Speedo Conversion mph -kmh

Hi I have a question on speedometer,
I've a workin speedo in mph, and the original fitted on the bike (not working) in km/h,
If I mind to convert the working one in km/h what to do?
I presume change the dial is not enough...
Please advice
Mario

Thomasdunstall said:

I presume change the dial is not enough...

Click to expand...

If you were to change the dial, the odometer will still record in miles.

I am not sure this is relevant, but there are two speedometer drive gearbox ratios ..... 2:1 and 1.25:1. If one divides 1.25 by 2, the result is 0.625 which is nearly the exact ratio between kilometers and miles.

A 15:12 ratio gearbox is effectually 1.25:1.

Therefore, it would seem if a 1.25:1 gearbox were substituted for a 2:1, and coupled to a speedo calibrated in miles, the speedo will then accurately read km/ hr and km (that is the mph dial will read 100 at a true speed of 62 mph). The problem is, the speedometer will "top out" at about 93 mph or 150 km/h for a speedo with a 150 mph dial. Therefore, it would seem that speedos calibrated in km must have an internal gear ratio difference to keep the arc of display in reasonable bounds.

I hope this helps to sort it out.

Slick

L.A.B. said:

Thomasdunstall said:

I presume change the dial is not enough...

Click to expand...

If you were to change the dial, the odometer will still record in miles.

Click to expand...

Yes Les as I supposed,
I'm thinking to use with the dial also the old odometer gear on the new smiths instrument in miles.
Hope it works...
We'll see

I rode motorcycles and drive cars long before metrication came to Australia, so I always think in miles per hour especially when talking about race speeds and keep the equivalents of the speed limits in my head for when I am driving my car. I can divide by 8 and multiply by 5 and vice versa, in my head. In my professional capacity, I used to also carry many of the conversion factors between the British and metric system in my head - all now redundant information clogging up my brain. Have you noticed that Amal needle jet sizes are in inches ? When I'm tuning, I use both number drills and metric drills to get the various size holes up them.

thanks all,
very useful help,
the speedo has been repaired,
I midex parts from the original not working speedo in km/h with the working but ugly speedo in MPH...
and it works!
It just looks fine for a non professional job...
Mario