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Rear end ratio; What would be ideal


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Hi Everyone,


If you could pick the ideal rear end ratio for your truck what ratio would you pick. Or what rpm's would we want to hold at 60 mph ? I would not think you would want to run over your trucks engine torque range. I can understand that there is an ideal range for your engine. If you could choose the ratio for your truck what would you like ?


My thought is that a 3:23 would work with a Super 10. I have seen the chart on ratios vs rmp's. This is where I am coming up with my opinion.


Looking for opinions,


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Well, there are lots of things to consider I think. My coach weighs 29k with full water and fuel tanks. I often pull at trailer that weighs under 10k. I've got a Gen 2 Eaton 10 speed autoshift, three pedal. I don't know what ratio the top gear is on that trans. I have a 3.42 rear end ratio. I'm at about 1425 rpm's at 72 mph. I'd rather be lower rpm's at that speed. I never use 1st gear and never need 2nd gear. So, if I was to change it I would go lower numerical rear end ratio. I'd like to cruise at 72 mph at about 1250-1300. But I don't think it would be worth it for me to just change out the gear ratio for that. Now, if there was a gear failure or some other reason to dig into that rear end then that would be the time to see about changing the gears. If you're only looking to cruise at 60 then I think that 3.42 ratio might be about right. I can't remember what rpm's I'm turning at 60. I'm pretty sure my trans shifts into 10 at about 52-54 mph.

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That question has many determining factors. Besides the differing engine power characteristics. Load, terrain and tire size are also factors that must be applied. I live out west and we have mountains to climb, so out here unless you have 500 plus horsepower those high ratio trucks will be in 9th gear alot. 3:55 to 3:42 seems to be a good place to start, with this gearing you can still run 70 to75 mph in the relative sweet spot on most engines on the flats and still pull most mountain passes above 60 mph. But as I said, a midwesterner would not necessarily need that gearing, 3:23 to 2:93 or higher with a 400 plus hp engine might be better for him in his area travels. Really have to consider alot of things to answer that question.


My 2 cents.



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When I spec'ed my truck I went with 2.67 ratio. Like Curt mentioned above with 500/1850 have no problem with a 21K trailer. It also has the lower RPM eco-torque engine that makes a lot of torque down low. 1150 RPM@65 mph and it doesn't downshift until 950 rpm. There was very few hills through the mountains last summer that the truck ever shifted down to 11th on the i-shift 12 speed.

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