So i just had 4.56 gears installed from 3.73's. I have not changed out my speedo gear yet so that might be part of my trouble. For starters i have not really noticed a huge difference, but i really have not got on it, and im not 100% sure where i should be feeling it? Also so far it appears gas milage didnt change a bit? should i have went 4.88's or 5.13's? I currently have a 4.0, Automatic, running 35's. the TJ is a 03? what do u all think?
did i choose the wrong gears???
- Thread starter 288sunny
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Bounty__Hunter
Super Moderator
You probably should have went with 4.88, as 3.73 to 4.56 isn't much of a bump.
A couple of reasons why you haven't noticed it much. The auto transmission multiplies torque and thus made up somewhat for being undergeared before. Second, and it also applies to mileage, is that your speedo gear needs to be corrected in order for the jeep's computer to be happy and run as efficiently as possible.
A couple of reasons why you haven't noticed it much. The auto transmission multiplies torque and thus made up somewhat for being undergeared before. Second, and it also applies to mileage, is that your speedo gear needs to be corrected in order for the jeep's computer to be happy and run as efficiently as possible.
phall92139
New member
I agree with Bounty Hunter.
Yellow = Highway Driving, Good Fuel Economy
As you can see in the chart (borrowed from Quadratec), with the change from 3.73 to 4.56 on 35's, you've gone from just barely too little gear to the conservative side of a good choice for a daily driver. 5.13's would have given your rig some extra grunt in the low end but your engine would really be screamin' along at 70-75 mph and your mileage would suffer. Personally, I thing 4.88's are pretty much the sweet spot but you'll get a lot of different opinions on this, as well.
Also bear in mind this disclaimer that the above chart "is based on 65 MPH and a gear ratio of 1:1, on a manual transmission in 4th gear. Please NOTE: If you have an automatic transmission your RPM will higher due to slippage in the transmission and the torque converter. With an overdrive transmission your RPM in overdrive will be 15% to 30% less than indicated."
Yellow = Highway Driving, Good Fuel Economy
Green = Daily Driver, Best Overall Performance
Blue = Most Power and Towing, Reduced Fuel Economy
Blue = Most Power and Towing, Reduced Fuel Economy
As you can see in the chart (borrowed from Quadratec), with the change from 3.73 to 4.56 on 35's, you've gone from just barely too little gear to the conservative side of a good choice for a daily driver. 5.13's would have given your rig some extra grunt in the low end but your engine would really be screamin' along at 70-75 mph and your mileage would suffer. Personally, I thing 4.88's are pretty much the sweet spot but you'll get a lot of different opinions on this, as well.
Also bear in mind this disclaimer that the above chart "is based on 65 MPH and a gear ratio of 1:1, on a manual transmission in 4th gear. Please NOTE: If you have an automatic transmission your RPM will higher due to slippage in the transmission and the torque converter. With an overdrive transmission your RPM in overdrive will be 15% to 30% less than indicated."
Bigcountry10
New member
Imyself started with a 4cyl six speed 3.07 gears running 33s. I switched to 4.88s, it was like night and day. Then my tires became so dryrotted they could not stay balanced and wrecked my front end so when I fixed everthing I went to 35s being they were the only tires I could find in stock in my area. Now its like I never changed my gears.
but again; from 4.56 to 4.88; little or no difference noticeable. I have 3.07s as well; I don't 'wheel it much (mostly have 4WD because I live in the country and we do get a bunch of snow here) with 235/75/15 tires my 5th gear is about useless. and my Wrangler with the 3,07s is worse on fuel than is my Cherokee with 3.55s and the same 235/15s.
Bounty__Hunter
Super Moderator
Nobody is recommending he swap 4.88 for his 4.56, you are correct in stating that change is pretty insignificant. What I was saying was he should have went from 3.73 to 4.88 for a more noticeable improvement and the proper gearing for 35" tires.
AA-CJ7
New member
You could have gone with 4.88, but there's nothing wrong with your choice, especially for the highway. You made a 19% change in gearing which is substantial.
One thing to remember is you added rolling weight, rolling resistance and wind resistance to your Jeep, all of which taxes the power of your engine. Gearing can correct the engine RPM to vehicle speed ratio, but it can't make up the added power it now take to move your Jeep.
It gets even worse when you start adding large axles and gears in your diff's, transmission and transfer case. None of it effects gear ratio, but it saps the power from your engine and brake system.
I hope this helps.
One thing to remember is you added rolling weight, rolling resistance and wind resistance to your Jeep, all of which taxes the power of your engine. Gearing can correct the engine RPM to vehicle speed ratio, but it can't make up the added power it now take to move your Jeep.
It gets even worse when you start adding large axles and gears in your diff's, transmission and transfer case. None of it effects gear ratio, but it saps the power from your engine and brake system.
I hope this helps.
Bounty__Hunter
Super Moderator
Very well explained, that's why it's best to gear slightly lower than recommended.
Pretty sure your transmission isn't gear hunting at cruising speed on the high way, plus there will be a lot less wear and tear on the drive train components since they will be operating with in the stock specs.
The gears searching while driving is the #1 benefit to gears swaps in autos, also, give 4lo a whirl, you will definatly notice an increase (rather speed decrease) in your crawl ratio.
Ideally 4.88 would have been the way to go, but there are definate benefits of running 4.56 as opposed to the 3.73's as a daily driver and don't discount that.
The gears searching while driving is the #1 benefit to gears swaps in autos, also, give 4lo a whirl, you will definatly notice an increase (rather speed decrease) in your crawl ratio.
Ideally 4.88 would have been the way to go, but there are definate benefits of running 4.56 as opposed to the 3.73's as a daily driver and don't discount that.
phall92139
New member
As you can see from most of the comments, no need to lose sleep over your gear choice, it's gonna be fine unless you're just into serious crawlin' then, in which case I'd be thinking about an Atlas 2-speed.
For what it's worth, here's a look at your overall Crawl Ratio:
> 2.84 trans 1st gear * 2.72 t/c * 3.73 axle = 28.81:1
> 2.84 trans 1st gear * 2.72 t/c * 4.56 axle = 35.23:1
> 2.84 trans 1st gear * 2.72 t/c * 4.88 axle = 37.70:1
Not that much difference. Now replace your NV231 with an Atlas II 4.3:1 2-speed transfer case and the difference gets real...
> 2.84 trans 1st gear * 4.3 Atlas II * 4.56 axle = 55.69:1
For what it's worth, here's a look at your overall Crawl Ratio:
> 2.84 trans 1st gear * 2.72 t/c * 3.73 axle = 28.81:1
> 2.84 trans 1st gear * 2.72 t/c * 4.56 axle = 35.23:1
> 2.84 trans 1st gear * 2.72 t/c * 4.88 axle = 37.70:1
Not that much difference. Now replace your NV231 with an Atlas II 4.3:1 2-speed transfer case and the difference gets real...
> 2.84 trans 1st gear * 4.3 Atlas II * 4.56 axle = 55.69:1
