Thoughts on 4.56:1 and 31"

In the past 3.5 years I have been around the forums, the topic of "what Gears for ___tire-size" comes up and gets beat to death pretty regularly. Most answers fit a common theme: Stock for up to 30-31", 4.10-4.56 for 32-35", and over 35" is getting into worryland for the D30, strength and braking-wise. 4.88:1 being the 'lowest' available for a hi-pinion 30. Those swapping in HP44 or 9" etc...have a few deeper ratios to choose from, but disregarding that for now...we're talkin RR30s.

Anyway way back when, I built mine with 4.56:1 for a 4.0l/5speed running 33". Recently swapped those axles into my 4.0l/AW4 XJ (going from 33" and 3.55:1) What a huge improvement! But alas ruined a wheel and tire last weekend, so I swapped back on some 31x9.5 TSLs until I get a set of new shoes.

What I have found is that 4.56 with 31" isn't a purely unliveable combo for my daily use (45 miles of paved twisty/hilly 2-lane) I suppose it would rev a little too much for a highway commuter, but it gets off from stoplights nicely. The one time I 'had' to do a throttle-mash 3>2 downshift to get out of a jam...it responded like a pro-stock car Fuel mileage hasn't been ciphered with the 31" yet, but it seems that it's no better or worse than the 33" were (approx 16-18)

In the long haul, I think 4.10:1 would be 'perfect' for a Jeep that will see 31" for daily use, and probably be OK for 30" as well. My other XJ will see no more than 2-3" lift and 30-31", be used as a daily driver + some towing. It will likely get 4.10s in the diffs at the same time I lift it and install the tires. (keeping in mind that the D30 needs a different carrier for any ratio higher # than 3.55:1, and one might as well do it right the first time)

Summing up my point, low gears and smallish tires aren't the big-bad-wolf some make it out to be...especially if going up a size or 2 later on is in the cards. Of course with low-range engaged, OEM ratios aren't 'terrible' off road, esp. out east where sometimes a little wheel-speed is in order...adding the lower ratio gears just made the experience (both on-road and off) a whole lot better for me.

Hey Woody,
I would keep running the 4.56s for a while with your 31s and see in time how liveable they are. If you will eventually be doing some towing with that thing in your Smoky Mountain region, you might end up really loving the set up. You'll use less throttle getting to speed and I've found that with the 4.56s and 33s here in the Rockies, while towing my trailer (900lbs) and my quad (400lbs) and all my camping gear, fuel, and coolers, mine likes to be kept in drive and still bags me 14 mpg running the passes. I've got 4.88s for my D60 and am contemplating running them instead of the 56s with my 33s.
JMHO,
Crunch

Can't wait to see y'all in Tellico

I agree! Ive always like the lower gear option. Most rigs we build wont fly out to vegas at 90mph. I think if you can do 75mph and be in the 3000ish range, it isnt that bad at all
I ran 33s and 4.56 for a long time (with a 700r4)
my speedo was off by like 2mph at 75 according to a few GPS clocked runs.
My street car came with a 3.08 rearend and Ive upped it to 3.42. Some of the other guys are running 3.73!!! And boy they get great in town driveability.

LOL 'that thing' is the thing I may end up towing with the other (stock for now) XJ

89 XJ 4.0/AW4/231 (presently on 31"/4.56 @ 6" +-) hopefully on fresh 33"-36" MTs/Allied beadlocks before Tellico...

88 XJ Limited 4.0/AW4/242 (to be built on soon - presently 205-75/3.55 @ OEM height) No more than 2-4"/31" ATs and a Mommie-imposed 'no-wheeling' mission statement for this one ya right...

I have a 4.56:1-TrueTrac 30 axle that could slip right in this one...that would be cheaper and easier to swap (the whole axle) than refitting that carrier with 4.10s and installing in the 88 housing...I'll build a rear 44 same flavor-either way (gears and a TrueTrac) so the parts/gearing expense would be the same with any ratio.

I can see the logic of 4.56:1 and 31's...especially for towing up in the Smokies (or anywhere) and we don't do a lot of hi-speed interstate travel so it'd probably work fine for me. I anticipate an XJ towing an XJ would encourage being somewhat slow and safe...so the lower gears would pay off in that mode.

Hey woody I run the exact gearing 4.56 gears with 31s and I absolutely love it too and I get plenty decent gas mileage ( much better on highway than stock). When I go up to 35s or so soon I will really miss the gearing. I took my advice from Beezil and I am glad I did. -------Kyle

I'm glad it worked out!

there are two misconceptions:

1) is that the 4.0 is *supposed* to hum along on the highway at 2000 rpm.

2) best gas mileage is achieved the slower the engine is turning.....

Good thing about naxja is, that most of the people answering these questions for the jeep folks out there, know that both are totally false.

I'm running 33" BFG's, 4.56's, 4.0L , AX-15. Meauring the actual weighted diameter of the half-worn-out tire at 25 psi, it comes out to exactly 31". At 65 mph, 5th gear, it revs about 2500. Avg. about 16-18 mpg...not much worse than stock.

I like the way it works both on hwy and off-road. I'd like to buy Swampers, but I think I'd get 31" or 32"....otherwise I'd probably wish that I had 4.88's.

I think mine would make for a good drag racer too

Woody, I'm glad to hear you like that gearing. I was a little worried about running my 32ATs on 4.56s(sorry Beez, those myths were firmly planted in my mind, but they're slowly dieing). Also glad you're getting plenty of use out of my old 31s, hope they're holdin up for ya. I miss running swampers for their indestructability, may have to trade the MTRs for another set, we'll see. Peace

Ary

P.S. How's the braking with the 4.56s and 31s? I'd assume it's worse...

Why would the braking suffer with 4.56 & 31"s? Am I missing something here?

I was wondering the same thing. If anything they would be better on the trail because engine braking would be improved. Mostly unaffected on the street.
Crunch

Not sure if this is correct, but:

More rolling mass with the same size brakes = diminished stopping power. I don think the gearing would affect stopping distance on the trail, or on the street. Someone call SPOBI if my post is incorrect.

Fergie

he probably didn't mean gears, and without having to do with rolling mass, he was probably wondering about tires size....

as we all know, bigger tires means diminished braking power.

Ya

I was talking how XJ brakes are less than ideal when significantly larger/heavier tires & wheels are added on...specifically over 35". Though the bigger MJ rear brakes and braided lines (new MC and booster too) help out some - compared to the 8.25 XJ brakes. But I could lock up the 33x12.5s before if I wanted too.

Note from the trail I ran today: 31" and 4.56:1 is YUMMY. Effortless wheelin, and if I had a 5 speed, I prolly could have let it idle along the whole trail. Just when things got uphilly, I broke off my 1-2 shift solenoid toggle switch...luckily it was in the '1' position because things got downhilly pretty quick/steep after the minor climb.

I wish you'd be more outspoken about that eagle, but nnoooooooo, you like to see me hang!

tell these young kids how a few jeeps came from the factory with 5.38's oem!

I was saying that with 31s and 4.56s that the overall gearing(takin tire size into account) would be deeper than stock gears and tires, no? Therefore, I was wondering how much worse it was, if noticeable at all.... Am I making any sense to anyone??

Ary

I've been kickin' myself in the rear for the past two years for going with 4.10s over 4.56s. and now I'm thinking that 4.88s and 33's would be a great combo but that means a new rear axle. Thanks alot guys.

Do I go with a 8.8 or go right to the 9"?

Now I'm getting depressed.

I'm regearing soon and was sure 32s and 4.10s are the ticket.....Now lost again.....Much to old and stiff to kick myself anywhere, better rethink this deal.

Am I making any sense to anyone??

Click to expand...

not me.

Beezil, if you put 4.56s on stock tires, would it not require more effort to stay stopped?? Like when you put it in low range, it's harder to stop 'cause there is more torque workin against the brakin system. Therefore, I was asking if there was a noticeable difference in going from 33s to 31s because you have in essence deepened the gear ratio. Am I making sense now?

Ary