4.56 gears with 33's highway speeds?

[60thAnivrsryXJ]

If you are turning 2500 rpm at 60 with 33's and 3.55 gears then you must have the t-case in low range or somthing, if that is even possible. And by the way with every drivetrain change I made, I replaced the speedo gear so the was all accurate.

 

[00XJFAN]

Does anyone have the 4 speed auto with 4.10's and 32's (or 265/75-16's) and can tell me what RPM's they turn at 70 MPH and how they feel the power is? Also does someone have 4.56's and 32's and can tell me the same info?

 

[sidriptide]

If you want to drive 90 on the highway use a car not a lifted Jeep.

Bingo!

 

[60thAnivrsryXJ]

I have 265/75-16's with 4.56's and 75 is about 2900, 70 is about 2750, 65 is about 2500, and 60 is about 2200. The shifts come real quick with this setup. By the time I hit 40mph the trans is in overdrive, which is about 15rpm. It takes a little getting used to because you feel like you need another gear after that. It is perfect for cruise control on the highway, it just cruises right up the hills no problem, with a higher gear I'd say it would probably be downshifting to 3rd everytime you went up a hill. That is what it was like before the gear swap. 4.10's probably wouldn't do it as much as 3.55's did though. Is that enough info?

 

[00XJFAN]

So do you like the RPM's with the 4.56 on the hiway with 32's or would you rather have 4.10's?

What's your gas mileage like with the 4.56's?

 

[Ivan]

So do you like the RPM's with the 4.56 on the hiway with 32's or would you rather have 4.10's?

What's your gas mileage like with the 4.56's?

For me it's a mutual split. The nice low end power for off roading I get with my 5 spd, 32's and 4.56 gearing; makes up for the slightly higher, but tolerable rpms on the highway....

 

[90Pioneer]

I run 4:56 gears and 33x12.5 tires. I noticed a difference in hiway power with the new set up over my old, 3:55 gears with 29" tires.

I get 11mpg.

 

[60thAnivrsryXJ]

I like it. Like I said though I think I would like the rpms just a little lower. I think 4.10 would make it to low though, but increasing the tire size to 33 would make it perfect I think. I don't know for sure though cause I havent experinced it. I think my next tire will be a 285/75R16 (32.8") and hopefully that will give me the small decrease in rpm without a noticable loss in power. By the way my disliking the higher rpm is due to the noise not the gas mileage, I wouldn't have lifted my jeep if I worried about that. If you want to get an idea about the sound just shift your trans in a lower gear and see what the engine sounds like between 2500 and 3000 rpm to see if you don't think it'll bother you.

 

[PapaPump]

you'd better build a rear end first !

heh well i bought this sweet 44 a while back and it's just chillin' on my garage floor, that should work. but you knew that.

i start thinking about things a little more, and taking some advice, i should go with 4.56 like everyone is saying. as it is i have 3.07s and 235s. the rpms are fine on the highway, but i have to downshift for the grades that are around 7%+

so i would be looking at slightly more rpms and torque, but it will sound like i'm driving on the freeway in 4th.

as far as the comment about 80mph...that is a comfortable speed. our freeways are 65, i usually go 70 sometimes 75. oregon's interstates are 75 and i'll push it up to 80 there. mine is barely beyond stock though, so we'll see what that's like with 33s!

 

[CartsXJ]

As everybody said already, you'll want at least 4.56's with 33's. Don't listen to anybody who tells you they are too low. The 4.0L loves to live in the high 2000 to low 3000rpm range. That is where it starts to hit its peak torque curve, specially the late models. I use to cruise the highways all the time at 75, 80 sometimes 85 with my Xj on 33's with 4.56's staying right around 2750 to 3100 rpms. I also got the best mileage in that area. Now with 35's my rpms have drop down at 500 or so. And I am already looking at swapping axles for lower gears, that 8.25 is a b!tch like that.

And he's right if you want to do 90, get a car, though I think we have all been guilty of that once or twice. Though I do like the look of people when you pass them in a lifted jeep on the highway. The looks are classic :wave:.

 

[PapaPump]

looks of terror and horror? like maybe you will drift over and run them over? heheh, you said you cruise 85 and then tell people who want to go 90 to buy a car...what is the difference? either way unless you have big brakes, you better only do that on open highway, because a 80+ mile per hour XJ with 35s is going to take more than 350 feet to stop.

even with stock tires braking can become marginal at those speeds because of fade.

i would like to maintain reasonable cruising speeds with reasonable RPMs. i dont think 3000+ on the freeway is reasonable. most people started with lower gears than the 3.07 that the manuals came with. i feel like that gear ratio is just a little too tall. accounting for tire size increase to 33s, to keep the same highway RPMs i would have to go to 3.73s. of course since i feel like it could use lower gears already, and accounting for the weight of bigger tires, i would want to go lower. i was thinking 4.10, before all these contrary opinions on that ratio. the problem is, 2000 rpms for me right now is 70, with 4.56s and 33s it would be more like 55. to achive 70, i would have to run 2600 rpms with 4.56s, 2350 with 4.10s...hmm not that much difference....okay after doing all that calculation, i'm thinking the RPMs are going to be lower than expected....4.56s it is

i was trying to be cheapo, and rather than regearing the front, i wanted to pick up a 4cyl fron D30 with 4.10s. if i do that than maybe i would be better off with 32s or even 31s, as far as power is concerned.

anyhow i should have just listened to Ivan way back early in the thread, since he cruises the same freeways i do!

 

[60thAnivrsryXJ]

I will give exact rpms for you guys that are wanting something more than a ballpark that you get from looking at your speedo and tach. These were taken from a very reliable calculator off a computer program not a website. These are as close to being exact as possible given that with different amounts of tire wear would cause slightly different tire diameters and if your torque converter clutch was malfunctioning then there would be some slippage. The calculation was based on 31.65" for a 265/75R16 tire, a 0.75:1 4th gear ratio, and 4.56:1 ring and pinion ratio. According to the program; 60mph = 2191rpm, 65mph = 2374rpm, 70mph = 2556rpm, 75mph = 2739rpm, and 80mph = 2922rpm.

 

[CartsXJ]

looks of terror and horror? like maybe you will drift over and run them over? heheh, you said you cruise 85 and then tell people who want to go 90 to buy a car...what is the difference? either way unless you have big brakes, you better only do that on open highway, because a 80+ mile per hour XJ with 35s is going to take more than 350 feet to stop.

even with stock tires braking can become marginal at those speeds because of fade.

i would like to maintain reasonable cruising speeds with reasonable RPMs. i dont think 3000+ on the freeway is reasonable. most people started with lower gears than the 3.07 that the manuals came with. i feel like that gear ratio is just a little too tall. accounting for tire size increase to 33s, to keep the same highway RPMs i would have to go to 3.73s. of course since i feel like it could use lower gears already, and accounting for the weight of bigger tires, i would want to go lower. i was thinking 4.10, before all these contrary opinions on that ratio. the problem is, 2000 rpms for me right now is 70, with 4.56s and 33s it would be more like 55. to achive 70, i would have to run 2600 rpms with 4.56s, 2350 with 4.10s...hmm not that much difference....okay after doing all that calculation, i'm thinking the RPMs are going to be lower than expected....4.56s it is

i was trying to be cheapo, and rather than regearing the front, i wanted to pick up a 4cyl fron D30 with 4.10s. if i do that than maybe i would be better off with 32s or even 31s, as far as power is concerned.

anyhow i should have just listened to Ivan way back early in the thread, since he cruises the same freeways i do!

I take it you drive on flat highways if you think a 4.0L is going to like to cruise at 200rpms at highway speeds on 33's. And yes I do cruise at 85 some times, not much now on the 35's(unbalanced), but when I was on 33's all day long and at 2750rpms, plus 22mpg to boot. Yes hard to believe but an engine will produce its best mpg when closer to peak torque, thats why diesel pickups have higher gear ratios than there gas counter-parts, closer to there peak torque. Once you put that Xj on 33's and create a huge brick going threw the wind, you'll definately want lower gears.

And if you have the right suspension set-up with correct shocks and sway-bar, it handles better than a stock one. And yes I only do 90 if there is open highway and the weather permits it.

 

[PapaPump]

in my previous post you can see that i don't cruise on flat highways. i usually have enough power though i do have to use 4th for the steeper grades. i had originally figured that since 4.10s would still be lower overall than what i have now, that that would be fine. i have decided to go along with what just about everyone else has suggested though, and do 4.56s.

 

[Roxtar]

Jesus poeple, a little math goes a long way.
Eveyone going through the RPMs and opinions and what not.

It's very simple:
4.56 gears on 33" tires is almost identical to 3.55 gears on 27" tires (stock)
IOW 4.56 gears will get you down the highway on your 33s the same way your stock gears did on stock tires.
If you want lower gearing than stock go to 4.88s.

 

[planefixer]

Those figures don't sound right at all. With 33s and 3.55s you should be cruising doing 60-65 at about 2500. Anything faster makes the RPMs scream.

Just some input:
I've been running 33s and 3.55s for quite some time (going to 35s and re-gearing VERY soon) and at 80-95 mph on the interstate I'm running at 2100-2200 rpm and have seen as much as 21+ mpg. :gag:

 

[60thAnivrsryXJ]

Thank You! That's exactly what I was trying to say through three different posts. Hes got his numbers backwards. Large tires plus high gears equals low rpms. Small tires plus low gears equals high rpms.

 

[PapaPump]

Just some input:
I've been running 33s and 3.55s for quite some time (going to 35s and re-gearing VERY soon) and at 80-95 mph on the interstate I'm running at 2100-2200 rpm and have seen as much as 21+ mpg. :gag:

ha! just as soon as i decide to go with 4.56s someone else comes in and says i can get 21 MPG if i stay on stock tires! sorry though, i'm going to go with the majority here.

Jesus poeple, a little math goes a long way.
Eveyone going through the RPMs and opinions and what not.
It's very simple:
4.56 gears on 33" tires is almost identical to 3.55 gears on 27" tires (stock)
IOW 4.56 gears will get you down the highway on your 33s the same way your stock gears did on stock tires.
If you want lower gearing than stock go to 4.88s.

I did do some math. Those numbers I put up a couple of posts back are real calculations (even if not perfect because of variations in tire size), not opinions.

however my calculations were based on my current setup, which is already much taller geared than your example (slighly taller than stock because of the 235s). with an ax15 (3.07) and 205s, the caluculations come out a lot different than your example with 3.55s.

 

[Kevlar]

heh screw highways, im hopin to get 4.56 for my 31's. It's all about the crawl speeds!

 

[60thAnivrsryXJ]

Yes it is possible to get 21mpg on the highway with bigger tires and stock gears because of the very low rpms. You just have to make sure to slow down and not try to maintain you speed when you hit a hill otherwise the tranny'll downshift and jump the rpm up to like 3200 and if you let that happen a lot there goes your 21mpg. Me personally I'd rather have it staying a constant 2800rpm or thereabouts and be able to hold 70 or 75 on a hill without the transmission downshifting to third.