What Rear Gears do I want on a 13 speed

What hills? That only one around MM126 in VA? How about real hills? Like on I-26 or I-64?

Sorry, I just think that if you feel hills on I-81, than you have way too little power, which having driven the same exact spec Volvo back in 2k13, was cenrainly the case for me.

 

If your happy with it stick with it what you'll really have to weigh up is whether the money you'll spend on a different ratio diff is worth the amount your going to actually save on fuel, perhaps just drive a few miles per hour slower and this will also get you better economy, idle less at trucks stops all this adds up and is so much cheaper then the option of a different diff, you may get better economy with a lower ratio diff but you will also lose out on pick up too. the idea being to get the engine to rev less at higher speeds keep in mind though that different diesel motors have different economy rates at different revs as well.

 

Hey, hey...I never said I like to climb the cliffs of I-64 across the shenandoah's ... lol

I have no desire to pull 80K, when there's lighter, better paying loads...and when I do go uphill, I never break a sweat.

 

A mile quicker on a same rpm. 10 speed FR series are .74 to 1. 13/18 speed and 10 speed advantage series are .73 on top gear.

 

Again not enough to get bent over. New tires verse worn tires will give more change than that.

 

I run 2.64 and there was almost no loss in pulling , the little D13-455XE outpulls 75% of the trucks on the mountain. Dropping to direct she pulls awesome!

 

Those are ratios for a direct drive transmission. With an overdrive you wouldn't have enough power to maintain speed.

 

9-10-13-18 will all be .73od. Have you considered switching from low pro to reg 22.5 or a little pricer mod would be to swap in an old school rtloo 13 double od. With a .62 in the big hole. The old school ones where you actually have to be a driver to shift or you'll blow it

 

3.55 on LP24.5s and a 13 speed. With a 750 CAT it does quite well.