Another wheel build day (and so on). But first.
There's a bearing standard called 6902, which has
inner diameter / outer diameter / thickness (mm) of
15 / 28 / 7.
Some older freebodies from Novatech and similar makers
used 6902 bearings, but
with an outer diameter of 28mm, the wall thickness around
the bearing press-fit area becomes extremely thin.
So, wanting a bearing that takes the 6902 and just reduces
the outer diameter by 2mm, a non-standard bearing was created: 15267.
This uses the same dimensional notation as 6902—
three numbers arranged as 15 / 26 / 7—
and simply uses those numbers as the name.
The origin of 15267 is as a bearing for sport bikes.
If Shimano's HG freebody dimensions were just a bit larger,
6902 would work fine, so 15267 might never have been created.
But if we go back even further, a chain link pin spacing is
1/2 inch, or 12.7mm, and
for chain sprockets, if you want to make an 11T cog,
the HG freebody dimensions become a necessity.
The original HG freebody design assumed
a minimum of 12T.
Another wheel build day (and so on).
I received a disassembled ALEXRIMS Boondock 3 complete wheel
hub and rim from a customer.
Today I'm building the front wheel, but
the front hub rotation is really gritty.
The image top is the right side and bottom is the left (rotor mounting side),
and both are bad, with the right bearing being worse.
It might be from over-tightening the through-axle.
When I rotate the bearing removed from the hub by hand,
the right bearing is definitely gritty, but
the left bearing, which felt rough when pressed into the hub,
looks fine as a standalone bearing.
This is common with cartridge bearings.
The seal on the removed bearing said
6903-18 2RS (2RS means dual rubber seals on both sides).
6903, using the notation from before,
is 17 / 30 / 7 in dimensions, but
with a 12mm through-axle passing through a
hub shaft with 12mm inner diameter and 17mm outer diameter being
a bit sketchy, a bearing was made taking 6903 and
changing just the inner diameter to 18mm:
this is the 18307 bearing.
Incidentally, there's no standard bearing size with
an 18mm inner diameter.
This 18307—seeing a seal marked like this one as
6903-18, indicating "6903 with just the inner diameter changed to 18mm"
is a first for me.
↑This is marked as 18307 and is actually an 18307, but
some just reuse a standard 6903 seal, so
an 18307 bearing only shows 6903 markings.
I've never seen a 15267 with 6902 markings or 6902-26 style markings, but
I fairly often see 6903 marked 18307s,
so I've developed a habit of suspecting that if a hub bearing
says 6903, it might actually be an 18307.
↑From left to right:
regular 6903, the 18307 that was in this hub,
and the 18307 we have in stock.
The middle bearing's inner race is remarkably thick, and
I thought maybe the other side was thinner,
suggesting an angular contact bearing, but
both sides had the same thickness, so that wasn't it.
Wheel is built.
24H, half-comp Italian 4-cross, reverse laced.
Wire tying comes later.
This hub, not by accident,
completely copies the dimensions of Crisking's R45D front hub body.
The shape of the hub body is different, but
the flange-to-flange hole diameter and flange width are identical.
Addendum:
Looking it up now, DT's MTB complete wheels with
BOOST front hubs use 15mm through-axles, but
on the cross-country model (XRC1200)
the hub bearings are 6802, which is
17 / 26 / 5.
With the bearing's 17mm inner diameter, they figured
a 1mm thick hub shaft is fine.
But on the freeride/downhill model (FR1500),
the front hub bearings became 18307.
Depending on whether the bearing is 26mm or 30mm outer diameter,
the appearance of the hub body changes quite a bit, so
manufacturers might be considering that as well.
The XRC1200 front wheel's stated weight is 649g, but
if it were hypothetically 685g and
the single-bearing weight difference between 6802 and 18307 was
10g, then two would be 20g difference, so
depending on which bearing size is used,
the whole wheel weight could cross the threshold between
the 600g range and 700g range, which changes
its appeal to buyers who only understand wheel weight
as posted information.
...So I think manufacturers are considering this and
choosing smaller bearing sizes, so I weighed
the 6802 and 18307 we have in stock and got
6802 at 15.8g and 18307 at 15.2g—
oddly enough the larger bearing came out lighter.
The inner race thickness or cage ball spacing (ball count)
must be different.
The two bearings in the image are from different makers, so
whether the same result holds for DT's 6802 versus DT's 18307
is unclear.
There's a bearing standard called 6902, which has
inner diameter / outer diameter / thickness (mm) of
15 / 28 / 7.
Some older freebodies from Novatech and similar makers
used 6902 bearings, but
with an outer diameter of 28mm, the wall thickness around
the bearing press-fit area becomes extremely thin.
So, wanting a bearing that takes the 6902 and just reduces
the outer diameter by 2mm, a non-standard bearing was created: 15267.
This uses the same dimensional notation as 6902—
three numbers arranged as 15 / 26 / 7—
and simply uses those numbers as the name.
The origin of 15267 is as a bearing for sport bikes.
If Shimano's HG freebody dimensions were just a bit larger,
6902 would work fine, so 15267 might never have been created.
But if we go back even further, a chain link pin spacing is
1/2 inch, or 12.7mm, and
for chain sprockets, if you want to make an 11T cog,
the HG freebody dimensions become a necessity.
a minimum of 12T.
Another wheel build day (and so on).
I received a disassembled ALEXRIMS Boondock 3 complete wheel
hub and rim from a customer.
Today I'm building the front wheel, but
the front hub rotation is really gritty.
The image top is the right side and bottom is the left (rotor mounting side),
and both are bad, with the right bearing being worse.
It might be from over-tightening the through-axle.
When I rotate the bearing removed from the hub by hand,
the right bearing is definitely gritty, but
the left bearing, which felt rough when pressed into the hub,
looks fine as a standalone bearing.
This is common with cartridge bearings.
The seal on the removed bearing said
6903-18 2RS (2RS means dual rubber seals on both sides).
6903, using the notation from before,
is 17 / 30 / 7 in dimensions, but
with a 12mm through-axle passing through a
hub shaft with 12mm inner diameter and 17mm outer diameter being
a bit sketchy, a bearing was made taking 6903 and
changing just the inner diameter to 18mm:
this is the 18307 bearing.
Incidentally, there's no standard bearing size with
an 18mm inner diameter.
This 18307—seeing a seal marked like this one as
6903-18, indicating "6903 with just the inner diameter changed to 18mm"
is a first for me.
↑This is marked as 18307 and is actually an 18307, but
some just reuse a standard 6903 seal, so
an 18307 bearing only shows 6903 markings.
I've never seen a 15267 with 6902 markings or 6902-26 style markings, but
I fairly often see 6903 marked 18307s,
so I've developed a habit of suspecting that if a hub bearing
says 6903, it might actually be an 18307.
↑From left to right:
regular 6903, the 18307 that was in this hub,
and the 18307 we have in stock.
The middle bearing's inner race is remarkably thick, and
I thought maybe the other side was thinner,
suggesting an angular contact bearing, but
both sides had the same thickness, so that wasn't it.
Wheel is built.
24H, half-comp Italian 4-cross, reverse laced.
Wire tying comes later.
This hub, not by accident,
completely copies the dimensions of Crisking's R45D front hub body.
The shape of the hub body is different, but
the flange-to-flange hole diameter and flange width are identical.
Addendum:
Looking it up now, DT's MTB complete wheels with
BOOST front hubs use 15mm through-axles, but
on the cross-country model (XRC1200)
the hub bearings are 6802, which is
17 / 26 / 5.
With the bearing's 17mm inner diameter, they figured
a 1mm thick hub shaft is fine.
But on the freeride/downhill model (FR1500),
the front hub bearings became 18307.
Depending on whether the bearing is 26mm or 30mm outer diameter,
the appearance of the hub body changes quite a bit, so
manufacturers might be considering that as well.
The XRC1200 front wheel's stated weight is 649g, but
if it were hypothetically 685g and
the single-bearing weight difference between 6802 and 18307 was
10g, then two would be 20g difference, so
depending on which bearing size is used,
the whole wheel weight could cross the threshold between
the 600g range and 700g range, which changes
its appeal to buyers who only understand wheel weight
as posted information.
...So I think manufacturers are considering this and
choosing smaller bearing sizes, so I weighed
the 6802 and 18307 we have in stock and got
6802 at 15.8g and 18307 at 15.2g—
oddly enough the larger bearing came out lighter.
The inner race thickness or cage ball spacing (ball count)
must be different.
The two bearings in the image are from different makers, so
whether the same result holds for DT's 6802 versus DT's 18307
is unclear.