BMC Streampost 73.5 Carbon Seatpost
- Item: BMC0018 Claimed Weight:"Claimed Weight" is an unconfirmed weight provided by the manufacturer. 236 g
The BMC Streampost 73.5 Carbon Seatpost may look like an integrated seat mast when installed, but it's not. BMC's Streampost lacks a turbulence-causing seat clamp, offering the aero-advantages of a seat mast with the adjustment of a traditional post. BMC was able to do this by adapting an age-old stem fastening system to a carbon-friendly, modern application.
Quill stems use a wedge inserted into a forks steerer tube that's tightened by a long bolt on top. They were once a mainstay of cycling, and graced just about every form of pre-90s bicycles. BMX, mountain, road, and cruisers all used quill stems. The design wasn't exactly ideal for twisting forces, and they'd either loosen up over time, rendering the bicycle un-steerable, or the quills would completely seize, making headset service a hammer-swinging affair. It's amazing that the fragile quill stem was accepted as sufficient for its purpose for so long. They've since been replaced with modern stems, and are now the bane of bicycle technicians, sending shivers down spines whenever a client uses the term 'goose neck.'
However, the use of a wedge makes perfect sense for non-steering applications. BMC uses a teardrop shape for the seat tube and post for obvious aerodynamic reasons. But, unlike round posts, this shape is hard to clamp without creating stress risers to a carbon frame. BMC's simple solution is to use a wide, force-distributing wedge.
Simple-to-adjust and near-impossible to over-tighten, the teardrop profile self-aligns the saddle so it's always dead center. To install the Streampost, you match up lines on the post and wedge with the bottom bolt, and then drop the post into the tube. With the post set to your height, you give the 6mm hex bolt next to the seat clamp a half turn to lock it in place. That's it, you're ready to ride.
On top of its ingenious use of an old technology, the carbon Streampost 73.5 Carbon Seatpost uses BMC's Tuned Compliance Concept as well. TCC features a unique weave that allows slight flexing for vertical compliance. This provides a noticeable boost in comfort while slowing the onset of fatigue. The post comes in two lengths, 350mm and 290mm.