I have a chevy 350 trns with a Explorer 3.71 ratio differential and 670-15 coker radials on my 46 Plymouth.. Getting tired of changing speedometer gears...My latest calculations are a # 7 drive gear and a 24 tooth driven gear...Had a # 8 drive gear and a 24 tooth driven gear which made the speedometer read 35 when it should have read 30...Any math whizzes or fellow experiencers out there ? Yes, I should have kept her stock... LOL