18sp with ???? Rear end. What would you choose ?

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Dirtmonkey

Member
I'm looking for a new / used truck. I would prefer something 474/500 hp with an 18 but not sure about the rear end ratio. The reason I ask is I've never had an 18 so I'm not sure what ratio would best. I'm off road more than highway but when I'm on the highway I want to be able to " GO ". Legally of course :angel I'm looking to the future and possible heavier loads than I have now but nothing over a D6R.
I'm used to 373 and 411 rears. Just curios what y'all's thoughts were. Thanks !
 
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mike in idaho

Member
I run a 475 horse 3406E with an 18 speed and 4.11 rears. It will start a 90,000 pound load anywhere in the woods with ease, runs about 1300 rpm at 55 miles per hour.
 
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Oxbow

Well-known member
The newer 18 speeds, like a RTLO 18918B, have a 19.72:1 low gear for starting out, and a .86:1 and .73:1 overdrive. Kinda the best of both worlds anymore. So, as Mike pointed out, great startability and decent top end with 4:11s.

I have an older truck that has an RTOF 15918. My overdrive ratio is only .85:1, and with 2 speed rears @ 4.10 and 5.92, I have no problem starting loads on hills or in soft ground, but I am at 1800 rpm @ 65 with tall 11 24.5s. I am waiting for the million plus miles on the tranny to tell me it is time to replace it, but it is working so well now I can't afford to change it out until there is a problem with it.
 
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Shimmy1

New member
Unless you're starting 120,000+ lb loads in the bush, there is absolutely no reason to have an 18 sp. over a 13. I think some guys get an 18 so they can run around the truck stop sayin "I got an 18 speed"
 
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mike in idaho

Member
I've hauled 100,000+ lb loads in the woods with a 13 speed. You can do it with 13 speeds, but those 200 rpm splits in low side of that 18 speed sure make it easier to keep the motor in its rpm sweet spot. Pretty nice not having to deal with that big gap between 5th and 6th in the 13 speed too.
 
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Oxbow

Well-known member
mike in idaho said:
I've hauled 100,000+ lb loads in the woods with a 13 speed. You can do it with 13 speeds, but those 200 rpm splits in low side of that 18 speed sure make it easier to keep the motor in its rpm sweet spot. Pretty nice not having to deal with that big gap between 5th and 6th in the 13 speed too.
Click to expand...
It often is the difference between being able to grab a gear and being stuck in the one your in for a long time!
 
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