rev counter / speedo Ratios

[saxby]

any one know what the Ratio is for the rev counter / speedo ?
is it going to matter massivly and low speeds [under 60mph]

[matthewmosse]

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.

[SteveD CB500K0]

This from eurban on sohc4.net:

"As far as I know all the SOHC have speedos with the ratio of "2240:60"  which I think means that at 60mph the speedo cable is spinning at 2240 rpms.  This is the same ratio used by Harley on some of its bikes which means that you can find a number of aftermarket guages that are calibrated correctly for the SOHC Honda's.  Most of the aftermarket guages also are set up to accept the 12mm (i think) speedo cable to guage fitting that is stock on the SOHCs.  The ratio you mention on the beemer would seem to be way off but I don't know if it measuring something else."

[SteveD CB500K0]

From what I have gleaned over the years:

350/400/500/550 use a tach ratio of 20:3
750 uses 4:1

Don't have any info on the 650 but I would be surprised if it was different from the 550