Are your 30mm tyres killing your aero gains? A wind tunnel test

Wide road bike tyres are the future, or so the marketing departments tell us as they roll out frames with clearance for 35 mm or even 40 mm rubber. But as GCN Tech asked in a recent video, "are these wider tires killing the performance of your expensive aero wheels?"

It’s the right question. To get some hard data, the GCN team took the two most popular tyre sizes—28 mm and 30 mm—to the wind tunnel at the Silverstone Sports Engineering Hub.

For many riders, the choice between a 28 mm and a 30 mm tyre is a practical one, often dictated by what an older frame can handle. The results offer a clear look at the trade-offs between pure aerodynamics and real-world ride quality.

The Test Setup

To get a clean comparison, GCN's methodology was straightforward and robust, controlling for key variables.

• Wheels: Hunt 5AM Limitless
• Tyres: Pirelli P ZERO Race TLR in 28 mm and 30 mm widths
• Test Speed: 45 km/h
• Protocol: A full yaw sweep from +20 to -20 degrees

The 45 km/h test speed is a classic wind-tunnel benchmark, typical of the professional peloton but faster than most amateurs average.

The yaw sweep is crucial, as it simulates performance not just head-on, but in the crosswinds experienced on the road.

What the Tunnel Said

After running both tyre sizes through the protocol, the data showed a small but measurable difference. Speaking with Hunt's Head of Engineering, Rob Fields, the takeaway was clear: the narrower tyre is aerodynamically faster.

According to Fields, "the 28s definitely hold that... aero advantage a little bit higher at wider yaw angles." He also noted a small advantage at lower yaw angles, closer to a direct headwind.

This isn't just about raw drag numbers. Performance at high yaw angles relates directly to stability, and the 28 mm tyre helped maintain clean airflow for longer, making the wheel more stable in simulated crosswinds.

So, case closed? Not quite.

Does It Actually Matter?

At 45 km/h, the 28 mm tyre holds a small aerodynamic advantage. The question is, how often does the average rider hold that speed?

The GCN presenter made this point himself. "The reality of my riding is a 30 kilometers an hour average speed, not 45," he said, anticipating the difference at that speed would be "next to no difference."

This is before considering the giant, unmeasured variable: rolling resistance. The wind tunnel measures aerodynamic drag only, not the energy lost to friction between the tyre and the road surface.

This is where wider tyres have their revenge. On the imperfect tarmac most of us ride, a wider tyre at lower pressure deforms more easily over imperfections, reducing vibration and lowering rolling resistance. The test was clean; the real world is not.

The Verdict: Go Wide, Worry Less

The data quantifies the penalty: a 30 mm tyre is fractionally less aerodynamic than a 28 mm on this particular Hunt wheel. For a professional chasing marginal gains or a time trialist at high average speeds, sticking with 28s might make sense.

For the rest of us, the argument for the 30 mm tyre is overwhelming. The improved comfort, increased grip, and likely lower rolling resistance on typical roads will be a far greater benefit than a few watts saved at speeds we rarely hold.

The GCN presenter summed it up: "If you really don't care about going fast, there's almost no good reason to not just use the widest tires that you can fit."

I’d take it a step further. Even if you do care about going fast, unless your rides are on glass-smooth surfaces, the wider tyre is probably the faster and smarter choice overall. Don't buy a new bike just to fit 30 mm tyres, but if your frame has the clearance, this test should give you the confidence to use it.