G'day to all,

                  I am brand new to this site, and am hoping you are smarter than the people I have been speaking to.

I have a 1972 FLH, which I love to death, but I have a problem that I am getting confused about. My old girl has a 73 mag wheel (to do away with the drum brake ) and I am running a 48 tooth rear sprocket. My speedo (1:1 ) is reasonably accurate at 60 kmh, but as I speed up it goes out incramentally, so at 100 kmh on my speedo the boys reckon I'm doing about 120.

     To my reckoning as the standard sprocket is 51 teeth, this must be what is throwing the speedo out, but after trying to order a 51 tooth sprocket, one shop doesn't know what could be wrong, one shop says it definately isn't the sprocket , one shop says it's the speedo (which is reasonably new ) and one shop says to buy a new bike.

Any help would be appreciated.

Simple, buy a GPS check what speeds are what and memorise. Or mount one somewhere inconspicuous.

I have a GPS mounted on my bike as the speedo drive on the front wheel was for a 19" and doesnt work on a 16" wheel. My 100 kliks is about 134 on the speedo.

It's driven from the gearbox

It is a Zodiac speedo, you reckon thats the problem, not the sprocket ?

This is just an opinion, but I don't think the speedo could read correct at one speed and be wrong at another. And along the same lines as Kiwidave points out, the speedo in my work van was reading way above the right speed, and was actually making a whining sound too, because the cable was dry. A dose of graphite powder fixed that.

Thanks Fella's

                    Will buy a genuine speedo. dose it with graphite powder, borrow a mates GPS and see how we go. Funny how the bike shops can't give you help like this.