Spoke Calculator

Hub

Drive Flange Diameter
Non-Drive Flange Diameter
Drive Flange Offset
Non-Drive Flange Offset
Spoke Hole Diameter

Rim

Effective Rim Diameter

Spokes

Spokes Pattern Drive Spoke Length Non-Drive Spoke Length

Spoke Length Calculation

Ok, here's the formula we use to calculate the spoke length. That trigonometry I learnt at school wasn't so useless afterall! I'm not going to go through the proof of this formula... I'm sure you can search for it on Google if you're really mathematically inclined.

l is the spoke length
rr is the radius of the rim
rf is the radius of the hub flange (measured to the centre of the spoke hole)
f is the offset of the flange from the centre of the wheel
x is the number of times a spoke crosses over another spoke
h is the total number of spokes in the wheel
dh is the diameter of the spoke hole in the hub

I guess there is a slight inaccuracy in the formula in that it assumes the actual diameter of the spokes to be infinitely thin. This will give spoke lengths which are a fraction of a millimetre too short. However, this is balanced out in the real world because the holes in the hub stretch when the spokes bed in, so these 2 factors pretty much cancel each other out...