Being able to take off with 2.64's and a 18 speed shouldn't be a huge concern. The 18 speed has a 14.4:1 low gear. The math:
14.4 X 2.64 = 38.016:1
Direct drive 10 speeds are only 14.8:1 in first gear. The math:
14.8 X 2.64 = 39.072:1
Not a huge difference, how about regular setups? 13 speed and 3.36 gears:
12.31 X 3.36 = 41.3616:1
10 speed "b" gear and 3.55 gears:
11.06 X 3.55 = 39.263:1
18 speed and 3.36 gears:
14.4 X 3.36 = 48.384
So I would consider anywhere from 38:1 to 41:1 to be "normal" start gearing. Of course it depends on tire size as well.
Cowpies setup is interesting. You are supposed to gain 2%-3% or so by running in direct. If it takes you 250 hp to go down the road, you've just found 5 to 7.5 free horsepower. But I think he might be giving up a bit with the 18 speed over a 10 speed direct. More moving parts = more loss. I think the 2-3% is assigned to the 10 speed direct compared to a traditional overdrive.
Rear ratios
Discussion in 'Trucks [ Eighteen Wheelers ]' started by NFDDJS, Aug 24, 2012.
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I'd think for that kind of weight a 18spd with a 3.70 or 3.91 would be pretty sweet.
bender Thanks this. -
Here's some charts I made many moons ago:
superhauler Thanks this. -
I think running fuel efficient 22.5LP tires with 3.73 gears at 63-65 mph would be a good compromise here. Engine RPMS would be 1340-1370. You would gain easily .7 MPG if not a full MPG over running whatever gear ratio with 11r24.5 tires at 70 mph. Plus it will be easier on the driveline and driver.
bender Thanks this. -
18 speed, 3.73 rears and 24.5 tall rubber. Works good hauling heavy in the northeast but your FL runs not so much. Your looking at a compromise here!
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From late spring till the end of fall we run from Ellsworth Maine most of the time to anyplace from Maryland to Florida depending on the market pricing. During the winter 90% of the runs we do we pick up from the Boston MA area, Portsmouth NH, or Portland ME to any where from water town NY and Colebrook NH.TankerYankerD001 Thanks this. -
Last edited: Aug 26, 2012
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I have not had one time that startability was an issue. And I have taken gross loads to the house which the route is very hilly on narrow gravel roads. No easier running than what the grain and livestock haulers who run in my area have to do. And not even a pause running that with 2.64's.Last edited: Aug 26, 2012
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I use a road speed calculator spreadsheet that I can plug any tire rotation, tranny gear ratio, and rearend ratio in to, and it will give all the speeds from 1200 - 1600 rpm. I can change things on the fly and get new values. Using .86 hooked up to 3.36 rears on low pro rubber, the road speed at 1400 is 56 mph and 1600 is 65 mph. Direct drive is 49 mph at 1400 and 56 at 1600. Seems like plenty of room to work to me.Last edited: Aug 26, 2012
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