Speedo

[Phil C]

Hello everyone, I was just thinking: while I've got my rear wheel off (1965 B40F), should I be having a look at my speedo? It tells lies, in that it says I'm going faster than I am. So if I'm really doing, say, about 40mph, it tells me, say, about 60mph (these figures not at all accurate, just to illustrate that it is a long way off, not just a couple of mph out.)

So do you think I should be trying to sort it? Or is it a specialist job? I know nothing about speedo's, by the way, but would be very pleased to learn, if it's pretty simple and needs no expertise or special tools/equipment. If you think I should be doing something to fix it, er...could you tell me how to do it please?

Thanks again, as ever,   Phil.

[Phil C]

Actually, sorry, just realised I asked this back in November. Of course if there are any thoughts from anyone who wasn't involved in the discussion back then, they'd be much appreciated.  Phil.

[idie]

You may have the wrong drive ratio in the unit on the rear wheel. It may for instance be meant for a larger wheel then the one you have. If it is correct for your bike you will need to have the speedo recalibrated.

[Blackthou]

I had a similar problem with my 70 T120R. I removed the speedo cable at the rear wheel, rotated the wheel one revolution to see  the ratio. I found a calc somewhere or info saying the ratio of the speedo. Bought the correct drive for the rear wheel and now spot on. If I can find it, I'll post more.

[Phil C]

Checked the ratio at the speedo gear unit, using the matchstick method as advised by Hoogerbooger back in November and by Rupert Ratio on his book. Ratio is 2:1, which is correct, so my problem must be at the clock end, which is almost certainly beyond my abilities. Thanks anyway everyone.  Phil