Final Ratios

[Mopar1973Man]

I know there are a lot of guys out here that love their oversized tires and I will admit they look super cool. Now to make it all come together and make it a rocket ship on rails you need the proper final ratio. Optimal for most daily drivers that are here optimal final ratio to the ground is 3.73:1 after the tires. The problem is any size larger than a factory 265's on 3.55 gears is going to lower the ratio. I created a chart of the final ratio with some tire sizes to see the results. 

 

Subscribing members only... 

 

Edited March 7, 2023 by Mopar1973Man

[Doubletrouble]

 Good info if you thinking about larger tires. There is a lot to consider if you want the truck to pull the same as it did on stock size and just behave the same while not towing. Keeps your EGT's down and keep the engine in the power band without stressing the drive train to the point of failures.

[jlwelding]

And the hidden things going on like added heat in everything. Eng,turbo,trans, rearend, axles and bearings, fuel mileage. 

Edited March 11, 2023 by jlwelding

[Doubletrouble]

 To add to that @jlwelding, a lot more stress in brake parts slowing the increased rotating mass of the larger tires and or wheels.

[VMac822]

On your chart how does it work with the different transmissions? ie Automatics you definitely want smaller tires or go with 4.10s sooner than you would with a NV4500 or NV 5600.

 

I do like bigger tires and I'm right on the cusp of crossing over into the "red zone."  I have a G56 (later version) in my short box 4x2 98.5 Ram, 3.54 axle with 275/55R20 tires.  Being a lighter truck (scales right at 6000) and lower ride height I think I can get away with it.  EGTs are fine, it's snappy on the highway.  I have my speedo corrected and show about 2020 RPM at 70 mph  I generally get 22 on the highway doing 70-75.  I had two tanks right at 24 mpg driving to Wisconsin last fall.   Running just under 80 across S. Idaho and Utah netted 21.  Running some 75hp injectors Weston Shupe modified and Smarty CO3, as well as Colt Stage 3 cam and exhaust header with ball bearing 63mm turbo.

 

Towing my 24' Airstream Argosy I get 13.5 to 16 mpg.   Swapping over to the G56 from the auto sure made it nice for towing!