Re-Gearing

[XJWheelie]

I've still got stock gears, but I've upgraded my tires a little bit to 30". The next step will be either 32" or 33", most likely the 33"s if I can get them to fit. What I'm in search of is an article that contained a chart showing what gears to use with different sized tires. Does anyone out there know where I found this neat little article and chart. I thought that I had printed it out, but alas, I had not.

Robert

[Beezil]

don't use charts!

charts are formulaic, "one size fits all" and most do not take into account overdrive ratio, or the powerband of the engine.

use calculators!

grimm's is one of the best.

if I were in your shoes, I'd do 4.56's for 32 and 4.88's for 33's for the auto.....

[Centrevillemx]

According to the Jeep 4x4 Performance Handbook: To obtain the effective gear ratio: old tire diameter x original ratio/ New tire diameter= effective ratio of new combination. In your case , with 3.73 gears currently, your effective ratio with 33's would be 3.90.

[CRASH]

Huh? What is this effectve ratio of which you speak? :confused:

CRASH

[CRASH]

4.56 would do you nicely with 32's or 33's. 4.88's would be better, but I don't like them in a D-30.

CRASH

[Beezil]

According to the Jeep 4x4 Performance Handbook: To obtain the effective gear ratio: old tire diameter x original ratio/ New tire diameter= effective ratio of new combination. In your case , with 3.73 gears currently, your effective ratio with 33's would be 3.90.

this assumes that the jeep was geared correctly fromt he factory....that equation proves my point.....

NO ONE here could argue that 3.92 (even if you could run them) is an effective ratio for those tires.

[KY Chris]

Don't even think about 4.10s. Go straight to 4.56 or 4.88s.

[Beezil]

crash, I think 4.88's in a dana 30 can be made stronger using a little different set-up approach......I contend that 4.88's themselves are not weak, its the dana 30 housing flex and the way they are set up makes them break in some cases....

I'd be willing to debate on another thread if you disagree

[2xtreme]

I have the 4.0, Auto and I have 33x12.5's and 4.88 gears. I could not be happier. If I were running 32's I would have gone with the 4.56's.

When I called Randy's Ring and Pinion to get gears they told me that to go back to stock gear ratio with 33's I need 4.10's. There is no way that I would recommend 4.10's on anything more than a 31" tire.

I agree with above, forget the charts, forget the ratios, go with what people (with the same platform as you) have learned over time.

Michael

[marcusguy]

I have 32s and just put in 4.56's and I love them; city, hwy, offroad.

marcus

[CRASH]

I'd be willing to debate on another thread if you disagree

No need to debate. We are on the same wavelength. As hard as I've tried to super pre-load the carrier, under hard use, even 4.56's open up.

Then the pinion wants to ride over the top of the ring gear, causing even more flex, and it all goes to hell.

Trussing is the answer. We'll see if Lazy Gary(E)'s trussing helps his 30 live.

CRASH

[What Rd]

So what direction or plane is the one (or most important one) to truss to keep the ring gear and pinion cozy? Is it the flex of the pumpkin itself or the flex between the tubes and the pumpkin that causes the most trouble?
A really stout cover (like those of OxTrax or Crane, for example) helps to some extent, right? But what other trussing - a vertical rib running along the upper surface? Does this need to be tied into the pumpkin to be effective?

[ThePhantum]

Here's a pretty good chart based on 65 MPH and a gear ratio of 1:1, on a manual transmission in 4th gear. Your best bet though would be to do the math.

http://www.quadratec.com/cgi-bin/sgdynamo.exe?HTNAME=tech_corner/gear_ratio.html&UID=2003080806361105',%20700,%20420


Rock On!

[Beezil]

No need to debate. We are on the same wavelength. As hard as I've tried to super pre-load the carrier, under hard use, even 4.56's open up.

think tighter backlas, around .003", and centering the pattern a little toward to the root and toe of the tooth, near as I can figure, when the backlash opens up during high torque loads (carrier flex) I'm thinking the contact pattern move to where it should be, not away from where it should be onto the topland and heel of the tooth where they are weakest, and where I've seen them break.....

maybe goat would let me set up some 4.88's for him, and he could go out and try to break them......

[BrianJr]

marcusguy:

What are you getting for mileage now (and compared to stock if you can). Thanks.

-Brian

Originally posted by marcusguy
I have 32s and just put in 4.56's and I love them; city, hwy, offroad.

marcus

[CRASH]

think tighter backlas, around .003",

Oh, I've been doing that since the begining. Usually around .005 on non-disconnect axles, and .003 on discos. I've always been afraid of running the constantly spinning designs that tight.

Maybe it wouldn't matter, without power actually going to it.

I think the truss needs to go in the horizontal plane, around the back of the housing. It needs to be beefy, and care needs to be given to welding to the casting properly.

CRASH

[marcusguy]

Brain JR-

Well, I've only had them on for about half a tank so far, but when I hit the halfway mark, I had the same miles as I did before the swap. I would get about 20 hwy and about 17.5-18 mixed and it seems like it will be about the same now.

Mileage is important to me so I drove around in 3rd (AW4) for about a week, hwy and city. By my calculations, 3rd gear ration of 1:1 with 32s and 3.55s came in to be about 50 rpms higher than after the swap in 4th with 32's and 4.56s. (so it was a good way to predict what the results of the swap would be like) I took some road trips in 3rd and just let it hum along at about 2600-2700 RPM and my gas mileage was basically the same, and that is what made my decision to go with 4.56s instead of 4.10s. I'll probably see a little better mileage when I get used to it and can keep my foot out of the fun pedal.

Marcus

So far it hasn't had to down-shift for any of the grades around here.

[What Rd]

Originally posted by Beezil
think tighter backlas, around .003", and centering the pattern a little toward to the root and toe of the tooth, near as I can figure, when the backlash opens up during high torque loads (carrier flex) I'm thinking the contact pattern move to where it should be, not away from where it should be onto the topland and heel of the tooth where they are weakest, and where I've seen them break.....

maybe goat would let me set up some 4.88's for him, and he could go out and try to break them......


Hey Beezil -
PM'd you.

[Bronco]

I made up a speed sheet that will graph your RPM over speed after you enter in all the numbers when I was looking into all this. It lets you put in up to 3 different setups at a time and chart them together so you can compare them. Anyone who want a copy to play with need only PM me.

[robs]

If you got MSExcel... here's a calculator that will compare two different set ups and what you can expect for the outcome...

http://members.intertek.net/~simons/misc/rpm.xls