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Re-gearing: Are 4.10's Too Big?

Darky said:
More power will make it move better, you are correct there Milford. Just, don't let it go to your head. However, more power will just brute force its way through the transmission, forcing the transmission to work harder and generating more heat. Heat kills transmissions. Going for a deeper gear ratio moves the stress away from the transmission. Instead, the diffs now multiply the available torque further. Your transmission lasts longer, you have better control in the dirt, and you don't lose out on the highway. With 4.88s and 33s, I spin up around 2700rpm at 70, but that's right in the powerband. It cruises fine at that speed, has power in reserve, and (if mine were running properly all around) gets decent mileage.

I don't know how many times you've tried this same argument only to have people who've had multiple XJs with multiple setups tell you that the extra rpm isn't hurting their mpgs.
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Ditto.
 
Milford Cubicle II said:
Apparently you guys just aren't going to understand that gearing is the wrong way to fix a problem cause by additional rolling resistance, drag, and weight. Which is why those "bean counters" don't factor it. It is the right way to fix the change in final gearing caused by adding larger diameter tires. Gearing is a band-aid or a short cut way to cope with losing performance from more weight and more rolling resistance and drag. While more power output is the correct way to compensate for those factors.
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Again, math can make you look smart or make you look like an idiot. It's actually physics making you look foolish, if I'm to be accurate. As previously stated, without the right gears, you run the risk of overworking your transmission. More so, if you have a lot of power. Gears allow the trans to work more efficiently, stay cooler, etc. True, your RPM's will increase, but that's to be expected.

The sad thing is that you immediately came into this conversation with an attitude of arrogance and superiority which put everyone else on the defensive. That destroyed any likelyhood of anyone taking you seriously. Next time, have a little more respect and consideration of others. Present your argument politely. That whole "golden rule" thing isn't just for elementary school.
 
sixty7ss said:
The sad thing is that you immediately came into this conversation with an attitude of arrogance and superiority which put everyone else on the defensive. That destroyed any likelyhood of anyone taking you seriously. Next time, have a little more respect and consideration of others. Present your argument politely. That whole "golden rule" thing isn't just for elementary school.
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You must be new here. Milford, I think, intentionally takes a different tack from everyone else on issues that are well proven just so he can argue. I respond because I'm easily suckered into arguments with idiots. I should really work on that...:D
 
Talyn said:
Keep in mind that there was a 3.73 option on XJ towing packages.
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I had a set of factory 3.73 axles in my junk.

With a 5sp and 31's it was pretty much the same as factory.

for 31's and an auto, 4.10

keep in mind that most of those charts are showing RPM at a 1:1 ratio, the AW4 has OD.

I'd rather have too much gear than not enough. Easier on the trans and all of the other driveline components.

Don't be afraid to spin a 4.0 @ 2500-2800 RPM on the freeway. It's not that big a deal. The Mj is running 4.56's with 35's and a 5spd. I'm too lazy to do the math and it doesn't have a speedo that works, but I've been spinning the hell out of a 4.0 for a long time. My motor has seen north of 6 grand. Still fine, other than a little valvetrain noise ;)
 
You guys need to invest in intake restrictors, otherwise you're going to risk burning up your tranny's with all 230 ft/lbs of the 4.0. Forget all the people with very potent strokers (not to mention Jeep Speed) with AW4's that are doing just fine.

I really can't believe that's actually being used as an argument for more gearing :roflmao:

If you're honest, you'll admit that there are just as many if not more disadvantages to spinning your engine and drive-line at a higher RPM all the time.

I think I've said it 3 times now but I'll say it again since some of you don't seem to care to read. It's your money, and your Jeep. Do whatever makes you happy with it. I posted mainly to correct someone who said that 4.10's and 4.56's are about the same as the factory ratio with 31's. Ya know, to benefit those who aren't into the over gearing garbage :D
 
well just got my jeep back.. went w/4:10s for the 245/75 on rubi wheels. threw a truetrac in front, and aussie in rear. power is back, but it's not THAT much more torquier than before. Take off is slightly better than w/the 3:55s, but once it gets going, i can tell the difference. if my mpg is around 16ish mixed, i'll be happy.

my friend has 31s on 3:55s and gets 11 mpg mixed.
 
5.38s and 35s here, steel beadlocks, 3/4 ton axles, lots of weight added, 3 guys,full of camping gear and tools with barely any space to spare, 15mpg when loaded up. cruises at 70 mph all day long.

It doesn't do any harm going a little deeper, your transmission can stay in one gear on the highway in hilly regions, no downshifting or slipping of the torque converter. Your motor never struggles trying to turn all the added rolling weight. More control offroad.

And this argument is dumb. Its been accepted that lower gears arent the devil.
 
4.46 with 36 Mickey MTZ's locked and I wish I had more. They were fine in my 85 XJ Chief with a Ford small block V8 but lack with the 4.0. Offroad is good with the dual t-cases but hiway hills tend to be longer than need be. I would like to up grade to 4.88 5.13.
 
What Milford is saying is that regearing for tire size is the right way to go, going slightly deeper is ok...but trying to make up for weight and lack of aerodynamics by spinning the engine to the moon on the highway, and trying to fool us into thinking that you're suddenly pulling wheelies and getting better fuel mileage than stock is a bit hard to swallow. I know he's tired and frustrated with the same thing I am here...the constant preaching to run tons of gearing with little tires.

I have never had a properly running 4.0 HO/AW4 accelerate from a stop better with too much gearing vs. not enough. That's because the 4.0 is not a quick or high revving engine, and gearing it so that it needs to rev quickly and high to row through the gears (in stock form) does not aid in acceleration for this particular engine. I've had plenty of them, and I've regeared hundreds for paying customers.

I've also had plenty of Samurai's...guess which one has given me the best acceleration and fuel mileage? Yup, the one with factory gearing and an engine upgrade on 31's (that's the same tire increase as going from stock to 32-33" on an XJ). All the ones I geared to the moon accelerated better than stock geared ones with bigger tires(but not better than this current one), but just screamed at 65 with my foot on the floor...huh, I thought gearing as deep as possible was the wonder cure, and would supply me with tons of new found "power"?

Guess what I did to get better acceleration and better fuel mileage out of my Dodge/Cummins? Added a power tuner and increased tire size to 35" to slow the rpm's on the highway...but based on the advice here, I should have geared it to 4.88 and just let it scream:nosmile:

Guess what I did to drop my fuel mileage in my '01 XJ from 18+ to barely 14...added 33's and geared to 4.56. Now it doesn't accelerate any better (but it sure makes more noise and shifts quicker), revs way higher than I want it to on the highway (4.10's would have made me much happier, but I had these) making the fuel mileage suck, the driveline sing and vibe, and it still downshifts if I'm too aggressive with the right foot trying to accelerate (wonder where my magic "more power" went), yet the engine ends up revving too high when it does downshift to actually do anything productive.

A good mix of regearing the diffs for tire size for the road, regearing the transfer case for off road, and adding some power is the "right way" to go...but to each their own. I totally get gearing super deep for a rig that is a toy...for wheeling...not a DD that sees lots of road/highway time though.

There is a happy medium, and gearing super deep doesn't make up for the need for more power efficiency from the engine.
 
bobnoxious said:
What Milford is saying is that regearing for tire size is the right way to go, going slightly deeper is ok...but trying to make up for weight and lack of aerodynamics by spinning the engine to the moon on the highway, and trying to fool us into thinking that you're suddenly pulling wheelies and getting better fuel mileage than stock is a bit hard to swallow. I know he's tired and frustrated with the same thing I am here...the constant preaching to run tons of gearing with little tires.

I have never had a properly running 4.0 HO/AW4 accelerate from a stop better with too much gearing vs. not enough. That's because the 4.0 is not a quick or high revving engine, and gearing it so that it needs to rev quickly and high to row through the gears (in stock form) does not aid in acceleration for this particular engine. I've had plenty of them, and I've regeared hundreds for paying customers.

I've also had plenty of Samurai's...guess which one has given me the best acceleration and fuel mileage? Yup, the one with factory gearing and an engine upgrade on 31's (that's the same tire increase as going from stock to 32-33" on an XJ). All the ones I geared to the moon accelerated better than stock geared ones with bigger tires(but not better than this current one), but just screamed at 65 with my foot on the floor...huh, I thought gearing as deep as possible was the wonder cure, and would supply me with tons of new found "power"?

Guess what I did to get better acceleration and better fuel mileage out of my Dodge/Cummins? Added a power tuner and increased tire size to 35" to slow the rpm's on the highway...but based on the advice here, I should have geared it to 4.88 and just let it scream:nosmile:

Guess what I did to drop my fuel mileage in my '01 XJ from 18+ to barely 14...added 33's and geared to 4.56. Now it doesn't accelerate any better (but it sure makes more noise and shifts quicker), revs way higher than I want it to on the highway (4.10's would have made me much happier, but I had these) making the fuel mileage suck, the driveline sing and vibe, and it still downshifts if I'm too aggressive with the right foot trying to accelerate (wonder where my magic "more power" went), yet the engine ends up revving too high when it does downshift to actually do anything productive.

A good mix of regearing the diffs for tire size for the road, regearing the transfer case for off road, and adding some power is the "right way" to go...but to each their own. I totally get gearing super deep for a rig that is a toy...for wheeling...not a DD that sees lots of road/highway time though.

There is a happy medium, and gearing super deep doesn't make up for the need for more power efficiency from the engine.
Click to expand...

I truthfuly posted my experience. Maybe someone sprinkled pixie dust all over my jeep when i built it.
 
i went the "cheap route" and got an 8.8 w/factory 4:10s, and re-geared my front to match, to help my newly installed 34" tires on my old xj. i consistently averaged 12 mpg. my jeep would sometimes downshift to 2nd gear on grades.. i regretted not going 4:56 or 4:88. true story.
 
djlarroc said:
i went the "cheap route" and got an 8.8 w/factory 4:10s, and re-geared my front to match, to help my newly installed 34" tires on my old xj. i consistently averaged 12 mpg. my jeep would sometimes downshift to 2nd gear on grades.. i regretted not going 4:56 or 4:88. true story.
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You're in friggin Denver...you're already down on power compared to stock.

Man up and give the engine a power upgrade.
 
To answer the OP's now moot question...4.10's are over geared for 31's, but you don't have many options, and I wouldn't reccomend paying for regearing unless making a big change.

They'll be fine
 
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