Gear and transmission ratios.

I just swapped out the 13 speed out of my truck, the guy I am leased to had a 18 speed that was a warranty replacement for another truck that he had to have up so he put another trans in it, my 13 speed was on its last legs howling so loud you could hear it over the turbo.

Got a deal on the trans, stuck it in, thought everything was going to be great because I thought they would have the final drive ratio, not so, the 18 speed is an A model, the 13 was a B. Thus when I fired up the truck and hit the road I found out all the sudden at 1700 rpm I was doing 59 mph, somehow I lost about 10 mph somewhere.

I had thought my truck had a set of 3.70's out back because that is what it was built with. It turns out somewhere along the way someone replaced them with 4.10's.

So since it is going to need them anyways soon I will be swapping new rears into the truck for the sake of my sanity. I have been playing with my options hence forth the charts below.

Eaton "A" series transmissions .85:1 final drive ratio.

[TABLE="width: 777"]
[TR]
[TD="colspan: 2"]4.10 Rears[/TD]
[TD][/TD]
[TD="colspan: 2"]3.90 Rears[/TD]
[TD][/TD]
[TD="colspan: 2"]3.70 Rears[/TD]
[TD][/TD]
[TD="colspan: 2"]3.55 Rears[/TD]
[TD][/TD]
[TD="colspan: 2"]3.36 Rears[/TD]
[/TR]
[TR]
[TD]Tire Dia:[/TD]
[TD="align: right"]41.3[/TD]
[TD][/TD]
[TD]Tire Dia:[/TD]
[TD="align: right"]41.3[/TD]
[TD][/TD]
[TD]Tire Dia:[/TD]
[TD="align: right"]41.3[/TD]
[TD][/TD]
[TD]Tire Dia:[/TD]
[TD="align: right"]41.3[/TD]
[TD][/TD]
[TD]Tire Dia:[/TD]
[TD="align: right"]41.3[/TD]
[/TR]
[TR]
[TD]Tire CIR:[/TD]
[TD="align: right"]129.7478[/TD]
[TD][/TD]
[TD]Tire CIR:[/TD]
[TD="align: right"]129.7478[/TD]
[TD][/TD]
[TD]Tire CIR:[/TD]
[TD="align: right"]129.7478[/TD]
[TD][/TD]
[TD]Tire CIR:[/TD]
[TD="align: right"]129.7478[/TD]
[TD][/TD]
[TD]Tire CIR:[/TD]
[TD="align: right"]129.7478[/TD]
[/TR]
[TR]
[TD]Rear Ratio:[/TD]
[TD="align: right"]4.1[/TD]
[TD][/TD]
[TD]Rear Ratio:[/TD]
[TD="align: right"]3.9[/TD]
[TD][/TD]
[TD]Rear Ratio:[/TD]
[TD="align: right"]3.7[/TD]
[TD][/TD]
[TD]Rear Ratio:[/TD]
[TD="align: right"]3.55[/TD]
[TD][/TD]
[TD]Rear Ratio:[/TD]
[TD="align: right"]3.36[/TD]
[/TR]
[TR]
[TD]Trans Final:[/TD]
[TD="align: right"]0.85[/TD]
[TD][/TD]
[TD]Trans Final:[/TD]
[TD="align: right"]0.85[/TD]
[TD][/TD]
[TD]Trans Final:[/TD]
[TD="align: right"]0.85[/TD]
[TD][/TD]
[TD]Trans Final:[/TD]
[TD="align: right"]0.85[/TD]
[TD][/TD]
[TD]Trans Final:[/TD]
[TD="align: right"]0.85[/TD]
[/TR]
[TR]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD]RPM[/TD]
[TD]MPH[/TD]
[TD][/TD]
[TD]RPM[/TD]
[TD]MPH[/TD]
[TD][/TD]
[TD]RPM[/TD]
[TD]MPH[/TD]
[TD][/TD]
[TD]RPM[/TD]
[TD]MPH[/TD]
[TD][/TD]
[TD]RPM[/TD]
[TD]MPH[/TD]
[/TR]
[TR]
[TD]1300[/TD]
[TD="align: right"]45.83282[/TD]
[TD][/TD]
[TD]1300[/TD]
[TD="align: right"]48.18323[/TD]
[TD][/TD]
[TD]1300[/TD]
[TD="align: right"]50.78772[/TD]
[TD][/TD]
[TD]1300[/TD]
[TD="align: right"]52.93368[/TD]
[TD][/TD]
[TD]1300[/TD]
[TD="align: right"]55.92696[/TD]
[/TR]
[TR]
[TD]1400[/TD]
[TD="align: right"]49.35843[/TD]
[TD][/TD]
[TD]1400[/TD]
[TD="align: right"]51.88963[/TD]
[TD][/TD]
[TD]1400[/TD]
[TD="align: right"]54.69447[/TD]
[TD][/TD]
[TD]1400[/TD]
[TD="align: right"]57.00551[/TD]
[TD][/TD]
[TD]1400[/TD]
[TD="align: right"]60.22903[/TD]
[/TR]
[TR]
[TD]1500[/TD]
[TD="align: right"]52.88403[/TD]
[TD][/TD]
[TD]1500[/TD]
[TD="align: right"]55.59603[/TD]
[TD][/TD]
[TD]1500[/TD]
[TD="align: right"]58.60122[/TD]
[TD][/TD]
[TD]1500[/TD]
[TD="align: right"]61.07733[/TD]
[TD][/TD]
[TD]1500[/TD]
[TD="align: right"]64.53111[/TD]
[/TR]
[TR]
[TD]1600[/TD]
[TD="align: right"]56.40963[/TD]
[TD][/TD]
[TD]1600[/TD]
[TD="align: right"]59.30243[/TD]
[TD][/TD]
[TD]1600[/TD]
[TD="align: right"]62.50797[/TD]
[TD][/TD]
[TD]1600[/TD]
[TD="align: right"]65.14915[/TD]
[TD][/TD]
[TD]1600[/TD]
[TD="align: right"]68.83318[/TD]
[/TR]
[TR]
[TD]1700[/TD]
[TD="align: right"]59.93523[/TD]
[TD][/TD]
[TD]1700[/TD]
[TD="align: right"]63.00883[/TD]
[TD][/TD]
[TD]1700[/TD]
[TD="align: right"]66.41472[/TD]
[TD][/TD]
[TD]1700
[/TD]
[TD="align: right"]69.22097[/TD]
[TD][/TD]
[TD]1700[/TD]
[TD="align: right"]73.13525[/TD]
[/TR]
[TR]
[TD]1800[/TD]
[TD="align: right"]63.46083[/TD]
[TD][/TD]
[TD]1800[/TD]
[TD="align: right"]66.71524[/TD]
[TD][/TD]
[TD]1800[/TD]
[TD="align: right"]70.32146[/TD]
[TD][/TD]
[TD]1800[/TD]
[TD="align: right"]73.29279[/TD]
[TD][/TD]
[TD]1800[/TD]
[TD="align: right"]77.43733[/TD]
[/TR]
[TR]
[TD]1900[/TD]
[TD="align: right"]66.98644[/TD]
[TD][/TD]
[TD]1900[/TD]
[TD="align: right"]70.42164[/TD]
[TD][/TD]
[TD]1900[/TD]
[TD="align: right"]74.22821[/TD]
[TD][/TD]
[TD]1900[/TD]
[TD="align: right"]77.36462[/TD]
[TD][/TD]
[TD]1900[/TD]
[TD="align: right"]81.7394[/TD]
[/TR]
[TR]
[TD]2000[/TD]
[TD="align: right"]70.51204[/TD]
[TD][/TD]
[TD]2000[/TD]
[TD="align: right"]74.12804[/TD]
[TD][/TD]
[TD]2000[/TD]
[TD="align: right"]78.13496[/TD]
[TD][/TD]
[TD]2000[/TD]
[TD="align: right"]81.43644[/TD]
[TD][/TD]
[TD]2000[/TD]
[TD="align: right"]86.04147[/TD]
[/TR]
[/TABLE]

Eaton "B" series transmissions .73:1 final drive ratio.

[TABLE="width: 777"]
[TR]
[TD="colspan: 2"]4.10 Rears[/TD]
[TD][/TD]
[TD="colspan: 2"]3.90 Rears[/TD]
[TD][/TD]
[TD="colspan: 2"]3.70 Rears[/TD]
[TD][/TD]
[TD="colspan: 2"]3.55 Rears[/TD]
[TD][/TD]
[TD="colspan: 2"]3.36 Rears[/TD]
[/TR]
[TR]
[TD]Tire Dia:[/TD]
[TD="align: right"]41.3[/TD]
[TD][/TD]
[TD]Tire Dia:[/TD]
[TD="align: right"]41.3[/TD]
[TD][/TD]
[TD]Tire Dia:[/TD]
[TD="align: right"]41.3[/TD]
[TD][/TD]
[TD]Tire Dia:[/TD]
[TD="align: right"]41.3[/TD]
[TD][/TD]
[TD]Tire Dia:[/TD]
[TD="align: right"]41.3[/TD]
[/TR]
[TR]
[TD]Tire CIR:[/TD]
[TD="align: right"]129.7478[/TD]
[TD][/TD]
[TD]Tire CIR:[/TD]
[TD="align: right"]129.7478[/TD]
[TD][/TD]
[TD]Tire CIR:[/TD]
[TD="align: right"]129.7478[/TD]
[TD][/TD]
[TD]Tire CIR:[/TD]
[TD="align: right"]129.7478[/TD]
[TD][/TD]
[TD]Tire CIR:[/TD]
[TD="align: right"]129.7478[/TD]
[/TR]
[TR]
[TD]Rear Ratio:[/TD]
[TD="align: right"]4.1[/TD]
[TD][/TD]
[TD]Rear Ratio:[/TD]
[TD="align: right"]3.9[/TD]
[TD][/TD]
[TD]Rear Ratio:[/TD]
[TD="align: right"]3.7[/TD]
[TD][/TD]
[TD]Rear Ratio:[/TD]
[TD="align: right"]3.55[/TD]
[TD][/TD]
[TD]Rear Ratio:[/TD]
[TD="align: right"]3.36[/TD]
[/TR]
[TR]
[TD]Trans Final:[/TD]
[TD="align: right"]0.73[/TD]
[TD][/TD]
[TD]Trans Final:[/TD]
[TD="align: right"]0.73[/TD]
[TD][/TD]
[TD]Trans Final:[/TD]
[TD="align: right"]0.73[/TD]
[TD][/TD]
[TD]Trans Final:[/TD]
[TD="align: right"]0.73[/TD]
[TD][/TD]
[TD]Trans Final:[/TD]
[TD="align: right"]0.73[/TD]
[/TR]
[TR]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD]RPM[/TD]
[TD]MPH[/TD]
[TD][/TD]
[TD]RPM[/TD]
[TD]MPH[/TD]
[TD][/TD]
[TD]RPM[/TD]
[TD]MPH[/TD]
[TD][/TD]
[TD]RPM[/TD]
[TD]MPH[/TD]
[TD][/TD]
[TD]RPM[/TD]
[TD]MPH[/TD]
[/TR]
[TR]
[TD]1300[/TD]
[TD="align: right"]53.36699[/TD]
[TD][/TD]
[TD]1300[/TD]
[TD="align: right"]56.10376[/TD]
[TD][/TD]
[TD]1300[/TD]
[TD="align: right"]59.13639[/TD]
[TD][/TD]
[TD]1300[/TD]
[TD="align: right"]61.63511[/TD]
[TD][/TD]
[TD]1300[/TD]
[TD="align: right"]65.12043[/TD]
[/TR]
[TR]
[TD]1400[/TD]
[TD="align: right"]57.47214[/TD]
[TD][/TD]
[TD]1400[/TD]
[TD="align: right"]60.41943[/TD]
[TD][/TD]
[TD]1400[/TD]
[TD="align: right"]63.68534[/TD]
[TD][/TD]
[TD]1400[/TD]
[TD="align: right"]66.37628[/TD]
[TD][/TD]
[TD]1400[/TD]
[TD="align: right"]70.1297[/TD]
[/TR]
[TR]
[TD]1500[/TD]
[TD="align: right"]61.57729[/TD]
[TD][/TD]
[TD]1500[/TD]
[TD="align: right"]64.7351[/TD]
[TD][/TD]
[TD]1500[/TD]
[TD="align: right"]68.2343[/TD]
[TD][/TD]
[TD]1500[/TD]
[TD="align: right"]71.11744[/TD]
[TD][/TD]
[TD]1500[/TD]
[TD="align: right"]75.13896[/TD]
[/TR]
[TR]
[TD]1600[/TD]
[TD="align: right"]65.68245[/TD]
[TD][/TD]
[TD]1600[/TD]
[TD="align: right"]69.05078[/TD]
[TD][/TD]
[TD]1600[/TD]
[TD="align: right"]72.78325[/TD]
[TD][/TD]
[TD]1600[/TD]
[TD="align: right"]75.8586[/TD]
[TD][/TD]
[TD]1600[/TD]
[TD="align: right"]80.14822[/TD]
[/TR]
[TR]
[TD]1700[/TD]
[TD="align: right"]69.7876[/TD]
[TD][/TD]
[TD]1700[/TD]
[TD="align: right"]73.36645[/TD]
[TD][/TD]
[TD]1700[/TD]
[TD="align: right"]77.3322[/TD]
[TD][/TD]
[TD]1700[/TD]
[TD="align: right"]80.59976[/TD]
[TD][/TD]
[TD]1700[/TD]
[TD="align: right"]85.15749[/TD]
[/TR]
[TR]
[TD]1800[/TD]
[TD="align: right"]73.89275[/TD]
[TD][/TD]
[TD]1800[/TD]
[TD="align: right"]77.68212[/TD]
[TD][/TD]
[TD]1800[/TD]
[TD="align: right"]81.88116[/TD]
[TD][/TD]
[TD]1800[/TD]
[TD="align: right"]85.34093[/TD]
[TD][/TD]
[TD]1800[/TD]
[TD="align: right"]90.16675[/TD]
[/TR]
[TR]
[TD]1900[/TD]
[TD="align: right"]77.99791[/TD]
[TD][/TD]
[TD]1900[/TD]
[TD="align: right"]81.9978[/TD]
[TD][/TD]
[TD]1900[/TD]
[TD="align: right"]86.43011[/TD]
[TD][/TD]
[TD]1900[/TD]
[TD="align: right"]90.08209[/TD]
[TD][/TD]
[TD]1900[/TD]
[TD="align: right"]95.17602[/TD]
[/TR]
[TR]
[TD]2000[/TD]
[TD="align: right"]82.10306[/TD]
[TD][/TD]
[TD]2000[/TD]
[TD="align: right"]86.31347[/TD]
[TD][/TD]
[TD]2000[/TD]
[TD="align: right"]90.97906[/TD]
[TD][/TD]
[TD]2000[/TD]
[TD="align: right"]94.82325[/TD]
[TD][/TD]
[TD]2000[/TD]
[TD="align: right"]100.1853[/TD]
[/TR]
[/TABLE]

This chart is based on the 285/75R24.5's I am running (24.5 LP) They are 41.3" in Diameter.

I am torn between 3.55's and 3.36'es, the 3.36'es might turn it into a total dog on the hills, but the 3.55's still leave me at 1600 rpm to go 65 mph, 1700 would give me 69 mph and change.

Where as with the 3.36 rears 1550 or so would give me 65, and 1700 would give me 73 mph.

Since I do run western states I do see a lot of 70 and 75 mph zones, I don't generally run that fast, but having the option is nice.

I still haven't made up my mind, but figured everyone would enjoy getting to see the difference changing gear ratios and transmission ratios can make.

 

I have a 3406E 5EK right now it is set at 475/1650 I am definitely going to crank it up. Also looking at a PDI air 2 air and turbo. might even go nuts and get a cam.

 

I think it is going to be 3.55's, I don't want this thing to get too long legged and not be able to pull the hills.

There is a part of me that really wishes id had got a B series trans, then with the 4.10's I could still hold down highway speed but it would be a boss in the high country, especially with the big motor.