Another day of wheel building (and so on).
But first.
I built a wheel with the ALEXRIMS R390 rim, and
the recent R390 is completely different from before—the seam finish has improved significantly.
Aluminum rims are made by bending and joining a curtain rail-like material,
but with small-wheel rims,
the difference between inner and outer circumference is large, or rather the curvature is tight, so
the seam finish tends to be rough.
The R390 20-inch rim I built today
had precision that didn't feel rough despite the small inner diameter.
Though I'm praising it, what if only these two that I received happen to be good ones.
When you say "20-inch rim," there are two types: WO rims and HE rims,
and these have different rim inner diameters (the blue line in the diagram above).
The 20-inch WO is 451mm, and the 20-inch HE is 406mm—
they're different specifications altogether.
Roughly speaking, WO is for thin tires on road bikes,
while HE is for large-volume MTB-style tires.
The rim inner diameter is determined by the specification,
but the spoke support length shown in the diagram above (the red line)
varies depending on rim height and nipple type,
and this is the value needed to calculate spoke length.
So I built the wheel with the 451mm WO spec R390 rim.
The front wheel is HB-9000, 24-hole, full champagne-colored radial-laced spokes,
and the rear wheel is FH-9000, 24-hole, all Champion spokes laced without eyelets.
This time the all Champion spokes are 1.8mm (15-gauge) plain.
This is the customer's preference, but
if they hadn't specified anything,
I would normally use 14-gauge Competition spokes.
Since short Competition spokes are unavailable for this wheel build,
I'd end up using 15-gauge Champion anyway, so
if the customer specified 15-gauge Champion thinking the same way,
that shows good judgment.
Since color was no issue, I went with silver.
Since the nipples are constantly in contact with brass ferrules,
rather than worrying about galvanic corrosion and choosing brass nipples,
I selected aluminum nipples which resist that problem.
(Though they're the same ones I always use.)
When the rim is smaller than 20 inches
or when the hub flange dimensions are large,
it becomes difficult to weave the final spoke crossing,
so I build without lacing. But this time there was plenty of room, so I wove it.
I build the wheel so that the hub body phase visible from the valve hole
aligns with the DURA-ACE marking,
but this is something I do arbitrarily and has no effect on performance.
In the case of Shimano complete wheels,
the phase visible from the valve hole is
positioned exactly opposite to the side where the grade name is written.
I'm deliberately choosing the DURA-ACE side for the valve hole, so
don't worry about it.
The Dura-Ace hub was brought in by the customer,
and that's also a good choice.
Small-wheel hubs rotate more per distance traveled
than large-wheel hubs,
and since the spokes are shorter, they transmit road impacts well.
(Small-wheel bikes often have suspension frames for this reason.)
Another consideration is that with the hub positioned closer to the road,
water ingress from mud spray is more likely.
What's strong against these conditions is
a cup-and-cone bearing hub with a high-sealing-quality seal,
and currently the Dura-Ace hub
is the strongest option under these conditions.
Chris King hubs are also good, but
their seals aren't as robust as Dura-Ace (though the rotation is lighter)
and the bearing balls are smaller than Dura-Ace,
so they're the second choice.
But first.
I built a wheel with the ALEXRIMS R390 rim, and
the recent R390 is completely different from before—the seam finish has improved significantly.
Aluminum rims are made by bending and joining a curtain rail-like material,
but with small-wheel rims,
the difference between inner and outer circumference is large, or rather the curvature is tight, so
the seam finish tends to be rough.
The R390 20-inch rim I built today
had precision that didn't feel rough despite the small inner diameter.
When you say "20-inch rim," there are two types: WO rims and HE rims,
and these have different rim inner diameters (the blue line in the diagram above).
The 20-inch WO is 451mm, and the 20-inch HE is 406mm—
they're different specifications altogether.
Roughly speaking, WO is for thin tires on road bikes,
while HE is for large-volume MTB-style tires.
The rim inner diameter is determined by the specification,
but the spoke support length shown in the diagram above (the red line)
varies depending on rim height and nipple type,
and this is the value needed to calculate spoke length.
So I built the wheel with the 451mm WO spec R390 rim.
The front wheel is HB-9000, 24-hole, full champagne-colored radial-laced spokes,
and the rear wheel is FH-9000, 24-hole, all Champion spokes laced without eyelets.
This time the all Champion spokes are 1.8mm (15-gauge) plain.
This is the customer's preference, but
if they hadn't specified anything,
I would normally use 14-gauge Competition spokes.
Since short Competition spokes are unavailable for this wheel build,
I'd end up using 15-gauge Champion anyway, so
if the customer specified 15-gauge Champion thinking the same way,
that shows good judgment.
Since color was no issue, I went with silver.
Since the nipples are constantly in contact with brass ferrules,
rather than worrying about galvanic corrosion and choosing brass nipples,
I selected aluminum nipples which resist that problem.
(Though they're the same ones I always use.)
When the rim is smaller than 20 inches
or when the hub flange dimensions are large,
it becomes difficult to weave the final spoke crossing,
so I build without lacing. But this time there was plenty of room, so I wove it.
I build the wheel so that the hub body phase visible from the valve hole
aligns with the DURA-ACE marking,
but this is something I do arbitrarily and has no effect on performance.
In the case of Shimano complete wheels,
the phase visible from the valve hole is
positioned exactly opposite to the side where the grade name is written.
I'm deliberately choosing the DURA-ACE side for the valve hole, so
don't worry about it.
The Dura-Ace hub was brought in by the customer,
and that's also a good choice.
Small-wheel hubs rotate more per distance traveled
than large-wheel hubs,
and since the spokes are shorter, they transmit road impacts well.
(Small-wheel bikes often have suspension frames for this reason.)
Another consideration is that with the hub positioned closer to the road,
water ingress from mud spray is more likely.
What's strong against these conditions is
a cup-and-cone bearing hub with a high-sealing-quality seal,
and currently the Dura-Ace hub
is the strongest option under these conditions.
Chris King hubs are also good, but
their seals aren't as robust as Dura-Ace (though the rotation is lighter)
and the bearing balls are smaller than Dura-Ace,
so they're the second choice.