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Product Comparison Test – Wednesday, 18 June 2025 – Alkmaar, Netherlands
Jacob Blattner Transition from VENTUM to TF1
In competitive triathlon, every marginal gain counts, and aerodynamic performance is often the key differentiator between victory and defeat.
Jacob joined the 18th June 2025 Kú Aerocamp at the Alkmaar Velodrome in the Netherlands with a specific objective: to evaluate the aerodynamic performance and equipment configuration of one of the newest triathlon bikes on the market, the VENTUM Tempus to his recently acquired Kú TF1.
This blog outlines the testing and analysis conducted to compare the baseline aerodynamic drag (CdA) and power-saving potential between the VENTUM and TF1, shedding light on the impact of bike setup, bike fit and frame geometry.
Testing Approach
Jacob’s evaluation involved baseline testing of both the VENTUM and TF1 in configurations without race hydration. The primary goal of the testing was not to measure micro-effects due to equipment matching across the two bikes but to assess how Jacob’s performance would vary between the two bikes in their respective “as supplied” configurations.
The test protocols included removing the crank and power meter from Jacob’s new TF1 for testing the VENTUM. CdA was measured using the same Aerosensor device and standardizing all other data recording equipment between the two bikes to ensure comparable data acquisition.
Frame: VENTUM Tempus size M,
Standard cockpit configuration of Profile Design Wing Ultimate S base bar and Profile Design 52 ASC aerobar extensions.*
Wheels: Zipp 454 NSW
Tire Size: 25mm Conti GP5000 TT TR tires.
Frame: TF1 S620.
Upgraded cockpit of Fast TT Aerobars.*
Wheels: Kú spoked rims, with a 60mm rim on the front and an 80mm rim on the rear.
Tire Size: 25mm Conti GP5000 TT TR tires.
A critical factor in Jacob’s improved performance on the TF1 was his bike fit. Both his VENTUM and TF1 fits were handled by the same experienced Kú fitter, Jo Spindler, ensuring consistency in his biomechanical setup. However, while Jacob was being tuned by Jo to the VENTUM, the geometry of the bike using the as supplied Profile Design cockpit did not allow for an ideal position.
The FastTT cockpit was not compatible with the standard VENTUM Tempus requiring additional mounts and conversion plates.
The cockpits of the two bikes were therefore matched as closely as possible using Zipp Vukka extensions and conventional short armrest cups on both the VENTUM and the TF1.
The geometry of the TF1 S620 still provided him with scope to achieve a better position that enhanced both his comfort and aerodynamics. A good fit not only minimizes drag but also maximizes power output and reduces fatigue over long distances.
The key aerodynamic parameter measured was Jacob’s drag coefficient (CdA), which directly influences how much power is required to maintain speed. Lower CdA values represent better aerodynamic efficiency.
The data below was achieved in a velodrome test with values compared at a constant velocity of 42kph or a normalised power of 230W
Jacobs CdA averaged across both baseline runs on the VENTUM was 0.266.
After these two baseline runs it was clear the Profile Design cockpit of the VENTUM lacked the adjustment range Jacob required to get a reasonable aero position.
After replacing the Profile Design cockpit with the Zipp Vukkas, Jacobs reach was extended by 70mm to get a good aero position.
Jacobs baseline CdA averaged across both baseline runs on the VENTUM with the Vukka cockpit was 0.251.
This positional change gave Jacob a 5.6% improvement in CdA equivalent to a power saving of 14.5W @42kph
Replacing the Zipp 454 NSW wheels of the VENTUM with the Kú race wheel set up of a rear disc and front tri-spoke gave Jacob his best CdA on the VENTUM of 0.226.
This represents an improvement of 9% on CdA equivalent to a power saving of 21W@42Kph
To eliminate any doubt from some erroneous power data and the Rotor crank based power meter was replaced with Assioma power pedals.
The Zipp wheels were retested using the new power meter data and the previous CdA of 0.248 was repeated.
Retesting the Kú race wheels confirmed a CdA of 0.226. This was Jacobs lowest CdA on the VENTUM.
The data below was achieved in a velodrome test with values compared at a constant velocity of 42kph or a normalised power of 230W
Jacobs TF1 was configured to closely match the VENTUM:
FastTT cockpit replaced with Zipp Vukka cockpit with identical stack and reach and to the VENTUM set up.
Kú spoked wheels 60/80 Vs Zipp 454 NSW’s
Jacobs baseline CdA, averaged across both baseline runs on his TF1 in this configuration, was 0.227.
This is an 8.5% improvement over the equivalent VENTUM set up with Zipp 454 NSW’s and represents a power saving of 20.5W@42kph.
Replacing the standard Kú wheels with the Kú race wheel configuration of rear disc and front tri-spoke resulted in a further improvement of CdA from O.227 to 0.208.
This is an improvement of 8% over the VENTUM configuration with the same wheels equivalent to a power saving of 19W@42kph.
Jacob would save 8 minutes over a full Ironman distance ridden at a constant power of 230W.
Adding the FastTT cockpit to the TF1 gave a marginal gain in CdA reducing to 0.200.
Jacobs lowest CdA of the test was 0.196 with a new World Triathlon compliant hydration set up of a double BTA.
CdA on the TF1 alone improved by a total of 13.7% from a baseline of 0.227 to a final of 0.196.
This represents a saving of 30W@42kph from tuning and equipment, or a time saving of 12 minutes 46 seconds over a full Ironman distance ridden at a constant power of 230W.
Aerodynamic Efficiency: The comparison between Jacob’s best setup on the VENTUM and the closest comparable set up on the TF1 showed a significant aerodynamic improvement on the TF1. The difference in CdA between the VENTUM, (0.227) and the TF1, (0.208) was 8%.
Power Savings: At an average speed of 42 km/h over an Ironman distance, the 8% difference in CdA corresponds to a 19-watt power saving for Jacob on the TF1 compared to the VENTUM.
Time Gains: This power saving would result in a time reduction of 8 minutes over a full Ironman distance when riding at a consistent power output of 230 watts.
The data below was achieved in a velodrome test with values compared at a constant velocity of 40kph or a normalised power of 230W
The Kú TF1
demonstrates a 8% saving
over the VENTUM
The Kú TF1 saved
Jacob 19 watts at
42kph over the VENTUM
Over a full Ironman distance ridden
at 230W Jacob would save 8 minutes
on the TF1 compared to the VENTUM
If Jacob had raced the set-up he acquired directly from VENTUM, using the Profile Design cockpit and his Zipp 454 NSW wheel set he would have been giving up 34.62W@42 kph compared to a standard base model TF1.
This is a time lost to a standard TF1 of 13minutes over a full Ironman raced at a constant power of 230W
With a cockpit change and specialised tuning of his fit by Jo Spindler, (a service that is included with any TF1 purchase) it was possible to find similar saving modifying the VENTUM.
The best recorded CdA for Jacob with the VENTUM was achieved by adding the Zipp Vukka cockpit and the Kú race wheels and was easily matched by a standard base model configuration of TF1.
At any comparable level of configuration of fit and or equipment the TF1 conservatively offered close to 20W@42kph or a time saving of 8 minutes over a full Ironman ridden at a constant power of 230W.
As a fun point of interest; the total savings from first baseline test on the VENTUM to the last tuned TF1 configuration represented a 27% improvement in CdA. This is equivalent to 70.25W@42kph or a time saving of 27minutes and 26 seconds over a full Ironman distance ridden at a constant power of 230W.
The meticulous testing and analysis conducted for all athletes attending Kú Aerocamps underlines the importance of tailored bike fitting, equipment configuration, and continuous refinement of race setups for achieving peak performance in competitive cycling.
For Sales Enquiries:
Ed Grace
ed@ku-cycle.com
+44 7894 307395
Media Contact Kú Cycle:
Alex Bok
alex@ku-cycle.com
+31 (0) 683 033 920
About Kú Cycle
A Dutch based company with a mission to design bikes and performance solutions that will change the sport forever – the perfect fit between body and machine. We believe a rider’s position should be established independent of the bike and will therefore reposition bike fitting services from a post-purchase service to a pre-purchase service. A new production process (built-to-order) and a completely different sales model are introduced with a single objective: athlete performance delivered!
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Email: info@ku-cycle.com
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