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US FlagWednesday, July 24, 2024
January 26, 2019  I'm building a 1974 850 Commando, and both wheels need new rims.  So, I'm going to build them with new rims and spokes.  Before taking them apart, I am documenting the measurements and I'll detail it all here.  This page covers the rear wheel.

This wheel is not true so it made measuring more difficult.  Generally, you'll find that the rear wheel is supposed to be offset 3/16" to the right.  What does that really mean?  It means that the centerline of the rim is 3/16" to the right of the centerline of the hub.  That's not easy to work with!  By measuring two gaps, it's much easier to build the wheel.  If your old wheel is fine and you're replacing the rim with a rim very close to the same width,  then measure the gaps and build the wheel.  Otherwise, here's how to figure it out exactly.

All measurements here are for WM2 rims.  The original Dunlop rim in the picture is 2.646" wide (outside).  The new rim I'm installing is 2.700" wide so I have to deal with the 0.054" difference (0.027" offset difference - less than 1/32").  In truth, a few hundredths either way is not that important.  The idea is to get the rim centered on the bike and it's just not that critical for a general use bike.

So, the measurement in the first picture (see arrow) is 0.265" and the measurement in the second picture is 0.120".  So 0.265-0.120=0.145" so it's a little less than it should be 0.1875 (3/64").

Double check: The hub in the picture is 2.790" wide and the rim is 2.646" so the gap on the drive side should be (2.790/2)-(2.646/2)+0.1875" = 0.2595", so 2.260 which is only 0.005" off from the measurements.  Considering how out of true the rim is, that's very close!

So, here's my target for the new rim: (2.790/2)-(2.700/2)+0.1875" = 0.2325", so 0.233"

Drive Side Measurements
Timing Side Measurements

The spoke pattern is easy if you get started right.  On both the drive side (first picture) and timing side (second picture) you'll see that there is a spoke aligned with the valve stem hole and the spoke goes to the right to the nipple hole four away (skip three holes) from the valve stem hole.  From the first spoke, every other spoke is installed like the first on both sides (total 20 spokes).  Once those are all in, then the outer spokes are installed, going the other way.

The pencil marks on the timing side of the hub prove that this wheel was redone at some point.  This wheel came from the parts bike I bought that sat for a very long time.  I'm sure the bike was ridden very little after the wheel was rebuilt - it would have been a wobbly ride and the pencil marks are still on the hub.

Drive Side First Spoke
Timing Side First Spoke

January 27, 2019  After disassembling the wheel, the first step is to make the hub pretty. Since it is cast like the engine, I cleaned it like I do engines.

Hub Cleaned

The inner and outer spokes are different.  The spoke with the longer bent end is the outer.  To get started, I opened the inner spoke package from my set, and applied anti-seize to each nipple. To do that, I dip a spoke in anti-sieze, screw a nipple on and off, and set the nipple aside. Once all 20 are done, I clean up that one spoke and wipe any excess from the nipples.
Spoke Inner/Outer

After installing the new bearings, I lightly greased the rim on the inside to make sure the nipples don't gall the rim when tightening.  Then I installed all inner spokes. Notice that the outers often cause marks on the hub, so I ensured that I started in a hole with no mark.

Inners Done

It just went to hell on me! I took the spokes from the outer package and started applying the anti-seize when I realized that there is a problem. All told, I was given 28 inner spokes and 14 outer spokes! So, eight too many inner and six too few outer. So, now I'm stuck.

January 28, 2019  Update.  The supplier is out of spoke sets but has a partial set with the outers I need.  They are on the way.

January 29, 2019  I went ahead and installed the drive side outer spokes and set the wheel aside while I wait for the spokes to arrive.  Note that all nipples are only screwed on 3-4 threads at this point.

Drive Side Outers Done

February 1, 2019 The replacement spokes arrived and I once I had them in and started truing, realized that they are too long by 3/16".  So, now I'm stuck on this wheel.

March 2, 2019  Finally got a set of CWC spokes.  Carefully measured each one to be sure they were the same length and then re-laced the wheel.  It's now trued and this page won't be very instructive because this was another nightmare that took hours.  I have places where the spokes seem way too long and others where they seem short - but there's nothing wrong with spokes, truing, or offset.  It turns out that there are two issues. 1) The holes in the hub are drilled wrong in one area.  2) The dimples in the rim are not as consistent as they should be.

The red circle is around the worst spoke - no more threads, fortunately it's properly tightened.  Note that it is right next to the weld in the rim.  The yellow circle is around the second worst - not a big deal - there are a few of these.  The blue circle is around one that still has threads showing on the other side.

I'll grind off the long ones - that's not abnormal - you just don't expect any to need so much taken off.  I even took the wheel partly back apart, remeasured the spokes, and then put them in different locations to prove it wasn't the spokes.  The last picture shows it trued.  Truing was not a big deal, but trying to figure out why some spokes seemed too long took many hours.  At least I have a good rear wheel now.

Next time I do one of these, I'll update this page as I originally intended showing the truing step by step. Basically, I got rid of the centering issues first using only my fingers and then got the offset right, again using only my fingers, and then finally started tightening all equally while keeping an eye on the centering, offset, and side-to-side movement.

Spoke Length

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