Lacnig a Hub Motor


A few years ago I picked up a large amount of the rims below, they originally were used on the early model " Zero Electric motocross " bikes, when the rear wheels were 20" .. they since moved up to 24's etc and i got what was left of the inventory.. I have used them on my Chaos and on the Chopper i have shipped some all over the world to various other ebike enthousiasts..

They are double walled, with eyelets, and have a reinforcing rib shown in Red below


These are painted rims, so disk brakes are best, as rim brakes would wear the paint but it would work in a pinch.... disk brakes recommended..

When lacing a bicycle wheel, you need a rim, a hub and spokes, the common question that always comes up is " How long should the spokes be ? "

Well, one of the things you need to know is E.R.D ( Effective Rim Diameter ) ..

Sheldon Brown's website Reference

ERD = A + 2B

Effective Rim Diameter (ERD) is the diameter on which you want the ends of the spokes to lie. Most people prefer it near the end of the spoke nipple. If you want to measure your own rim (recommended, just to be sure), then follow these instructions:

  1. Insert two old spokes into holes exactly opposite each other on the rim. Count holes to be sure.
  2. Screw some nipples onto the spokes.
  3. Pull them tight and measure dimension A in the figure (the diameter to the edge of the nipples, where the spokes dissapears into them). Do this at several spots around the rim and average the measurements.
  4. Measure the length of a nipple (dimension B in the figure) and add it twice (once for each nipple). The result is Effective Rim Diameter (ERD). Thus,


Effective Rim Diameter (ERD) is the dimension you type into the spreadsheet for "ERD, effective rim diameter". Of all the dimensions you actually might measure, ERD is the most critical dimension affecting spoke length, so it makes sense to measure it a few times at different places around the rim. Always count to make sure you use spoke holes that are actually opposite each other!


So, to measure the ERD of this rim, i dug into my pile and found 2 old spokes with nipples.

I made sure to screw both nipples to the same depth on both ends

Put a piece of tape at the spot where i can make a mark on both of them once put into opposing ends of a rim

Once i pulled both spokes inwards so the nipples were tight against the rim walls, i made a mark on both pieces of tape.

Then i removed the spokes from the rim, put the nipples back on all the way down as shone above, and set them down on a piece of paper.. to measure the " A " distance..

As you can see below, 35.5cm = 355mm

Then, for the " B " measurement, the spokes used = 15mm



So, if

ERD = A + 2B

ERD = 355 + 15x2

ERD = 355mm + 30mm = 385mm


( alot more to come , video of fixing eyelet size issues, lace patterns, spoke types, how to true a wheel, tires, etc. )


Ypedal Forum !

Back To Projects Page