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Best Rear End For Running Reefer In The West

Hi guys,

I am in the market for a newer truck and will go 2008 or newer because I run THROUGH california and only pick up there once in a while.

I run reefer from seattle to dallas and run through the mountains on a weekly basis. Fuel economy is a priority even with the dpf issues...

I would like to know what rear end would be suited for my business. Like I said I run reefer grossed out at 80k and run from seattle to dallas and some cities inbetween.

I will be going 13spd and was wondering what rear end I should go.

All I know is that the lower the ratio...the lower the rpms but won't pull hills and the higher the ratio...3.36 3.42 3.55 the higher the rpms but hills will be easier.

I don't race uphills so I would like a well rounded rear end for my needs. I guess tire size will also affect the rpms?

Would 3.36 or 3.42 or 3.55 be better? I usually dont go past 65mph on 13th and was wondering what rpm i should be at?

Also, if i go 10spd what rear end would be better for that?

Is there a link on where to find out how much your rpms will be with a certain transmission rear end and tire combo that is easy to use? I think I tried the eaton one and I couldn't figure out what number to input for

"transmission final drive ratio"

Thanks Guys

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7 Replies

The 3.55 rears with a 13 speed will work well for you.

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I run 3.08s, pulling tankers at 80,000... 3.08s will pull a mountain at the exact same speed as any other rear, you'll just be a half-gear lower. Cruise RPM is what you need to aim for, don't worry about a gear for pulling mountains. 2.64s will pull a mountain just as good as 3.55s, you'll just be a full gear lower at the same speed.

With the 3.08s, I can run 72 mph at about 1350 rpm to save a little time when empty and not kill the mileage.

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I have a 13 speed with 3:58 gears and I don't like to go over about 62 MPH because it makes my RPM's too high. I really notice my MPG drop when I go over 62MPH.

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I have 3.58 gears now with 13 speed OD and if you have to run anything over 60 mph it uses more fuel. I would suggest using something different. I had a FLD 120 Freightliner back in 91 with the first electronic Cat motor with 3.21 and 13 speed that I ordered set up this way and it got best fuel mileage of any truck I've owned and use to run it at 70 mph most of the time.

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2.64 / 3.08 / 3.55 are identical, just 1/2 gear apart at the same road speed. i.e 2.64 in 16th/11th Will give you the same road speed as 3.08 in 17th/12th or 3.55 in 18th/13th (assuming 18 or 13 spd here). I am doing very well with 2.64 behind an 18 spd. You can cruise quite comfortably in 16th or 11th (both direct drives for max efficiency) at 60 mph doing about 1350 rpm.

As for 2.64 lousy at pullng hills, that is nonsense. I regularly pull gross loads up and down and all around hills that are not for newbies. Sure, where I run is not the mountains out west, but I run some grades that make Cabbage and Cajon a joke. Just shorter stretches. And neither of those big hills have Amish buggies on them or 20 mph corners at the bottom of the hill before the next grade like the hills I normally run. And I also have to do about 20 miles of gravel roads a week, that has a couple of grades that will make your back end pucker up. Not for the faint of heart. So the idea that tall rears won't pull, pure BS.

For most folks, 3.08 would be perfect. You would be in the first over at normal cruise (which is far less parasitic than double over) and your first drop would be into direct drive which is maximum efficiency. There are a million ways to got with trannies and diffs. Get a road speed calculator and play "what if" games on it with various combinations of rear end ratios and transmission ratios and find what would work best for your particular operation. No two people are the same. Find your niche and then go with it.

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i run 3.58 in 12th 1650-1700 rpm @480hp to the ground i get up the hills@65mph.no problem and very easy on the truck.this truck is built for climbing.no dpf no egr no scr.1995 engine allows me to go to california.i also have pittsburg programming on my truck.572hp@flywheel

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Thanks for all your info guys....I feel a lot better and a bit more inclined to go towards a lower ratio because I will need the lowest rpms at cruise speed.

I tried the road speed calculator on the eaton site and I did not know what to put for the first entry labeled "transmission final drive ratio"....it goes from 0.73 to 1.00..

One thing I didn't understand though was "cdowning" comment

"you would be in the first over at normal cruise (which is far less parasitic than double over) and your first drop would be into direct drive"

does this mean that if I am cruising at 55 and can get there at 10th then only go to 11 and not in top gear....(I count low as one, then 2,3,4,5...range up...6 split 7, 8 split 9, 10 split 11 and 12 split 13; for me it was easier to remember that the beginning of every shift was an even number and the splits were all odd;

what is double over?

how would it work if I were to go with a 10spd and a 3.25....I would not be able to split gears so does that mean I would be in 10th all the time at cruising....

there are parts of my route that are around 60 miles of flat road with little bumps/hills but limit is 45mph...I just assumed that once the truck is moving it needs less to keep it moving and that top gear is the best...because I can keep my rpms on my current 13spd at 1150.

is this doing more damage than good?

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Comments:

Most 13 speeds are double overdrive, meaning 13th gear is your second overdrive, 12 gear is your first overdrive, and 11th is your direct gear. Direct is a 1:1 ratio for the final drive out the transmission.

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