Going Aero: New(ish) trends in tires.

I’ve spent quite a bit of time gushing about my love for my ENVE Smart 3.4 Carbon Clincher wheelset.  They’re the car-bomb, and aero to boot.  Bike design is going aero all over, and yet trying to stay within UCI rules.  The serious players are integrating brakes, using modified, truncated airfoil shapes (e.g. Trek’s Kammtail frame shaping), and otherwise doing everything possible to make bikes more aero without sacrificing ride quality, efficiency, weight or handling.  As the options for obvious improvement start to narrow, companies are looking for an edge–literally.

Today’s post will cover two different approaches to a common problem: minimizing wheel/tire drag.  Back in 2010, Trek released the R4 Aero, which features a modest change in sidewall profile intended to create a little aero spoiler/lip to shuffle airflow past the seam where the tire bead meets the wheel.

If you look closely at that picture, you can just see that above the brake channel on the wheel, there is a slight bevel in the sidewall, just above the edge of the rim.

Mavic has taken a different approach with their Cosmic CXR 80 wheel set/tire combination.  Their approach is to use a wheel and tire designed to work together, and then a separate rubber seal designed to smooth airflow between the two, and prevent turbulent air from being generated by the edge of the wheel.

In that picture (above), you can see how it has a little lip that engages the groove between tire and rim.

Here, you can see that the strip is soft, and doesn’t pose any issues relative to bump absorption.

And here’s the combined interface, installed.

The above-pics are originally featured on Bike Rumor’s post on this topic.

I’ll be curious to see whether these efforts are adopted by other manufacturers.  On one hand, for a race bike, if these provide a tangible aero benefit, there is a minimal weight penalty.  For racers who don’t have to worry about quick tire changes, the hassle of dealing with that issue isn’t a problem.  On the other hand, for everyday riders, this isn’t likely to be a hugely meaningful piece of kit.

What I do like about it, however, is that it is a relatively cheap, simple solution that cleans up another area of the bike.  Given the amount of surface area of rim/bead that is exposed to the wind while riding, this is a sensible place to look.  I’d put this into the category of “things that are clever, but which I’m likely never going to actually use.”


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