Whats a good rear axle ratio for a TC2000 bluebird 5.9 cummins?

-cycosis- · 05-25-2016, 11:29 AM

As the title states, I have read a lot here that the 5.9 is not ideal and underpowered. Whelp, I bought one.

So for highway use, whats a good rear axle ratio?

EastCoastCB · 05-25-2016, 11:33 AM

Quote:

Originally Posted by -cycosis-

As the title states, I have read a lot here that the 5.9 is not ideal and underpowered. Whelp, I bought one.

So for highway use, whats a good rear axle ratio?

4 something should be good. Lower 4's are better.

-cycosis- · 05-25-2016, 11:41 AM

SO Im alright with a 4.44?

EastCoastCB · 05-25-2016, 11:46 AM

Quote:

Originally Posted by -cycosis-

SO Im alright with a 4.44?

Oh, absolutely. I don't have the cummins, but that's the axle ratio I'm running with my 195 hp/520 tq engine.

skoolie_n00bie · 05-25-2016, 11:52 AM

Besides calculations, is there a way to figure out rear diff. ration?
Should it be on the diff. itself, maybe on a plate somewhere?
Haven't really looked, yet....

Where/how did you figure yours out?

Tango · 05-25-2016, 11:56 AM

Run some numbers here...

Engine RPM Calculator

skoolie_n00bie · 05-25-2016, 12:01 PM

Quote:

Originally Posted by Tango

Run some numbers here...

Engine RPM Calculator

thanks, Tango!
I've see this calculator from other posts, was just wondering if anyone from the top of his/her head recalls if there is a plaque/note of rear gearing anywhere...

Tango · 05-25-2016, 12:29 PM

On most units there is a plaque...somewhere. And it usually states the axle ratio but then, it could have been changed out.

Another way to find out what you actually have is to put it in neutral...jack up the driver side rear tires...align a mark on the tire and ground...and, put a mark on the driveshaft. Rotate the tire one full rev...and count how many turns the shaft makes. That will be your ratio or at least get you close enough to look up what is/was avail on your rig and get a match. I had to do that on mine and discovered the rear end was NOT what was indicated.

BlueBirdman · 05-25-2016, 12:33 PM

Quote:

Originally Posted by skoolie_n00bie

Besides calculations, is there a way to figure out rear diff. ration?
Should it be on the diff. itself, maybe on a plate somewhere?
Haven't really looked, yet....

Where/how did you figure yours out?

There are usually two metal information plates attached above the driver's seat/windshield area. One of them will have the rear axle ratio.

There also may be a tag on the axle itself.

BlueBirdman · 05-25-2016, 12:43 PM

Quote:

Originally Posted by -cycosis-

As the title states, I have read a lot here that the 5.9 is not ideal and underpowered. Whelp, I bought one.

So for highway use, whats a good rear axle ratio?

The 5.9 Cummins came in Dodge pickups. This engine is an industrial engine - very heavy duty. There are many inexpensive ways to increase performance on the 5.9 - it's no big deal.

Your 4.44 rear axle ratio is pretty good. The lower the number, the better for highway cruising. The higher the number, the better for acceleration.

We could tell you more if we knew what transmission you have!

turf · 05-25-2016, 01:24 PM

i have a cummins 5.9, at545, and a 4.7 rear. the math on the calculator works out perfectly. top speed of 67mph at 2500rpm

a 4.4 would be ideal imo

that should get close to 75mph

Robin97396 · 05-25-2016, 02:09 PM

This special needs bus has a 3.54, but that's apparently to make up for my small tires.

cadillackid · 05-25-2016, 02:16 PM

yeah thats another thing to look at is not just axle and transmission its also tire sizes.. like robnin mentioned some handicap busses have smaller rear tires so it can have a flat floor inside..
like a VAN

-Christopher

Robin97396 · 05-25-2016, 04:18 PM

Not LIKE a van. It's a van. Yes, I may have an inferiority complex about my little wheels.

Jolly Roger · 05-25-2016, 04:24 PM

Quote:

Originally Posted by Robin97396

Not LIKE a van. It's a van. Yes, I may have an inferiority complex about my little wheels.

Your little wheels are fine. They get the job done. Just not as quick as bigger ones.
Just messin around.

2kool4skool · 05-25-2016, 05:35 PM

Quote:

Originally Posted by Robin97396

This special needs bus has a 3.54, but that's apparently to make up for my smallish tires.

Same here but a 4.10 would be ideal for my driving style plus I live in hill country.
My bus will do way past it's stability capabilities not to mention tire speed limits.

Fixed it for you Robin!

Robin97396 · 05-25-2016, 06:57 PM

Yes, smallish sounds much better. It's the "ish" that neutralizes the sting. As long as they keep getting me to the grocery store I'm ok.
Wow, a 4.10. And I have so much trouble climbing hills. If I put on air bags I could increase to big boy wheels, but that would give me less power. Everything seems to center around this darn 545.
Gimme back my stick shift. But yeah, in traffic during rush hour when my leg gets tired on that clutch somebody is likely to get rear ended. I've got to remind myself to not fix things that don't need fixing.
I'm not sure if these tires are smallish or RVish.

crazycal · 05-25-2016, 09:26 PM

It's all about the sweet spot for your engine. It is a very specialized technical term and should not be used loosely. You don't want to be driving down the freeway at 2700 rpm just because that is where the governor stops you. In case you didn't know, that's not good. My 1995 International has a DT408, AT545 trans, 9R22.5 tiresand a 4.78 rearend ratio. I'm at 2500 rpm @ 55mph. It kills me to drive with the engine turning that fast so I drive about 45-50 mph. The world goes by really slow at that speed.

What am I going to do about this? In this order, I will

1. Go to a larger tire size. Probably 11R22.5..
2. Swap my trans to a lockup trans. I have an AT1545 out of a 2 1/2 ton military truck.

These two things should drop rpm to about 2100 @ 55mph. If that is not enough, I will swap the 4.78 to a 4.44 rearend. I want to be at 2000 or a little under.

Tango · 05-26-2016, 12:56 AM

Cal's got figger'd out. You have to take it all into consideration and aim for that sweet spot unless you want to burn a motor and suck way too much fuel doing it.

turf · 05-26-2016, 08:46 AM

ive heard about that sweet spot, but never found it.

plenty of peeps on the interweb say that you can run the cummins 5.9 pegged to the redline all day.

on the interstate, mine sure is. if i swapped to a 4.3 and got 75mph, i'd still peg it on the freeway for 75mph.

you'd need to gear it for max speed of 85mph before you got the sweet spot in a cruising speed. i honestly dont think the cummins 5.9 makes the kind of power to push that gearing. not at my weight of 20k lbs+. i can barely go uphill now.

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