Don'd know numbers wise but following are accurate swaps at road speeds. 500/4 can use cb250 superdream speedo, (even fits into the same cases) since tyre sizes are the same therefore speedo drive probably works too, (spindle is I think the same.) cb250 nighthawk uses 18" front hoop but is also accurate using superdream speedo unit, also fits in nighthawk binicle. cb550 I'd geuss is same ratio as 500/4 as I've almost cirtainly mixed the speedo drives up a few times, A bad habbit of keeping a spare wheel and tyre ready assembled for easy fixes.