Wind tunnel development of the new Hadron 485 & 800+ aero wheel models.
The Swiss Side Hadron 485 and 800+ wheel sets, establish two new aerodynamic benchmarks for the cycling wheel industry.
Following the extensive CFD (Computational Fluid Dynamics) development of the new low profile Hadron 485 (48.5mm profile) and the deeper section Hadron 800+ (80mm front, 85mm rear profile), reported in the recent Hadron Update 22, the development process turned once again to the wind tunnel. As always, one of the key targets of these wind tunnel sessions was to confirm the drag and side force performance of the new 485 & 800+ wheel models, relative to the highly successful Hadron 625. However in order to better test and evaluate the ‘real world performance’ of road bike wheels, an all important new measurement system was implemented for Steering Torque. Swiss Side invests a great deal of development time in reducing and optimising the steering response characteristics of the wheels. The reason is simple:
The front wheel response & stability, plays a major roll in keeping the rider in the aero position. Thereby the rider drag is minimised, which accounts for 75-80% of the total system drag.
This is what Swiss Side means by ‘real world performance’. – The end goal is not the lowest drag wheel. The goal is the lowest drag complete bike and rider unit, for which the wheels can have a significant influence if engineered correctly.
Independent media reviews, as well as subjective feedback from pro-riders and customers alike, all confirmed that the (CFD developed) response characteristics of the Hadron 625 had successfully resulted in an extremely stable and low sensitivity wheel. With the newly implemented steering torque measurement capability, it was therefore possible to scientifically and objectively quantify the front wheel response as part of the Hadron 485 & 800+ wind tunnel development program.
Testing was also extended to a wider range of the latest aero bike frames. Further tyre aerodynamics evaluations, this time for tubeless tyres was also completed. Finally, some industry pioneering aerodynamic R&D projects from Swiss Side were also evaluated during these wind tunnel sessions.
The complete details surrounding the Swiss Side wind tunnel testing & development methods can be found in the previously published reports:
Update 9 – Wind Tunnel Testing Methods
Update 13 – Hadron 625 & Tyre Wind Tunnel Testing
Update 15 – Eurobike Wind Tunnel Battle
What was tested & how?
For the new Hadron 485 and 800+ wheel sets, the best wheel design solutions from CFD were again produced using rapid prototype (3D-printed) rim covers, applied to the Hadron structural wheel. These prototypes were then tested in the wind tunnel to confirm the performance predicted by CFD.
The front wheels were first tested stand-alone without the bike for evaluating the pure aerodynamic performance of the wheels alone. Then to obtain final accurate numbers regarding the absolute wheel performance on the bike, as well to evaluate the rear wheel performance, complete bike testing is also required.
Once the final specification of prototype wheels were chosen based on the wind tunnel testing results, the tooling for the production wheels was released and the first pre-production wheels produced. These wheels were then tested again in the wind tunnel to confirm the expected performance seen on the prototypes.
Performance data for Drag, Side Force and Steering Torque were collected. The primary testing speed was done at the industry standard 45km/h, however additional speed scans from 25km/h to 75km/h were conducted to identify any speed sensitivities.
In this latest wind tunnel testing session, the Swiss Side aerodynamics team also had the opportunity to test and collect data on a variety of the latest aero bike frames, including:
– BMC Time Machine TM01 (reference frame),
– Specialized Shiv,
– Cervélo P5
– Canyon Speedmax CF.
The primary purpose of testing on different frames was to investigate any performance variation on differing frame geometries.
Finally, tubeless tyres are beginning to break light on the road cycling scene. Although there is much debate regarding whether these are practical, or offer a real performance benefit for road riding, the aerodynamic performance of two tubeless tyres was tested:
– Schwalbe Ironman Tubeless, 700x22c
– Specialized S-Works Turbo Road Tubeless, 700x24c
These two tyres were chosen since their sidewall profiling looked as though it could be adequate for the all important boundary layer tripping. (See in Update 13 – Hadron 625 & Tyre Wind Tunnel Testing for details).
Hadron 485 & 800+ Testing:
The performance of the Hadron 485 and the Hadron 800+ wheels once again matched very closely with the CFD predictions. Relative to the already independently acclaimed Hadron 625, the wind tunnel confirmed the expected steps in terms of the drag and side force performance of the new wheel models. Also very importantly, the steering torque measurement installation gave the Swiss Side aerodynamics team the ability to scientifically quantify the steering sensitivity effects.
The performance steps through the range of Swiss Side Hadron aero wheels can best be summarised by the ‘wheel mapping’ chart below, showing the weighted average Drag Power, plotted against the weighted average Side Force. This shows almost purely linear performance steps across the wheel range: Hadron 485 – 625 – 800+. The intermediate steps are also shown where for example, a Hadron 485 front wheel is combined with a 625 rear wheel.
The results here are excellent. The drag reduction steps across the range are very well distributed. Each step results in proportionally equal increased steps in side force response. Regarding the steering torque and sensitivity, see details further below.
*Data based on measurement on BMC Time Machine TM01 at 45km/h.
To recap, the weighted average performance characterises the total aerodynamic performance across the complete yaw (cross-wind) range by applying a Gaussian (bell curve) law to characterise how often each yaw angle occurs out in the real world. Complete details regarding Swiss Side’s weighting systems and how they are used in both CFD and wind tunnel testing can be found in Hadron Update 7.
*Power and Side Force data measured on BMC Time Machine TM01 at 45km/h.
The Drag Power curves, as well as the Side Force curves above, show the detailed performance across the yaw range. In general, the deeper profiles benefit more from the cross-wind ‘sailing effects.’ As the yaw angle increases, so does the lift produced by the profile. This lift produces thrust in the riding direction and this is the primary aerodynamic mechanism that reduces the drag. However this lift also responsible for the side force increase.
The steering torque and sensitivities measured were excellent. As predicted by CFD, the Hadron 485 shows the expected reduction in both steering torque and a reduced gradient in the response. The deeper section Hadron 800+ front wheel as expected showed the marked increase in steering torque magnitude and the gradient of the response with yaw. This was the primary reason that the rim depth of the Hadron 800+ front wheel was limited to 80mm, whereas the rear wheel depth was designed at 85mm. The magnitude of the steering torque is the key trade-off between the deep section and shallow section wheels. Very importantly however, the steering torque response curves with yaw, remain perfectly linear for all Hadron wheels.
This is one of the most important features for stable aerodynamic wheel characteristics.
One of the ‘Big Brand’ competitor wheels tested, shown by the red dotted line, offers the perfect example of an unstable aerodynamic response. The changing, unsteady steering torque response would be felt by the rider as an unpredictable pushing and pulling on handlebars in changing wind conditions. This massively reduces the rider’s confidence and forces them out of their aero position, or even to reduce their power output to be prepared to react. Although some competitor wheels come within 1-2W of the Hadron aero wheel drag performance levels, the rider lifting even slightly out of the aero position results in a drag penalty in excess of 30W! This is where the wheels can play an important role in reducing the rider drag.
For this reason the wheel stability is extremely important to ‘real world performance.’
Hadron 800+ production wheel set
Hadron 485 production wheel set
Wheel evaluation on a variety of aero frames:
The purpose of this block of the test was not to evaluate the performance of the individual aero frames, however to check for any change in the wheel performance and response with those different frames.
The group of frames tested showed quite a significant spread in aerodynamic performance, with the Cervélo P5 offering the lowest drag (17% lower than the highest drag frame) and the BMC Time Machine TM01 offered lowest side force (13% less than the highest side force frame). However despite the spread in aerodynamic characteristics between the frames, the wheel performance contribution and response remained the same regardless of the frame geometry.
Hadron 800+ production wheel set on Cervélo P5
Hadron 800+ production wheel set on Specialized Shiv
Tubeless Tyre evaluation
The Schwalbe Ironman was the best of the tubeless tyres tested. However, it did show a strong speed effect, with deteriorating performance at lower speeds. This indicates that the boundary layer tripping / mixing offered by the tread is not quite sufficient.
The Specialized S-Works Turbo tyre, apart from being almost impossible to install on the rim, showed poor aerodynamic performance, similar to that shown by slick tyres. This shows that the sidewall texture is not adequate to trip the boundary layer into the turbulent state.
The Continental GP4000s II remains the best tyre in terms of overall aerodynamic performance, as well as offering one of the lowest rolling resistance tyres available on today’s market.
SUMMARY & CONCLUSIONS
The performance of the new Hadron 485 & 800+ wheel models successfully proved to reach the absolute top levels expected.
Using the already independently tested and proven Hadron 625 as the reference, the performance steps of the new Hadron 485 and 800+ wheel models are summarized in the table below. The numbers given are the weighted average performance for each parameter. Note that the same weighting system is applied to the Steering Torque as for Side Force, (higher yaw angles are weighted more strongly than the lower angles).
The data listed below is the complete bike performance as measured on the BMC Time Machine TM01 frame set. The performance deltas between the wheels are therefore in context of the complete bike system.
The Hadron 800+ wheel set offers another step again in reducing drag compared to the Hadron 625. Although the magnitude of side force and steering torque increases, the all important steering response characteristic remains stable and predictable as with Hadron 625. The Hadron 800+ is the ideal wheel set for absolute minimum drag in low to medium wind conditions.
The Hadron 485 wheel set offers a step in further reducing steering torque and side force compared to the Hadron 625, for a minor increase in wheel drag. The steering response characteristic is also shown to remain perfectly stable. The Hadron 485 offers the perfect performance characteristics for high wind days or for riders who desire an extremely low sensitivity from the front wheel response.
The performance benefits of all the Hadron wheel models wheels remains consistent regardless of the bike frame on which they are tested.
This table puts the Drag Power numbers in context by defining realistic time gains out on the road. In order to represent both professionals as well as normal amateur athletes, calculations were made for the typical power outputs and average speeds for those riders.
Note that these numbers are purely based on wheel drag performance. As highlighted in this report, when also considering the importance of front wheel stability and its response in the wind, these gains can in fact be significantly higher due the implications for total rider drag. Since Swiss Side wheels are designed with a strong focus on stability, this is where the Hadron wheel models can offer further significant performance gains over other brand wheels.
Stay tuned for the next updates-
Update 24 – Final Specification & Pricing.
The final specification for all of the 2015 Swiss Side Hadron wheel models will be released together with the pricing.
Publication Date: 18th March 2015
Update 25 – Hadron 485 & 800+ Pre-Order Launch.
The shop will open for the Hadron 485 and 800+ which will be made exclusively available for purchase through the Swiss Side online shop.
Launch Date: 26th March 2015
…and more to come.
Consistent with Swiss Side’s ‘real world performance’ drive, the aerodynamics team has been working on some pioneering development projects, which will be completely new and groundbreaking for the cycling industry. These have been born through the team’s unique experience from Formula 1 motor racing. Initial tests were successfully completed during this most recent wind tunnel testing session and the projects are set to break cover during 2015… Stay tuned!