Here's some examples:

http://i130.photobucket.com/albums/p...13speed355.jpg

http://i130.photobucket.com/albums/p...13speed373.jpg

http://i130.photobucket.com/albums/p.../direct279.jpg

http://i130.photobucket.com/albums/p.../direct264.jpg

I just used microsoft works spreadsheet, and created a graph out of the calculated values.

It takes me a matter of seconds to change two numbers, and it recalculates the whole graph.

What I need:

Differential gear ratio
Transmission final gear ratio, OR make and model #, I *NEED* the model number, as some transmissions have several different ratios(for example, eaton 10 speeds).

So as you can see from the graph, it's pretty easy to visualize where your sweet spot is, and to see how much of a difference a tire change would make.

I just realized I put the RPM and MPH labels in the wrong spots, we must have some damn FAST trucks!

It would be real interesting to see MPG graphed in as well. Might help keep a light foot

If engine manufacturers released a BSFC chart, I could.

Trans# FRO16210C
Rear Diff= 4.11
Tires= 22.5 not lopro
C12
I looked up trans once before and I think, if I read the
chart right the 10th gear was .73
My trach reads 1650 rpm's @ 65 mph
When you say sweet spot do you mean the best engine speed
to get the best mpg?? 8) 8)

http://i130.photobucket.com/albums/p...10speed411.jpg

Wow, that thing is really geared aggressive.

My dad's truck has 4.10s, but he runs tall 24.5's.

I don't know what cat recommends for your c12, what year is it, and is it multi-torque?

Cat recommends 1400 rpms at 65 mph for their c13, multitorque 1325 rpms at 65 mph, both with a max speed of 1500 at 65 mph.

I'd say to get good fuel mileage out of that thing, you shouldn't run a hair over 60!

Do you want me to expand the graph up?

Wish I knew my final drive. When my super 10 died for the 3rd time, I dug an old 9 speed out of the sand out back, turned the gears around in it and put it in. I have 3.58 rears and turn 1650 at 70mph with 24.5 low pro's.

Thanks Allen it looks pretty close, today I kept my foot out of it and held
it down to about 57 to 60 and your graph shows about what my tach was
reading. Yes you can expand it if it's not to much trouble. Diesel is $3.13 here and I been averaging about 5.3 to 5.8 but thats with a lot of stop and go and me running 65mph. My c12 is 2002 model truck I think it is mulity torque, but have never seen the boost gauge go above 22.5 psi. and it will only develope that much boost till it hits about 1400 to 1500 rpm's & up.

Can you get me a model # off the tranny? Or at least a make?

Are you sure 70 mph at 1650 is right? How accurate is your speedo?