line. I also want to just use 4th gear as the standard because I would like to change the tranny to a 4 speed. Does anyone know if 4.88 will do the trick or will I have to go with the 4.56s? Also is one set better than the other?

Thanks,
Bryan

I currently have 3.55 in my 89 YJ. I have 33 inch tire and converted to a 3 speed automatic from 5 speed. The output for my auto 3rd gear is 1:1. Basically, in a manual 5 speed the 4th gear is 1:1 and also for a 3 speed auto. If you have a 4 speed auto (4th is overdrive) then 3rd gear will be 1:1. With my setup (3 speed auto) I am doing about 2500 rpm's at 60 mph and 2700 r's at 65 mph. I have a Gear Ratio Guide for Larger Tires (4 Wheel Parts Performance Center 2002 Catalog). It says this: "This chart is based on 65 mph and 1:1 gear ratio, on a manual transmission (4th gear). Please note: If you have an automatic trans the true RPM will be higher than shown, because some slippage will occur in the trans and torque converter. With overdrive, your RPM's in overdrive will be 15-30% less than indicated, depending on the vehicle".
Here are some of the numbers for 35 tires:
For reference to your current setup. How this compares to your actual rpm's is up to you
3.21 - 2003 rpm
3.31 - 2065 rpm
For your new setup
4.11 û 2565 rpm (highway driving, good fuel economy)
4.27 û 2664 rpm (daily driver, best overall performance)
4.56 û 2845 rpm (daily driver, best overall performance)
4.88 û 3045 rpm (daily driver, best overall performance)

I am changing gears this weekend to 4.11. My guess is that I will be pushing 3000 rpm. I am still in the green meaning good for a daily driver, best overall performance. My jeep is a daily driver.

Good luck,
4x4david