Wheel Component by DT Swiss Inc.

In this article, we’ll be discussing a Wheel Component in Particular for Bicycles by DT Swiss Inc., US publication 20210354517. The publication date is Nov. 18^th, 2021 and the filing date is May 14^th, 2021 (US). This patent is not granted in the US, yet, but it was granted in the EPO late last year.

I was asked by DT Swiss to write this article for you all. I’d like to thank them for allowing me to share a really cool idea with you all. I’m a huge fan of engineering-driven marketing, and I hope this gives you some deep understanding of their possible new product.

Brief Summary (tl;dr)

DT Swiss are developing their own aerodynamic tire, which includes a bunch of little depressions called ‘aero elements’. These little aero elements are spaced apart, and surround the outside faces of the tire, causing a small amount of turbulence in the surrounding airflow. As a result, the tire produces the ‘sailing effect’, which effectively induces a level of propulsion at higher yaw angles. The advantage here is the tire produces this sailing effect at reduced speeds compared to the competition, allowing for a wider range of speeds that can leverage the sailing effect. This means regular people can enjoy the aerodynamic benefits, rather than only racers. Basically, a tire for everyone.

Intro

Webster’s Dictionary defines aerodynamics as a branch of dynamics that deals with the motion of air and other gaseous fluids. We all deal with some level of aerodynamics after a good Taco Bell run. The advantages of aerodynamic performance aren’t a secret in the bike world. Companies and race teams are continuously improving their aero, from frames to water bottles to bars – this is a huge focus for these companies because winning sells. Win on Sunday, sell on Monday.

In general, drag reduction is the primary goal of most aero improvements on a bike. Drag is defined as the mechanical force opposing a moving body through fluid, generally colinear to the direction of movement, meaning forward/backward direction. Drag can be a function of both high pressure or low pressure, depending on where you’re looking at a moving body. Let’s take a car, for example: high pressure would be at the front of the car pushing backward, and low pressure would be at the back of the car pulling backward.

The Wind Wizards at DT Swiss are working their magic by designing their own aerodynamic componentry, namely, a new tire. Simply put, there is a relatively large amount of drag produced by a rotating tire. More specifically, rotating wheels/tires produce high turbulence flow around a tire, which promotes flow separation, thus causing relatively large low-pressure areas behind the tire. It’s a lot more complicated than those two sentences, but that’s the gist.

Why

While they don’t go too deep into this, weight appears to be a small goal here. The primary focus is aerodynamic gains, specifically drag. They also mention reduced steering torque requirements, as well.

It has also been found that the wheel component [tire] according to the invention results in a comparatively lower steering torque. On the whole, it can be shown by wind tunnel data that the wheel component reduces both the aerodynamic drag force and also the steering torque resulting therefrom.

This is pretty cool. They also say this tire isn’t dependent on a certain rim:

In the scope of the invention, it has been found that competing products tend to show high dependence of the aerodynamic properties on the combination of tire and rim and the relative speed. The invention has shown, however, that wheel components combined from different rims and tires achieve advantageous effects in a great variety of relative speeds.

What

FIG. 2a starts this off with an image of this new tire. The first thing you’ll likely notice are the little squares on the outer area of the tire. These little squares, called aero elements, are the primary focus of this idea.

FIG. 2b shows a cross-section right in the middle of one of these aero elements. We can see that the aero element is a little depression in the tire itself. So, what are they trying to do here with these little depressions?

On the whole, a (nearly elliptical) tire shape has an advantageous effect on the air drag, wherein the aero elements achieve an ideal turbulence level (whirling)… with average speeds of 37.5 km/h, according to the invention a sailing effect can already be utilized in many situations, wherein air impinging obliquely from the front is utilized for generating propulsion.

The term ‘sailing effect’ or ‘sail effect’ is an important concept in bike tire aerodynamics, and they’re describing it as the ability of the tire to ‘generate propulsion’. Jux et al¹ define the sailing effect as ‘…effectively “pulling” the wheel forwards and thereby further reducing its resistance in the direction of motion’. We’ll get into this later on.

FIGs. 3 and 4 show a front view and a side view of this new tire. The number of these aero elements are important. According to DT Swiss, …48 aero elements each are provided distributed over the circumference of the tire on each of the sides… because … It has been found though that too many aero elements may cause too much turbulence which increases drag, and that too few aero elements generate too little turbulence. Specifically in slow and average speeds.

It sounds like they’ve done quite a bit of testing for an optimal number of aero elements based on the dimensions of the aero element.

It has been found that a relatively small number of aero elements for whirling the impinging air can obtain very advantageous, aerodynamic properties. Due to the planar configuration of the aero elements, a very small surface proportion is sufficient for achieving high efficiency even with relatively slow speeds. The high efficiency is also retained in high speeds though.

Here’s a little unsolicited background based on my work experience. Conceptually, when you have situations like this with multiple variables (length, width, depth, quantity, etc.), you’ll set up a matrix, where at least two input variables give you an output result, just like any matrix. With a two-variable matrix, an optimized answer is pretty simple, and can be considered two-dimensional (X + Y = answer). When you add another variable, the matrix is then three-dimensional (X+ Y + Z = answer), and gets much more complicated. When you go further than three variables, lordy does testing get difficult. You effectively create multiple three-dimensional matrices, into a matrix. But I digress.

FIG. 6 shows a detailed cross-section of the tire, right through the aero element. It appears as though their testing has led to very specific positioning of these elements. Angle 3a refers to the angle between the inside face/band of the aero elements, which are about 26° from center. We then have an outer face/band noted with 10a/b, which is ‘…close to an angle of 60°…’. So, we can deduce that the aero elements start at roughly 26° from center to roughly 60° from center.

FIG. 7 has a lot of stuff going on with the surface of the tire. First, the aero element 10; ignore the square on the left, that’s just a simplification. The schematic on the right shows the profile of this aero element, where there are steps/chambers/edges in the profile. This profile is very important to the aerodynamic nature of this tire, where this profile creates the whirling of air we noted prior.

We’re also seeing some ideas for wear indicators 30. There are two different concepts. The variation at the top (31, 32, 33) are three different depths, each indicating a wear level, when the surface of the tire reaches said depth.

The other (bottom one) has four progressively deeper semi-circle-shaped wear indicators in the circular depression (31-34), where each semi-circle wear indicator is a different depth from the surface. The interesting part of the indicators are the fact that they’re tied to the aerodynamic performance of the aero elements.

…each of the indicator units shows a number of indicator elements or indicator levels or the like, so that, at a glance on an indicator unit, the user is given the degree of the aerodynamic quality respectively the state of the tire in aerodynamic terms… it has been found that with increasing wear, the aerodynamic properties of the tire decrease.

Here’s a cool little tidbit from their testing. DT Swiss are saying it’ll take 9% more output (wattage) to move a 500km used tire vs. a new one. Today we learned.

…the averaged output required for overcoming the aerodynamic resistance of a rotating front wheel by means of the tire, increases approximately 9% with a used tire, after ca. 500 km.

The indicators also suggest replacement time, but that’s a given. There are four indicators, evenly spaced around the tire. That being said, DT Swiss says there can be only one, so the number of these doesn’t really matter. You probably just need one anyway.

FIG. 8 continues to show the aero elements. There’s not much to talk about here, but we can say that the length 14a can be roughly 7mm. We can also see the steps/chambers from this perspective.

FIG. 9b shows a detailed cross-section of the aero element. DT Swiss state the angle 24a is roughly 9°. Though not stated, this should create what’s called an adverse pressure gradient (APG), which coerces a little bit of flow into the aero element, which then creates a little bit of turbulence behind the aero element. The term ‘defined’ below is important because it’s a calculated amount of turbulence.

Turbulent flow adheres better to the tire and the rim of the wheel component than does an even, laminar flow… A substantial aspect of the invention is that the tire of the wheel component converts the air flows to a defined turbulent state without generating too much turbulence. Thus, the air does not adhere to the tire but it detaches early.

So, it sounds like they want a kind-of muddy flow, but not too muddy, around the tire.

Here’s another super awesome drawing showing a rough representation of the concept. Flow (at yaw) stays attached a bit longer, shown on the right. 

Fun fact: A NASCAR car has an extreme adverse pressure gradient at the back window, and there’s lots of fun games you can play with it to create a bunch of downforce, like moving the right-side roof rail or the holes in the back glass. Lots of fun games the fabricators and engineers are playing.

This is where it gets fun for me, and this is where we’re going to talk about the ‘sailing effect’ or ‘…generate propulsion…’. FIG. 11a is a graph showing wind tunnel data comparing required watts and ‘impingement angle’ of the DT Swiss tire 40 vs. competitors (they don’t say which competitors) at 30kph. The impingement angle should be the yaw angle of the tire. We can see that the DT Swiss tire produces negative watts at higher angles, which DT Swiss refers to as propulsion or ‘positive assistance’, and is the sailing effect.

FIG. 11b shows the same graph, but at 37.5 kph. Again, we’re seeing negative required watts at higher angles.

DT Swiss reference some prior art, which they say attempts to solve the same issue, but ends up being less efficient due to friction. It sounds like the aero benefits of some prior art don’t outweigh the mechanical friction created by the surface changes. Very interesting.

…prior art, attempts were made to use large numbers of aerodynamically effective elements. This increases the effective surface roughness, and in fact, efficiency was reduced compared to the invention.

FIG. 11c is, again, the same graph, but at 45 kph. Although DT Swiss say their tire still performs the best, other tires begin to exhibit the sailing effect.

So, the big takeaway here from these three graphs is the DT Swiss tire requires negative wattage at lower speeds compared to the competition, meaning the sailing effect can be had at a larger range of speeds. With that knowledge, we can deduce that the aero advantages at lower speeds can be enjoyed by average cyclists that aren’t going Mach 3. That definitely includes myself…

Another considerable advantage of the present invention is that the sailing effect does not only show in high speeds, but already in considerably lower speeds.

FIGs. 12a and 12b show required steering torque (probably Nm) over impingement angle at 30 kph (12a) and 45 kph (12b). Long story short, DT Swiss are just saying that their tire doesn’t require any more or less steering input compared to other tires. We can see it’s pretty well in-bound with everything else on the graph.

Conclusion

This is a really fascinating idea, especially coming from the aero world myself. The mixture of creativity and shear level of optimization is pretty astounding. Assuming they didn’t use a HEEDs-type software, I cannot imagine the number of CFD cases needed to narrow this down with reasonable confidence. Then, once you get some variations through CFD, you then need to actually make the tires. Then, you’ve got an array of wind tunnel runs to verify the CFD results, and wind tunnel time ain’t cheap. I’ve read Honda’s new tunnel will run you $3000/hr. While that’s a much larger tunnel than needed for a bike, it’s pretty easy to spend 16 hours in one, powered only by Red Bull and pizza.

DT Swiss make it pretty clear that this idea isn’t just for racers, but can be used by semi-professionals as well, so you’ll likely see this in your local shop in the future. That being said, there’s no reason an amateur can’t use this new tire. The combination of aero drag reduction and improved steering torque requirements sounds like a win-win in my book. Assuming they can sell these are a competitive rate and win races with them, this could turn out to be a real step forward for their business and their racers.

Thank you again to DT Swiss for bringing their technical prowess to the forefront for all of us to enjoy. Everyone of us benefits when a company presents real information like this. I learned a lot writing this, and I hope you learned something reading it. This is my own interpretation of the idea and shouldn’t be considered anything other than a fun read.

1. Jux et al., 2023, Tire dependence for the aerodynamics of yawed bicycle wheels, Journal of Wind Engineering and Industrial Aerodynamics, vol 223, https://www.sciencedirect.com/science/article/pii/S0167610522003907