Ecodiesel on 40’s: is 4.88 regear too much

[CerOf]

The “on paper” is a good starting point. Factor in extra weight, wind resistance, and a bit more gear in my experience, is usually needed.

if paper says 4.56, then 4.88 is probably the sweet spot. .3 isn’t that much more.
it’s about what? 200rpm more than 4.56?

Sponsored

 

[Wheelin98TJ]

Keep more meat on the pinion !

It's common misconception that the smaller pinion heads with deeper gear ratios are weaker.

The strength of the gear set depends on the tooth contact surface area and sometimes it's actually higher with deeper ratios.

 

[nocoast_jt]

I do think 4.88 is too much for 40s with the EcoDiesel. I was running 39's with the stock 3.73 gears and still got close to 20mpg and ~16 towing a 3.5k trailer. Now I am running 4.56 with 41" Iroks and I get around 16mpg. On the highway at 75 MPH I am at around 2200 RPMs which is just too high for the ecodiesel. If I were to do it over again I would go 4.10s to keep the highway RPMs lower. The diesel engine is just the opposite of the gasser...I always geared lower on all my rigs but I recommend gearing higher than you think with the diesel.

 

[DavoSmith]

I do think 4.88 is too much for 40s with the EcoDiesel. I was running 39's with the stock 3.73 gears and still got close to 20mpg and ~16 towing a 3.5k trailer. Now I am running 4.56 with 41" Iroks and I get around 16mpg. On the highway at 75 MPH I am at around 2200 RPMs which is just too high for the ecodiesel. If I were to do it over again I would go 4.10s to keep the highway RPMs lower. The diesel engine is just the opposite of the gasser...I always geared lower on all my rigs but I recommend gearing higher than you think with the diesel.

Thank you for the real world insight. What gears would you recommend for a heavy overland type set up? 4.56 or 4.10? Build: EcoDiesel JT, 40" tires, DynaTrac XD 60/80 axles, DeckedDrawers (270 lbs), Go Fast Camper (300lbs), 10 gal water, 10 gal fuel, Frig...

 

[nocoast_jt]

Thank you for the real world insight. What gears would you recommend for a heavy overland type set up? 4.56 or 4.10? Build: EcoDiesel JT, 40" tires, DynaTrac XD 60/80 axles, DeckedDrawers (270 lbs), Go Fast Camper (300lbs), 10 gal water, 10 gal fuel, Frig...

With all that weight the diesel will still motor down the highway at 1900 rpms...I'd go for the 4.10s personally. Or, perhaps Dynatrac can throw 4.30s in there since you are dropping all that coin. If you ever plan to go 42s in the future you might consider the 4.56. Or, if you plan on doing any substantial towing. I don't think you can really go wrong with either option, good luck!

 

[Tommyd]

No kidding look how fat those tires are. That must be such a heavy wheel and tire combo

 

[WesternJeep401]

4 88 would be suitable for that tire/wheel combination.

 

[gates007 [scammer]]

just offroad it

 

[Jteakus]

Old thread but I will add some real world experience. I ran 38's on factory 3.73 gears but when wheeling I felt it needed a regear especially in reverse. I went with 4.56 gears and it seemed geared too low. Next tire change I went with BFG 39 KO's and it is just right. 2,000 rpm at 75 mph and getting 20 mpg when running 55 mph. Full delete.

 

[BlueScapegoat]

5,000 miles in the last two weeks on 40s 4.88s loaded at 7700 lbs. Through mountains, plains, 11k+ ft, 20°, 105°, Rubicon Trail... Deleted.

Feels perfect to me.

19-24 mpg at 75 depending on wind. EGTs rarely above 1300 on the steepest climbs. Holds 8th most of the time. Never has to drop below 6th, even on the Eisenhower Tunnel pass. Has never derated on me.

I've driven a lot of these same roads with 3.73s on both 37s and 40s. The 4.88/40s combo is by far superior in drive-ability over the other two.

 

[Jteakus]

Km's run on the small side. If your 40's run close to true we are most likely less than 100 rpm apart at 75 mph.

Sponsored