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Re-gearing misconceptions and questions

Iwillnc

Well-Known Member
Messages
236
Location
NC
I’ve searched just about everything on regearing these trucks, going 4.56 or 4.88. I’m currently running 37”s but they’re the small KO2 35.6 inch 37s. I plan on going to a tire size closer to true 37 or maybe eventually 38s(37.5ish)

Technically 4.56 would be fine with 37s and would only be a very few RPMs out of range for 38s, no where as bad as it currently is with the 4.10s now.

I’ve read just about every review, unfortunately no one seems to have experienced both sets. Everyone that gets 4.56s seem to be happy but wish they went to 4.88s, but I never seen any word of issues with the 4.56.
Everyone that goes 4.88s are very happy, even those still running stock size tires, but I also hear of some with 4.88s blowing them up due to the smaller size of the gears. I also heard one poster state that their transmission shifted more often above 75MPH, this makes no sense half of the purpose of the gearset is to get rid of the unnecessary shifts and transmission strain? I am lost on what that could be?

I’ve planned this for a long time and always assumed I would go 4.88s without a second thought, but now that I’m actually getting money together towards it, I’m having second thoughts.

Will 4.88s be okay on the highway? I like to drive 80MPH but I don’t want to be running 2,800 RPM to do it.
Will I destroy 4.88s?
Will RPMs be too high for daily driving?
 

Sam!

Probationary Member
Messages
2
Location
US
I have done 4.88 to two former trucks, A Dodge Ram 1500 and a Toyota Tacoma Gassers. everything about the change was positive and worth it, not once never considered going back or different like (4.56). yes it eliminated OD in/out. Trans ran cooler, towed easier, 75 mph RPM was perfect. more take off power when needed. and now that i have an H2 i have been thinking of doing this change based on how heavy and big these are then i will be towing a SXS on a flatbed dual axle trailer and pretty sure that will be the breaking factor for the change.

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High Five H2

Well-Known Member
Messages
1,574
Location
West Texas
is 4.88 geared lower than factory with the bigger tires? I wanted to go 4.56 with my 40's which would put me a hair below factory gearing with the 6 speed, but maybe 4.88 would be better.
 

Zach

Mall Crawler
Messages
4,812
Location
So Cal
I’m running 4.88’s on 37’s, have had them for years. Way way happy with them. Before the gear swap, the trans would search for gears on inclines. Since the gear swap, no issue with that. Sometimes, I do have to lift on the accelerator pedal to get it to shift. No biggie. On the highway, 80 MPH no problem. If swapping gears, you will need to get a tuner to adjust for it. As far as, the teeth being to high, ehhh! I took out the ring and pinion wheeling it. Then destroyed the rear diff the next time after breaking teeth off, part of that was driving it off the trail to get to the road for a piggy back ride home on a flatbed [emoji1783]. Really can’t say it was the gears that gave out. The conditions probably had play in it too. With that, I’d still make the same choice with 4.88’s
 

Iwillnc

Well-Known Member
Messages
236
Location
NC
Sounds good on the 4.88s, how about towing experience with 4.88s? RPM @ 80MPH?

As long as the engine is not screaming at 80MPH on 37s I think the 4.88s is going to be it.

Also not that it makes a huge difference but I’m getting 10.5MPG with the 4.10s and 37s, I don’t want my MPG to drop to 8 with the 4.88s.
 
Last edited:

Zach

Mall Crawler
Messages
4,812
Location
So Cal
Sounds good on the 4.88s, how about towing experience with 4.88s? RPM @ 80MPH?

As long as the engine is not screaming at 80MPH on 37s I think the 4.88s is going to be it.

Also not that it makes a huge difference but I’m getting 10.5MPG with the 4.10s and 37s, I don’t want my MPG to drop to 8 with the 4.88s.

Really haven’t towed, well at freeway speeds, only towing is with a tow strap[emoji1787][emoji1787]
80 MPH, think around 2500 RPM’S. Will verify tomorrow on the way to work.
Currently around the 9’S for gas mileage. But, the extra weight with add ons, front end higher, etc etc...

Plus, if you’re worried about gas mileage, shoulda bought something else HAHA
 

Iwillnc

Well-Known Member
Messages
236
Location
NC
I’m more worried about range, at 10.5MPG I already have to stop and fill the tank long before I need to pee, dropping the fuel economy by over 20% would make that much worse.

But yes if you get a chance let me know those RPM, 2500 doesn’t sound too bad.
 

MaxPF

AGNTSA
Messages
1,394
Location
The dark side of the globe
This should help you decide:

http://www.grimmjeeper.com/gears.html

Your t-case isn't listed, but don't worry about that since you aren't calculating crawl ratio. Just choose 4L60/4L60E for trans, none for t-case and underdrive, 4.56 for gears, and 37" for tires. Scroll all the way down to "Road RPMs at given speed in miles per hour" and choose 45, 65, and 80mph. Then click the bottom "Copy Form ->" button, scroll back up to gear ratios, and enter 4.88 in the second column. Then scroll back down and you can see RPMs at the road speeds you entered with the different gear ratios you chose.

FWIW, I already did the calcs for you, and assuming true 37" tires with 4.88 gears you will be turning 2016 RPM at 65 MPH and 2482 RPM at 80MPH. By way of comparison, a stock Alpha with 265/75R16 tires and 4.10 gears turns 1980 at 65 and 2437 at 80. So, the difference is only 45 RPM at 80MPH. That makes 4.88's the best re-gear for 37's on an H3 if you want stock RPMs vs MPH.
 

Iwillnc

Well-Known Member
Messages
236
Location
NC
Thanks Max, I’ll have to look at that in more detail this afternoon, it should be easier on something other than my phone haha.
 

MaxPF

AGNTSA
Messages
1,394
Location
The dark side of the globe
Greg! Good to see you here, thanks for the help. FYI, he's here for an H2 vs. an H3

Thanks Alex! I didn't notice that I was in the H2 forum. In that case, I would say either 4.56 or 4.88 would work. As you know, Todd has a 6.0 in his Jeep with a 4L80E and 4.56's turning 37" KO2's. It's fine, but he could use either more gear or a better cam. Were actually looking into one of the cams distributed by Summit racing that is designed to give more torque at lower RPM's, which is where Gen III and later engines are really lacking IMO. I still haven't talked him into an LS-injected 502 big block :deal:
 

Iwillnc

Well-Known Member
Messages
236
Location
NC
Update, I called two well known local shops to get a quote on the work, my quotes range from $1,900 to $4,800, yea that’s not a typo. I’m assuming the latter just didn’t want the work they are a big off-road shop, the former is a very well known axle shop that I’ve always heard great stuff about.
 

Zach

Mall Crawler
Messages
4,812
Location
So Cal
Update, I called two well known local shops to get a quote on the work, my quotes range from $1,900 to $4,800, yea that’s not a typo. I’m assuming the latter just didn’t want the work they are a big off-road shop, the former is a very well known axle shop that I’ve always heard great stuff about.

Sorry for the lag, around 80MPH mid 2500 RPM’s on freeway.

If I remember correctly, been quite awhile since I did the swap. Want to say it was like $2400, and with that, added a Eaton e’locker in the front diff.
 

Iwillnc

Well-Known Member
Messages
236
Location
NC
Alright I didn’t think the $1,900 was bad, I’m sure there will be extra work putting new bushings I supply in the front axle and new seals all around, but it’s all in the ball game.

Thanks guys
 

Sam!

Probationary Member
Messages
2
Location
US
Alright I didn’t think the $1,900 was bad, I’m sure there will be extra work putting new bushings I supply in the front axle and new seals all around, but it’s all in the ball game.

Thanks guys
Is it getting done?

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Iwillnc

Well-Known Member
Messages
236
Location
NC
It will in March/April, I’m getting my mind made up on gearset to best suit me and I still need to order my front diff bushings to have those installed at the same time. The money is set aside it’s just finding time to get everything together and March/April work best.
 

Rockhound

Active Member
Messages
43
Location
Colorado
Have had both, once you go to 4.88s you are stuck at 38s or bigger, very nice as long as you stay with the larger tire,
 

CostaMesa H2

Probationary Member
Messages
4
Location
Costa Mesa, CA
Hi Everyone, I've got a H2 that has 37's so I'm going to install 4.88 gears in about a week and get it re-tuned / programmed for the gears. I'll post a picture of it shortly
Screenshot_20221101-231408.png
Screenshot_20221101-231444.png
 

Iwillnc

Well-Known Member
Messages
236
Location
NC
Hi Everyone, I've got a H2 that has 37's so I'm going to install 4.88 gears in about a week and get it re-tuned / programmed for the gears. I'll post a picture of it shortlyView attachment 31143View attachment 31144
There are other thread where I posted later but I ended up going 4.56. At the time it just made more sense since I had smaller 37s and did a lot of Highway, it boosted my average MPG up to 12.5 and made 13-14 easy depending on drive.

Truck drives great at 80MPH, absolutely fantastic RPM is great not too high but plenty enough to pull without ever shifting. I never planned on going bigger than 37s. And now with 37s increasing about 30% in price over a couple years ago it was probably the right decision - I just don’t do enough off-roading to justify the cost of moving up to 38s+.
 

Booch

Active Member
Messages
30
Location
Maidens Virginia
I'm debating doing this in the next few weeks so you went up to 12.5 MPG on 37s on the H2 ? My Tire size is 37x12.50 x17. I won't be going bigger so I've been debating on 4.56 or 4.88. Max I tow is around 3K and I'm trying to improve the current power I have, and the transmission /overdrive searching I have with 4.10s
 

Iwillnc

Well-Known Member
Messages
236
Location
NC
I'm debating doing this in the next few weeks so you went up to 12.5 MPG on 37s on the H2 ? My Tire size is 37x12.50 x17. I won't be going bigger so I've been debating on 4.56 or 4.88. Max I tow is around 3K and I'm trying to improve the current power I have, and the transmission /overdrive searching I have with 4.10s
It’s frankly a hard decision, with my 4.10s and 37s frankly I found the truck nearly un-drivable at high way speeds every little hill or gust of wind caused it to kick down the trans and it was gutless. I hated driving the truck on the highway.

As for 4.56 vs 4.88s you can find a lot of opinions on 4.88s and only a very small number of us that did 4.56. I can’t tell you the right answer only what I did and my view point.

With my smaller 37s (KO2s) 37x12.5r17 the 4.56 make the truck drive better than stock 4.10/315s. I can feel a little more torque, if I don’t go crazy I can pass a car in 4th gear on a two lane without down shifting. I can get on the highway and set the cruise control and it takes a pretty decent hill to make the trans downshift. 80MPH is around 2,450 RPM which is perfect for my imo.

More gearing is always going to feel better but I was worried 2,600+ RPM at 80 with 4.88s would just feel excessive and eat into my MPG. By all means if you rarely exceed 70MPH then 4.88s are probably your best choice.

As for MPG I recently moved into the city and my driving is 100% stop and go so I get about 11MPG but I drive the piss out of it.
Back country roads are easy to average 13.5 just cruising at 60-65MPH. Overall if your gentle (such as when I was breaking in gears) I was getting 12.7 and once that process was over and I didn’t mind getting into it a little more I was around 12.5 average. I’m happy with all this.
 

Iwillnc

Well-Known Member
Messages
236
Location
NC
Now with all that said you won’t notice a huge difference with 4.56s, the truck will just feel “right”. It will feel like it should have felt from factory IMO. If you want to feel the money you spent on gears I think you may be more satisfied with 4.88s.

The 4.56s just feel natural. If you still want a little more a tune should get you all the way. That’s what I would like to eventually do just for the fun of it - not because I feel I need more.
 
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