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Topic Review (Newest First)
08-11-2010 01:49 PM
up2nogood Thanks for the advice Jerry, actually i have had 35" thoughts once or twice. It will be a year or so depending on how well these new 33's wear. I lifted my Jeep enough to run either size, i went with 4.5" total, 3.25 RC, and machined my own 1.25" BL from 6061-T6 aluminum. M.O.R.E. products was kind enough to post the dimensions on their website for the spacers, the rest was just nuts & bolts......
08-11-2010 01:41 PM
Jerry Bransford
Quote:
Originally Posted by up2nogood View Post
I just don't want to go from bad gas mileage to worse mileage, i think it will return close to normal (before the lift), if it is geared correctly. It worked out that way on my Ranger, with 33's and 4.10 gears. When i sold it, it was getting 21 mpg average with the 4.0 V-6. This is my first Jeep though, so I don't know anything except what i read on the web. I just don't want to waste my money.
Again, 4.56 is appropriate for your particular Jeep and 33" tires, definitely don't go 4.88 since you also drive your Jeep on the road. I would only install 4.88 if 35" tires are on your radar for the near future. Your 5-speed transmission is the AX-15.
08-11-2010 01:38 PM
up2nogood I just don't want to go from bad gas mileage to worse mileage, i think it will return close to normal (before the lift), if it is geared correctly. It worked out that way on my Ranger, with 33's and 4.10 gears. When i sold it, it was getting 21 mpg average with the 4.0 V-6. This is my first Jeep though, so I don't know anything except what i read on the web. I just don't want to waste my money.
08-11-2010 01:09 PM
Jerry Bransford
Quote:
Originally Posted by Ibuildembig View Post
I always run a 4.56 on a 33 whether its a manual or auto...it will get your 5th gear back
It will definitely get 5th gear back but at least in my personal opinion, 4.56 with 33" tires would not be a good choice for either the 3-speed 32RH or 4-speed 42RLE. While 4.56 would be a great offroad ratio for the 32RH and would produce similar rpms to my 32RH with 35" tires and 4.88, that'd be a bit too low of a ratio for the highway when trying to cruise at 65-70 mph. I ended up moving my cruising speed from there down to 55-60 mph on the highway with those rpms.

And 4.56 is definitely too high of a ratio for the 4-speed 42RLE with 33" tires, that transmission has such a deep overdrive ratio that 4.88 is needed to prevent the engine from lugging with 33" tires. After my last TJ was stolen, I bought an '04 with the 42RLE and it came with 4.88 gearing which isn't low enough for my 35" tires, 5.38 would have been a much better choice. I'm always having to click my overdrive off to stop the engine from lugging, it shifts into overdrive at too low of a speed which creates way too low of an engine rpm.

So at least in my personal opinion, 4.56 is not a good choice for any of the most common automatics used in our Jeeps when you're running 33" tires if you're using the Jeep for both onroad and offroad uses. Maybe it'd be ok for the AW4 but in my personal opinion, it would not be a good choice for 33" tires when running either the 32RH or 42RLE.
08-11-2010 12:56 PM
Ibuildembig I always run a 4.56 on a 33 whether its a manual or auto...it will get your 5th gear back
08-11-2010 12:52 PM
up2nogood Thanks for the info, i am running the I-6, but not sure on the trans, i just assumed it was the AX-15, it is a 97' sport 4.0. I have looked in my area for a D30 like what was mentioned, but haven't found one yet. I have a friend who will do the R&P swap on both ends for $100, I have everything but the gears. Don't they make a set in like 4.27 or something? How would that do?
08-11-2010 11:53 AM
TheTJRod I have the I6, NV3550 with a .78:1 overdrive ratio, factory 3.73 axle gears, and 33" tires.

I hate to assume but I am going to. You have the I6 with either the AX15 or NV3550(not much difference with .79 and .78 overdrive gears respectively). 5th gear is not gone to me, though there is very little pickup and slows on inclines when under 70. I can use 5th to maintain and slowly increase speed at 40mph. You could hold off changing the gears in the 8.8 you got and install it now to see what you think. Though I want to change gears and will be getting 35s some day, so I am going to 4.88s. I think 4.56 is to much for a DD you will be much more comfortable with 4.10s. 4.56 and definitely 4.88s would give you horrible mpg. Oh and I would look around for some more 8.8s as some come stock with 4.10s. Then just find a d30 that was on a 4banger that has 4.10s. Buying the axles with the gears you want already in them is much cheaper.

Look for these axle codes on the door sticker:

42 = Open 4.10
D2 = Limited Slip 4.10

Or on the axle tag

4 10 = 4.10 open
4L10 = 4.10 LS
08-11-2010 11:32 AM
Jerry Bransford It's not that such gears are "that low", it's that with such large tires, installing ratios like that are simply required to return the performance lost when bigger tires are installed, so you're really just regearing to obtain the performance it had with the factory size tires. Engines lug when too big of a tire is installed and are undergeared.

The factory installs 4.10 gearing with even small tires with the 2.5L engine so the gear ratio chosen is simply that which causes the engine rpms to be at the point that work the best for the tire and engine size.

It's not as important to regear when you have an automatic as they are more forgiving but with a manual transmission, it becomes more important.

When I installed 33" tires, it wasn't long before I regeared. It's not just for offroad reasons, it simply restores how well the engine worked before the bigger tires were installed. The factory geared it to produce certain engine rpms with stock size tires, regearing the axles to produce those same rpms with bigger tires is all we are doing with bigger tires.
08-11-2010 11:31 AM
530ktm I have 3.73 gears now with 31 inch tires and it turns around 2400 rpm at 70 mph. I am in the process as I type of putting on 33 inch tires and regearing to 4.56 gears. With this set up it should turn around 2600 to 2700 rpm at 70 mph in 5th gear. This is perfect for cruising and not having to downshift for any incline. I also do some off roading and I like to have a nice low 1st gear for the tight stuff. That is not going to happen with 3.07 gearing on 33's or even 3.73 gearing.
08-11-2010 11:26 AM
Cons_Table Most of it depends on what motor you have and what tranny
08-11-2010 11:18 AM
up2nogood
Why 4.56 or 4.88 gears?

I read a ton of posts everywhere on the net advising us to install 4.56 or 4.88gears when running 33"+ tires. Is this really what everyone is doing or does it soley depend on the usage of the vehicle? My Jeep is a daily driver, currently running 3.07 gears on 33's, i know i need to regear, but i can't see putting gears that low in a daily driver. At the same time, i can't decide on what gears i should run, and this is a big decision that i don't want to screw up on. I wheel ocassionally, and even with the 3.07's, i haven't had a problem on the trail. The biggest problem i have is on the highway, 5th gear is useless unless you are running 75+, and the smallest grade bogs it down. In my mind, after looking at the gearing chart for tire size / rpm, i need 4.10 gears to make up for what i lost with the 33's. I just don't want my Jeep turning 3,000+ rpm on the highway at 75 mph. I am putting together a 4.6 stroker to install next spring, so the increase in torque should help with the hills and on the trail. I have also aquired a 96' 8.8' rear axle to swap in as well, it is already equipped with 3.73 gears and a trac lock, but I want to swap the gears before i install the axle.

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