P00Man

i heard that semi trucks, the big rigs, whatever you wanna call em, have like 12spd manuals in em.
is this true?
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Spining Ncnratr

Some like the heavy duty logging trucks have 24+ gears
My cousin is an independent hauler and his 87 WesternStar
had 15 gears

1st had Ultra Low or (Creeper Gear) ,then Low, then High
2nd had Ultra Low, low, and High
3rd had low Mid range and High
4th had Low, Mid range High and cruising high< best way to describe this
5th High, overdrive 1, and over drive 2< again only way to describe how these last 2 gears worked.

but you had a finger switch to go through each gearing in the gear series so you shifted it to first then you slide the Finger switch through those 3 gear settings then you shifted to second and done the same thing and ect. ect.

With out a full load or trailer he could do a good 110 MPH impressive when the truck weighed over 24,000 LBS!!!!!!!!!!!!!!!


But the most impressive Semi I seen was a 78 Kenworth with a 404 Cummins with twin S/Cers done I think 650 HP and 9,000+ Ft Lbs of torque He done a lot of hauls out west had a 2.75 final gear ratio and got tagged for doing 145 MPH with a 60,000 LB trailer behind and the ticket in 1978 dollars was over $500 dollars US.

Zoom2X

Semi Tractors often use multiple transmissions and/or multi speed differentials. For example in the above discripiton of the 15 speed it has a 5 speed transmission with a either a secondary 3 speed transmission or 3 speed rear end. The number of gears is the multiple of the 2 (or more) transmissions, just like is done on a 10 speed bike. The above truck should also have 3 speeds in reverse.

P00Man

yeah, thats what he said, i figured it was something like that, thanks for clearing it up, trucks a truly incredible machines IMHO, and i have tons of respect for the guys that pilot the big rigs
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