Looking for help/advice on truck purchase

[Rawze]

I see all the great discussion about the engines, but none much whatsoever about ...


What type of freight the guy is hauling...

What speeds and weights he is looking to run them at ...

If any of those trucks are geared and spec'd properly for what he wants to do with them ...

Engine is important, but it also be about getting something that you can actually spec correctly to suit your needs and make a decent profit on.

Then finally, what his buisness model is for making them turn a decent profit with the specifications of those trucks he is looking at? -- no decent game plan = no decent profit.

[RStewart]

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.

[RStewart]

I appreciate this info. I'm not sure if I want to put up with the fuel pump issues.

[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.

[RStewart]

I appreciate the breakdown of this. I never would've thought that a truck would get better fuel mileage running 70 vs 60 when heavy.
I guess this does make sense though. I used to drive a 1997 KW T600, 430/470 Detroit, 10 speed, & 3.90 rears. Set the cruise at 75 mph (1800 rpm) & the truck avg 6.5-6.75 mpg. My current DD15 won't do that good at that speed.

These particular trucks are geared all wrong. The 386s have 3.36s & the 579 has 3.25s. I guess I could run in 10th instead of using all the gears.

That's interesting that the sweet spot is so high. My dd15 sweet spot is around 1350 rpm. My truck has a straight 10 & 2.64 rears. At 60 & a light load with minimal wind & hills I can get high 9 mpgs to low 10s. With a heavy load, wind, & hills I've seen it drop into the high 5s but usually mid 6s.

[Waterloo]

Rawze is spot on regarding the gearing, something I did not give much thought to when looking for a truck. I was looking for the accessories, mainly big hp, 18 spd, lockers, with a lift axle and wet kit, the Tri-Pak was the icing on the cake with the truck I purchased. The gearing was the last thing on my list as I did not have the time to spec a new truck and was in a rush to put the truck to work. Looking back, I screwed up.

I'm running 3:42, which suck for what I am NOW doing, local/regional. 3:70 gearing would suit me much better, or even that 3:90 which I used to have in one of my old Volvos. That truck was getting 8 mpg driving in its sweet spot at around 60 mph.

Then tractor length. I have a 244 inch wheelbase which is right at the max for what I do in my ProStar. I wish it were shorter now that I have went from the oil field pulling a tanker to a dry box pulling automotive freight. Most of the places I now go are set up for day cabs, which can get interesting at times.

And, what truck? I hate to say it, but I would more than likely buy another ProStar just because I know what the issues are and how to fix the majority of them in my driveway. And I like the dealer network, there is an International dealer in almost every small town, unlike say Volvo or Pete. Something else to consider, as I have had my bacon saved more than a few times when in need of a part asap.

Just some thoughts.

[Rawze]

(08-13-2017 )RStewart Wrote:  I appreciate the breakdown of this. I never would've thought that a truck would get better fuel mileage running 70 vs 60 when heavy.

I think you may have seriously mis-read that... So I edited the post and clarified it a bit more. it was worded a bit cryptic.

(08-13-2017 )RStewart Wrote:  These particular trucks are geared all wrong. The 386s have 3.36s & the 579 has 3.25s. I guess I could run in 10th instead of using all the gears.

I could not agree more for anyone hauling up to 80,000 lbs. Taller gears only help those guys who don't haul any freight and/or are only having really light loads, as the extra hp output is wasted when geared with a better ratio. the idiots who came up with those theories about tall rear ratios and directs and all that other BS never got in a truck with 80,000 lbs in it and tried slinging it around on the roads all day. -- Text-book smart and road dumb!.

(08-13-2017 )RStewart Wrote:  ...
That's interesting that the sweet spot is so high.
...

As far as fuel efficiency goes, there is not real "sweet spot" for the ISX. It has a VG turbo and other things that make it very fuel efficient across the board unlike older engines of the past. However,.. when it comes to longevity vs engine load,.. 1600 will produce a lot less engine wear and increase lifespan while under medium/heavy engine output (fighting those extra forces because your climbing that hill, or maybe going fast and sucking more fuel like a fool).

When we grab a load and gross at 78 - 80k, we will sit on 1600-1700 rpm for hours and hours at one gear down + jumping in and out of neutral, letting it roll (we have a 10-speed) when in hilly country (PA and the most of northeast). Same thing whenever we get to any kind of need for hp to keep speeds up, like grabbing the higher rpm before slowing down as we are hitting a hill climb. We only grab that highest gear when its perfectly flat, and we are loaded to 80k.

On the extremely rare occasion where we would go 65+, we just left it a gear down and used the 1600+ rpm range when we were heavy. It is overall slightly more fuel efficient than the same speed in top gear (only when heavy though) than when only doing about 1400 rpm. It can also be seen on our pyro gauge with the probe mounted to the outside of the manifold. However, when we are loaded light or empty,.. the complete opposite becomes true. It all comes down to terrain, power requirements, and weights.

When we are light or empty, our entire driving style changes to minimum rpm instead of working it. -- When Heavy, the higher rpms are your friend and when empty, the lower rpms are your friend.

-- Any question on our driving style vs longevity and using a wide range of rpm to our advantage can be measured in the rod/main bearings in my engine re-build series on Youtube. As well, is the fact that our million mile fuel average to the pump by the receipts is 8.03 mpg and still slowly climbing.

My wife has been reporting last couple days or so the fuel receipts are showing 9.4 - 9.7 mpg, running 58~ish on the hazmat load from PA to new mexico. Load itself weighs only about 28k in a 53-ft dry box. Its nice to get those lighter loads once in a while. If i were geared 3.36's or 2.79's and direct,.. there would be no way in hells creation I could get those kind of numbers, simple as that.

[Blake]

Man I'm glad I stumbled on this post. All the trucks I was looking at where geared wrong for what I would need ( 53' dry van otr). Ill be looking for 3.55 to 3.70 in the ISX motor and 10 or 13 speed tranny. Been seeing a lot of 3.36.

[Rawze]

(01-28-2018 )Blake Wrote:  Man I'm glad I stumbled on this post. All the trucks I was looking at where geared wrong for what I would need ( 53' dry van otr). Ill be looking for 3.55 to 3.70 in the ISX motor and 10 or 13 speed tranny. Been seeing a lot of 3.36.

Yes, it is truly sad how many trucks are geared wrong out there.