Not so ZIPP now...!
Last week I got an e-mail from Rob, he lives locally and wants me to have a look at his Zipp 404 clinchers, that seem to have gone a bit mushy, from the original Zippiness... he uses them for racing rather than for cafe' glory, so zippiness does matter when he aims for the line. We agree it might be a problem with tension that might have gone down.
I am always interested to see what the market leaders have to offer, when it comes to the pinnacle of technology, or at least the pinnacle of price tags. These are the pre-Firecrest ones and did come at 1250 pounds. Zipp uses a technology to bond carbon and aluminium into a single structure. The advantage over Mavic's Cosmic fairing is that the composite actually contributes to the overall structure of the rim, which in turn becomes stiffer. It also means it can be built with conventional external nipples, for ease of service. The nipples are alloy of course, to save roughly 15 grams on the vital outer part of the wheel. They are laced with straight pull Sapim CX ray spokes onto proprietary hubs, with ceramic bearings featuring all the latest acronyms.
I have a look at the front wheel first, which seems roughly OK: the tension distribution could be better for a simple wheel built radially, but overall it is acceptable and averages 110 KgF, which exceeds the Zipp specifications for their carbon rims. Then I measure the rear. The non drive side cannot be measured with normal tension gauges, this is normal in the case of 0.9 mm thick spokes. Anything below 70 KgF will give a deflection exceeding the scale. The drive side is a bit of a mess. Apparently one spoke has been replaced by the local shop, which clearly did not use a tension gauge, the result is that around the valve one spoke is loaded with 160 KgF and the next one cannot be measured (see above). As I try to rectify the issue, I encounter the classic Bummer! The alloy nipples are seized onto the spoke. Annoyingly, CX ray are so thin that it is impossible to un-seize the nipple without twisting (and damaging) the spoke, even using a Sapim aero spoke holder. All the other nipples are also seized beyond repair, which means the wheel is untruable. There is virtually no solution to this, as no WD 40 will penetrate the threads which are gunked with bonded oxide. The only solution would be to cut everything off and rebuild with new spokes at great cost (roughly 90 pounds worth of spokes only).
I guess the moral is: for the sake of saving 15 grams, the wheel is virtually compromised, which is very very annoying. Of course this wheel is still usable, although it could do with a good service, but it can no longer be serviced. The problem with alloy nipples bonding is well known, yet manufacturers seem to ignore it, keen to compete for the ultimate weight saving. It is a shame that the only thing that seems to matter is the result from the wind tunnel and the one from the kitchen scale, both of which don't have much impact in real life...