4.88 or 4.56?

[Mojo Troll]

TRL just brought up a great point. Engine output, tranny/transfer case gearing, tire weight, drag, type of driving etc... all have to be considered for regearing, not just tire hieght.

I have a freshly rebuilt non HO with a header and freeflow exhaust (still not close to a HO motors power), AW4, 4:56's and 33" Swampers. It's a total pig, mostly used for trail. When I do drive pavement, I have to manually shift through the gears to accelarate onto the hwy. Only to down shift to pull all but the slightest of hills. Swampers are great for offroad but suck on the pavement.

Theres a huge difference in the rotational wieght of a 6 ply tire (especially one loaded with mud). We'll save what those monster heavy tires do to brakes for another thread. Just fuel for thought.

 

[Phil]

Good point, I'm running a stock 4.0L/AW-4/231, with 35" MT/Rs. 4.88s should be pretty nice.

 

[red87cherokee]

Just to back up Beezil I run 4.56s with 31s and I can still highway drive fine and the Jeep is great offroad. I love my gearing and when I get 35s I am going to miss the extra gearing.

I just installed 4.88's and lockers (Detroit and Lockright) in the Fall and I ran 31's for several months before putting on my old 235/75R15's studded snow tires - 35's are going on in the spring. And I absolutely agree that I'm going to miss the extra gearing. Unless you need to fly down the freeway at 90 MPH, any tires larger than 31's NEED 4.88's at the very least!

 

[basalt51]

Well after trying many combinations on Randy's calculator and many others I think 5.12 are the way to go. I have the aw-4 auto and I drive 120+ miles per day. With 34.5" tires here are my calcs:

To Calculate RPM If Rear End Ratio Is Known:
Rear End Ratio: 5.13
@ Desired MPH: 75
Tire Diameter (Height) in Inches: 34.5
Overdrive Ratio (1 for no OD): .69

RPM at Given MPH: 2586



To Calculate RPM If Rear End Ratio Is Known:
Rear End Ratio: 5.13
@ Desired MPH: 75
Tire Diameter (Height) in Inches: 34.5
Overdrive Ratio (1 for no OD): .69

RPM at Given MPH: 2460


Not a big difference, but if you then calc at 65 mph:

To Calculate RPM If Rear End Ratio Is Known:
Rear End Ratio: 4.88
@ Desired MPH: 65
Tire Diameter (Height) in Inches: 34.5
Overdrive Ratio (1 for no OD): .69

RPM at Given MPH: 2132

The RPMs are getting awefully low in OD; It'll be shifting into drive all the time at any small hills withthe 4.88s. Hell, if I was planning on cruising at 65 all the time I would want 5.29s+.

Whats the deepest gear you can run in a Ford 9"? Maybe that will be the decision maker for me.

EDIT: Looks like 6.50 - that doesn't help at all

 

[mbryson]

Well after trying many combinations on Randy's calculator and many others I think 5.12 are the way to go. I have the aw-4 auto and I drive 120+ miles per day. With 34.5" tires here are my calcs:

To Calculate RPM If Rear End Ratio Is Known:
Rear End Ratio: 5.13
@ Desired MPH: 75
Tire Diameter (Height) in Inches: 34.5
Overdrive Ratio (1 for no OD): .69

RPM at Given MPH: 2586



To Calculate RPM If Rear End Ratio Is Known:
Rear End Ratio: 5.13
@ Desired MPH: 75
Tire Diameter (Height) in Inches: 34.5
Overdrive Ratio (1 for no OD): .69

RPM at Given MPH: 2460


Not a big difference, but if you then calc at 65 mph:

To Calculate RPM If Rear End Ratio Is Known:
Rear End Ratio: 4.88
@ Desired MPH: 65
Tire Diameter (Height) in Inches: 34.5
Overdrive Ratio (1 for no OD): .69

RPM at Given MPH: 2132

The RPMs are getting awefully low in OD; It'll be shifting into drive all the time at any small hills withthe 4.88s. Hell, if I was planning on cruising at 65 all the time I would want 5.29s+.

Whats the deepest gear you can run in a Ford 9"? Maybe that will be the decision maker for me.

EDIT: Looks like 6.50 - that doesn't help at all

I know the math works out, but I have 4.88's and 35" MT/R's (whatever they measure). For arguments sake, let's say they are 34.5. I live at 5400 ft. and take hills quite a bit. The 4.88 is plenty of gear (I do have a TIRED motor with 180K and more vertical than it should have had) and when I'm on the flat, I'd like to have 4.56.

I do not stay in OD on hills as I'm climbing from 5400 ft. to about 8000-9000 on most 'common' highways.

 

[basalt51]

I know the math works out, but I have 4.88's and 35" MT/R's (whatever they measure). For arguments sake, let's say they are 34.5. I live at 5400 ft. and take hills quite a bit. The 4.88 is plenty of gear (I do have a TIRED motor with 180K and more vertical than it should have had) and when I'm on the flat, I'd like to have 4.56.

I do not stay in OD on hills as I'm climbing from 5400 ft. to about 8000-9000 on most 'common' highways.

Thanks for the info. Do you drive long distances on relatively straight, flat freeways? What's your Hwy mileage? Rpm's? Cruising speed? I have troble going less than 75, but maybe deeper gears will force me to slow down!

Thanks for the info! I should just find someone with 4.88s and drive it.


Thanks again.

 

[CaptTrev]

this is probably a stupid question, and i think i know theanswer already but here goes:

im on 31's right now with stock 3.55 gearing

when i go to 4.56's, what will my "off the line"/0-60 speed do?

i ask this because i want to do gears and (some form of) lockers NOW, and have it still work well for when i go to 33's (and possibly, eventually 35's)

this is 100% my DD rig, but it DOES see some good weekend wheelin...

thanks!

CaptTrev

 

[mbryson]

Thanks for the info. Do you drive long distances on relatively straight, flat freeways? What's your Hwy mileage? Rpm's? Cruising speed? I have troble going less than 75, but maybe deeper gears will force me to slow down!

Thanks for the info! I should just find someone with 4.88s and drive it.


Thanks again.

Hmmmm.....I've never driven the XJ out on the salt flats or anything......I do drive it to Moab and it's 'relatively flat' after you get off the freeway. That's about 40 miles or so......It does fine. It doesn't like to go much over 70-75 or the mileage just plain goes to he11. I'm about 16-17 on the highway and probably 13-15 around town depending on weather. At 65, I think my RPM's are 2400-2600......don't hold me to that.


Oh, and Captn......I'd probably go with the 4.56 with what you've indicated.

 

[89TrailXJ]

Well I am going to 33's and want to re-gear as well.
Here's what I found:
4:56's with install kits- $326
Add a Detroit EZ Locker- $252

So for $580ish I can upgrade gears and to a rear locker. Sound about right?

Website is: http://www.drivetrainsuperstores.com/

 

[sintax]

$580 assuming you have all the proper tools to install gear, and have the knowledge to do so. A gear install is not something that should be tackled by just anyone.

You also need to add the cost of a carrier into the mix as well, unless you have 4.10's from the factory.

As for the EZ Locker....I'd spend the few extra dollars on a full detroit soft locker. I think you'll find it a better option in the long run.

-Scott

 

[Mojo Troll]

this is probably a stupid question, and i think i know theanswer already but here goes:

im on 31's right now with stock 3.55 gearing

when i go to 4.56's, what will my "off the line"/0-60 speed do?

i ask this because i want to do gears and (some form of) lockers NOW, and have it still work well for when i go to 33's (and possibly, eventually 35's)

this is 100% my DD rig, but it DOES see some good weekend wheelin...

thanks!

CaptTrev

4:56's and 33's are'nt to bad. If your considering 35's in the future you might want to consider 4:88's. You going to run stock axles with 35's???

I've got a fresh rebuilt non HO (no where close to the power of a HO) 4L, AX 4, 231, 4:56's, 33" Swampers (actual 33.7" according to TSL), Dana 35/30. At 65mph I'm turning 2100 rpm in OD, flirting with 3 grand in 3rd. The only time I drive my pig on the freeway is to get to dirt. Around town I run in 3rd. I live in mountainous terrain, so on the freeway I have to shift into 3rd a lot. The heavy Swampers (suck on freeways) and non HO motor don't help.

Get it in the dirt and thats a different story. I like 33's/4:56's pretty well. The only complant I have is in tacky mud. My non HO motor does'nt have the power to spin the heavy, mud caked tires enough to shead mud on long climbs. Which has nothing to do with gear ratio anyways, simply lack of power. I'm going with a little less aggressive more pavement friendly tire when I wear out the Swampers.

If your going to run Dana 35/30 with 35's you want 4:88's or lower if possible for sure. Personally I would'nt run 35's on a 35/30 (which would negate you spending money to lock them), especially on a DD. Thats asking alot of 27 splines IMHO. If your considering building that big down the road, think about swapping axles rather than building 35/30's. My axles are deffinatly my weakest link. Its always funny to see my XJ flexed, then I look at those toothpick axles and laugh. On the other hand sometimes its not so funny when you get into a tough section and start worrying about those toothpicks snapping.

BTW If you build as big as your considering, "off the line" will be the last thing running through your mind. It will be more like "where is the next gas station" and "Do you think I can crawl over the top of that Honda Civic". eace:

 

[xj92]

I just find it amusing that everyone talks about highway usage and in the same sentence uses calculations for 65mph. I always run 10 over, so I drive 75 and 85 on the highway, depending on the limit. So when I look at how my gears perform on the highway, I think about up to 85mph, not 65mph. Right now I run bald 31's (currently 29.5") with the 5-speed, and at 85mph I'm right above 3000rpm. 3000 rpm's for 9 hours straight on a trip to Moab isn't bad if my cat is removed, because it seems to move the power band up the rpm range a little. With the stock cat & muffler though it's awful and feels like the motor is screaming for relief.

 

[Mojo Troll]

I just wish my pig could maintain 65mph in the mountains. :laugh:

 

[crazy4mopar]

I'll be running 4:88's with my 35's. In OD I will only be pushing 2436 rpm's at 65 and about 2623 at 70

 

[Neil]

I went with the 4:88's My transmission loves me again! I woulden't recomend anything deeper for a DD. I spend very little time in first gear, the engine winds up real fast (even with the auto) I'll let you guys know how they work off road as soon as I get the front regeared. But as for the street 4:88 and 35's are a great combo.

 

[Phil]

Cool, I'm sitting about 10' away from my 4.88s and full spool. What do you think about them on the highway?

 

[basalt51]

Ok, 4.88s it is and I'm never reading another gear thread until they're in

 

[Neil]

There a little low on the freeway, about 2500 rpm's @ 70 mph. That's about the same rpm's that I pulled in 3rd gear with the 3:55's. With the 4:88's the engine is not working near as hard to hold 70 and I can use 4th gear again. All in all I think that the 4:88's were a great choice. With as low as 1st is in 2wd I can only imagine how low it will be in 4low.

 

[PhatXJ]

I run 4.88's in my D30/44 with ARB's. AW4, and 35's.

It's perfect.

It's not my daily driver, but when I go wheelin, I drive all the way there on the freeway. Drove from WA state to Moab last Oct. No problems. At or near 2500 rpms at 75mph.

 

[REDXJ4FUN]

I had 33s on mine when i went to 4.56 and loved them but now with 35s I wish i had gone with the 4.88s but its no an issue now since my old axles are in my friends XJ turning 32s and hes having a blast with it. I'm now going to 5.38s :yelclap: :cheers: . ya i'll turn some rpms on the high way a little over 2500 at 70 witch is fine with me oh a whole 400 rpm more than the 4.56.