Speedometer gear question

General Discussion

  1. Histoy

    Histoy Well-Known Member

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    I'm hoping to get some help from you guys, even though my question is about a GTO. My car must have had the rear gears changed from the original factory one. I'm also running larger tires than factory correct. Here's my problem...

    The speedometer reads 14% higher than the actual speed. At 35 mph in town the speedometer reads 40. At 65 on the highway it reads 74 mph. It's 14% higher in both cases. I'm thinking that I need to add more teeth to the gear that's driven by the transmission. For example, if the driven gear has 34 teeth, I would need one with 14% more teeth or 39 teeth. Is my thinking correct?
     
  2. R/T Boy 67

    R/T Boy 67 Well-Known Member

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    Yes.
     
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