Given they offer 6, 10, 13, and 18 gears (and others) in the trannys why are so many needed and why the large range in numbers? Is it the limited RPM range of these large engines? Are the trucks with fewer gears more suitable to lower weights?

to keep the engine running in the "sweet spot"....which means at the spot on the rpm range where the engine is operated at the most efficient level for maximun torque-speed-fuel efficiency....geof

So the more gears you can keep the RPM per gear within 300 to 400?

That would lead me to assume that given most conversions are a lot lighter than an OTR truck/trailer you can get away with fewer gears because you don't work the motor nearly as hard and can wider the "optimal" range.

For me, I'm not wildly interested in shifting, hence a preference towards the Freedomline tranny (12 and 16 speed).

Also, for me my trailer only weighs about 8000 pounds so my GCW won't most likely exceed 40K.

Actually in the case of a conversion a 9- or 10-speed would be more than enough, and you won't be using all of THEM!

So at the most in normal situaions with a 10 speed manual-you are only going to have to shift 4 to 6 times....with an auto transmission or other modern transmisssion even less-an autoshift you only use the clutch for starting and stopping...keeping it in the power band or "sweet spot" is almost automatic now....truck driving is getting almost like a SUV.....and a lot more women are driving for a living and require more comforts as well as research indicating driver fatigue is reduced by automation...geof