2002 IC RE3000 - rear end gearing

[halfdime]

Ok. I’ve done some research and some calculations on the rear end ratio.

The Bus
40’ Bus
DT466E - yet to determine High Torque model or not; serial # is covered or the motor is a transition year motor. Not in the spot I would expect to see a 2002 SN.
Allison MD3060 (6th still locker for now) Final drive 0.75:1 for the transmission as standard. 1st is 3.49 I believe but need to check my notes. It’s a close ration MD3060CR

Rear end 6.17:1 Dana Spicer 23080S, air suspension, air brakes.
11R22.5 tires (42.2” diameter)

Have not weighed it yet, but would guess it will be in the 23k range built with 6k in tow.

Also plan on adding an electric fan and removing the engine driven fan foe more HP.

The Plan
Drive the bus through the mountains with2 adults, 4 kids and a dog.
Pull a Subaru Ascent on a car hauler

The Questions

1. Has anyone got a similar setup with a 4.63 rear ended? Good for highway, how about start-ability?

I’ve run numbers and while the star-ability is not dramatically reduced from stock, it’s a number that lacks context and is a reference number.

2. How about traveling in the mountains? 20mph would be painful, but may be what it is. Any experience on what to expect here?

I realize that there are a lot of variables here, but looking for some advice ans experience.

 

[CHEESE_WAGON]

42.2 seems a mite big even for a truck tire. Is that the circumference or diameter?

 

[TJones-SKO]

42.2 seems a mite big even for a truck tire. Is that the circumference or diameter?

I have been researching gear ratios for my bus. I don't think I would go to a ratio higher than a 4.78. If you can get 6th unlocked you could go as low as 5.38 and still get lower engine rpm at highway speeds. Cummins has a very good free gearing calculator in PowerSpec that lets you put in transmission, tire size, vehicle weight ect. You would have to pretend it is a current cummins engine to get gradability information. Choosing a 6.7 with your engines hp and torque ratings would give you a good idea how your engine would perform.

Ted

 

[halfdime]

42.2 seems a mite big even for a truck tire. Is that the circumference or diameter?

11R22.5– noted rim and tire size. Yes, it is a commercial truck tire size. The all knowing google spits out the diameter as 42.2.

 

[CHEESE_WAGON]

Google is only as good as the info it finds.

Diameter = distance across a circle
Radius = diameter divided by 2
Circumference = 2 x 3.14 (pi) x radius.

This calculator shows a 245/75-22.5 to be 37 inches tall (PSI / load dependent). 11 inches width is 279 mm, but 11R22.5 does not indicate aspect ratio (sidewall height), a critical element in calculating MPH / RPM, unless these have a standard sidewall height I'm not aware of. But going by 75% AR, the same calculator shows 280-75R22.5 would be 39 inches tall. Bridgestone's site shows the height as 42.2 as you state, but it just doesn't sound right to me. That's like a 90% AR. If there is something I don't know here, let me know.

This calculator shows a 39" tire with a 6.17:1 rear and 0.74:1 trans top gear pushing 2500ish RPM at 63 mph. Any way you slice it, I think you'll be playing with fire pushing your bus much past 58-60 with that low of a rear.

If you're looking to cruise at 70 mph, you'll have to take your chances unlocking 6th (may or may not drop RPM sufficiently, even if you can get it done) or go to a higher rear (numerically lower), say, 5.29, which would still turn 2350ish at 70 running the same tire without unlocking 6th. Does anyone even make a 4.63 for these differentials? It's not a ratio I've heard of, but it would turn 2100ish at 70 with that trans and 39" tires. However, if your tires are truly 42.2", a 5.29 would be at 2200ish at 70 mph without unlocking the 6th gear. A bit more RPM than I would run a diesel at, but somewhat reasonable at least.

Most of these engines are meant to run around 1600-2000 - that is where most of them are most efficient. They may governed for more RPM, but just because you can doesn't mean you should. Diesels don't like RPM the way gassers do. Even if it is safe at a given RPM, it definitely takes a toll on long term durability.

Also, for some applications, your engine could have been built a year or more before the bus was built. So your 2002 bus could have 2000-2001 parts.

 

[halfdime]

Google is only as good as the info it finds.

Diameter = distance across a circle
Radius = diameter divided by 2
Circumference = 2 x 3.14 (pi) x radius.

This calculator shows a 245/75-22.5 to be 37 inches tall (PSI / load dependent). 11 inches width is 279 mm, but 11R22.5 does not indicate aspect ratio (sidewall height), a critical element in calculating MPH / RPM, unless these have a standard sidewall height I'm not aware of. But going by 75% AR, the same calculator shows 280-75R22.5 would be 39 inches tall. Bridgestone's site shows the height as 42.2 as you state, but it just doesn't sound right to me. That's like a 90% AR. If there is something I don't know here, let me know.

This calculator shows a 39" tire with a 6.17:1 rear and 0.74:1 trans top gear pushing 2500ish RPM at 63 mph. Any way you slice it, I think you'll be playing with fire pushing your bus much past 58-60 with that low of a rear.

If you're looking to cruise at 70 mph, you'll have to take your chances unlocking 6th (may or may not drop RPM sufficiently, even if you can get it done) or go to a higher rear (numerically lower), say, 5.29, which would still turn 2350ish at 70 running the same tire without unlocking 6th. Does anyone even make a 4.63 for these differentials? It's not a ratio I've heard of, but it would turn 2100ish at 70 with that trans and 39" tires. However, if your tires are truly 42.2", a 5.29 would be at 2200ish at 70 mph without unlocking the 6th gear. A bit more RPM than I would run a diesel at, but somewhat reasonable at least.

Most of these engines are meant to run around 1600-2000 - that is where most of them are most efficient. They may governed for more RPM, but just because you can doesn't mean you should. Diesels don't like RPM the way gassers do. Even if it is safe at a given RPM, it definitely takes a toll on long term durability.

Also, for some applications, your engine could have been built a year or more before the bus was built. So your 2002 bus could have 2000-2001 parts.

Thanks. I’ve got all that. Confirmed ratios available for axle and carrier; confirmed the rpm against a final drive calculator. Looking more for the answer to the questions above.