What does rear ratio in a semi means?

Most likely will be a 13 speed with a 2.16 RAR if talking Volvo or Mack with Turbo Compound .

 

Using your graph, how did you arrive at an overlap/intersection point of 1600 rpm?

 

So you're driving one of the newer model 12-speed automatics?

 

I reckon it’s probably closer to 1500.

 

Yes. I ordered the Paccar 12 speed in the 579 I got a year ago.

 

Nice. How is it spec'd with the hp and rr? What kind of mpg are you getting?

 

I wasn't questioning your accuracy. I was just wondering how you figure it out. My graph is posted on this thread also and I wanted to figure out what my sweet spot was.

 

It would be easier if you could overlay the two. But if you look at mine peak torque is at 975 rpm’s with a fairly flat curve all the way out to 1450 and just begins to really fall off at 1500. But horsepower is climbing pretty steep from around 350 at 975 to 575 at 1500. So at around 1500 you are running most of your horse power and you’re at the top of the power band. The motor only loses torque or hp on either side.

I’m not sure I explained it clearly. I apologize if I didn’t

 

If you are running the 515 s60 it looks like around 15-1550 is where you need to be running. Probably no lower than 14 and No more than 16

 

510/1850 Paccar, 12 spd Paccar, 2.79 rears. The software wouldn’t let me order 2.64 with the 510. Without looking in my book I want to say my lifetime mpg on paper is a little over 7.2. I give up some fuel economy because of my wheelbase and drive tires and I’m not willing to go with the efficiency program in the transmission.