Okay, looking at the manual Kevin linked to, there's a few interesting items.
A. Looks like the biggest gear ("first gear") might be 80 teeth, and the next biggest gear ("third gear") might be 36 teeth, according to parts list. The small gears aren't numbered in the parts list though.
B. There is a third optical sensor, just for centering. Very much like 720 (skate or die). This makes at least two arcade games with a optical "center" sensors.
C. The manual is specific to the upright cab. Not only are the diagrams of the upright, but the dipswitch page says that the first two dipswitch must be closed, which is what mame labels as "Upright, steering lock".
D. Mame uses paddle (pot based, limited turn) input type. And either mame isn't emulating the centering sensor, or that is being bypassed as not needed to be emulated because the chip being bypassed converts into a normal, pot like, data.
djuret, is your manual the same as the one Kevin linked? If not, I'd like to see the differences. (What I really want is to see the cockpit manual, and see the differences.)