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730 with 2.47 rear end gearing too tall?


mrrrl2

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I see a lot of the 730's with D13 currently on the market with 2.47 rear ends. Is this too tall for most of the users here? I did some searching and saw a video Greg (RV Hauler WILSON Intro Model 730 ishift with 2.64 rear end ratio) did on a 730 with 2.64 gearing but is 2.47 just too tall? I understand that there are a lot of variables here and that there maybe several different iShift models with different gearbox ratios. Currently looking for a 730, adding Smart on back with 36-38' 5th wheel just not sure about this tall of a rear end.

 

Any one here with this rear end?

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You've seen multiple trucks with 2.47 rear ends? Most everything I see out there is in the 3.08 and up. Sometimes a 2.64 pops up, but I don't think I've seen any 2.47 pop up? Interesting. It seems for a truck carrying 80k lbs, that would be a high ratio, but maybe not too bad for the weights most carry here?

 

I noticed on the older trucks, you seem to see even higher ratios, with many in the 3.50-3.73 range. I guess they are getting more efficient as they get newer.

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You've seen multiple trucks with 2.47 rear ends? Most everything I see out there is in the 3.08 and up. Sometimes a 2.64 pops up, but I don't think I've seen any 2.47 pop up? Interesting. It seems for a truck carrying 80k lbs, that would be a high ratio, but maybe not too bad for the weights most carry here?

 

I noticed on the older trucks, you seem to see even higher ratios, with many in the 3.50-3.73 range. I guess they are getting more efficient as they get newer.

 

The fleet trucks coming out for Freightliner and Western Star are set up with a 400hp DD15 the new DT12 transmission and 2:41 rear ends. The new drive line is all built by Detroit and all work together to increase mileage. They have a few really good videos on this setup. The afore mentioned drive line averages 9.3 mpg while hauling a GVW of 79k lbs on a 2,400 mile cross country trip.

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Discussing the rear end ratio without the second half of the discussion-the transmission and it's ratios/spec's is a fruitless endeavor. The torque characteristics of the engine is also part of the equation. The only concern I would have with a tall ratio like a 2.64 or 2.47 is start ability, i.e pulling out a an inclined dock with 80,000k gross. And the manufacturer is well aware of that possibility and has designed a transmission 1st or 2nd gear with a gear reduction to address the need.

The current school of thought, having the transmission in a direct drive(straight thru) configuration which is more fuel efficient than an overdrive arrangement has been popular for some time.

Since the HDT/RV application doesn't call for weights anything close to the original truck design, I wouldn't be too concerned about it.

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Since the HDT/RV application doesn't call for weights anything close to the original truck design, I wouldn't be too concerned about it.

I'm with Jeff on this. It will work for you, if you have reasonable expectations. However, It MAY NOT work well for you depending on your average driving speed on open roads. For example, You may like to drive at 63 mph like I do. But the truck gearing/trans may not like to be in 12th gear at that speed, and keep you in 11th. OR it may put you back in 11th on ANY mild grade. That may require you to drive at 68mph, instead, to avoid that issue. YOU MUST DRIVE THE TRUCK to determine this quirk, and if it will work for you. No simulator is going to get that answer right.

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I'm with Jeff on this. It will work for you, if you have reasonable expectations. However, It MAY NOT work well for you depending on your average driving speed on open roads. For example, You may like to drive at 63 mph like I do. But the truck gearing/trans may not like to be in 12th gear at that speed, and keep you in 11th. OR it may put you back in 11th on ANY mild grade. That may require you to drive at 68mph, instead, to avoid that issue. YOU MUST DRIVE THE TRUCK to determine this quirk, and if it will work for you. No simulator is going to get that answer right.

Jack you bring up some good points and I will throw in my two cents worth and it relates to Jeff's comments regarding transmissions as well.

 

The Dollytrolley is a old Shaker with a M11 Cummins, 3:08 drivers AND a 10 speed Road-Rager tranny .....at first glance this combination would seem to be a economical HDT RV rig for cruising down the highway....and so far this has been the case....However, as Jeff mentioned sometimes low speed operations are "compromised" and with the Dollytrolley the tranny has a high speed reverse gear and IF the bone-head driver bumbles into high range reverse the Trolley could easily out run big5er'$ DOT rig...in REVERSE...

 

High-speed reverse is a pain in the keister so I simply engage in chronic clutch abuse when I need creep-speeds in REVERSE....

 

Couple of times I have pondered cobbling a brownie four speed behind the Road-Rager but do I really need FORTY gears to mismanage....answer..NO..

 

Like Jack says RV'$ are a study in .... compromise...

 

Drive on.....(what's your gears today)

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I understand that there are a lot of variables here and that there maybe several different iShift models with different gearbox ratios.

As I understand it, the iShift has always had the same gearing. The only variable as Stekay pointed out is the AT vs. ATO (overdrive vs. non-overdrive): the splitter can be "plumbed" two different ways, as an overdrive or as an underdrive. If it's overdrive, 11th is direct and 12th is overdrive.Otherwise, 12th is direct. Volvo was/is proud of the fact that the iShift has consistent ~27% gear spacing across the entire range, something that can't be said for the 9/13/18 crowd.

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Because you're talking about changing Tires & Rims times 10 along with the fact that 24.5's are rather rare if you need service. So let's say we go $500/tire then another $150/wheel even with your trade ins you're looking at a boat load of cash even if you're singled. So no, not way cheaper. Also, noone said anything about "changing ratio'

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Bigger tires eat mpg. More rotating mass.

Ya know.....inquiring minds want to know Glenn.... just wonder what the dynamic(z) are between 22.5'$ and 24.5'$....this homework assignment might be perfect for ....Stekay. ...

 

We could sling around some hot terms like...coo-efffecntz-fiction, monimentz-0f-ontererza, and biaza-verza-raodial-plyei-internactional+ gravitational -xttatresteral-forcez'$..... and a bunch of engineering-geek-terms as space permits...

 

Talk'n tires often leads to.....a well "rounded" discussion (I could not resist the punn).

 

Drive on....(into the engineering...vortex)??????♎❔〰❎➕➖➗☢

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Guys really like big tires on ldt trucks. They all loose mpg and pulling power.True our trucks have power to spare but the same happens. Just not as pronounced on our trucks. I have considered doing this. My ratio 3:50ish. But I do not believe I would gain any mpg due to the increased rotating mass.

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Dolly, howd'ya fergit radius of gyration?

Shucks big boy...ya got on that de-tail, so.....will you record just raw-data or....will ya kalkulate it in half-A$$ed-fornieer-Log-$cale....

 

Don't forget themtheree db'z an powers of perswaziatinz...

 

How could ya have more fun with your clothes on.....

 

Drive on....(Stekay Is getting in da groove)

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My, oh my....... In the end, Sammy Hagar mentioned something about Mental Mast............. Talking hypothetical mileage is just that. In the real world, your driving habits will decide which gearing works best, and whether you are happy with your mpg.

 

I have a son-in-law that had to have a diesel Touareg, for the mileage. The he drives like a bat-out-of-hades, and gets crap mileage in spite of his aftermarket air filter (which violated the warranty) and all the other doo-hickeys he's had to add. These trucks are no different. I'd bet someone like BroncoHauler could extract decnt mileage out of the worst truck in this group, v. someone in a hurry to get there.

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