Well, this past Friday we heard a peep – a die-hard randonneur on one of our Boulder Bicycles who really accumulates the miles reported the classic Synergy OC problem. We then looked at the shop demo bikes and wheels. The 700c rear wheels with only modest miles on them are fine. But the 650b rear that has been on multiple bikes and had lots and lots of miles on it did show the cracking around the drive side eyelets.
So, that meant immediate investigation. Our first step was to contact Velocity and ask them if they have widespread problems and also for a take on what the ideal drive-side tension should be on the Synergy OC rims. The person we spoke with said they build the rims to 120 to 130 Kilograms. That seems very high. The Velocity contact indicated that there were some Synergy OC rims that seemed to have “issues”, but those were limited to some small batches from extrusions that weren’t up to spec. They also indicated that the overall defect (= return rate) on the Synergy OC rims is extremely low. They admitted, though, that many folks may not have inspected their rims to and realized there is a problem, though. But good news is they stand behind the product and a dealer can get a replacement rim on warranty which is very reassuring.
But, is that the whole story? What is a wheel builder to do? The consensus is that with the OC design, the rim can essentially “rock” and stress the rim near the eyelets more than a non-OC design. We did some calling around, and the vibe from others who have used these rims (and also seen similar issues) is that it is important to not tension the Synergy OC as high as one would a typical modern rim. The typical rule is to take a modern rim up to about 110kg. Based on what we heard talking with others, it seems that 100kg is the upper limit. So our thoughts are that a Synergy OC rear should be built with extremely close tensions in the 95 to 100kg range for the drive side rear. Interestingly, the Velocity contact felt that tension that is too low could also cause problems. And in any case, the tension we were building at should not be an issue. But it is an issue.
Even better news is that nobody has had a serious failure that we’re aware of due to this issue. It seems that over time, the nipples may start to pull inward, resulting in reduced tension and a failure of the wheel to stay true or dished. But because the rim is a box section, the upper web keeps the rim intact. Of course, if one waits for cracks get really bad, all bets are off. But it is likely that many folks may have this issue and not noticed because the wheel can remain quite true, dished, and tensioned, even with some pretty sizeable cracks forming.
So what should one do if you have Synergy OC rims? We’ll we’re still building with them, but at lower tensions and expect they will be fine. We’ve also double checked our tensiometer calibrations more carefully to be sure we’re not erring on the high side. If you are on a bike with these rims, have the tension checked and see if it is over 100kg on the drive side (you will probably need a good bike shop for this). If so, and there are no cracks present, have the shop (or yourself if you do your own wheelbuilding) back off the tension on the drive (and non drive to maintain dish) to that 100kg max.
If you have wheels that do show cracks, Velocity will provide replacement rims – your shop can take care of this (or if you’re the wheelbuilder you can probably just contact Velocity) although you will probably need to pay shop labor and buy new spokes.
If we built the wheels for you, we’ll do what it takes to make sure you’re taken care of. We’ll either take care of it at our shop, or assist you in getting them re-tensioned or rebuilt if the tension is high. While sidewall wear of a rim is normal wear and tear, cracking of a rim at an eyelet is not normal and is something we warranty (assuming the wheels weren’t terribly abused or ridden for so many miles that they were near the end of their lifespan anyway, rim sidewalls do wear out after all!)
Just this week, a Boulder Bicycle frame customer had their bike assembled and wheels built at their local (and very reputable) shop and they tensioned the wheels beyond what we’d now suggest. So a bit of extra shop time now to reduce the tension a bit may prevent a reduction of the rim’s useful lifespan.
So this is our take on this, and Velocity DOES NOT agree about going with the 100kg limit as they think higher tensions are fine according to the person we spoke with. But based on all the information we have at this point, we feel that the reduction in tension for drive side rears to a target 100kg max is wise. And for fronts, about 95 to 100kg should be good as well (no reports from anyone of failing front (i.e non-OC) rims.
Mike Kone in Boulder CO USA
Rene Herse Bicycles inc.