Tacx Dynamic Carbon Assembly Paste
As parts get lighter, they are generally less tolerant of error. Yes, they may be stiffer and stronger in terms of applying forces typical of bike riding. But they might be less able to tolerate the overloading of force in ways the part is not designed for. A carbon fiber frame tube, for example, can resist the sprinting force of a 80kg ProTour rider, but it cannot well withstand the direct force of a curb on a tubing wall.
In order to make parts light, it is necessary to make manufacturing tolerances tighter. A consequence is that the components are not designed to go past those tolerances. Take an old TTT Merckx-bend handlebar from the last century. Put it in a stem. Tighten the handlebar-fixing bolt until the stem bottoms out. You can ride like this. Maybe the bolt will break someday, but most likely you will not have adversely affected the bar or the stem. Take a lightweight carbon fiber handlebar. Clamp it in a stem. Tighten the bolts until the faceplate is bottoming out. Wait. Are you really doing it? Do you want to risk cracking those bars that set you back at least $150?
That's why we were interested in, and reviewed, a torque wrench. We want confidence and security. We want our parts to last. We want our parts destroyed because we accidentally tussled with a car, not because we went to town on our bolts.
It's also why we wanted to test out the Tacx Dynamic Assembly Paste. Also called Carbon Assembly Compound and sold in small packets by FSA, Ritchey and others, it is another way to further ensure the long life of ultra-light components and secure components to one another.
Essentially, the paste comprises tiny plastic balls suspended in a grease. The compound is designed to increase friction. How about that for a contrast, a lubricating compound that increases friction? The tiny plastic balls work as grit -- think compressible sand with smooth edges -- and that grit helps hold surfaces to one another. A number of carbon-fiber handlebar producers apply a rough finish to the clamping areas on their handlebars. This is the same concept, just in a medium that can be applied wherever you want.
The importer refers to the tiny balls as "teeth." Think of the little beads as, when compressed, biting a bit both ways, into the clamp and into the tube that is being clamped. They also tell us that the grease is a waterproof grease that will withstand the moisture that bikes face and keep the surface areas smooth and clean.
The over-arching idea is that using the paste decreases clamping force necessary to hold a component in place. The places that immediately come to mind are where the stem meets the steerer tube, the handlebar meets the stem, and the seat post meets the seat tube. It can also be used on seat rails, on the inside lip of bolts, where brake lever clamps meet handlebars. There must be others; we're just not thinking of them at the moment.
Tacx claims the paste reduces necessary clamping force by 30%. While we're a bit uncomfortable recommending decreasing torque spec by 30%, it's probably safe to say that you don't have to clamp down as hard. For those who don't use torque wrenches and want a little insurance when clamping down on parts, this should be a balm to soothe the mind.
Cervélo did their own research on assembly paste. They found that with the R3 frame, they could reduce clamping force necessary to hold the seat post by 50%, though they still recommend using the full torque spec for safety. Their internal research further demonstrated that the paste had value on the steerer/stem/handlebar clamping surfaces.
Despite the wealth of places it can be used, the compound should not be used on bolt threads. Keep the threads lubed, greased, Loc-tited, or dry as per manufacturer's instructions. If there's creaking, there's some kind of slippage, so figure out the creak and put one of the substances on the creaky part -- cleaning it first -- and then torque down to the proper value and the creak will disappear.
Carbon fiber handlebars, stems, and seat posts are the components that first spring to mind. Slippage in any of these places would be at the least uncomfortable and the precursor to catastrophic failure at the worst. But any point at which parts mate could potentially benefit from assembly paste. Slippage is never any fun.
We're currently running aluminum components for the seat post, stem, and handlebars. Maybe not the most obvious places to use the assembly compound, but lightweight aluminum isn't necessarily as strong as lightweight carbon fiber. The paste should work on the surface areas all the same. We pulled out the post, cleaned off the grease, applied the paste, pushed it back in. It sounded gritty and took more effort than with a greased post, though upon eyeball inspection, we saw no scratching. We're also testing out some new bars and a new stem, so we applied the paste to our carbon fiber steerer tube and the handlebar clamping area at the front of the stem. Pushing the stem onto the steerer took more effort than we expected. It almost felt as if we didn't need to tighten the pinch bolts. We did to their proper spec all the same. Up front, the paste on the handlebar clamping area didn't present anything different than leaving the area dry.
After a number of weeks and hundreds of miles in wintry conditions, we haven't had a problem. Of course, aluminum clamping on aluminum has been common among bike components for a long, long time. There have been few problems with the interface. Carbon fiber is still very new as a component material, "in its infancy," as more than one person told us. Component manufacturers have hardly found solutions to all the issues that this new material has brought up.
Assembly paste could well be the solution. Maybe in the early days of ball bearings, people thought grease would eventually go by the wayside. After over 100 years, grease is still essential. The great thing about the assembly paste is that it's a simple solution that is easy to use, cheap, and effective.
The old adage about an ounce of prevention being worth a pound of cure is something to consider. This compound is probably about a gram of prevention that could result in many pounds of cure.