• Notice for iPhone users: DO NOT use the image size reduction option when uploading photos to the forum. This causes portrait images to post as landscape. We have added a warning to the image insert pop-up as well.

New gears

*JOKER*

*JOKER*

Basic User
City
Norfolk
State
VA
Since my move to NJ, I've been averaging about 40 hwy miles a day on my 8 and the fact that it lugs badly in overdrive has never been more apparent. In other words, I need to change my gearing.

I run 75 mph (@ 2500 rpm in 4th gear) with 35" BFGs and 3.73s. In OD, I hardly get 2000 rpms while running 80 mph. This has never been an issue before, as it only saw trails and "around town" use. My 1st gear has always allowed me to crawl pretty slow (even in 4 high) and as a result I've always cycled from 2nd through 4th gear on the street. This highway routine, however, requires a bit more tailoring.

I know this is no more than math, but I don't know how to calculate what diff gears I need to run 75 to 80 mph between 2500 and 3000 rpm in OD. 4.10? 4.56? 4.88?!

Oh yeah...let me add that I plan on going back to 33" tires soon.:D

Help?
 
Last edited:
Gears

Joker,
According to my chart, for 33" tires @ 65mph, the 4:56 gears should put you at about 3018 rpms. Subtract 15-30% for overdrive. Hope this helps - Dwain
 
Gears

Muchos Gracias, Dwain. That should be just right! By the way, what equation did use to give you a solution without the tranny's output ratio? Thanks again.
 
4th gear in a 5 speed is a 1:1 ratio in every 5 speed that I know of. I'm sure that is how he figured it out. The overdrive gear (5th) tends to change a bit depending on the transmission, but is usually around .70.

Kyle
 
Ratio

Joker,
I can't claim any credit for calculations. I have a chart that I got from a parts house. Apparently, CJ8RockCrawler is dead on though. The chart is based on 65 mph and a 1:1 gear ratio. It also give a "simple formula for finding a new gear ratio from stock when changing tire sizes": New Tires over Stock tire size=%of change X original gear ratio = new gear ratio.
 
Last edited:
You must log in or register to reply here.
Back
Top