Stiffness testing in practice

So we do all this fancy testing and figure out which wheels are stiff and which wheels aren't and all of that fancy stuff, but what good does any of it do? How does it help us make better wheels for you? Numbers ALWAYS tell a story, and sometimes they tell several all at once. The stories we try to look for in these numbers are ones about points of diminishing returns, points of transferability, and stories about use optimization.  

First, let's take a quick look at why a stiff front wheel is a good thing, and some of the other factors going on there. To me the primary benefit of a stiff front wheel is in steering. A soft front wheel can lead to noticeable understeer. You don't want this. A soft front wheel will also potentially clang back and forth on the brake pads as you climb out of the saddle, or especially when you sprint. When you sprint, you typically weight the front of the bike much more than just in general riding. Without crashing because of it, take note of what your tire does the next time your sprint - yup, that bounciness is because you are weighting and stressing the wheel much more than you just just riding along.  Other factors are strength, which can be described as the wheel's ability to handle unusual stresses (airborne instances, crappy roads), and durability. The more spokes you have, the less work each one has to do - many hands make light work. Last, you have to think about the hub flange. Radial lacing is great for 20 and 24 hole fronts, but start putting 28 holes in that same circle and all of a sudden there's not much meat to handle the higher radial spoke load. Crossing works much better with higher spoke counts.  

We've advocated 24/28 laced alloy wheels for a long time. Where other people said a 20/24 build was appropriate for 190 pound riders, we were saying you should be thinking about going to 28/32 for the same weight. Among the things we've learned is that we were both right and wrong. With rear wheels, we were right. There's a lot going on with rear wheels, especially with the move to 11 speed hubs, and this piece is mostly about fronts, but a 28 spoke alloy rear does a lot of stuff a lot better than a 24 hole alloy rear. Up front, not so much. Because front wheels are inherently such better wheels than rears, front wheels with stiff rims really start to get quite good at 20 spokes.  A Pacenti SL23 (quite stiff for an alloy rim) laced to a White Industries T11 front hub with 20 spokes isn't appreciably less stiff than the same setup with 4 more spokes.  Some people understandably like a bit of redundancy in their setups, so there's still plenty of room in the world for the 24 spoke alternate, but you're not getting what you might call primary benefit from it. Note that one of the next things we're taking a look at is the implications of 1x lacing on 24h fronts, just in deference to the flange issue discuess above.  

Conversely, yesterday I talked about a 28h Stan's Alpha 340 being a nice stiff wheel. The rim is soft enough that it needs a lot of spokes, but when you add enough spokes such that the distance between them gets small enough that adjacent spokes are working together to keep the rim in line, that rim comes into its own. With any of the front hubs we use, that's going to be a nice wheel. It's not the most aerodynamic wheel under the sun, but it's quite light (a 20h Rail front with equal hub is the only lighter front wheel we do) and also quite stiff.  The 2x lacing relieves stress on the hub flange, and the spoke count means that if you somehow manage to break a spoke, you're still riding home.  Add the benefit of tubeless and this is an ideal high mileage winter wheel.  

When spec'd properly, an amazing wheel Disc front builds will never be as good as rim-brake front builds for the simple reasons that disc hubs have narrower flanges, and the wheels are dished, so it works out fine that disc hubs start at 24h. Even then, a 20h build on a rim-brake hub is going to be stiffer than a 24h disc build using the same rim and spokes. Disc rims also highlight suitability for application. As an example, a Rail 52 on a CLD hub, with 24 spokes, is a bit stiffer than a 28h HED C2 disc specific tubular with a CLD hub. But it's also about 80g heavier. On a road disc build, where aerodynamics still matter a bunch, the 52 makes a lot of sense.  On a cx disc build, where you might still really want to use tubulars, and weight seems to be at a higher premium (**the debate on the actual value of which may never end), and where aero is quite distantly far from everything, all of a sudden the higher spoke count C2 looks really good.

It's always going to be a challenge to correlate bench test results with real world application, but that's no excuse not to learn everything you can about how wheels react to stresses designed to mimic what they will see in use.