Monday, May 12, 2014
Box Section Rims - Walking the Tightrope with High Dish Wheels
Hardly a day goes by when we don't get asked about rim selection. As our customers tend to be "traditionalists" they want to get our opinion on using a box section rim on a high-dish wheel because they love the looks of classically styled rims.
Unfortunately, we just can't give the go-ahead for classic box section rims on modern high-dish setups. There is a reason that major manufacturers stopped using classic section box rims when high-dish wheels became the norm. It is just too delicate of a balancing act to get a wheel with enough tension that the non-drive spokes aren't "too loose" while at the same time the tension on the drive side spokes won't crack the rim at the eyelets.
Of course, if the rim is heavy enough, this isn't a problem. But that isn't much fun...
We won't say that box rims and high dish can't be done, but we really like having wheels that aren't "on the edge". Plus, many of the wheels that seem fine even after a year or so may develop cracks a bit later on. And on some lightweight box rims, the failure can be rather sudden and dramatic.
Rims that are aero or semi aero are much less prone to eyelet cracking (or cracking around the spoke hole if there are no eyelets). The rim may distort a smidge under tension, but it doesn't actually fail.
And some classic box rims often are made with drillings that make the dish issue even worse! If the eyelets are significantly staggered from center, there may be even less bracing angle on the drive side then there would be if the spoke holes are staggered just a little bit.
For these reasons, the use of an OC (off-center) rim really makes sense. It is possible to get non-drive tensions that are much more reasonable.
Of course, if you use a 135mm space rear (which isn't easy with Campy hubs) or if you are using a more retro set-up with lower dish wheels, then the classic box section rims make sense. It just comes down to using the right parts for the right application.
Posted by Mike Kone at 1:47 PM