Bike From Scratch

In my last post I talked about picking the parts for the wheels. I glossed over one super important detail. Picking out the length of your spokes. Spokes are sold in all different sizes (and shapes as well). The size you need depends on what hub you are using and the rim you are using, and how many times you want the spokes to cross other spokes.

There are three different measurements that contribute the spoke length you need to use. The first is the distance from the center of the hub to the flange (the thing the spokes connect to on the hub). The second is the diameter of the flange (well the spoke holes technically), the third is the effective diameter of the rim. The last thing that effects spoke length is the cross pattern.

The first measurement we will tackle is the flange to center measurement. To take this measurement hold the hub as if you were looking at it from the saddle. The label,  not where the axle goes through is what you should be looking at. The distance from the center of the hub to the outside of the flange is what we want to measure here. Its rare, if ever I think you would have to measure this as hub manufacture it. For example on my Shimano LX front hub the center to flange measurement on both the left and right side is 38.5mm.This gets more complicated on rear wheels because the center to flange measurement takes into account the free wheel. So the center is not the middle of the space between the flanges, but the middle of the hub as a whole. See the picture in Step 3 here to if you’re unclear. For example on my rear Shimano LX hub the right side (drive side) center to flange measurement is 22mm and the left side is 37.2mm.

The next measurement that matters is how far apart opposing spoke holes are on the same flange ( 1/2 of this distance would be the center of the axle). Again hub manufacturers document this, on my rear hub its 45mm and on my front it’s 38mm. I’ve seen this measurement called a few different things, flange diameter and spoke hole circle usually.

The third measurement is the effective rim diameter (ERD). This measurement is basically the distance the top (where the tube goes) of one nipple eyelet to the top of the one on the opposite side of the rim. The page linked above has a good drawing of this as well. For the Mavic a719 the ERD is 603mm.

The last thing to take into account is what lacing pattern you want to use for your new wheel. The “standard” for 36 and 32 spoke wheels is three cross on bikes other than racing bikes. This means that each spoke crosses three other spokes. Two of these crosses are very close to the hub and sometimes hard to see.

Now that you have all these values, you can plug them into a spoke calculator. I used the one provided by DT Swiss. It will spit out spoke lengths for front and rear wheels. For me I ended up with spokes of 293mm for my front wheels, 292mm in the back on the non drive side and 290mm on the drive side, with 12mm nipples all around.

Its arguable that I needed to buy different spoke lengths. After building up the wheels (post to come on that soon, with lots of pictures) I think I could have gotten away with 292 all around. Live and learn.

A quick note on lacing patterns. There are a ton out there, and its worth doing some research before you decide which one to pick. I went with three cross because people say its strong, and aside from my road bike its all I’ve ever used. It also is what most of the instructions are written for when lacing.