There has been a bit of a stir on various internet forums and blogs about “exploding Zipp hubs”, referring to the 88/188 model, as fitted in the pre-2014 very popular Firecrest 202/303/404 series. The 303 Firecrest in particular have proved themselves tough as nails when Tom Boonen brought them to victory in the Paris-Roubaix in 2012. Nonetheless, the images of ripped hub flanges and collapsed wheels you can see on the web are a bit disconcerting, to the point that even Zipp have taken action, modifying the hubs in the 2014 series. You can argue that maybe a recall was due, but apparently the number of failures is pretty tiny… internet goes a long way in acting as a magnifying lens. Nonetheless, the problem exists.
I have been asked to rebuild a 303 Firecrest onto a more reliable hub, so I took the chance to have a play with a rear 188 hub to get an insight in what I think it’s wrong with it.
1) Lacing pattern: the rear hub is laced radial on the drive side, a malpractice made popular by Mavic, which relies on having a set of very strong and stiff spokes and an equally strong flange to support the high tension required. Zipp have built their rear Firecrest with Sapim CX Ray straight pull spokes, tensioned at around 1300 N, according to my gauge. This is a very light spoke with a rather high tension.
2) Flange design: the inappropriate radial pattern should be supported by a solid flange, while Zipp have designed a flange with a step and the top part is only 1.7 mm thick. The spoke is then further protected by an alloy retaining ring, which has virtually no structural function
If that thin step fails, not one but two adjacent spokes can jump out of the hub altoghether with potentially catastrophic consequences. Interestingly, there was enough space to design a thicker step, at least 1 mm if not thicker, which would have probably solved the problem altogether at a handful of grams weight penalty. Also, the step could have been designed with a notch so that only one spoke at a time is allowed to fail, whilst the continuity of the design means two spokes will fail at the same time.
Luckily all these issues have now been addressed and Zipp have come out with a 2014 hub laced with a more traditional crossed pattern, which goes a long way to resolve the issue. But what if you are stuck with the old 188 hub? Well, you can leave it as it is and hope it will never happen to you or you can take action, depending on your budget.
1) Reinforcing the drive side hub flange: there is enough room to fit some custom washer, which would help spreading the load. While I have no evidence of this being a solution, washers are used by Zipp inside the rim for the very same reason, so I don’t see this practice having an ill effect. Of course such washers do not exist and need to be custom machined. All hypothetical, of course.
2) Rebuild the wheel on a different hub. This is the most expensive option, as new spokes are required and Sapim CX Ray spokes are not cheap. Of course you can use Sapim Race and cut the bill significantly, but you lose in aerodynamics on a wheel designed to be the most aerodynamic on the market.
The rebuild is something you can do yourself, as long as you know what you are doing and take care in a few key steps:
1) The rims are fitted with Sapim oval washers… they are a bit of a PITA to get out of the rim and you might well spend an hour just shaking the rim to get them all out. Once they’re out, they need to go back in with the new spokes and ideally you want to fit some new ones, as the used ones are deformed according to the internal shape of the rim. They are not overly expensive and they can be bought in small bags. Fitting them requires a bit of practice, but it’s overall easier than working with internal nipples, so not too challenging for someone brave enough.
2) The rim is drilled with an offset to narrow the gap between the drive side and non drive side tension. You need to remember that the holes with the most offset from the centre of the rim are those that need to be laced to the non drive side. The rim does not have any label telling you which side is which.