Quote:
Originally Posted by Jan Heine
Even at the very high speeds you tested – few of us can hold 30 mph for very long – rolling resistance differences between different tire models has a much greater effect than the wind resistance you measured. That is why the pros always ride on hand-made tires for the important TTs...
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You've probably seen the tests done by Flo Cycling to find the best tires to use with their aerodynamic wheels:
http://flocycling.blogspot.com/2016/...ire-study.html
In this study, they did wind tunnel tests using 20 different tires (some were the same model but in different widths) on one of their aerowheels, and also had rolling resistance tests done on the tires. They combined the aero drag with the rolling drag to come up with the overall best performing tire. If you take a look at their data, you'll see that tire rolling resistance was the biggest factor in wheel performance. The tire at the top of the list placed only 11th out of 20 on aerodrag, but was tied for 1st for rolling drag.
Digging deeper into the data, some interesting things can be seen. The wind tunnel test was performed at a speed of 30 mph. At the yaw angles experienced most frequently by cyclists, the average drag experienced by the different tires varied between about 90 and 125 grams, which results in drag powers of about 12 - 16 Watts. The rolling resistance tests were performed at 35 kph (21.8 mph), and produced drags of between about 12 and 20 Watts. Scaling up the rolling resistance losses to 30 mph yields drag powers of between 16 and 27 Watts. So it can be clearly seen that even at 30 mph rolling resistance is greater than aero drag, and also that variations in rolling resistance between tires is greater than the variations of aero drag between tires. Since very few people spend a lot of time at 30+ mph, and because aerodynamic losses increase with the cube of speed (rolling resistance losses only increase linearly with speed), at the speeds most people ride rolling resistance losses will be proportionately even larger than aero losses than is shown in the test data.
Flo Cycling designed their latest aerowheels around the 23mm Continental GP4000s (a natural choice as they had found that this tire was the most aero in a previous test of several tires). So it is not surprising that this tire had the lowest aerodynamic drag of all the tires in this test. But what they found in this new test is that not only did the GP4000s only place 4th when both aero and rolling losses were combined, but that the wider 25mm version of this tire was overall better, even though the wider version was not as well aerodynamically matched to the wheel.