10-Speed Peterbilt 379 - Save Fuel with 13-Speed Upgrade?

9 speed is best for fuel economy because it prevents drivers to make unnecessary shifts. Every shift spends fuel, engines are made to be lugged down and use the whole rpm range. I see and hear 90% of the drivers using too many gears with 13-18 speeds.

 

If anything change out the 3:70 rear ratio for a long legged ratio, like 3:58. You want something where your turning 1500 rpm and be able to do 65 mph in high gear.

 

some 13 dont have much od like 9s & 10s

 

From Eaton:

 

may save fuel economy with a 9-speed, but from a sales POV, a 13 speed is a better sell when you get ready to dump the truck. The conversion kit is around $2400 or so. Just quoted one the other day.

 

Um....Just because you have 13 choices doesn't mean you have to use them. If you don't split the high gears you have a 9spd but it's nice that they're there when you need them.

I don't believe that a 9spd is better on fuel. I had one and the jump between some of the gears is so great you find yourself leaving it in a lower gear and running a higher RPM than you would normally.

 

Tell that to most of the drivers, especially those driving Fuller. It's harder to skip shift with non-synchronized box so they go through all the gears to prevent grinding.

 

Nothing to skip shifting. Maybe you need more practice...

 

skip shift? WTH are you talking about? Your not skipping anything your just not splitting the gears. A 13 is just a 9spd with a splitter box on the rear, you could just remove the 13spd knob and replace it with a 9 and no one would be able to tell without looking under the truck.

 

Wrong 13s have the same od as 9s and 10s.