Originally Posted by
rpenmanparker
I think the author agrees with you. What he is saying that a flexy wheel caused by a flelxible rim will behave differently from a flexy wheel having a stiff rim but too few or too light spokes. He is saying if the rim is very stiff but if too few spokes are the problem the rim will tilt at the axis defined by the hub and cause brake rub. If the rim is not so stiff, you may not notice the flex even with too few spokes, because the flex will constitute a bend at wheel's mid point, no brake rub. The "upper" part of the wheel won't be much affected. Yep, more or heavier spokes will work to fix both problems. He is trying to show that stiffening the rim may not do so. So if you are weight conscious at all, once you go with a heavy duty rim you may be screwed as you will still need substantial spokes to prevent brake rub. If you favor high spoke count or heavy spokes, you may be well served to save a little weight in the rim. That will help with the brake rub and won't hurt much elsewhere. That is, as near as I can tell, the principal learning from the article.
Robert
Yup. My issue was how he was choosing to explain it. Almost as though they were two different entities...when it's a system. The spokes themselves don't do anything for the stiffness....but the number and how they are laced can and does affect it. I just think that point wasn't as clear as it could have been.
In general I have almost always leaned towards a lighter rim that has a lot of stiffness and then backed it up with the appropriate (in my mind) spoke count. By contrast the industry of prebuilts has a different set of problems. They don't know what rider is going to ride them so they have to over build. Yet the 3 things that consumers care about at the retail level are: how much, how light, and does it look cool. As a result the vast majority of prebuilts have low spoke count for aerodynamics and looks as well as low weight. In order to preserve some system performance they have to put the strength of the system or durability and stiffness back into the rim. Another word for strength, durability and stiffness is....weight.
So - long story short you end up with a wheelset that has a lot of rim weight, is low weight overall meaning that it is actually underspoked and usually feels like a wet noodle when sprinting.
For the longest time when Zipp was using the alloy brake track in the 404 dimpled it was really easy to illustrate this. The rims weighed anywhere from 550-650g each. By contrast a Kinlin XR300 rim is about 465g. An ENVE 45mm carbon traditional clincher is about 430g. Yet Zipp 404 set would compete with other in terms of overall weight. They did this by having a low spoke count, lacings that would reduce weight but not be as durable (the whole radial DS or NDS thing is a bust. Sound theory but bunk in practice - go through the years and see how many times they have changed it from one to the other. They both break spokes) and hubs so light that they failed constantly due to poor stiffness and undersized bearings.
It's the price you pay for a stiff durable rim with alloy braking surface.
They didn't get into the full carbon clincher (firecrest) deal because they all of a sudden "discovered a new resin that is far superior" - rather they had to finally get into the full carbon clincher market because their mixed rims were just too heavy to continue to hold market share and they had pushed the hub and spoke structure too light to sustain. They are still playing catch-up to companies like ENVE. Near refusing still to go head to head with them in aero tests - the one place that Zipp is supposedly king.
Another good example would be Mavic. They use beefy rims that aren't necessarily light or deep/aero as the strength center on overall lighter builds. They could reduce rim weight and add more spokes and have a much better riding wheel. I prove it time and time again when I provide someone a similar weight build that they come back and rave about simply because the weight is at the hub and not the rim and there is an appropriate spoke count.