speedo gear question

i have a 40 tooth driven gear on the end of the speedo cable. the speedo reads 30 when i'm doing 40 and when the speedo reads 40 i'm doing 50. how many teeth on the driven gear to make it right?.....thanks

 

Need to some remembering, in the mean time whats your rmp at 60 mph?

 

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Your goal is to have the cable turning 1000 rmp when @ 60 mph. So next question would be whats the tooth count on the output shaft. Thats the gear that would be used to do the math.

 

You have about a 30% error, so you need 30% fewer teeth on the gear. Try to find a 28, 29, or 30 tooth gear. The numbers you gave don't really add up though.

 

Read this article, it explains it

http://novaresource.org/speedo.htm

 

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