Originally Posted by Nekura
Also, I thought the calc was (chainring)*(wheel size)/(cog)
From the data I have 700c x 23 has a cirucmference of 2085 mm
for 40x13 and 700c x 23 the gear inch is calculated as:
gear inches = ( chainring ) / ( cog) * (wheel diameter in inches)
gear inches = ( chainring ) / ( cog) * (wheel circumference in inches) / ( pi )
gear inches = 40.0 / 13.0 * ( 2085 mm * 1 in / 25.4mm ) / 3.14159... [hey, it's pi day!]
gear inches = 80.40...
An issue in the software could be the wheel circumference lookup table. circumference isn't truely fixed across all scenarios and changes with tire brand, psi and rider weight. differences should be minor... i.e. if you're a bigger guy running low psi your gear inches could be a *little* lower than you think but we're spliting hairs...