Starfire speedo drive

[Bees]

Does anybody know the drive ratio for the Starfire?

I've seen a speedo thats 2 to 1 but not sure of the dtive ratio.

Cheers

[hoogerbooger]

See the posts on B25 Speedo a few days ago

If it's a 1600 revs per mile speedo and 18" wheel & 3.5" tyre then a 2:1 drive is right.

[Bees]

Much appreciated

[MICKREEVES]

I think that all speedo drives on the rear wheel are a standard 2:1.
Therefore the only variable for different bikes, would be the wheel diameter.
As this does not vary very much, it follows that any speedo would work on any bike
and would be somewhere near to correct readings.
I am correct is this Idea?
Mick

[AdrianS]

Depends also on the speedo head.
Also depends how accurate you want to be. A 19 inch wheel will give a slower reading of about 5% and a 17 inch wheel will give a faster reading of also about 5%

[Bees]

Cheers for the replies. The bike has the std 18 inch wheels and tyre and standard drive uniy but the speedo was missing.

I bought a new replica 150mph speedo 5 years ago as I couldnt find a 120mph one, but it is wildly out  when I'm going 30mph it reads 50mph.

I've done a bit of research and it seems that some speedos run at 13:15 or something strange like that so I assume I have a mis match.

I was offered a new replica 120mph speedo but was told it needs a 2:1 ratio drive. But have decided against it and will probably save up for a reconditioned original one.

Once again. Cheers.

[hoogerbooger]

One reason your current speedo may be wildly out is that is may be a 1000 turns per mile rather than a 1600 turns per mile unit. Do you know ? It may just not be a compatible speedo.

(The speedo and mileometer are driven by the same cable/turn speed. As far as I can see the drive unit only really adjusts for the wheel/tyre size to get mileometer approximately right. Then to get the speed right there is a calibration screw which moves a metal 'amplifier' plate and changes the strength of the magnetic field on the drag disc. I am not sure but it is also possible that the magnet strength and return coil spring strength may vary from unit to unit to allow for different speed ranges on the dial (mph per degree of deflexion). However these are all set at manufacture and getting to the calibration screw requires taking the speedo head out of the case and a calibration set-up).


IN short, getting a properly refurbished original speedo seems a sensible option.

You can check the drive unit ratio by sticking a bent  large match in it and rotating the wheel. If its the original it sounds like it should be a 2:1.

[Bees]

That's probably it, 30/1000 x 1600 = 48.

It doesn't really bother me but I was offered that other one and was briefly tempted, but I'm glad I didn't now. I'll wait for an original one.


 

[MICKREEVES]

I think the cheap speedos you see on Ebay, are just a poor copy which does not give correct results.
Mick