[27mtaylor]

I have a 5 speed and running 35" BFG MT's with a 3.07 ratio. In the near future I want to put a D44 in the rear and regear. I've looked at the gear ratio charts and the 4.56's and 4.88 seem to be best for dailey driving performance. Most people on the forum say to use the 4.88 for the manual transmission. Why is that? Would you get a little better milage out of the 4.56's and just a little more power out of the 4.88's? I use my jeep for trail rides and I will drive it to work 3 times or more a week. Would the 4.56's not be better for economy? Anyway, tell me what you guys think and the reasoning behind it. Thanks!

[shredswithpiks]

Personally, I'd go with the 4.56 gears because it would be just a little more sane on the highway. But, I'm also spoiled on a 4:1 teralow so I'm not sure what would be the best balance for trails and the highway.

[ajmorell]

The reason that people suggest 4.88 for the manual has to do with the gearing of the transmission itself. I can't say with any certainty, but would guess that the 5 speed transmission's gearing is a bit higher than the auto's. FWIW, I won't run 4.88s with a dana 30 front due to the pinion only having 9 teeth. There are plenty of people out there running them without problems but it's the last thing I would want to break on the trail.

[palmrose2]

Originally Posted by ajmorell

I won't run 4.88s with a dana 30 front due to the pinion only having 9 teeth. T

That's the way I feel about it.

[ClimbStuff]

4.01 x 4 x 4.88 = 78.275 rpm / tire rotation

If you let it idle at 500rpm and pt it in gear, it will crawl at a rate of 6.38 tire rotations/min... on a 35" tire, 109.95"/min, or 9.16ft/min, or .104 mph..... so as you can see... it'll take a mighty large force to bog your motor down in gearing that low... you could pull just about anything id think... train maybe?

[mdm]

Originally Posted by ajmorell

... I won't run 4.88s with a dana 30 front due to the pinion only having 9 teeth. There are plenty of people out there running them without problems but it's the last thing I would want to break on the trail.

As you said, there are a lot of people running that nine tooth pinion. How many times do you hear about one of them having a pinion related problem? With the D30, you'll normally have something else break before it gets to the pinion.

[ajmorell]

Originally Posted by mdm

As you said, there are a lot of people running that nine tooth pinion. How many times do you hear about one of them having a pinion related problem? With the D30, you'll normally have something else break before it gets to the pinion.

Yeah, that's the thing...you really don't hear about it unless people have upgraded everything else including the joints and shafts. I do know of a few people who were running locked fronts and upgraded shafts and joints that were blowing through R&Ps. I think that the reason you don't hear much about it happening is because people either don't have the motor to cause that carnage, aren't running a locked front, or are running reasonably sized tires (33-35). I think most people know that the 30 has it's limits so they are only willing to dump so much money into it before upgrading altogether.

[AzBuckfever]

Originally Posted by ClimbStuff

4.01 x 4 x 4.88 = 78.275 rpm / tire rotation

If you let it idle at 500rpm and pt it in gear, it will crawl at a rate of 6.38 tire rotations/min... on a 35" tire, 109.95"/min, or 9.16ft/min, or .104 mph..... so as you can see... it'll take a mighty large force to bog your motor down in gearing that low... you could pull just about anything id think... train maybe?

May be just me and maybe I'm wrong, but I think your math calculations are off.

#1. You have to figure the transmission ratio as well which will affect everything with your travel speed, but we're not talking that.

If you're talking travel speed....the math is a little off, I believe.

3.83:1 (1st gear tranny [AX-15]) x 4:1 (t-case) x 4.88:1 (diff) = 74.76:1 crawl ratio....

We're talkin' reductions, not multiplying....

So, takin' 500RPM out of the engine brings it down to 130.54 coming out of the tranny, into 32.63 RPM comin' out of the T-Case....to 6.68RPM to the wheels....

With 35" tires, you're talking a foot print of 109.9" per revolution....at 6.68 RPM is 734.13" or 61.17 ft/min.

With 4.56...you're talkin'....785.78"/min....or 65.48 ft/min....Not much of a difference...

An easier method would be to take your crawl ratio and multiply it by your wheel circumference to get your travel in inches....then reduce from there.

Just thought I'd help out. Not much of a difference but it sure aint "Walkin' the Crawler"....

Now with terms of speed and using a vehicle as a DD

I'm assuming you have the same 5 speed as I do (AX-15)
Gear ratios for the AX15 are: 3.83, 2.33, 1.44, 1.00, 0.79, for first through fifth, respectively.

At a cruising speed of 2500 RPM in forth gear (as with my current 3.55 gears in the crapshack D35, I can't even get into 5th)....

With 4.56 gears my speed would be: 57 MPH increased to 72mph in 5th

With 4.88 gears, it would be: 52.8 MPH increased to 67.2 mph in 5th.

Obviously, the equation of the T-Case is out because no one in their right mind is gonna lock into 4th gear in 4:1 low range

As for fuel economy, I don't think you'll see much of a difference, if any. You're only talkin a few MPH faster with the 4.56 gears. Keep in mind that if you have 4.88s and you want to reach the same speed as what you would with 4.56 in 5th; you would have to rap your engine out higher (such as around 2700 RMP = approx. 72.6 MPH) which would decrease your economy.

Hope this helps...and happy wheeling.

[ClimbStuff]

Originally Posted by AzBuckfever

May be just me and maybe I'm wrong, but I think your math calculations are off.

#1. You have to figure the transmission ratio as well which will affect everything with your travel speed, but we're not talking that.

If you're talking travel speed....the math is a little off, I believe.

3.83:1 (1st gear tranny [AX-15]) x 4:1 (t-case) x 4.88:1 (diff) = 74.76:1 crawl ratio....

We're talkin' reductions, not multiplying....

So, takin' 500RPM out of the engine brings it down to 130.54 coming out of the tranny, into 32.63 RPM comin' out of the T-Case....to 6.68RPM to the wheels....

With 35" tires, you're talking a foot print of 109.9" per revolution....at 6.68 RPM is 734.13" or 61.17 ft/min.

With 4.56...you're talkin'....785.78"/min....or 65.48 ft/min....Not much of a difference...

An easier method would be to take your crawl ratio and multiply it by your wheel circumference to get your travel in inches....then reduce from there.

Just thought I'd help out. Not much of a difference but it sure aint "Walkin' the Crawler"....

Now with terms of speed and using a vehicle as a DD

I'm assuming you have the same 5 speed as I do (AX-15)
Gear ratios for the AX15 are: 3.83, 2.33, 1.44, 1.00, 0.79, for first through fifth, respectively.

At a cruising speed of 2500 RPM in forth gear (as with my current 3.55 gears in the crapshack D35, I can't even get into 5th)....

With 4.56 gears my speed would be: 57 MPH increased to 72mph in 5th

With 4.88 gears, it would be: 52.8 MPH increased to 67.2 mph in 5th.

Obviously, the equation of the T-Case is out because no one in their right mind is gonna lock into 4th gear in 4:1 low range

As for fuel economy, I don't think you'll see much of a difference, if any. You're only talkin a few MPH faster with the 4.56 gears. Keep in mind that if you have 4.88s and you want to reach the same speed as what you would with 4.56 in 5th; you would have to rap your engine out higher (such as around 2700 RMP = approx. 72.6 MPH) which would decrease your economy.

Hope this helps...and happy wheeling.

I see where my mistake was, but i was only off by about .5mph.

No sir, I dont have the same trans as you do.

NV3550 - 2000-2004
* 5 speed manual
* Used with 6 cyl models
* 10 spline input
* 23 spline output
* Ratios:

1st - 4.01
2nd - 2.33
3rd - 1.39
4th - 1.00
5th - 0.78
Rev - 3.57

Your ratios ARE the reduction rate. They compound each other. You have engine RPM / (gear ratio x final drive) = tire RPM... do the math from there. In this case all I did was add in the transfer case, which is another reduction...

With my trans, and a tera-low tcase, and 4.88's @ 1000rpm engine speed, I'd have a 12.775 tire rpm... which with a 35" tire is going to be 1403.97" /min... also known as 116.99ft/min, or 1.32mph, cut that in half and if you idle at 500rpm, you're moving at about .6mph.

[AzBuckfever]

I was referring to 27mTaylor's transmission/specs. I still don't see where/how you're getting a crawl rate of only 9 ft./min. That is hella slow, even slower than the Marlin Crawler. Guess that's where it confused me a bit. Anyway, not that it matters. His question was why 4.88 and not 4.56. Not how fast he's gonna get there. Long run, I don't think it makes much of a difference until you start discerning between 4.11 and 5.13....

[ClimbStuff]

Originally Posted by AzBuckfever

I was referring to 27mTaylor's transmission/specs. I still don't see where/how you're getting a crawl rate of only 9 ft./min. That is hella slow, even slower than the Marlin Crawler. Guess that's where it confused me a bit. Anyway, not that it matters. His question was why 4.88 and not 4.56. Not how fast he's gonna get there. Long run, I don't think it makes much of a difference until you start discerning between 4.11 and 5.13....

well i did it backwards... and forgot to carry a number or something... its actully 116ft/min... my point was choosing a 4.88 gear was going to be pretty worthless unless you plan on doing a lot of things hat may bog your engine down... otherwise 4.10's should do just fine.

[Wheelin98TJ]

Originally Posted by ClimbStuff

well i did it backwards... and forgot to carry a number or something... its actully 116ft/min... my point was choosing a 4.88 gear was going to be pretty worthless unless you plan on doing a lot of things hat may bog your engine down... otherwise 4.10's should do just fine.

4.10 will do just fine if you have to make a sacrifice.

If you can choose your ratio, most people would be much happier with 4.56 or 4.88 for 35" tires and a manual transmission.

I would go with 4.88. The I6 does not have much power. Gearing lower helps make up for this.

As far as MPG goes, I really doubt you would notice the difference between 4.56 and 4.88. You're stuck getting between 12-16 MPG based on the aerodynamics and the motor.

[leftlanetruckin]

IMHO, if you are going to pay for the gears anyways, may as well go as low as you can.
i ran a hp30, with 30 spline chromo's, arb, yukon super joints and 37's. this was under a yj with a bored/cammed 4.3 chevy/700r4/4.3 atlas. never had any issues with the pinion gear.
the strength difference between the 2 is marginal IMO.
i vote for 4.88's, that little extra gearing will help at times, but never hurt.

martin

[AzBuckfever]

It's all preferential. I would choose 4.88s because I'd have a little more gear for an engine with a little less, I live in a small town; so interstate speeds are few and far between, and when I would need to hit over 65, I can deal with eating a little more gas or taking more time to get to my destination. Even if I chose to run at 3000 RPM, I would be doing 81 MPH...so, I think it would suit just fine

Get whatcha want 27MTaylor, I think you have enough info

[27mtaylor]

Thanks for the info. So if the gas mileage will be about the same with either the 4.56 or the 4.88, I might as well go with the 4.88 and make the TJ a little stronger. Will the higher RPM's have much effect on engine life?