Optimal tire size for 4.56s gears and 42RLE?

[billiebob]

The grimmjeeper link is the best way to pick a gear ratio / tire size. And with the 42RLE pick the rpm you want in 3rd, direct drive. Then compromize to make the OD functional.

I run 33s thru 4.10s with the 6 speed. In the mountains, towing I often use 5th, which is the same as your 3rd gear, direct. With 4.56, I'd say as a DD like duty off roader, 33s should be about perfect with the 42RLE.

Lots of the advice to go deeper is coming from more off road use, less DD use. For me I like a taller ratio and use 4LO sooner. Easy to downshift. Impossible to add another overdrive gear on the Interstate as yer engine screams at 80mph. But the 0.69OD is almost like a double overdrive.

Ultimately, the best indicator of needing deeper gearing is lift from a stop. If you struggle to move from a stop, you need deeper gears. Be an idea to find a fellow Jeeper with 33s, and try them on your Jeep for a few hours.

 

[VAUGHN01TJ]

Put a blower on it and you won't need deeper gears

I like the way you think.

 

[Chris]

Hey Chris, wow! I read your project pissed off wife. Ha! Sounds like you have a great build going though. Appreciate the feedback here and love the forum. Curious though, if I pushed the tire size to say 33's with my 42RLE tranny and 4.56 gearing. Would you anticipate needing much of the other upgrades compared to what it takes to do a proper build around say 35's.

With 33s on the 42RLE you want 5.13 gears. The 4.56 gears will still suck with the 42RLE and 33s. It will be livable, but far from "perfect". I had 4.88 gears with 33s on the 42RLE, and even that was close to perfect, but not quite.

Glad you're enjoying the forum! And yes, my build is a coming along nicely, but expensive, that's for sure!

 

[Chris]

Put a blower on it and you won't need deeper gears

Yes and no. The deeper gears will help keep the 4.0 at the right RPM on the highway, in the 2000+ RPM range, which is ideal.

 

[mrblaine]

The grimmjeeper link is the best way to pick a gear ratio / tire size. And with the 42RLE pick the rpm you want in 3rd, direct drive. Then compromize to make the OD functional.

I run 33s thru 4.10s with the 6 speed. In the mountains, towing I often use 5th, which is the same as your 3rd gear, direct. With 4.56, I'd say as a DD like duty off roader, 33s should be about perfect with the 42RLE.

Lots of the advice to go deeper is coming from more off road use, less DD use. For me I like a taller ratio and use 4LO sooner. Easy to downshift. Impossible to add another overdrive gear on the Interstate as yer engine screams at 80mph. But the 0.69OD is almost like a double overdrive.

Ultimately, the best indicator of needing deeper gearing is lift from a stop. If you struggle to move from a stop, you need deeper gears. Be an idea to find a fellow Jeeper with 33s, and try them on your Jeep for a few hours.

At no point in time have I ever considered off road ability in recommending or picking a gear ratio. We need to be able to drive them on the street first, offroad is secondary since the lower gears in the t-case make up for a myriad of re-gearing errors.

 

[mrblaine]

Yes and no. The deeper gears will help keep the 4.0 at the right RPM on the highway, in the 2000+ RPM range, which is ideal.

Ideal is subjective in this case since you just recommended every gear ratio from 4.27 to 5.89 with 35's and the 42RLE. All of which put you at 2000+ at 70mph.

 

[John Young]

I'll play the contrairian. I have an 05 Rubicon w/42RLE, stock 4.10's and 33" Goodyear MTR's. Yes, I noticed a bit less punch off the line but still perfectly acceptable. No impact offroad, since most of the time I'm in 4lo. Doubt I'll ever go to 35's so unless something breaks I'll spend my money elsewhere.

 

[jjvw]

I'll play the contrairian. I have an 05 Rubicon w/42RLE, stock 4.10's and 33" Goodyear MTR's. Yes, I noticed a bit less punch off the line but still perfectly acceptable. No impact offroad, since most of the time I'm in 4lo. Doubt I'll ever go to 35's so unless something breaks I'll spend my money elsewhere.

What are the engine rpms at 75mph? (Fixed)

 

[mrblaine]

What are the engine rpms at 75rpm?

75

 

[mrblaine]

I'll play the contrairian. I have an 05 Rubicon w/42RLE, stock 4.10's and 33" Goodyear MTR's. Yes, I noticed a bit less punch off the line but still perfectly acceptable. No impact offroad, since most of the time I'm in 4lo. Doubt I'll ever go to 35's so unless something breaks I'll spend my money elsewhere.

It is easy to be contrary if you have never driven 33's with 4.88's or 5.13's. Had you said you had them and went back to 4.10's since you didn't mind the loss of off the line performance, that's a bit different.

 

[VAUGHN01TJ]

I like the way you think.

I have a 05 with 4.0 and 42RLE and plan to regear. I've used this link to look at different variations of gearing and tire size.

http://www.grimmjeeper.com/gears.html

What RPM do you see when running, say 65 MPH, with your 31" tires?

So looked like I was running about 2300RPMs at 65MPH.

 

[jjvw]

75

Correct!

 

[Mr. Bills]

Once upon a time,

5.38 gears with 35" tires and the 42RLE transmission.

And they lived happily ever after.

The end.

 

[Rob5589]

I'll play the contrairian. I have an 05 Rubicon w/42RLE, stock 4.10's and 33" Goodyear MTR's. Yes, I noticed a bit less punch off the line but still perfectly acceptable. No impact offroad, since most of the time I'm in 4lo. Doubt I'll ever go to 35's so unless something breaks I'll spend my money elsewhere.

Everyone has their own idea of acceptable. 4.10 isn't enough gear with the stock tires and the 42rle, let alone the effective 3.8 gearing you have with 33's curently. The 4:1 low in the tcase will mitigate the gearing off road but does nothing for you on. Like Blaine said, gear for on road, not off.

 

[Rob5589]

Put a blower on it and you won't need deeper gears

I know you are just goofing around but many people do think that more HP means you can skimp on gearing. Nope. You still need to gear appropriately for your engine/trans/tire combo.

 

[LukesfirstJeep]

Like Blaine said, gear for on road, not off.

I plan on following this advice, but wonder what RPM people prefer, or what RPM makes the engine happiest?

I'm shooting for 2300-2500 RPM when cruising the highway.

 

[Rob5589]

I plan on following this advice, but wonder what RPM people prefer, or what RPM makes the engine happiest?

I'm shooting for 2300-2500 RPM when cruising the highway.

2500-2800 for the 4.0

 

[jjvw]

I plan on following this advice, but wonder what RPM people prefer, or what RPM makes the engine happiest?

I'm shooting for 2300-2500 RPM when cruising the highway.

What speed do you cruise I the highway way. Mine is geared for 3k rpm at 75mph.

 

[astjp2]

I just took the wife's jk on the highway, 2000 rpms @75 mph, all stock
my YJ was 3000 with parastic loss in the 32RH with 4.10's and 34" tires

 

[mrblaine]

I know you are just goofing around but many people do think that more HP means you can skimp on gearing. Nope. You still need to gear appropriately for your engine/trans/tire combo.

Trying to explain to folks that you regeared to 4.88's to run the new 32's you bolted onto your supercharged TJ just gets you lots of blank stares.