Bicycle wheel fundamentals haven’t changed much in the last twenty to thirty years. Sure, there have been some attempts to radically redesign the wheel. For example, some have tried to make the hub, spokes and rim out of one piece of carbon fiber essentially creating a high tech wagon wheel. Yes, there have been a few successful advancements in technology that have affected the wheel; disc brakes, carbon fiber rims and tubeless tires come to mind. But even these advancements haven’t really changed the way we build and design the wheels. The majority of bicycle wheels still have somewhere between 24 - 36 steel spokes laced between the hub and rim in a two or three cross lacing pattern (awkward sentence here). This design endures because it works so well. A wire-spoked wheel is incredibly lightweight but can provide flex where desired. Generally speaking we want a bicycle wheel to be rigid side to side, compliant up and down and have zero wind up under pedaling (and disc-brake braking) forces. A wheel that flexes too much laterally will have a negative effect on steering/handling. A wheel that has good vertical compliance provides some suspension effect...but too much gives it a noodly unstable feel. A wheel that winds up during pedaling will rob your energy and slow you down. At some point you also have to consider durability in all of this. What it all comes down to is trying to put a wheel together in a way that gives us all the good stuff and none of the bad stuff. While this may sound simple there is a lot of misconceptions and poor execution when it comes to making the ideal wheel. When you focus on the basics it’s pretty easy to decipher what makes sense and what does not. And there are three basic goals that a wheel builder/designer is trying to optimize; lateral stiffness, vertical compliance and torsional resistance. All the while, one has to keep in mind that the wheel has to be strong enough to hold up to daily riding for about five years and be as lightweight as possible.
The combination of rim design (including shape and material) and hub dimensions are the main factors that determine a wheels personal characteristics. From there the wheel builder needs to select spoke thickness, spoke tension, spoke count and cross pattern in order to achieve the ideal wheel for the rider’s size, style, bike, location, etc… The Pub Red Spoke Customs take all of these factors into building the ideal wheelset.
To achieve the ideal lateral stiffness and stability the spoke angle on the drive-side (DS) of the wheel should be the same as the spoke angle on the non-drive-side (NDS) of the wheel. The ideal spoke angle is about 7°. The challenge to achieving identical spoke angles (left compared to right) is that the rear gear cluster forces the drive-side spokes to be anchored too close to the center of the hub. In most rear wheels this leads to radically differing spokes angles when comparing the drive-side to the non-drive-side. This “imbalance” can create an unstable wheel that is prone to coming out of true, spoke loosening, premature spoke failure, instability, and in the worst case scenario a wheel can collapse completely.
Spoke tension distribution refers to the looser side’s (usually NDS) spoke tension as a percentage of the tighter side’s (usually DS) spoke tension with the tight-side always being 100%. Our goal is to never have the looser side spoke tension less than 75% of the DS for an ideal wheel. Spoke tension distribution of less than 50% is considered unacceptable and borderline unsafe (lots of variables so this is not a hard line). Spoke tension is most commonly measured in kilograms-of-force (KGF). Spoke tension is in the range of 90kgf - 120kgf for most wheels. So if the DS spoke tension of a given wheel is 100kgf we would want the NDS to be 75kgf or higher with 100kgf being the ideal.
Increasing the number of times that the spokes cross over each other can increase the wheels vertical compliance. For example a radially laced wheel will have more vertical stiffness than the same hub and rim laced up with the spokes crossing three times.
Thinner spokes generally flex and stretch more than thicker spokes so building a wheel with thinner spokes will allow that wheel to have more suspension but it might also allow it to have more lateral flex.
Increasing the spoke tension can have a very small effect on the wheels ride characteristics but it is not significant. It is more important to base spoke tension on the rim strength and wheel design. Stronger rims will be built to higher tension than lighter weight, less robust rims.. Wheels with more spokes will be built to a lower tension than a wheel with fewer spokes.
A rim-brake wheel without a gear/driver does not experience torsional load, for example a front wheel of a bike with rim brakes. Disc brakes apply more torsional loads than a cassette. A wheel with more spokes will generally be more torsionally stiffer than a wheel with fewer spokes (assuming same rim, hub and spoke type, total tension). Thicker spokes will give a wheel greater torsional stiffness than thinner spokes.
Energy loss when pedaling due to low torsional stiffness from low spoke count is almost insignificant. When designing a wheel the reason to use more spokes to increase torsional stiffness is generally done to increase the fatigue life of the spoke.
Theories, Guidelines and Ramblings:
- Benefits of butted spokes: The elbow and threaded end tend to be the weak link and the place where a spoke most often breaks. Butted spokes will generally last longer because they are thinner in the middle than they are at the ends, for example 2.0mm at the elbow - 1.8mm in the middle - 2.0mm at the threads. The thinner portion of the spokes allows the spoke to stretch when it is tightened up in the wheel. When the wheel experiences a high-load event (landing after a jump, hitting a square edge bump) the spokes are already stretched more than a thinker spoke so as the rim flexes/moves the spokes are less likely to experience a zero tension moment where they snap back tight. The snapping back tight causes the spoke to fatigue faster than if the spoke had maintained some tension. Also, because the thinner middle part can stretch it prevents loads from concentrating at the elbow and threads, essentially creating a shock absorbing or stress relieving effect. You can mix spokes to achieve certain goals. It is common to use thinner spokes, for example 2.0- 1.6 - 2.0 on the loose side (usually non-drive -side) and thicker spokes, say 2.0 straight gauge spokes on the tight side (usually drive-side). This gives the benefits of increasing fatigue life on the loose side via spoke stretch but the 2.0 straight spokes will help resist wind up under pedaling.
- The more flex a rim has the thinner the spokes should be so that they can flex and stretch with the rim. If the rim flexes and the spokes do not stretch the rim can become weak at the spoke hole and the spoke can also wear out faster.
- Cross pattern is chosen to achieve spoke angle that is most tangent for torsional resistance or to tune vertical compliance.
- Disc brake wheels should have at least 28 spokes to handle the torsional load.
- The rim is the determining factor in deciding how tight the spokes should be. Usually the spokes can handle more tension than the rim.
- When you reduce the number of spokes in a given wheel the tension on each spoke usually needs to increase. For example, a rim and hub laced with thirty six 2.0mm straight gauge spokes will have an ideal spoke tension around 95kgf. If you used the same model of rim and hub but with only 28 spokes the ideal tension would be more like 110kgf. In a hub and rim combination that results in an extreme amount of dish the loose-side spokes will generally be so low that they are at risk of coming loose and/or breaking prematurely. If you were to lace the loose-side with half as many spokes as the tight-side (16 spoke on the tight-side and 8 spokes on the loose-side) it would help even out the spoke tension when comparing the two sides.
Sound complicated? It is, but our Master Wheelbuilder has over 30 years experience and knows exactly how to balance these factors when building a stock Pub Carbon wheel set or building your Red Spoke Customs