*Warning, lots of pictures. If you guys want I can delete them all and link an imgur folder*
Had some "fun" today trying some things out in the name of science. I was curious whether you could use a Tarmac stem using the Allez conversion top cap. So I swung by my local shop and picked up a Tarmac/Allez compression ring for $25. Fired up the 3D printer and printed the top cap, which came out pretty nice.
This is where I started to run into problems. The top headset bearing included with the frame is ID 40mm, which is ever so slightly smaller than the Tarmac bearing, which is ID 40.5mm. You'd think that 0.5mm wouldn't make a difference, but it did. The main body of the compression ring woud snap into place, but the inner shim wouldn't fit because the compression ring was compressed.
As you can see, the slot was pinching, and the shim didn't have room to slot in. Almost just gave up, but I had a spare bearing, so I experimented...with the sander. Used a dremel and sanded the inner surface of the bearing to widen the ID. Got it to around 40.3mm before I ran out of sandpaper drums. But the good news was that it was just enough to get the compression ring and shim to fit. Woohoo!
On to the next problem. The Tarmac compression ring sits lower in the bearing, and I was running into the same issue as a lot of people here. The top cap was hitting the frame and couldn't preload the bearing.
Ended up not being a huge issue. I considered buying a thicker bearing (8mm probably would have worked), but I just made a quick change to the top cap design and reprinted. 5 hours later I had a new top cap the worked.
Routed the cables.
And mounted the stem.
And....new problems. As you can probably see, the spacers cause a tight bend in the white shift cable, enough so that I couldn't pass the cable. And after taking it off, you can see it kinked.
New plan. The Tarmac can use mechanical shifting, so I knew there was a way. In the end, I just drilled a hole for the shift cable.
Didn't look too bad, and a little better with the bat.
But the bat caused another kink in the shift cable so I left it off. A little piece of shrink wrap kept things tidy.
So, what did I learn? The Tarmac stem is possible and looks pretty good in my opinion. The Allez top cap will not work without either getting a thicker bearing or changing the design (I can post the STL of both if people want). The compression ring and bearing will have to be modified a little to get a bigger ID. Mechanical shifting will work but won't look as good as electronic.
