2021 40” Rubicon Diesel Build

Mr. Curti

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Did you get the 72” Dynatracs?

I called and talked to them about it. They are working on a diesel spect kit but said it’s challenging them to say the least. They hope to have it out this summer.
Yes, we went with the 72” and big bell RCV with 5.38 gears. Originally we were going to do 5.13’s, yet we decided to change and go with lower gears because of the tire & rim size. 42x13.5X20 on Trail Ready bead-locks with the World Series bead-rings.
 

Gorilla57

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Stock I was doing 76 MPH in 8th gear at 2,000 RPM

Now I’m doing 69-70 MPH in 8th gear at 2,000 RPM
Just for reference, as I know it is a different setup, my 1500 4x4 diesel turns 2,000 RPM at 72mph. This is with the 3.92 gears and 33x12.5x22 on the stock heavy ass 22's. At 75mph, it gets 24-25mpg. So, the diesel can still get good mpg turning more RPM.
 
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40”JLURD

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Just for reference, as I know it is a different setup, my 1500 4x4 diesel turns 2,000 RPM at 72mph. This is with the 3.92 gears and 33x12.5x22 on the stock heavy ass 22's. At 75mph, it gets 24-25mpg. So, the diesel can still get good mpg turning more RPM.
I’m going to try putting a little more PSI in the tires. At 27 cold I am getting about 12-13 mpg city driving. Which is what’s killing my overall mpg. Highway isn’t too bad and I can probably average around 20 maybe. Haven’t done a trip long enough to test it out yet though.

But the other day just running errands close to home I put about 30 miles on it all city driving and think it returned around 13 mpg. 😕

Definitely worse than I was hoping for with the diesel......
 
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40”JLURD

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Quick update - apparently KMC (which I now have the KMC Grenade wheels) says these wheels are designed for guys why run up to 8 & 10 ply tires; up to 65 to 80 PSI!!!

This is absolutely insane for beadlocks and is great for me. The Mickey’s I’m running max out at 35 psi cold and that’s what I inflated them to today.

So far results are great.. will update later with more miles
 

Jteakus

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Good info on the 4.88's, I would have done the same. I'm also waiting for the PSC kit, stuck in limbo. Steering in these jeeps are barely adequate in stock form.
 
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40”JLURD

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Good info on the 4.88's, I would have done the same. I'm also waiting for the PSC kit, stuck in limbo. Steering in these jeeps are barely adequate in stock form.
Welcome!

What size tires you planning on going with? Do you also have a diesel?

Yup I’ve got 40’s on the stock steering box right now and it sucks pretty bad. Barely adequate for daily driving and parking (turning tires at low speed) it really shines like a turd 💩 lol
 
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40”JLURD

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I have the 3.0 diesel. Looking to run a 39” KM3 on front and rear Dynatrac 60’s.
You should definitely get the 72” wide ones. I wish I had gotten those instead of the 69.5” Dana Ultimate 60’s I ended up getting.

4.11 gears will give you more MPG than stock (before you throw on big ole meats), while 4.56 would be slightly more POWER than stock - which DID NOT work out well for me. 4.88 with 39” (actual measurement) tires is terrible on MPG. So if you want to stay as close to stock as possible MPG go 4.11

If you don’t care about MPG at all or don’t mind getting 10mpg less than it was stock then go 4.56 - power wise you won’t be able to tell a difference. It’s still going to be a diesel motor either way (slow)

04A3B11E-D03E-4A71-90AE-04032940BE9F.jpeg
 

Jteakus

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Just can’t wrap my mind around 4.10’s and a 39.
Dynatrac doesn’t show a ratio below 4.88 but I’m sure arrangements can be made. I was leaning towards 4.56.
All on hold till PSC gets the steering kit ready, that’s my next step.
 
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40”JLURD

40”JLURD

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im curious what you have that I don't that is killing your mpg so much. I mean I know I have 37's and you have 40's but I have stock gears and I've added lots of weight including heavy ass rims and im averaging (hand calc) 24.5 and I just did a 760 mile trip mostly all hills, and mostly uphill and my hand calc with the 2 tanks it took was 24.9 going 72mph. that's badass and way better than any gasser I've ever seen in a jeep. note: I also had 350 pounds give or take in the backseat/cargo area of metal. not including me and passengers (310 pounds)
Just can’t wrap my mind around 4.10’s and a 39.
Dynatrac doesn’t show a ratio below 4.88 but I’m sure arrangements can be made. I was leaning towards 4.56.
All on hold till PSC gets the steering kit ready, that’s my next step.
Look at @Howardlv22 post above. He’s on 36.8” tires and stock 3.73 gears and getting almost 25 MPG highway.

His actual gear ratio is 3.24 with that setup.

3CB7CF22-E52D-4B99-8578-CEE81C017EBB.png


The BFG 39” measures 37.5” when mounted.

Even with 4.11 you would have more power than Howard on those 39” BFG (and less MPG)


C62A9846-FB58-4C43-BC03-8EA563A85503.png


That would probably be perfect to make up the extra weight of the 39’s. I personally would NOT go to 4.56 having just spent $15k on axles geared to 4.88 and 39” actual height tires. I quite dislike the combo for the diesel and wish I would have gone with a 4.56 - and that’s with the 39’s.

F8B3CFF2-6717-4A62-B7D8-1E425F625DA0.png
36D3CCCD-454B-4809-B9E5-36BB80562735.png


My tires measured 38.5 when I had them at 27 psi and my mileage was absolutely awful. Choose the ratio you wish but here is some tips

Best MPG I’ve ever got on my current setup is 16.16 MPG with mostly highway driving .....
 
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Jteakus

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I'm on 35's (34.4" actual) and 3.73's now. Even with my lead footed wife driving to and from work mixed city/hwy she gets 25 mpg average over the week. I can easily get 27-28 in it when I drive it.
 

Jteakus

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I hate to admit this but after reading this thread 4 times I'm gonna leave it alone. We have a buggy for the fun stuff and on 35's I can still have a lot of fun with the JL. I still admire your build and wish you the best of luck!
 

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