Direct vs. OD setups

The clairify, the only driect trans i can go out and but today are:

Volvo 12 speed ishift (but then i need a Volvo motor and can use the cummings)

Ultrashift 10 speed Direct

10 speed Direct

Are there any others?

What about that new alision trans. Can that be bought with a direct top gear? What about the new Detroit transmission?

OD trans work, but you do loose the bottom gears since your wasting 2 on the top end. I'd rather not haul around 2 extra gears just because they are to stupid to make a direct drive trans. but that might be my best option. Has anyone confirmed if the low of an 18 is lower then the 1st of a direct 10? The site I always used to find trans ratios was taken down. Anyone know a good new resource for trans ratios?

 

A typical 10 speed direct (RTF-14710B, FRF-15210B) has about 14.8 1st gear ratio.
18 speed Low/Low is 14.40.
The 10 speed has a small advantage for startability when using same rear axle ratio, but the difference is only 3%

Volvo I-shift direct drive has 14.94 in 1st, DT12 direct 14.93. Not much of a difference.

ZF AS-tronic, very common in Europe in DAF(Paccar), MAN and Iveco has 15.86 in the direct drive versions

Note that Volvo are using overdrive transmissions in their latest XE Packages, maybe because there are no rear axle ratios available for what they want to do, 0.78 OD and 2.64 rear axle ratio. To do this with a direct drive transmission you would need a 2.06 rear axle ratio.

 

What i've seen on some volvo's is an OD trans speced with a 2.64. This allows a driver to go 65 in direct all day, but 75 when they need to with OD. Its kind of liek useing a 13 in a dirrect set up. To do this with a direct trans you would be red linign as you go past 70 mph ish

 

I spec everythign based on the XONE Line Energy D. Its the most fuel efficient drive tire on the market. (lowest rolling resistance ) So, any other size wouldn't work for me personaly.

But, you bring up an important point not discussed much int he other thread. You can change speed with: RPM, trans gearing, rear end AND TIRE SIZE. This is generally overlooked since it doesn't make nearly as much of a difference as a rear end or final drive on the trans. It can be valuable of your rear end is just a little off the spec you want.

Given a new truck, id still speck the 2.64 with line energy d...but that tire isn't for everyone. Also you need to consider you intended cruise speed and motor peek rpm when selecting a rear

If you havnt checked it out, google Eaton rear end calculator. You can play around with ratios and speeds all day long

 

Some food for thought.
Courtesy of: http://www.worktruckonline.com/chan...drive-axle-ratios-for-medium-duty-trucks.aspx

I realize that they are talking about a smaller class of trucks in this article, but the principle still remains the same.

 

Saw it on the web, it must be true lol.

In all reality, I feel that artical is does not translate to big trucks. The reason we keep saying you can have the same performance with a shorter gear ratio is because you can drop a gear to compensate for the shorter gear when you need to and maintain the same speed as a taller rear. Trans in a taller gear with a shorter rear gear is the same as trans in shorter gear with a taller rear.

Since a big truck has so many gears, we can keep the motor in ideal torque range since the rpm doesnt change more then 3 or 400 rpm (depending on trans). On a small truck with less gears, the gaps between gears are much bigger and thus by shifting you may be shifting out of the ideal area of the motor. One gear, or a split gear in a big truck is 5-10 mph, while in a 5 speed truck it could be 15 or 20. Basically since there are fewer gears you cant compensate for the reaar as well. This is just my math again. no real world experience specking a small truck.

Off the line is the biggest concern, small or large truck.

 

The only thing I haven't seen much discussion about on the 2.64 set up, is all the extra strain it will put on everything. Don't you know if the carrier bearing closest to the ring gear could talk, it would say wtf, I don't know how long I'm gonna be able to take the strain. That extra stress continues all the way to output shaft gear set and bearings, as well. Wonder why they're rated lower? Another thing that takes out diff gears is shock load, and you're definitely risking a greater shock load when running a 2.64. No doubt the ring gear will be heavier with the fewer teeth, but what about everything else? When you're running that 2.64 in direct final drive, you're passing that extra torque load all the way to the splines in the clutch disc. Common sense tells you that a taller gear (2.64) takes more torque to set in motion and maintain that motion than a lower gear(say 3.73). But I guess if you drive a fleet truck, you don't have to worry about duration of components.

 

What do you have for a transmission and rear gears in your truck now?