Ecodiesel on 40’s: is 4.88 regear too much

[txred38]

I have a JTRD on 40x15.50r20 w/ the EVO 4.5 lift. My take off is fine, but my truck shifts down in speed when I hit any type of incline. I’ve read a lot about the 3.6 and regearing for 40’s, but I can’t find information on the 3.0 in terms of regearing. Will 4.88 completely kill my MPGs? It’s already down to 19 mpg. Also I’m hoping this would make it easier on my transmission. Any help is appreciated

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[Gr8Hortoni]

4.88 on 40’s is actually quite low still. Probably ok with the 8 speed, but I’d probably just bite the bullet and go right to 5.13’s.

 

[txred38]

4.88 on 40’s is actually quite low still. Probably ok with the 8 speed, but I’d probably just bite the bullet and go right to 5.13’s.

Thanks for the quick feedback.

 

[ATX_Jeeper]

I've been playing with This calculator and it looks like a JTRD with 33s and 3.73s that moves to 40s should be running about a 4.56 gear. As for the transmission, re-gearing will allow the Jeep to use all the gears again and reduce the amount of downshifting / hunting for a gear.

Is there a Jeep shop in your area that has experience with JTRD re-gears that you can contact?

 

[Rusty PW]

Agreed. 4.56's will put you back being equal to 33's and 3.73's. If you offroad a lot. The 4.88's will help there.

 

[Glad_he_ate]

I hope he off roads a lot. Kinda silly to go to 40s for street use.

 

[Rusty PW]

I hope he off roads a lot. Kinda silly to go to 40s for street use.

You never know.

 

[txred38]

This is my JL I sold to get the JT

 

[MattK]

AEV does their JT370 (37" tires) builds with the Diesel engine with 4.56. My hunch is to step it up to 4.88 but I'm just web wheelin' here.

 

[txred38]

This was a tread to make sure I’m doing the right thing for my engine and transmission with this size tire. I don’t want to go to low of a gear ratio since the 3.0l has so much more torque than the gasser.

 

[Glad_he_ate]

I would not go lower then 4.88 5.anything is not necessary with the tq of the diesel

 

[Glad_he_ate]

Keep more meat on the pinion !

 

[txred38]

Keep more meat on the pinion !

Ok. Great. I know the sport and overland have 31’s and Rubicon has 33’s stock with the same 3.73 , so I would imagine anything 37 or more definitely needs a gear swap

 

[Glad_he_ate]

I’ve seen lots of guys say they don’t at 37s but I personally would myself if going any more than a 35. I don’t off road all the time however I tow on the highway a fair bit. So keeping tq to the pavement is important to me.

 

[Pescatoral Pursuit]

This table may help.

I have 37 KO2s and I'm waiting to see the real world application of a buddy's 56s on 39s to decide whether to go 4.10s or 56s.

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