REL1203

so i decided i dont want to do 35"s now, and since this is my daily driver (20 miles all highway each way), i am gonna stick with 33"s. I have 3.73 gears, and hate driving it at 60-65 because it has no power and when it shifts, it only accelerates and i just want to maintain. This is our travel car alot to (going up mountains, to the beach, ect..) so I do alot of highway driving. While my HyperTech Max Enegery helped aroudn town, doesnt do anything on the highway for me, so what are my options for a Regear with 3.73" Automatic 4dr. 4.56? 4.88? 5.13?

Let me know what you think, and would love to hear some real world experience.

Thanks

Calypso

4:88's IMO UNLESS you plan to go to 35's in the future and if so, then I'd wait on the gears and go 5.13's.

redrockin7

I'm in the same boat as you... except my commute is 25 miles each way most days, sometimes up to 45 miles one way. So, 35s are on the backburner for a while until I get another DD I like better than the JEEP... probably not likely for a couple years.

In any case, I plan to run some 295/75/16 tires on 16x8 wheels in the very near future and have been contemplating gears. The 295/75/16s measure up at 33.5" as opposed to 33" (and most 33" are probably more like 32.7 or 32.8"), so I think I am going with 4.88s. Plus i plan to tow a trailer with kayaks/bikes/etc. and occassionally 4-wheeler. And if I ever DID decide to go to 35s I could get away with 4.88s probably. What really sold me though is the following analysis (beware this is done via online calculator and not "real life" experience so to the extent the calcs are off it could be different). It looks like with the 295/75/16s and 4.88s I would be sitting around 2500 RPM at 75MPH. Seems perfect to me, but what do I know?

I did the analysis of the gearing/RPM/speed using an online calculator and pretty sure I got all inputs correct (if the .69 OD ratio is not correct though I may have problems):


I posted the RPMs at various speeds from 25-90MPH. The 4.88 runs a little higher RPM than the 4.56 at highway speeds (100 RPM or so until 90 where its 200RPM higher) as expected, but I don't think its that drastic that it would kill MPG or make the JK scream for mercy?

I would be interested to hear "real life" stories as well b/c although everyone claims 4.56 gears are best for 33s and then 5.13s for the AT, I have never seen anyone with 33s and 4.88s?! In fact, I rarely see anyone with 33s and 4.56. Most people don't regear for 33s then just go 5.13 when they go to 35s. I plan to stick 33" - 34" for a while, though so I don't want to go 5.13... but don't want 4.56 too small. Anyway enough blabber.

Heres the analysis:

3.8L, Auto Trans, 4.88 Gears, .69 OD Ratio
Assuming 33.5" Tires (295/75/16)

MPH RPMs in OD Not in OD
25 845
30 1013
35 1182
40 1350
45 1519
50 1688
55 1857
60 2026
65 2195
70 2364
75 2532
80 2701
85 2870
90 3039

3.8L, Auto Trans, 4.56 Gears, .69 OD Ratio
Assuming 33.5" Tires (295/75/16)

MPH RPMs in OD Not in OD
25 789
30 946
35 1104
40 1262
45 1420
50 1577
55 1735
60 1893
65 2051
70 2209
75 2366
80 2524
85 2682
90 2840

Difference between 4.88 and 4.56 with 33.5" Tire

MPH RPM Diff in OD
25 56
30 67
35 78
40 88
45 99
50 111
55 122
60 133
65 144
70 155
75 166
80 177
85 188
90 199

*Keep in mind this is assuming OD has kicked in. I guess if you wanted to know non-OD numbers you'd have to divide these by .69 and they would be a bit higher. But I think the primary concern is at highway speeds in OD...

REL1203

Great analysis..... Someone on here has to have regeared with 33"s

nthinuf

Just a side note for the analysis above. I have 295/75/16 Terra Grapplers, and they measure out right at 32" with current load and inflation. That 33.5 is the manufacturers measurement, so take it for what it's worth...

redrockin7

Thanks for the info - I would assume load bearing tires are always shorter. 32.8" manufacturer spec tires would probably end up at 31.5", 35.0" manufacturer specs probably end up being 34", etc.

Probably does mess with the calculation a bit though. I think 4.56 is the safe bet with 33s, but I still can't see a huge difference to 4.88.

I know there are people with 33s who have re-geared, but far less than those with 35s and 5.13s... And I personally have never saw a person with 33s and 4.88.

Outdoors

4.88's it's not that many more RPM's then the 4.56's and on any hills you'll be happy you went with 4.88's, if you live and wheel in a flat area then I might recommend 4.56's w/33's.. I had 4.56's on my LJ with the same auto and it was "occasionally" to high geared for me to keep in O.D.. But I live in the PNW. I will go 4.88's on my JK for sure.
Btw, w/33's and 4.88's you will be turning only "21" RPM more then 5.13's w/35's... It seems to be the sweet spot.
Good luck either way..
Plus you could survive with 35's as well, and you'l enjoy them with the 33's.

redrockin7

Just found this in another thread:

"I just got my 4.88 gears in my JK.

JK X, 2 door, 6 speed, 33" ProComps, 2" lift, Hypertech, air intake, exhaust.

It runs better than new! 70mph @ 2900 rpm , take off in 2nd gear, never shift down for hills or to pass."

Seems like he likes them, but appears the RPM are higher "in life" than this calculator? 2900 RPM seems a bit high to me but maybe I could get used to it. I just wonder how much lower 4.56 would really be...

REL1203

That number, i am can almost gurentee, is with OD off....

the JK OD saves about 30%, which would bring it down to 2100ish, much more inline with what calculations say...

redrockin7

Another good thread that seems to say 4.56 is the way to go for 33s:

https://www.jk-forum.com/forums/show...ighlight=Gears