Re-gearing for 33's

[AndyA]

Sorry if I missed it but what RPM range is ideal for 65/70mph on the 4.0 with the 42RLE?

if you put the stock tires into the grim jeeper site it will tell you what the stock RPMs would be. Then you can either target that or a bit above or a bit below, depending on if you want stock performance again or something else. At least that is my understanding of the process.

Andy

 

[jjvw]

if you put the stock tires into the grim jeeper site it will tell you what the stock RPMs would be. Then you can either target that or a bit above or a bit below, depending on if you want stock performance again or something else. At least that is my understanding of the process.

Andy

If that is what we are going to do, then it needs to pointed out that stock rpms were all over the place. Which factory rpm was the ideal rpm? Why did the Rubicon come with 3 different transmissions, but all had 4.10 gears? Which factory rpm do we want to emulate?

42rle / 29.5" /3.73 = 2052rpm @ 70mph

NV3550/29.5"/3.73 = 2320rpm @ 70mph (nearly 300rpm higher than the 42rle)

AX-15 / 29.5" /3.73 = 2349rpm @ 70mph (nearly 300rpm higher than the 42rle)

NSG370/29.5"/3.73 = 2498rpm @ 70mph (over 400rpm higher than the 42rle)

32rh/29.5"/3.73 = 2974rpm @ 70mph (nearly 900rpms higher than the 42rle)

 

[Rickyd]

If that is what we are going to do, then it needs to pointed out that stock rpms were all over the place. Which factory rpm was the ideal rpm? Why did the Rubicon come with 3 different transmissions, but all had 4.10 gears? Which factory rpm do we want to emulate?

42rle / 29.5" /3.73 = 2052rpm @ 70mph

NV3550/29.5"/3.73 = 2320rpm @ 70mph (nearly 300rpm higher than the 42rle)

AX-15 / 29.5" /3.73 = 2349rpm @ 70mph (nearly 300rpm higher than the 42rle)

NSG370/29.5"/3.73 = 2498rpm @ 70mph (over 400rpm higher than the 42rle)

32rh/29.5"/3.73 = 2974rpm @ 70mph (nearly 900rpms higher than the 42rle)

That idea also ignores the fact larger tires need more rpms(power) to turn. Especially at higher speed where weight and rolling resistance play a larger role. Offroad too where larger tires give obstacles more leverage against the jeep

 

[LONGJP2]

Sorry if I missed it but what RPM range is ideal for 65/70mph on the 4.0 with the 42RLE?

'Ideal range' can mean different things to different people.
The 4.0 is more in its power band above 2500.
For me, I hit 70 mph around 2500.
I can do 85 at 3000 if I'm going downhill with a tailwind.
YRMV

 

[Hokahay]

I have a 4.0 with 42rle. 5.13s. Kicks ass and takes names, I am thinking 2650 at 70mph. Right now 33x12.5 MTRs.

 

[TexasTJ2004]

I have 42RLE, 4.0 and 4.56 gears. Running 31 inch tires. It drives OK.
If I would do it today, I would take 4:88 gears for 31s. 5:13 for anything higher (cannot go higher with Dana 30).

 

[L J]

... so long story short... I guess my question is... do I go ahead and get lights... or lockers...?