Alright, this question is for anyone running an automatic with 4.88 gears. What rpm does your engine turn at hwy speeds? Please give specifics as to tire size and actual speed. I'm thinking of running this ratio for a while with my 33"s. Toyo M/Ts are notoriously heavy so I'm thinking it might not be to bad. I'm going crazy running 3.73s waiting for the 4.56s.

 

come on I know alot of yall have 4.88s, share your experience.

 

You should get a reply soon

 

Um...you do not need people to post their rpm...



Just take your old tire size, and your new tire size...and the difference in percentage is the same percentage your RPM will change for the tires.

Do the same for the gears...the percentage difference between 3.73's and 4.88's, or any other gear for that matter...will be the difference in RPM change for the gears.



So - Lets say you are running about 2,000 RPM at 60 mph with the 3.73's...

If you swap on 4.88's...you will raise your rpm by ~ 23.6%

2,000 + 23.6% = 2,472 RPM at 60 mph

If you went from 32's to 33's...you DECREASED your RPM by ~ 3%, or dropped from the 2,472 RPM all the way down to 2,398 RPM...a whopping 74 RPM drop.

So - with the 33's and 3.73's...if you cruised at ~ 2,000 RPM at 60 mph, and you swapped in 4.88's and 33's...you'd RAISE the RPM to about 2,400 RPM.

So, your mpg would drop, but, your passing and aceleration would be better.



If you did the same thing above, but for 4.56's instead of 4.88's...

You'd raise the rpms by 18.2% instead of the 4.88's 23.6%...

So on the 33's, you'd be cruising at 60 mph with ~ 2,293 RPM, instead of the ~ 2,400 RPM the 4.88's and 33's gave you, etc.

Hope that helps.

 

I can't help you with 4:88s but maybe I can help you anyway. I have 35s with 5:13 and a automatic and I can tell you don't want anything less than the 4:88s for sure. The 5:13s were an improvement but not anything I would say wow! about. Again don't get me wrong it helped but there's no way I would have been happy with anything higher. Hope this helps.

 

the formula above works close, tested in a buddys auto today not to shabby, 4.88 with 35s works well with auto, not very impresive unless you reflash the computer and get everything such as shifting etc.. back to read right gears and tire size, once speedo and tranny shift points set, runs better than stock, slightly over geared for highway....if you plan on upgrading bigger tires 4.88 will be the ticket, for my jeep with 6spd and 37s i dont feel the need for anyting higher 4.88, i do alot of road trips just want stock performance back, but that is my preference not bashing 5.13s, i ran mine for a year with 4.10s and 35 great on road trips, but 37s and 4.10 work, but can't tow much without banging through gears on inclines..

everybody has a picture and a direction that they would like to go......

 

Here's what I'm getting at, at 70 mph I'm turning around 1800-1900 rpm with 3.73s and heavy 33" tires. This is with an auto and the overdrive not turned off (no wind or hills). The tranny shifts down constantly trying to maintain speed. When I turn the overdrive off, my rpms are closer to 3000. Plenty of power, but economy is out the window. I do more hwy driving than anything, and if I want to keep the jk then that's where I need my best performance. I think If I could get around 2200 rpm at 70 mph everything would be fine.

 

Yea, I'm starting to lean towards the 4.88 option. I'd like to have more power, I used to love my cruise control I'm just trying to get all the info I can before I take the $1500 plunge.

Hell, I can even go back to the regular setting on the hypertech and save some cash at the pump!

 

https://www.jk-forum.com/forums/modified-jk-tech-2/speedo-calibration-36586/

check out this other thread...

 

checked it out, but don't know what I'm supposed to take from it. I recalibrated my speedo with the hypertech already.