prefered tranny choice.

3.55 or 3.70's some guys are even running bigger gears to keep the rpm's around 12-1300rpm's. Best thing to do is figure out what engine and where its peek performance is gonna be.

If you was to go with a RTLO16913A with 3.70 rears you could run 62mph at 1500rpm with 24.5 tall rubber in 8th gear direct (12th gear) and also run 72mph at 1500rpm in 8th gear OD (13th gear).

 

I do that with LO PROs with a .73 OD 18spd.

 

Hmmmmm!

Ive been told that bottom and top gears are the same in Road Ranger tranys

Example If 1st gear in a 13 spd at 1500 rpm = .5 mph then 1st gear in a 18 spd at 1500 rpm would be .5mph

and if 13th gear at 1500 rpm in a 13 spd = 70 mph then 18th gear in an 18 spd at 1500rpm would be 70mph

concidering rear gear ratio was the same in both trucks.

Have i been told wrong?

 

Yes! Trannys can have numerous gearing options. From 1997-2008 Eaton offered 117 different 10 speed trannys with first gear being anywhere from 8.81 to 19.58. Not only will the tranny gears make a difference but rear gearing and tires will as well.

Example a 13spd with .73 final with 3.36 rears and 22.5lp at 65 will turn 1307rpm. 24.5talls=1217rpm change the rears to 3.70 and your rpms will go to 1341.

The eaton 13 and 18 have the same final drive of .73 so if your tires and rears are the same they would have the same rpm at the same speed but then so would a 9spd or a 10 spd with a final drive of .73.

Now your first gears are very different from tranny to tranny as I said above.
Example If your 13spd has 22.5lp's and 3.70 rears with a low gear of 10.40 then 5mph would be 1577rpm. Same set-up in 18spd with low gear of 14.40 at 5mph would be 2183rpm = bye bye motor.

I sent you some info on a PM that should be helpful.

 

I'll take a 5x4, 5x5

 

Here is a link to roadrangers spec guide, everything you need is between pages 13 and 19 Other than a rt 15spd Deep reduction the 18 spd has the lowest first gear of any tranny and has overdrive unlikr the rt 15spd. Also the 13spd and 18 spd are double od trannys .86 and .73

http://www.roadranger.com/ecm/group...roadranger/documents/content/rr_rrsl-0001.pdf

 

I just got me a 15 can't go wrong with it I'm toting logs 90k

 

Just a couple quick clarifiers:

13's and 18's are visually identical. The splitter section on the 18 is beefed up to handle the extra torque multiplication of the low side gears. You old-school guys can probably remember being able to split the bottom gears on a 13 back before they integrated the controls in the shift knob.

And while the 13's and 18's both have 2 overdrive ratios, they aren't technically 'double overs.' The splitter section on these is underdrive-direct whereas the old RTOO had an overdrive splitter and top gear. They just stuck a really tall gear in the big hole of these newer units.

Just an aside, the Super 10 is an 18 with some gear sets missing. Moving the lever from the center to the right gate activates a range shift but uses the same main box gears for 2/4 and 3/5. It's actually a very good transmission as long as the lever never goes to center gate at high speeds! These got a bad rap as guys were kicking them to neutral (and the spring pushed the lever to the center gate) coming off ramps and such, and the synchronizer would spit pins in protest! If it had had some sort of speed interlock on the gate they'd have not had all the problems they did.