Forum

[Aethelric]

Hi all. I have just bought a new speedo for my 2004 sixty-5 from our hosts. The old one waved about quite a lot. Not too much to be unusable though. But it was in KPH and I wanted a one in mph.

Now the old one read high (taking into account the kph to mph conversion) by about 15%. So what read as 70mph was really only about 58.

My problem is that the new one, in mph, although rock steady, is still out by the same amount. IE it reads about 15% high. (against GPS)

I believe the speedos are calibrated so I would only expect a new one to be 5% out


Are there different ratio speedo drives?

[Leon Novello]

Just a thought, are all the sprockets factory- standard size? Are the tyres factory- standard size?

[Barry_Q]

The quick answer is: Yes. There are different speedo gearbox ratios. I know of three. 1.9-1. 2-1 and 1.25-1. The first two are for 1600RPM speedo heads. The third are for 1000RPM speedo heads.

[Aethelric]

Thanks guys.
Leon, the drive is off the front wheel, and yes standard wheels and tyre profiles.

Barry, looks like I need to take a measurement.

It just seems strange that two speedos, one old (maybe original, it's showing 11000km) and one brand new, are out be the same amount.

[Adrian]

ISTRC that Smiths actually had TWO variants on the 2:1 drive, the 19:10 and the 21:10. The Indian copies all seem to be 2:1 for 19" wheels, I don't know if the speedo heads were re-calibrated when the C5s first came out with 18" wheels.



A friend recently fitted one of the Puca-Smiths electronic speedos to his Sixty-5, using the front wheel speedo drive to power the sensor trigger. The set-up has a pre-configured option for 19" wheels. Using a 90/90 x 19 front tyre instead of a 3.25" x 19 will affect the readings slightly.



A.