Tuesday, April 24, 2007

Light bits

For weight weenies:

An already light 6AL-4V titanium nut is made even lighter by milling blind holes in 5 of the 6 faces, leaving some material between the thread and the bottom of the blind holes. One of the holes is drilled through and tapped, allowing the use of a grub screw to lock the nut. The side opposite the grub screw is left undrilled to balance the weight of the grub screw. USD$75.95 each.

Tune Gumgum steerer tube expander plug. The expander plug utilizes a silicone donut pinched between two 7075 T6 aluminum plates to grip the steerer tube. This method renders it compatible with carbon steerer tubes. While this set up admittedly possesses lower clamping force than traditional star nuts, one must remember that the steerer tube is held on to the stem by the stem's pinch bolts, not the top cap bolt. The top cap-expander plug assembly merely serves to pre-load the headset bearings.

Tune Gumgum steerer tube expander plug with top cap. EURO12.00

Carbon fiber derailleur cage for Shimano XTR RD-M970. (Only front part of the cage shown here.)

Not too sure about the durability of the carbon fiber cage though. Carbon fiber does not resist abrasion well, so drivetrain malfunction may rapidly destroy the cage. As for the carbon fiber jockey wheels, that's just the wrong material for the application. I won't expect it to last more than a couple hundred miles. What's sweet is the hollow titanium derailleur main pivot bolt (extreme left) — a possible upgrade for Ivy (she's already using the OEM Shimano (solid) titanium bolt), but not Cloe as her frame is titanium. I'm leery of threading a titanium bolt into her titanium dropout (a big no-no according to frame builder and bike tech guru Lennard Zinn).

Tuned Shimano Durace rear derailleur. A carbon fiber derailleur cage makes a little more sense here. One point of criticism: using aluminum for the derailleur main pivot bolt (large SRP bolt, in pink, on top) is a bad idea. Relative to steel and titanium, aluminum has no fatigue strength: each stress cycle weakens it. A few riders experienced catastrophic failure of aluminum rear derailleur main pivot bolts: when the bolt snapped, the derailleur whipped forward, smashed against the chainstay and cracked the frame tube. A hollow steel bolt (ala OEM Shimano) or titanium bolt (e.g. from HBC) is a better choice.

There's light, and there is "stupid light."

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