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HUB AND RIM MEASUREMENT INFORMATION
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The measurements of the hub and rim are very critical to getting the spoke
length right. Although spokes only come in 1mm or 2mm increments, in order
to get the desired length as close as possible, the measurements need to be
accurate.
The hardest measurement to get accurate will be the spoke radius of the hub,
refered to as the HSR in the main formula. For front wheels figuring out the
hubs flange offset, HFO, is fairly easy, you just measure the distance
between the two flanges and divide by two. The rear wheel on multispeed hubs
is trickier because these hubs have the two flanges offset unequally from
the center of the hub for clearance for the freehub/freewheel. For single
speed hubs, they might or might not be off-center, so it would be best to
measure them assuming that they are off-center to make sure the offset value
is accurate. The rim radius is fairly easy, you just divide the diameter by
two, but for the full measurement, figuring out the spokes penetration into
the hub can be a little tricky, especially with aerodynamic rims that have
the spoke heads set inside the rim or rims that require special x-long
nipples.
I will outline the measurements of the hub first.
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The first measurement to take will be the hubs spoke diameter, HSD. To
figure out the radius, HSR, for the main formula, you will divide this value
by two (HSR = HSD/2). If you have a set of calipers to use it will be easier
than if all you have is a metric ruler. The figure of importance is the
outside edge of the holes for the spokes. Spokes are measured from the edge
of the bend closest to the threaded end of the spoke, not from the center of
the head like might be assumed. If you do not have calipers, there are
several ways to make this measurement (HSD) with just a ruler. One of the
quickest ways will be to just eyeball it. Hold the ruler/tape measure as
close to the flange as possible, making sure it is parallel to the flange
and the spoke holes that you are measuring. You can put the ruler on the
flange at the edge of the bearing cups and sight down the measurement marks
of the ruler to the spoke hole edges.
One technique that can help is using just one eye looking at the hub as
depicted in the diagram below. Sight the edge of the two flanges until the
near flange just covers the far flange and take a reading off the ruler.
Then without moving the ruler, use the same technique for the opposite spoke
hole. If in doubt, take a couple of measurements and make sure they agree.
Another way that you can take this measurement is two use two extra spokes.
Make sure the spokes are a straight as possible. Feed the spokes through the
hub from the inside on two opposite spoke holes. Then place the assembly on
a table and either tape or block the hub with the spoke holes with the
spokes in them has parallel to the table as possible, measuring the distance
of the spokes at the hub flanges to the table might help. After the spokes
at the flange are parallel, equal distances, to the table, lay the spokes on
the table so they are in-line with the hub's axel. You can then use a small
weight on the threads of the spokes to keep them from moving. Take
measurements of the spokes seperation in two or more places down the spokes
and move the spokes until they are as parallel as you can get them, always
maintaining their alignment with the axel as closely as possible. Then
measure the outer edges of the two spokes has near the hub flange as
possible and this will be the diameter of the spoke holes outer edges on the
hub, this is the HSD value.
After you get a measurement that you feel is as accurate as possible, divide
it by two to figure out the value for the HSR figure. The following diagram
shows the measurement of the diameter you are looking for.
[Image]
The value of the spoke angle, SA, is easy to determine. Divide 720 by the
number of spoke holes on the hub. The SA values for common hubs are: 36 hole
hub, 720/36=20; 32 hole hub, 720/32=22.5; 28 hole hub, 720/28=25.71428571429
which can be rounded down to 25.71 for practicle purposes.
From the SA value, you now calculate the spoke anchor angle, SAA, for the
main formula. The SAA equals the SA times the number of crosses, for
standard crossed pattern, or times the number of holes away from the hole
that would be used for radial lacing, if you are doing an exotic pattern.
For example, in a 3 cross 36 hole wheel, the SAA is: 720/36=20, 20X3=60, 60
degrees. If you are doing a crows foot lacing with the three spokes of a
pattern right next to each other on a 36 spoke wheel, the middle one would
be a radial spoke and use the radial formula, the outer two are located two
hub holes away from the hub hole directly under the rim hole they will
attach to so they are 720/36=20, 20X2=40, the SAA for them is 40 degrees. If
you are doing a two leading four trailing pattern on a 36 spoke wheel, half
the spokes are 20X2=40 and half are 20X4=80, so you get two SAA values of 40
and 80.
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The next measurement you will need is the hub flange offset, HFO. For front
hubs all you need to do is measure the seperation of the flanges at their
mid point, like if the flanges are extremely thin. This is referenced as FW
in the diagram below. After you have this dimension divide it by two and
this will be the flanges offset from the center of the hub, the value to use
for HFO, HFO=FW/2.
For rear wheels this can be a little trickier because of the dish of the
wheel. For one speed wheels, that might not have any dish to them, it would
still be a good idea to take the measurement this way than to just assume
they aren't dished.
The first value you will need is the overall width of the hub assembly. For
common hubs this is 121mm for single speed, 120mm for 5 speed, 126mm, 130mm
or 135mm for 6 & 7 speed hubs and 130mm, 135mm or 140mm for 8 & 9 speed
hubs. The 126mm and 130mm dimensions are for most road bike hubs and the
135mm and 140mm are for mountain bike hubs. This is the figure for the
distance from the edges of the outermost locknuts where they rest against
the inside of the dropouts, HW in the diagram below. This figure is commonly
called the OLD for Outer Locknut Dimension. I couldn't find any information
about the width of three-speed or the new multi-speed internal hubs to share
with you. They will have to be measured if you are building a wheel with
them.
After you know this value you will need to measure the left side spacing,
LSS, and the drive side spacing, DSS. These measurements will be taken at
the center of the flange and the outer edge of the lock nut. An easy way to
get this value would be to put a very thin, flat wrench, like a hub cone
wrench, against the locknut, making sure it is against the face of the nut
evenly so it is parallel to the hub flange, then measure from the inside
edge of the wrench to the center of the flange. After you have accurate
measurements of these two dimensions, divide the overall width of the hub
assembly, HW, by two and then subtract the readings just taken. This will
give you the two flange distances from the center of the hub: for the left
side HFO=(HW/2)-LSS, for the right side HFO=(HW/2)-DSS. You now have the two
HFO values you will need to figure out the two different rear spoke lengths.
[Image]
You now have all the dimensions of the hub's that are needed, HSR, SAA and
HFO's (two rear, one front).
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For the rim dimensions the first measurement you will need to take is the
diameter of the rim. Using a tape measure, measure the distance between two
spoke holes that are exactly half way around the rim. For 36 hole rims this
will be two holes that have 17 holes in between them, not counting the ones
you are measuring, for 32 hole rims it's 15 holes and for 28's it's 13. For
rims without eyelets, take this measurement right off of the body of the
rim, trying to be as centered as possible. For rims with eyelets, this
reading should be taken from the inside edge of the eyelet because this will
make the factors from the next measurements easier to apply, in the diagram
below this is represented as RMP for rim measure point.
If you do not have a metric tape measure, you can use an english tape
measure, convert the reading to a decimal point, ie. 1/8=.125, and then
multiply the inch measurement by 25.4 to get millimeters. After you have the
diameter in millimeters, divide it by two to get the radius of the rim. It
is OK to round this number to the nearest millimeter.
You will now have to figure out how deeply the spoke will penetrate into the
rim. For most rims with eyelets that use standard nipples, this will be 4mm.
For most rims wihout eyelets this will be 3mm. To double-check these values
or if you have rims that need x-long nipples or are lacing an aerodynamic
rim where the nipples are buried in the rim, you will have to take
measurements.
The diagrams below show you the values that you need.
[Image]
For rims that use standard or x-long nipples, the first measurements you
will need to know are the length of the nipple and the depth of the nipples
driver slot that is worked by a spoke nipple screwdriver. These dimensions
are refered to as SNL, spoke nipple length, and SNDD, spoke nipple driver
depth. After you have these values you will need to measure the distance the
nipple will extend out of the rim, the SNE. Measure this by putting a nipple
in the rim, press on it firmly to make sure it is seated all the way, and
then measure from the edge of the eyelet if the rim has eyelets, or the rim
if it doesn't, to the end of the nipple, this is the SNE.
You now have four numbers, 1: the rim's radius, 2: the length of the nipple
(SNL), 3: how much of the nipple sticks through the rim (SNE), and 4: the
depth of the nipples driver slot (SNDD).
Start with the value for the rim's radius. Add the value for the length of
the nipple, SNL. Subtract the depth of the nipples driver slot, SNDD. Then
subtract the distance the nipple sticks through the rim, SNE. This will give
you the value for RRSP, the rim radius plus spoke penetration. For example,
lets say the rim's radius is 300mm, the nipple is 12mm long with 6mm that
sticks through the rim (SNE) and has a driver depth of 1mm. This gives you
300+12-6-1=305, 305mm for the value of RRSP in the formula on the home page.
If you are building a wheel with aerodynamic rims that have a deep V shape
and the nipple is fully inside the rim, things are a little harder. The
measurement to determine the rim's radius is the same, just make sure that
you measure on the center of the edge of the rim closest to the hub, right
next to the spoke holes. To figure out how far the spoke penetrates into the
rim, you will need to make a measurement like this:
[Image]
You will need to use a spoke and a nipple. Thread the spoke through the rim
from the direction of the hub. With the spoke sticking up far enough to have
access to the threads, thread a nipple on it and tighten it about as far as
depicted in the above diagram. Pull the spoke back through the rim until the
nipple is seated in it's depression and then wrap a piece of tape around the
spoke at the point where it comes through the rim.
Now unscrew the spoke from the nipple and measure the distance from the egde
of the tape on the side near the threads to the end of the spoke. Add this
value to the determined radius of the rim and that will give you the RRSP
value for the formula on the home page.
For example, the rim's diameter measured 550mm so it's radius is 275mm.
After doing the above, you figured out that the spoke penetrates into the
rim about 20mm. Adding the 275mm radius to the 20mm penetration gives you a
factor of 295mm to use in the spoke length formula for the RRSP value.
;; end measure.txt