speedo gear question

i have a 40 tooth driven gear on the speedo cable. at 40 mph indicated i'm actually doing 50 mph. what gear do i need?........thanks

 

ACTUALLY ... you have already asked this and the question was answered as well as it could be ... given the information you gave.

A speedometer is set to turn 1000 times in a mile. There are charts to HELP you do this. What type of transmission? What is the overall tire diameter and what is your rear end ratio ??



GO here and plug in your info.

http://www.tciauto.com/Products/TechInfo/speedo_gears.asp