Gear inch/ratio question

TheBrick(Tommy) Why do some people use 27 as their wheel size when they have 700c wheel and 23or 25 mm tyres? The entire point of using gear inches instead of gear ratios is so you can compare the gearing used between different bikes of different sized wheels. I know this is not as good a the gain ratio as this is dimensionless but it is a silly thing to use 27 as your multiplier as it removes the point and convince of gear inch to use as a comparison tool.

It is very simple to find your wheel size in inches.

700 cc rims are 622 mm in diameter.

Tyres are square so as 23 mm would add 23 mm at the bottom of the wheel and 23 mm at the top of the wheel so the wheel is now 622 + 23 +23 = 668 mm in diameter.

25.4 mm in one inch. (You can use google to look this up) So 668/25.4 is approximately 26.3 inches. Very simple. Now you can use gear inches for the purpose for which they where developed rather than negating their entire purpose by using such an extreme approximation.

If you are going to use an approximation use 26". For a start is is closer to the real value than 27" plus it is alway better to understate your measurement and surprise people when accurate measurement is done than to over state and disappoint.

Tell it like it is :)