Tyler from Bikerumor recently asked me to record a podcast with him about what makes a bike wheel radially compliant and what are some of the advantages and disadvantages around that. Naturally I was excited to be on his podcast and you can listen to that below but I wanted to put together a written piece for those who prefer that medium.
When marketing teams talk radial compliance in wheels, they are almost always talking about the rim specifically and rightfully so. There are a lot of factors that go into how smooth a wheel rides but the rim is certainly one of the biggest influences in the system but we will touch on all the big points.
First off, what is radially compliant? A simplified version is that the wheel is designed to absorb shock from the terrain before it ever even makes it to the suspension. It’s a wheel that is built in a way to absorb those sharp peaks of force from the ground leading to better traction and stability. If you have ever wanted to know how to stop “chatter” on really rough terrain, this type of wheel can help. While radially compliant is a very good thing, there is a point where you can go too far and loose some stability in the wheel so manufacturers are always trying to find the perfect balance there. Some of our favorites that do it well are the Zipp Moto rims and Revel’s RW series rims although the two attack the issue from different angles. If you are looking at aluminum, Spank has definitely cornered that market.
Rim makers will usually change the profile to a flatter and less deep shape over the more common V or U shapes we have been using for a long time. Changing the shape alone will make a significant difference in the way the rim handles impacts. With aluminum, you are pretty limited by the material to being able to only change the shape of the extrusion for the most part, even Spank’s Vibrocore is not addressing radial compliance but more so high frequency vibrations. The way they shape the profile of their rim absolutely does help though.
With carbon, you can not only change the shape but also the way the fibers are laid up and even the resins used to bind the carbon together. Considering lay up and resin type is especially critical when building a compliant rim because compliant means movement and when things move that are too brittle, they crack. Thankfully carbon is a truly amazing material and can be designed to handle this movement without failure in most cases if the rim was designed and built well.
Spokes play another major role in how a wheel rides, both with radial and lateral stiffness. Spoke type, spoke lacing pattern and spoke count all play a big role here. In general, the thicker the spoke and the more spokes you use, the stiffer the wheel will feel both radially and laterally. There are a lot of times I will recommend a higher spoke count to a rider simply to increase wheel stiffness, even if a lower count wheel would be sufficiently durable. This is especially true with road and track sprinters.
The spoke lacing pattern can also change how stiff a wheel feels. The short version is radial lacing is usually the stiffest option radially but you do lose some lateral stability. You also lose a huge amount of torsional stiffness. This is why you never see entire rear wheels laced this way. Moving up in crossings, typically 2 cross will feel stiffer than 3 cross, both radially and laterally on 28 and 32 hole wheels. One thing to take into consideration would be that using fewer crosses typically will place higher stress on hub flanges so if you are already running super light hubs it may be worth adding that extra cross if you are unsure.
This is a very large oversimplification and covering all the possible options would take pages so if you have more specific questions, feel free to reach out and we can discuss your specific case.
Hub geometry can also play a role in wheel stiffness. It can make a good difference when talking lateral stiffness but has very little effect on radial stiffness. In general, the wider and taller the hub flanges are, the more lateral stiffness you will have due to better bracing angles from the spokes. The bigger bracing angle is like using a long breaker bar to increase leverage except instead of trying to loosen a bolt, you are using that leverage to hold the rim in position. Don’t be fooled though, taller flanges are not always stiffer because some manufacturers will make hubs with very tall flanges but then place them very close together effectively lowering your spokes bracing angles.
Do I want radially compliant wheels?
This is the big question. For most riders the answer is yes but like all things in life there will be tradeoffs in performance. If you are a rider that likes a very direct feedback from your bike you may prefer the more raw feeling that stiffer rims can provide. If you are also the type of rider that does not notice minor difference in ride characteristics you probably won’t be able to tell a huge change between the two as the differences are subtle, especially on bigger bikes. The other rider who may prefer to stick with stiffer rims would be the rider who just wants wheels that are affordable and bulletproof. It’s very possible to have extremely durable and still compliant rims but typically they tend to be a bit more expensive as there is a lot of engineering and higher quality materials behind them. It’s much easier for manufacturers to build something that is strong if they do not need to use that part to change the ride characteristics. Ultimately though, like most things in the bike industry, there is no right or wrong in this decision and it comes down to personal preferences.
If you would like to talk more about what wheels are right for you, give us a shout at the contact form below.