1970 Bonneville Final Drive Sprocket

Discussion in 'Vintage Classics' started by jamesgraulty, Sep 18, 2020.

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  1. jamesgraulty

    jamesgraulty New Member

    Sep 18, 2020
    1
    1
    Pittsburgh
    I'm getting used to a recently acquired '70 Bonneville and have a question on the final drive sprocket. Bike runs great and has a lot of zip running up through the gears. But it feels like it is working too hard to run above 50 mph. Tach (which is rebuilt so should be accurate) shows 3,500 rpm at 50 mph. This led me to check and my sprocket is 49 teeth. The parts manual shows the final drive sprocket as 46 teeth, P/N W1499. Most my riding averages 40 to 50 mph on back roads, so I'm not looking for a long legged highway bike. But it would be nice to run up over 50 without feeling like it's straining. So I'm wondering if I should change to the 46 tooth sprocket. Any opinions or input on this would be appreciated.
     
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  2. darkman

    darkman Crème de la Crème

    Oct 26, 2015
    6,856
    1,000
    Southcoast of the UK Earth
    A great idea changing the rear :)
     
  3. speedrattle

    speedrattle Senior Member

    Feb 19, 2021
    621
    143
    appalachia usa
    #3 speedrattle, Mar 1, 2021
    Last edited: Mar 1, 2021
    old thread, but who knows?

    if you have a 1970 rear wheel, then your 49-tooth sprocket is a custom-made job. if you are running a standard 19-tooth front sprocket, then the 49-tooth rear will give you your 52 mph at 3500, using a reasonable rear tire. stock speed with 19/46 would have been about 56 mph.

    you can go with 46 or 43 teeth on the back. the 43 is a combo drum/sprocket, but will bolt right on. 43 teeth would give you 60 mph at 3500.

    can you post a picture of your rear wheel? if someone put on the 1971-72 conical rear brake, then the stock sprocket is 47, and you can't go any smaller. i have one of those with a 19/47 in it now, and at 3500 it runs right at 55, which always has me reaching for another gear. next time i take it down i'll put in a 20.
     
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