universal speedo

[manxr65]

i  bought a universal speedo for the bmw and fitted to orignal cable but it reads about 20mph all the time , is there any conversion i can do ,
the speedo im using is a 2:1 ratio i think, its  the  small chrome ones on ebay for sale.

[montmil]

Oops.

ManxMan, I hope you have not bought "a pig in a poke". I don't see how there could be a "universal" speedo. Am I missing something here?

Monte

[Dizerens5]

Maybe it's one of those that work with a magnetic pick-up fixed to a wheel spoke. But then how would you connect it to the original cable? However it would no doubt work if adjusted for wheel size.

[montmil]

Maybe it's one of those that work with a magnetic pick-up fixed to a wheel spoke. But then how would you connect it to the original cable? However it would no doubt work if adjusted for wheel size.

There you go, Connie. That's the question I have.

My '81 R65 has a digital Vapor instrument. The speedo has a Hall sensor on the fork lower and a rare earth magnet on the brake disc. Program the instrument with the o.d. of the front tire and you're golden. The speedometer cable was tossed.

Guess my original question remains, "Am I missing something here?"

Monte

[Barry]

I guess this won't help much but as an indication that your 2:1 speedo ratio is miles out a 3.44 final drive should have a speedo ratio of 1.267

If your final drive is different just divide the final drive ratio by 2.7 and you will come close to the correction speedo ratio needed.

[montmil]

... but it reads about 20mph all the time.

This point in ManxR65's question is the real puzzelment. :-?

Monte

[Bob_Roller]

That kind of puzzled me as well, you could take it, as even with the bike stationary, the speedometer reads 20 mph, or when riding the bike, the speedometer reads 20 mph .

If it reads 20 mph when stationary, it's probably been dropped, and needs calibration .

Another slight possibility, is a shipping restraint is installed on the mechanism, and needs to be removed .