Wheel 1 on 1

A2 Wind Tunnel Tire Study Part 1

In Part 1 of this series, we are going to look at the effect tires have on aerodynamic drag.  The first time we visited the A2 Wind Tunnel back in April of 2011, we were shocked by how much of a difference tires could make.  We always wondered how much better our results could have been if we had the budget to test a long list of tires.

In November of 2015, four and a half years after our first round of testing, Jon and I went back to the A2 wind tunnel with our new 2016 wheel line.  During our two day visit, we conducted what is rumored to be the largest tire study to ever take place at the A2 Wind Tunnel.  In total, we tested 20 different tires on our new FLO 60 Carbon Clincher to get an accurate look at how tires effect aerodynamics. 

What Will Be Covered in Part 2
Aerodynamic drag is only part of the tire equation.  On top of overcoming the aerodynamic drag created by your tire, you also have to overcome it’s rolling resistance while riding.  A tire that has a low aerodynamic drag, could have a high rolling resistance.  When you combine the two components, the tire as a whole would be a poor performer.  Tires that have the best combination of aerodynamics and rolling resistance are the best tires to use while racing.

I sent Tom Anhalt the majority of the tires we tested in the A2 Wind Tunnel to test on his rollers.  In Part 2 of this series, we will combine both aerodynamic drag and rolling resistance to find the best overall tire.

For now, let’s focus on the results of the aerodynamic testing.  

The Test
Below are the parameters of the aerodynamic drag test performed at the A2 Wind Tunnel.  We used the parameters listed below to eliminate as many variables as possible. 

– Wind tunnel wind velocity was set to 30mph.
– All tires were tested on the same FLO 60 Carbon Clincher.
– Tire pressure was set to 95psi and calibrated with a digital pressure gauge.
– Drag measurements were recorded at 0, 2.5, 5.0, 7.5, 10.0, 12.5, 15.0, 17.5, and 20.0 degrees of yaw.
– At each yaw angle, two measurements were taken and averaged.
– Tare was measured and removed from the results.



The Tires

We tested 20 tires in total.  The tires ranged in size from 22mm to 25mm in width.  We did not test tires less than 22mm because they are too narrow to use on our wheels, and we did not test tires wider than 25mm because they too commonly do not fit on today’s road bikes.  Here is the list of tires we tested.

* Listed tire sizes are based on the manufacturer’s naming conventions.  Please keep in mind that a tire’s width may not measure as stated when on a rim.  For example, a 23mm tire may measure 26mm in width when installed on a rim.  Please keep this in mind when selecting tires for your frame.
The Results
We have created two Drag Charts.  The first in Grams of Drag and the second in  CdA (m^2).  These interactive charts allow you to turn individual tires on and off.  Placing all 20 tires on the same chart makes things very cluttered, as you can see below.
 
 
Time Savings
Aero charts are great, but what does all of this mean.  Exactly how much time does each tire save you on the road, and which tire is the best aerodynamically speaking?  In the table below, we have listed how much time each tire will save you over a 40km race, and an Ironman.  We have used the slowest tire as the baseline with a time savings of 0 seconds.  These time savings are calculated using our Net Drag Reduction Value (NDRV) equation.  Our NDRV equation was developed using the 110,000 real world data points we collected while developing our new wheel line.  Learn more about NDRV.  
 
I hope you enjoyed this blog article.  Stay tuned for Part 2 of this series where we look at the rolling resistance of each tire, and combine that data with our aero results.  Please leave your questions and comments below.

Jon Thornham

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