Spur Gear Ratio: Optimal Ratio Explained

[failedengineer]

TL;DR Summary

Single stage spur gears ratio

What is an optimal spur gear ratio?

 

[jrmichler]

The ratio that best meets the needs of the application. A good search term is the word optimal.

That answers the wrong question, then you need to more carefully word your question.

 

[AZFIREBALL]

About 6.5 to 1

 

[jack action]

A single spur gear is generally selected to have a ratio range of between 1:1 and 1:6 with a pitch line velocity up to 25 m/s. [...] The minimum number of teeth on a gear with a normal pressure angle of 20 desgrees is 18.

The preferred number of teeth are as follows
12 13 14 15 16 18 20 22 24 25 28 30 32 34 38 40 45 50 54 60
64 70 72 75 80 84 90 96 100 120 140 150 180 200 220 250

 

[Baluncore]

The p/q ratio should involve integers p and q that do not share common factors, so the gears will wear evenly, with a "hunting tooth".