Truck Spes

Most popular gear ratio is 3.42. My dad's 2000 century had 3.42 on it and it ran well climbing up hills.

 

3.55s with a .73 overdrive trans. is 65 @1400RPMs.

 

I have a road speed calculator spreadsheet for you to fiddle with various rear end ratios, tire revolutions per mile, etc. It is set up right now for a 13 speed with low pro 22.5. You can change the tire revolutions, gear ratios, rear end ratios all you want to see how various combinations work. Cannot get it to upload in this post, but if you send me a PM with your email address, I will forward it to you.

 

http://www.roadranger.com/ecm/groups/public/@pub/@eaton/@roadranger/documents/content/ct_062746.swf

 

http://big-rig-road-speed-calculator.blogspot.com/2011/03/semi-truck-road-speed-calculator.html

Try this one.

 

With my series 60 pre-egr 12.7, I went with 18 speed with 2.64 rears and run in direct (16th) at road speed. Over all pretty good setup. Considered 2.79, but glad I didn't go with that. I would be tempted to go with 3.08 and run one gear higher though. 2.64 does affect start ability a little. Not terrible, but it does affect it. Other than that, there are no issues with pulling on hills. The 3.08 would give me a little better start ability, and I would only be in the first overdrive, which is more efficient than being in the 2nd overdrive. You progressively lose efficiency with each step of overdrives. 3.08 is kind of more balanced for more situations. The 2.64 and the 3.08 give the same RPM/Speed as being in the top hole with 3.55. Just 3.08 is one gear lower and 2.64 is two gears lower. The 3.08 would be better for many folks than 2.64 or 3.55. You would have good startablity, and if you needed to "put a wiggle in it" when bobtailing or empty and get on down the road, you would have the top gear still available to keep RPM's down while still moving along at a pretty good clip. 2.64 is really only great with a direct 10 or an 18 spd. 3.08 would work fantastic with a 13 or 18.

I run a lot of two lanes, hilly, with 40K + in the box. Many said 2.64 wouldn't work. It does. But, for most folks, I would recommend a balance between 2.64 and 3.55...... 3.08. That works out to 1400 to 1500 rpm between 60 and 65 roughly in 12th on a 13 and 17th on a 18. Still have one gear up in reserve for those times when you need to let the badger loose. And if on a very hard pull, the first gear drop would put you in direct drive on the 13 or the 18, where the most efficiency is and maximum power to the rear is happening.