All - considering purchasing a low mile 2018 3500 and the build sheet shows a 3:42 axle ratio. Anyone know if this was the default ratio? Imagine it was. I notice 2019+ models appear to have 3:73 gears with an option for 4:10s. 

3.42 is the default,   they seem like they might be too long, but they are actually fine.  

Just keep in mind don't put anything but stock tires back on these trucks. If it has the 4.10 then yes you can add oversized tires. Even the 3.73 you can add a mild increase in tire size. Just consider that with 3.55 gears on Beast, ONE INCH smaller tire (245/75 R16) makes it 3.69:1 final. Yes, with 3.73 gears you can go up ONE INCH and would be close to 3.55:1 final. With 3.42 gear I highly suggest just leave stock tires sizes on these trucks.

 

Fun note. I actually hunt for 4th Gens with oversized tires because in a street race I can easily whip them light to light with "Beast" because typically the 3.42 with 35 inch tires now makes the final ratio to the ground 3.09:1 making my opponent very tall geared and difficult to launch with power, EGT's are much higher, and doesn't have the low end power. 

Edited October 25, 20222 yr by Mopar1973Man

Yeah the tire size impact to final drive ratio is now burned into my brain! 

 

I would like to add that with my 2nd gen running 33" tires and 3:55 gears I achieved a hand calculated 25.6 MPGs this past weekend during a long 450+mile fishing road. Re-did my math a few times but that's what was achieved. Granted the truck was empty but still. 

42 minutes ago, Hutch24v said:

Yeah the tire size impact to final drive ratio is now burned into my brain! 

Must of done my task correctly...