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You will LOVE 4.56s with 32s....when you go to 34s, you'll be wanting 4.88s though. Trust me, I ran 4.56s with 32s for about 6 months and then went to 33s, and I wish I had deeper gearing, just between the two. I'm going to 4.88s and 35s here soon, and I wish I could go deeper, but it's not possible.
I suppose I will be finding out this weekend how the entire deal with the 4.56 with 32's will work.
Sat. Rawbrown (Ryan Brown) and I will be installing the R&P with lockers. Freeway speed should be better than the stock set up with the 32's...but onece again I will find out for sure this weekend!
Rick
I now run 4.56s with 33" BFG ATs and an AW4 and am perfectly happy. Things start to vibrate over 75mph on the highway, but not bad otherwise. By the way, a 38 tooth speedo gear is within 1 mph with this setup as verified by GPS.
mattk
YuppiXJ has my old axles with 4.56 and with dunlop 32s he gets 22 MPG on the highway(about 75 mph) and his 4.0 has over 200k on it, he loves it. but if 34s are in the future 4.88 sounds better. I'm goingto 5.38s in mine now and right now all I have are 35 SSRs.
4.56's and 32's will work perfect on the freeway with 32's. Like Ary said 4.56's will likely be a little high for 34's though. I ran my 4.56's with 32's and it worked great. I'm now on 33's and it is still fine. 34's would be pushing it though but I still think it would work though I'm sure 4.88's would be better.
i'm running 4.56s with my 33" MT/Rs.. i havent done alot of highway, and seeing as how my speedo doesnt work, my RPMs are 2050 RPM at 55 MPH(by GPS) and about 2300 at 65.... livable but more RPMs than my 250K mile 4.0 is used to...... but i will always sacrifice a little on the top end for better acceleration and crawl ratio..... i'm diggin' it!
I run 32's on my DD w/4.56's and an AW4. I tach 3,000 rpm at around 70 mph. Not rocket speed, but you can move it up to 75-80 without worrying too much. Gas mileage improved about 30% when I replaced the 4.10's with the 4.56's too.
I don't see why there would be any. If you were keeping stock gearing and trying to drive tires that were too large it would be a heavy load for the engine to deal with, but it would take a really marginal cooling system to register on the engine I would think. Stock gears, big tires and a 5k lb trailer...maybe register? Still doubt it.
Remember, with 4.56 gears and 32s you will be making the loads the engine sees LESS than the stock setup (ignoring rolling inertia of the tires).
No biggie.
If it was aproblem we'd have heard something about this long before now - not just with Jeeps either.
YuppiXJ has my old axles with 4.56 and with dunlop 32s he gets 22 MPG on the highway(about 75 mph) and his 4.0 has over 200k on it, he loves it. but if 34s are in the future 4.88 sounds better. I'm goingto 5.38s in mine now and right now all I have are 35 SSRs.
I think 3.55's would be way too tall. I took out the 4.10's after 6 months for a few reasons: (1) I'm heavy on the skinny pedal and mileage went from 18 to 12 mpg (2) accelleration was acceptable but not great, and (3) I tow a 3,500 lb boat and the tranny really struggled with the 4.10's. The 4.56's put me back up to an on-par performing XJ. 3.73's would obviously be better. This is a daily driver, too. I had OEM 3.73's on my 4.2L YJ with 32's, but a manual tranny. Never even was able to use 5th gear and mileage was crappy.
Sorry to hijack, but im going on the other side... I have 30's and am going to regear soon. I pull a big honkin trailer... would 4.56's be too much on 30's? This is mostly a DD, I ahve owned my new XJ (00') for 1 year and put 38,000 miles on it. After some thought i can see myself going up to 32's eventually, but i'd be running it on 30's for atleast a year. I can't make up my mind, because i don't have enough access to this information.(that's why i paid my dues on here- i need as much help as i can get) So the basic question is if 4.56 on 30s behind and auto (banks headers, bored throttle, 5"cone filter, snorkel, hiflo cat, banks muffler and 2.5" stainless pipes from down-pipe to the tip)
I was planning on 4.10s for my daily driver (200k 4.0, AW4) and going from P225 (28") to 31x10.5"
Serious enough that I had the gears on hand (for the 30 and stock 35 and also for my 44) but as I was thinking more about it, I had a change of heart: I have a spare front axle with low-mile Spicer 4.56/TrueTrac that is set up already & it worked well. Also I just got a great deal on new Spicer 44 4.56 gears & install kit... so I'm planning now to go with that setup instead.
4.56 on 28" will be a bit on the deep side, but should be perfect with 30-31" dia and extra weight of armor/aero drag of mild lift when that all comes around. The AW4 has a pretty good overdrive which will help keep the highway RPM down, but 99% of my miles are twisty/hilly rural 2 lane with maybe 10 miles per day of 'urban' at approx 400' ASL. 4.10s probably would have been fine with 225 to 30" tires... but I think 4.56 will be fine as well. "Anything" would be better than factory 3.55s - BTDT on 33" and it was less than fun.
A simple formula for figuring out speed @ a given RPM
tire diameter x RPM / Axle ratio x gear ratio x 336
ex: 30" x 3000 / 4.56 x 1 x 336 = (90000 / 1532) = 58 MPH @ 3000 RPM in 3rd (auto)
or in (?.7?) Overdrive: 90000 / 1073 = 84 MPH
This is just a guide and doesn't account for drag/parasitic losses found in the real world. (actual speed over ground will likely be less than the #s shown) Also use the tire's loaded radius (hub center to the ground) x 2 for the 'true' diameter.
Extended trips at +- 3000 RPM is IMHO not excessive for a solid 4.0l engine.
