Originally Posted by

**Lava**
Sure! Probably a good idea to check the work on that random online calculator!

To calculate trail I use this…

=((($B44/2)+$C44)*cos(I$54*3.1416/180)-I$55)/sin(I$54*3.1416/180)

B44 is 622 (for 700C) or 584 (for 650b)

C44 the tire size in millimeters (a number between 25 and 53)

I54 is the head tube angle in degrees

I55 is the rake (aka offset) in millimeters (typically somewhere between 45 and 55)

And while I'm at it, here's how to calculate gear inches…

=(($B44+($C44* 2))/25.4)*I$14

B44 & C44 are the same as above

I14 is a calculated value – the number of teeth on the chainring / number of teeth in the cog on the cassette