can someone explain the workings of range &splitter gears on lorries?

Question

if you have 12 gears on a lorry do you have 6 upper and 6 lower or with 8 is it the same a 4 shift system with a switch to go from 1 2 3 4 to 5 6 7 8

Answer 1

A 12 speed would be four gears with two splitters. You would shift 1 2 3 4, then split the main splitter, shift back to 1, which is now five. Your shift from 5 to 6 is made with the auxiliary splitter, then you shift the aux back and go to 2, which is now 7. I hope that makes sense. I do it everyday, so it has become automatic to me.

Your description of an 8 speed is accurate. This would be the same for a 10 speed, 1 2 3 4 5, split, 6 7 8 9 10. A nine speed is the same as an 8, but with an added low gear that you only use in low range. A 13 speed (what I have) is the same as a 12 with a low gear. An 18 speed is a nine speed with an auxiliary splitter that splits every gear, instead of just high range like a 12 or 13. A 15 speed is a 10 speed with aux to split the low range gears. It is typically used in dump trucks and off road situations.

Hope this helps.