Powered by Outside

Direct-mount Stem Adapters for Single-crown Forks

PB Forum :: Bikes, Parts, and Gear
Direct-mount Stem Adapters for Single-crown Forks

 Post Message | Latest Comment
Author Message
flag TurboDonuts
FL
Posted: Apr 3, 2025 at 11:21 Quote
Hi all,

Direct mount stem adapters! Snake oil, or clever?

Benefits:
+ Ease to swap stems (fork stays in place and bearing pre-load is maintained; don't need to re-align bars)
+ Low stem stack improves compatibility between L/XL/XXL frames and forks with short steerers.
+ Enables quick swaps from dual-crown forks to single-crown forks (for 180-200mm "freeride" frames, for example. Propain Spindrift, Norco Shore, Giant Reign, Turbo Kenevo, etc.)
+ Design permitting, ability to use the adapter as a reach/stack flip-chip.

Drawbacks:
- Weight. Call it a 50g penalty?
- Cost. $60 to mount a DM stem? Pfft.
- Stress on parts. A short-stack stem means higher stress concentration on the fork's steerer tube. Granted, if you have stiff stem spacers and decent bearing pre-load, perhaps this is less of a concern.

I'm aware of two models:
1) The HIT-N-RUN AXIS adapter. V2 features a 25mm stack, 1x M8 clamping screw, and weighs ~75g. $66. https://www.pinkbike.com/buysell/941192/
2) The Yoshimura Cycling ENDH adapter. 23.5mm stack, 2x M6 clamping screws, weighs ~56g. $60. https://yoshimuracycling.com/products/endh-stem-base-kit-dmb-base-k?srsltid=AfmBOortVAiAROyzJdS8xV_6WRTRWuk7F_B_rDAej2dK_jkOarqWhHVr

I've done some designing of my own. If anyone out there wants to steal the design, just send me a few free machined parts Wink Notable changes from the "norm":
+ Reach: -2.5mm reach from advertised stem reach (I.S. Boxxer 30x20mm M6 bolt pattern is 5mm forward of steering axis, versus my 2.5mm). I did this, as you could spin the adapter around and change the reach by 5mm. Your 40mm stem is now either 37.5mm or 42.5mm, depending which orientation you run the adapter.
+ Stem Stack: 28mm total, balancing stiffness with flexibility/compatibility.
+ Bar Stack: +22mm in high, and +16mm in low (relative to bottom of part). Compatibility in the -reach position in low position is likely to vary from stem to stem.
- Weight. 73g without M8 clamping screw.

photo
photo


-Nick
flag TurboDonuts
FL
Posted: May 5, 2025 at 21:29 Quote
Good to see all of the interest! Alas, I kept massaging the design. M8 screw, no more reach offset, and gave it some more style. FEA shows nearly identical stiffness in low and high stack configurations. Tempted to get 8-12 CNC’d and would go for electroless nickel plating.

Final form
flag 4rcgoat
Posted: May 6, 2025 at 15:40 Quote
I think its an interesting concept for sure, great idea.
flag muddytreker
Posted: May 8, 2025 at 5:13 Quote
Many years back we played around with a few old 3rd party CNCd Fox 40 top crowns,
with multi position reach adjust threaded holes to position a direct mount stem,
as stems back then didnt have wide bar clamps or offer good support when loaded with bar bags
and the like, used the stanchion clamps as mountings for rail bars for rack, lights amongst other stuff,
machined off the 40mm stanchion clamps on one of the top crowns and had similar to what you got there,
though nowadays with the stem choices and bars available there was no more need for such.
flag TurboDonuts
FL
Posted: May 9, 2025 at 16:35 Quote
I appreciate the input, thanks!

On the fence, whether I put in an order or not. I’m happy with the current design, but ordering less than 10 isn’t very economical. I have two bike/fork combos that would likely benefit from a product like this.
flag TurboDonuts
FL
Posted: Oct 1, 2025 at 0:21 Quote
Well, I put money where my mouth is! Quite happy with how they turned out. 11.5-12Nm is the sweet spot for the clamping bolt (with blue liquid loctite on the threads). Need to put some miles on it, now.

Multiple angles of final part
Mounted to the Megatrail
Clones 8 10
flag dirtyjoe4life
O+
Posted: Jan 1, 2026 at 17:54 Quote
How was the testing?
Do you have any of these adapters for sale?

I need this exact concept for my Vampire Fastarossa build. Depending on which fork I use (dual crown vs single crown) I need to swap stems, which is a pain.

I do not like the look of the Yoshimura stem.

I want to use my direct mount Renthal stem for the single crown fork, too.

Happy New Year!

TurboDonuts wrote:
Well, I put money where my mouth is! Quite happy with how they turned out. 11.5-12Nm is the sweet spot for the clamping bolt (with blue liquid loctite on the threads). Need to put some miles on it, now.

Multiple angles of final part
Mounted to the Megatrail
Clones 8 10
  • Previous Page
  • Next Page

 


Copyright © 2000 - 2026. Pinkbike.com. All rights reserved.
dv65 0.017870
Mobile Version of Website