What Rear Gears do I want on a 13 speed

2.53 on lp22.5 and a 10 speed direct
With ISX400ST, quite well, running same speed, same rpm just like on 3.55 with lp24.5.

 

Actually I have a Volvo with an ISHIFT the final transmission ratio is .78 with 2.64 rears on 22.5 rubber

 

I'd go with the 3.08 rear end gears if it was the 295/75/r22.5 tires on the truck with the 13 speed. I drove that combination for two years but mine was a manual. The best I ever got with it was 8mpg at 77k pounds in a Pete 386, 2012. Personally I would go no lower than the 3.08 gears. It really starts to affect the way the launches and how fast it accelerates.

 

that slightly blows my mind actually. I would have sworn the ISHIFT trannies were all direct drive. but, they do like to do that downspeed thing. the purpose there isn't power according to what I read, but simply getting rpms down so that it cruises at 1050 rpm or so as opposed to 1450

 

You'd think that low of a rpm would kill fuel mileage but what do I know

 

you'd think, but Volvo engines are extremely torque-y down low. they handle it nicely.