[derf]

I have 4.56 gears with 35's and a 6 speed manual and Pentastar. It's great for driving around and for moderate trail riding. But since my Jeep is a Sport it has the 2.72 low range Tcase. I can't crawl very well because I don't have a low enough low range. When I'm on a ledge I either stall or give it too much gas and lose traction. A Rubicon case would make a huge difference. But even around here they're hard to find. I may end up going with an Atlas instead.

 

[derf]

Gear Ratio Calculator

you have a nsg370 wide ratio trans and a np241 tcase.

yep thats in 6th at 70 mph no kph

There's a selector at the top to switch between SAE and metric so you can choose between MPH and KPH.

 

[derf]

yeah. and the calculator says you would be turning 2722. but you probably arent actually running a true 70.

my speedo was off bad from the factory (like 5mph at 70 stock) when i calibrated it i cal'd it at 70 and ended up punching in a 35.5in tire into the flash cal when im on 37s to get it to read dead on at 70

That's because almost no tire in existence measures as big as the advertised size. It's the difference between what the specs are on paper and the way things actually work in the real world.

If you put in the actual real world rolling diameter of your tire the calculator is spot on. If you insist on using published specs instead, you'll be off. Garbage in, garbage out.

 

[derf]

Neat. never had a need for that so I never noticed it. :beerdrinking:

It's easy to overlook. I may do something to make it stick out more next time I update it. But with spring teasing us I'm probably going to be up in the mountain trails for the next few weekends.

 

[derf]

Yep. there is that too. my MTRs were like a 34.5 mounted but they looked huge next to the same size km2. witch was closer to a true 34. my 37s look big but they are probably a 36.25 in reality. the 13.5 width makes them look monstrous

My Duratracs say they're a 35 but I had to tell my computer 33.48" to get the speedo to match the GPS. With that same size in the calculator it came out almost exactly right. My factory 255/75R15s were advertised at 32.1 but the computer was programmed at 31.01 to get the speedo accurate.

 

[derf]

With 5.13 and 37s, I can truly crawl the 4:1 transfercase. I built my rig to crawl - street performance was only secondary. 5.38 would have been amazing offroad but just too low on street IMHO. It is all about balance. I am an automatic.

2700+rpm is not a bad thing in the 3.6 like it may have been in older engines. I am not sure how true it is but read somewhere Pentastar 3.6 hits its optimum power band somewhere around 2800-3000rpm.

It's lower than that. Mid to low 2,000s, maybe 2,100 to 2,600 is where it's happiest on the freeway.

 

[derf]

So I really want to go with 4.88s but even with the cryo treatment I'm worried it's too much to stuff into a dana 30... really don't wanna blow up my $1200 locker

If you keep the locker turned off until you desperately need it, you can really extend its life. Leaving the differential open and allowing the tires to slip does wonders to reduce stress on everything in the front axle.

If you're really hung up on it, you can take all of the money you were going to put into the D30 and get one of the aftermarket D44's that are out there (Dynatrac, Currie, G2, and maybe others). They are all considerably stronger than a Rubicon D44 (which is really just a D30 with a D44 R&P/locker) and don't need any kind of truss/gusset additions. Swap a few parts over from your D30 and it bolts right in. It costs a little more than throwing parts at a D30 but it's a lot stronger.