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#884435 07/01/22 11:54 am
Joined: Dec 2018
Posts: 318
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Joined: Dec 2018
Posts: 318
Likes: 62
A couple of years ago Semprini posted the below:-

Wonder if anyone could throw some light on my speedo problem. The unit on the bike (A65S from Germany) is a km/hr one which flutters badly, so bought a repro grey-faced one from a classic bike company . Checking with my phone GPs, it seriously under-read the speed. He sent a second one out, this one reads 24mph at an actual 30mph. My original is SSM 5000/04A 1000. The gearbox is stamped 2:1, the rear tyre is a newish 4.00 x 18. A new cable has been fitted. A sticker on the base of the repro says M=2.0

I now have the exact same problem on a B441, does anyone know of the resolution? I know I should have a 1:25 drive with a 1000 speedo OR a 2:1 with a 1600.

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Joined: May 2013
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Britbike forum member
Britbike forum member
Joined: May 2013
Posts: 9,219
Likes: 342
maybe the speedo was built wrong, I had a B44 speedo(?) which was the 1600 type fitted to my A65 (15:12 or 1.25:1) speedo drive. at a registered 40mph it was doing something more like 70.

Just doing the math, that is very feasible.

a A65 setup would be 1000/1.25 =800

a B44? setup would be 1600/2 = 800

(the 800 is revolutions per 1mph)

If you wanted revolutions for 25miles (mph) it would be 800 x 25 = 20000

BUT... If you had a 1600 (B44) head unit with a 1.25 (A65) speedo drive, times: 25 miles = 32000

if you divide 32000 by 40 (mph) you get 800 revolutions per 1mph

likewise if you reverse the math with the other speedo head and drive.

So if you have a 2:1 speedo drive now, you'll want to fit a 2:1 for it to work properly.

But that would be a displayed value of 25 and an actual of 40.

Life is stressful enough without getting upset over the little things...

Now lets all have a beer!

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (now rebuilt)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

Moderated by  Allan G, Jon W. Whitley 

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