80's SBI expedition came with 48,44,28 crank FD was shallow back plate, but the rear gear was a 6 speed .. bigger gaps between the ratios needed, in order to make half step work , like a 13,15,17,20,24,30,[26.32] .. a shimano K cluster for cassettes

it adds a low gear , last 3 24,29,34 7 SPEED, 8 and 9 gain little but near-redundant ratios.