Hi We have a 1971 challenger, 499, 727, 4.30 rear gears. the car did 10.32 @ 129mph. Ok so we are in the middle of rebuilding the car for the road what ratio would we need to go to if we wanted to cruse the hiway at 70-75 @3000 rpm or a little under? Oh yeah we have 29.5x10.5w R15 tires on it now and will run a like tire on the street. thanks

 

3.23:1 should be close with that tire height.

http://www.ringpinion.com/Calculators/Calc_RPM.aspx

 

3.55 would drop you right in the middle at that RPM. 3.23 would give you a lower RPM.