Looking for help/advice on truck purchase

[Rawze]

(08-13-2017 )RStewart Wrote:  These trucks have been pulling refers since new. I'm sure that involved hauling dry freight as well & I know they will load them to 80k.

Myself, I pull a van right now but my plan is go get into flat/step deck work. I would be loading these trucks to 80k as well when I needed to.

I usually run 60mph but I've been know to run the speed limit if I needed to.

I run on % so my business model is to run for as much revenue possible with as little miles as possible. I also like to cut costs as possible so I can make a good profit at less revenue. I used to shoot for $4k a week in revenue & would normally run 65-68 mph to do it. Then I started running 60 mph (big difference in MPGs) to see if I could lower my operating expenses enough that $3200-$3500 a week in revenue would still give me the same profit. It's not how much we make but how much we keep that matters.

so, 3.55's or 3.58's,... possibly 3.70's with a 13 speed??

The ideal for longevity in an ISX engine is at 1600 at high engine load output.



A gear ratio of 3.70's would give the most working hp output at a top speed of 70 mph max, and be the most fuel efficient vs something taller when at 80,000 lbs. When empty or light, it would cost you a few tenths in mpg because the torque is wasted, but not much.

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When NOT at top rated speed, but your normal driving speeds,.. ~60 ish you said, everything becomes a LOT more fuel efficient because of the lower speeds and less energy needed to keep the momentum. If your cruising on flat ground in top gear and don't need a lot of hp output, the most efficient gear ratio at 60 would still be in the 3.55-3.70 range. Given 80,000 lbs, you would want to highest ratio while at speeds, so that would still be the 3.70's.



It looks like 3.70's still would win, as it would be at about 1320-1330 rpm when not under loads, and you can down-shift to bring it to the 1600+ range when under load.

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reference: http://www.roadranger.com/ecm/groups/pub...062746.swf

and gear ratios...
http://www.eaton.com/EN/rr/ProductsServi...PCT_486870

I.E> -- If you had rears spec'd at 3.70's -- your max speed in top gear for the truck would be 70 - 73 mph, and normal running speed would be roughly 60-63.

I.E> -- If you had rears spec'd at 3.55's -- your max speed in top gear for the truck would be 74 - 75 mph, and normal running speed would still be roughly 60-65, it makes little difference in rpm between 3.70's and 3.55's at the 60 mph mark.
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I have 3.55's and NEVER EVER drive 70 mph,.. MAYBE about 63 if I am in a hurry. I wish I had 3.70's or perhaps 3.90's, but have never justified the costs of switching them out, as the gains are so little at 60 mph because I am not geared too high to begin with. Someone else however with tall rears (3.36, 3.24, or maybe even worse) on the other hand will eventually see the gains if they re-geared.

Just my own thoughts on it, no one has to agree.