Another gearing question

[Jimmyburkitt]

Hi I need some advice, I have a 4 banger tj running 34s, 4" lift and need to regear, I blew out my drivetrain and replaced it with craigslist 30 and 35 from a 6 banger, so of course it's very slugsh, I want to regear it for calico, how low can I go? It is only really used for off road, no sway bars ect, but I would like to go around 55 or 60 on the hwy just to get to the trails, thanks for any help!

[Loki XJ]

I wouldn't go any lower than 4.56's. the Dana 30 doesn't like 4.88 gears, something about ring gears breaking in them cuz they aren't thick enough... And I'd be careful with that Dana 35, everywhere I read on my xj forum, Dana 35's can barely handle 33" tires locked or not. But I'd say 4.56's would bring you back to where you wanna be

[Jimmyburkitt]

[quote="Mikeys_cougar"]I wouldn't go any lower than 4.56's. the Dana 30 doesn't like 4.88 gears, something about ring gears breaking in them cuz they aren't thick enough... And I'd be careful with that Dana 35, everywhere I read on my xj forum, Dana 35's can barely handle 33" tires locked or not. But I'd say 4.56's would bring you back to where you wanna be[/quote]


Cool thanks! I have the rear locked and the front posie, I'm in the market for some Dana 44s I also have been trying to find someone to do a small block convert, but for now I have what I got, I don't know if it matters but I checked the tires this am and I do have 33" tires. Thanks for the help!

[gearheadLJ]

Cool little chart to help you decide....

http://4lo.com/calc/geartable.htm

Couple other things to consider.

Your 33" tires aren't. They are probably a little smaller. Tires rarely are exaclty the diameter the manufacturer says. My 33"s are actually 32.5".

Also consider static loaded radius. While a tire may be certain diameter when no load is on it if you apply the weight of your TJ the diameter is reduced. Air pressure also can make a difference in the diameter. As an example my 33" BFG AT KO's at 30 psi are actually a little over 32.5". Add the weight of the Jeep and the static load makes them only 30.75". Measuring for static load diameter is easy. With the tires on and the Jeep on the ground just measure from the ground up to where you thing the center of the wheel hub is. Take that measurement and multiple by 2. That's the static diameter and what the rear end actually "sees" for a tire diameter.

[Loki XJ]

When you find that d44 let me know. I want a locked rear axle and I already have a d35 with limited slip (I think) so a different 35 locked couldn't be worse

[Desert Dog]

[quote="Mikeys_cougar"]I wouldn't go any lower than 4.56's. the Dana 30 doesn't like 4.88 gears, something about ring gears breaking in them cuz they aren't thick enough... And I'd be careful with that Dana 35, everywhere I read on my xj forum, Dana 35's can barely handle 33" tires locked or not. But I'd say 4.56's would bring you back to where you wanna be[/quote]

Lots of folks running 4.88s in D30s with no issues. I have done it in my last 4 jeeps. I wheel with hundreds of folks that use 5.38s in their D44s. This is another internet rumor with no basis in fact, its always "my dads friend of a friend of a cousin". High gears break as much as low gears. Your shafts will go before the R&P unless you are running Chrome mollys or doing something stupid like pulling backward in 4WD. Check on Pirate, or most 4x4 shops if you don't believe me. I also have a TJ with a 4-banger in it and have 4.88 gears. I think they are adequate for the application and probably the only way you can even do more than 30MPH uphill with the 4-banger

I think you will regret getting 4.56s, as it's only a very minor improvement over the 4.10s that 4-banger TJs came with. You will kick yourself for not going 4.88, trust me.

As for the D35; one of the worst axles ever put in a Jeep and is a PITA (and sometimes impossible) to get the rig off the trail with a broken shaft. I wouldn't run more than 33s with a D35 and a 6 cyl, and take it very easy at that . That being said, some folks wheel the heck out of em and rarely have issues. Your 4-banger isn't pulling enough horsies/torque to easily break a D35, but I would still take it easy.

[Loki XJ]

desert my buddy has an 8.25 waiting for me whenever im ready to install it, i will put it in after i make my camping trip to jawbone, so hopefully by the weekend of the 1st ill have an 8.25 under my jeep and i can stop worrying about my d35

[Goatman]

Ditto what Chris said, no fact to the rumor that D30's don't like 4.88 gears. I have 4.88's in my XJ's D30 on 33's, and ton's of people have 4.88's in D30's. It's actually by far the preferred ratio for 33" tires if you have an XJ or a TJ with a stick. A TJ with an auto which has no overdrive could be happier with 4.56's. With a 4 banger I'd go 4.88's no matter what.

Get the 8.25 or find a D44. No sense wasting money on a D35.




Regarding the rolling radius of a tire, how does the circumference measurement change as you let air out? Yes, the effective radius changes, but you don't drive on the radius, you drive on the circumference. If the tread of a tire is like the track on a cat or tank, does the track length shorten if the track path is flattened on the bottom?