Speedo gear

[Speed]

What is the formula for figuring out the correct speedo gear. I have 29.1 inch tires and 3.91:1 gears. Thanks in advance for your help!

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Dave
74 Dodge 1/2 ton (440)
64 GTO (Tri-Power 4-spd)
68 Convertible Vette
86 McLaren Capri

[72Challenger]

Don't know of a formula, but there's a chart in the Year One catalog in the transmission section. It's based on ratio and tire size, but only lists tire sizes that came standard on B & E bodies (at least in my B/E Body catalog, imagine that!). Anyway, working the eqivalents as near as I can, it seems you need either a 35 or 36 tooth gear. The 35 would probably register a little higher than your actual speed, the 36 a little lower. We're looking at only about a 2% error either way, though.

[Speed]

Thanks for the help 72Challenger. I'll go with the 36 tooth gear (I might be changing to a shorter rear tire).

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Dave
74 Dodge 1/2 ton (440)
64 GTO (Tri-Power 4-spd)
68 Convertible Vette
86 McLaren Capri