I picked up a Topeak DP Mount product.
↑This thing
What DP Mount means
It stands for "Dropper Post Mount".
The clamp section is 27mm,
and it comes with spacers for 22mm or 25mm sizes as well.
It grabs the thinner section of the dropper post's
telescopic tube and serves as a mounting point for
bottle cage brackets, clip-style rear light brackets,
and seat bag (huge saddle bag)
seatpost-wrapping attachment points.
With a clip-style light,
you'd probably be able to mount it
without this elaborate bracket anyway,
and the bottle cage and seat bag
seem like they'd be risky from a load capacity standpoint.
Separately, there's another mount with the same idea—
the EP Mount, which has a 31.6mm clamp section
and spacers that downsize to
30.9mm and 27.2mm
(nominally it's marketed as a seatpost mount for e-bikes).
↑This is a D-shaped fork steerer tube offcut
that every household has lying around.
I drilled holes spaced at the same interval
as a bottle cage mounting pattern.
With an M5 bolt in a 4.8mm hole,
the bolts won't slip out and fall off.
Passing a bolt through the hole at the end of the pipe
is straightforward, but
↑This one took some work.
I also drilled a hole for an Allen key to pass through.
Mounted it on the DP Mount.
The thread length is just right—
it doesn't stick out past the body.
↑Looks like this
I have a Vaude seat bag,
and the fixing strap that wraps around the seatpost
has been bothering me slightly—it touches the back of my thigh
when pedaling. It bothers me especially at the start of a ride,
but once I've been riding for a while
it doesn't bother me as much.
It's like how if you suddenly become aware of where your tongue is
in your mouth, you notice it,
but eventually you forget you were even thinking about it.
However, considering the ride times when I actually need this seat bag,
I worry the fabric of my cycling shorts might wear through in that spot,
so I thought I'd install a dummy seatpost
behind the existing seatpost
and picked up the DP Mount.
It looks like the seat bag strap can be wrapped around it
even without attaching a D-shaped foam tube offcut,
but I did the machining above
to minimize stress on the strap's bends
and reduce wobbling.
The DP Mount's clamp is 27mm
and the seatpost is 27.2mm,
but mounting is still possible.
If that size difference bothered me,
I could buy the EP Mount and step down from 31.6mm
to 27.2mm, but I didn't like the idea
of squeezing in a spacer for the clamping,
so I went with the DP Mount instead.
I often use titanium sealposts on steel frames
to avoid seizing, and I've done that on this Niner too,
but for lightweight carbon sealposts,
I think the EP Mount stepped down to 27.2mm
would be safer.
Though really, you shouldn't be running a seat bag
on such a light carbon seatpost in the first place.
↑Looks like this.
The bag's mounting angle has changed too.
Just looking at the strap section,
a shorter tube would probably work,
but this length is necessary
to support the front end of the bag.
After taking it for a test ride like this,
the sensation of having the seat bag attached
completely disappeared.
Whether I'll actually use it this way
remains to be seen.
↑This thing
What DP Mount means
It stands for "Dropper Post Mount".
The clamp section is 27mm,
and it comes with spacers for 22mm or 25mm sizes as well.
It grabs the thinner section of the dropper post's
telescopic tube and serves as a mounting point for
bottle cage brackets, clip-style rear light brackets,
and seat bag (huge saddle bag)
seatpost-wrapping attachment points.
With a clip-style light,
you'd probably be able to mount it
without this elaborate bracket anyway,
and the bottle cage and seat bag
seem like they'd be risky from a load capacity standpoint.
Separately, there's another mount with the same idea—
the EP Mount, which has a 31.6mm clamp section
and spacers that downsize to
30.9mm and 27.2mm
(nominally it's marketed as a seatpost mount for e-bikes).
↑This is a D-shaped fork steerer tube offcut
that every household has lying around.
I drilled holes spaced at the same interval
as a bottle cage mounting pattern.
With an M5 bolt in a 4.8mm hole,
the bolts won't slip out and fall off.
Passing a bolt through the hole at the end of the pipe
is straightforward, but
↑This one took some work.
I also drilled a hole for an Allen key to pass through.
Mounted it on the DP Mount.
The thread length is just right—
it doesn't stick out past the body.
↑Looks like this
I have a Vaude seat bag,
and the fixing strap that wraps around the seatpost
has been bothering me slightly—it touches the back of my thigh
when pedaling. It bothers me especially at the start of a ride,
but once I've been riding for a while
it doesn't bother me as much.
It's like how if you suddenly become aware of where your tongue is
in your mouth, you notice it,
but eventually you forget you were even thinking about it.
However, considering the ride times when I actually need this seat bag,
I worry the fabric of my cycling shorts might wear through in that spot,
so I thought I'd install a dummy seatpost
behind the existing seatpost
and picked up the DP Mount.
It looks like the seat bag strap can be wrapped around it
even without attaching a D-shaped foam tube offcut,
but I did the machining above
to minimize stress on the strap's bends
and reduce wobbling.
The DP Mount's clamp is 27mm
and the seatpost is 27.2mm,
but mounting is still possible.
If that size difference bothered me,
I could buy the EP Mount and step down from 31.6mm
to 27.2mm, but I didn't like the idea
of squeezing in a spacer for the clamping,
so I went with the DP Mount instead.
I often use titanium sealposts on steel frames
to avoid seizing, and I've done that on this Niner too,
but for lightweight carbon sealposts,
I think the EP Mount stepped down to 27.2mm
would be safer.
Though really, you shouldn't be running a seat bag
on such a light carbon seatpost in the first place.
↑Looks like this.
The bag's mounting angle has changed too.
Just looking at the strap section,
a shorter tube would probably work,
but this length is necessary
to support the front end of the bag.
After taking it for a test ride like this,
the sensation of having the seat bag attached
completely disappeared.
Whether I'll actually use it this way
remains to be seen.