I use 15/48.. but I feel 15/50 would be a good set up..
Not being able to find 50 tooth rear sprockets I will go with
14/48.. gives 4500rpm @ 100kph , 500 revs above standard gearing...
I always buy 120 link chains... shorten them as required..

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Harley Davidson..
The easyest way to turn gasoline into noise with out the side efect of horse power...