The Impact of Tire Width on Carbon Wheel Aerodynamics

Introduction

In recent years, tire widths have grown from a skinny 23mm to the now-common 25mm, 28mm, or even wider. But how does this trend affect the aerodynamics of your carbon wheels? As it turns out, tire width isn't just a comfort or grip issue—it plays a crucial role in airflow, speed, and stability.

Let’s break down why choosing the right tire width is more than a personal preference—it’s a performance decision.

1. Wider Tires and the Aero “Teardrop” Shape

Modern carbon wheels are engineered with a specific tire shape in mind—often 25mm or 28mm tires. The goal is to create a seamless transition between the tire and rim, forming an airfoil-like profile that slices through the wind.

If your tire is too wide (say, a 32mm tire on a 28mm-optimized rim), this shape is disrupted. Airflow becomes turbulent, increasing drag and making your setup slower—especially at high speeds.

Key takeaway:

Matching your tire width to your rim profile maximizes aerodynamic efficiency.

2. Tire Width vs. External Rim Width: The 105% Rule

A common guideline is the “105% Rule”:

The external rim width should be at least 105% of the tire’s actual inflated width.

This ensures that the rim controls airflow better than the tire, maintaining laminar flow. For example, if your 28mm tire inflates to 30mm, the rim should be at least 31.5mm wide externally.

Failing to follow this rule can lead to a sharp aerodynamic penalty—especially in crosswinds.

3. Wider Tires = Better Rolling Resistance? Not Always.

Many riders believe that wider tires automatically mean lower rolling resistance. While that’s often true on rough or uneven surfaces, it’s not always the case at high speeds and smooth pavement—especially if the aerodynamic loss outweighs the rolling resistance gain.

For racers, where speeds are consistently 35–45 km/h+, aerodynamics start to dominate. A narrower, properly matched tire-rim combo might still be the fastest choice.

4. Crosswind Handling: Width Affects Stability

Wider tires can increase frontal surface area and change how your bike handles in sidewinds.
On deeper carbon rims, a too-wide tire can act like a sail, causing twitchy or unpredictable steering.

That’s why many pros still use 25mm tires in races with known wind hazards—even though they train on 28mm or 30mm tires.

5. The Tubeless Factor

Tubeless setups tend to inflate slightly wider than tubes due to lower internal pressure and tire construction. So your “28mm” tire might actually measure closer to 30mm once mounted and aired.

Always measure actual inflated width when planning an aerodynamic setup—not just what’s printed on the sidewall.

Conclusion: Tire Width Is Aerodynamics

Choosing a wider tire for comfort or traction is totally valid—but be aware of the aerodynamic tradeoffs.
For the fastest setup:

Check your rim's external width

Measure actual tire width once inflated

Follow the 105% rule for minimal drag

Choose the right width for your terrain and speed

In modern road cycling, tire width is no longer a “set it and forget it” spec—it’s a performance dial you can fine-tune.