In modern performance cycling engineering, the wheel and tire are not treated as separate components, but as one integrated aerodynamic and mechanical system. We define “speed” not by maximizing pressure, but by precise control of energy losses in tire deformation (that is, higher rolling resistance).
The modern speed model is based on minimizing two key variables: rolling resistance caused by friction of materials inside the tire, and energy losses generated by micro vibrations of the rolling tire.
1. Relation between tire profile and rim geometry
The match between tire and rim determines handling stability and smooth airflow. Mistakes at this stage create turbulence, which can cancel the benefits of a deep rim.
Moving beyond the 105% rule: The old idea that the outer rim width must be at least 105% of the tire width is losing importance with modern shapes. It was relevant for older V-shaped rims.
Wind tunnel tests show that system efficiency depends more on parameters such as frontal profile (rim shape geometry) and the vertical position of the maximum width.
Effect of internal width: Increasing internal width (current standard 21–25 mm) changes tire geometry in a fundamental way. Reducing the “light bulb” effect and moving to more parallel sidewalls increases air volume and lateral stability. This prevents the tire from “floating” in corners, which is very important when using lower pressure.
Key Conclusions:
Aerodynamic optimization of modern carbon rims shows that the old “105% rule” simply does not work in practice. Many new wind tunnel tests show no clear relation between rim-to-tire width ratio and final air drag. Because of this, changing tire width (for example in the 25–32c range) does not have to create big aerodynamic differences. These depend only on the individual rim shape and profile, not on a simple ratio. Even if there are some aerodynamic differences in this tire width range, at 40 km/h they are very small and within the measurement error of about ±2 W.
2. What is tire rolling resistance?
Tire resistance comes from the fact that during rolling it works like a “double spring”: on one side there is compressed air, and on the other side the rubber of the casing and tread, which constantly deforms at the contact point with the ground. Each cycle of bending and returning to shape uses energy because of internal friction.
Because of this, using very flexible materials, such as soft casings, tubeless system, or modern TPU tubes, reduces this “internal friction” and allows the tire to work smoothly without unnecessary energy loss = power = speed.
System analysis: Data from independent cycling industry tests show almost the same rolling resistance for tubeless tires and latex tube setups. The advantage of the tubeless system does not come from lower internal friction, but from the ability to safely use lower pressure, which greatly reduces deformation losses (in simple words: energy loss). TPU tubes are the best compromise between rotating weight and efficiency, clearly better than standard butyl tubes.
System comparison
(Speed 40 km/h, Pressure 5.5 bar, GP5000 class tire):
| System | Rolling resistance (1 wheel) | System weight (1 wheel) |
|---|---|---|
| Tubeless + Sealant | 11.5 W | ~ 100 g* |
| Latex Tube | 11.5 W | 80 g |
| TPU Tube (Continental) | 12.5 W | 35 g |
| Butyl Tube | 16.5 W | 105 g |
*tubeless: includes the weight difference of a tubeless tire compared to the same model for tube use; includes 60 ml of sealant and a 5 g valve.
Interpretation: Moving from a standard butyl tube to a tubeless system or latex tube can save about 10 watts for a full wheelset at 40 km/h. Choosing a high-end TPU tube like Continental or Pirelli is an effective way to reduce rotating weight while keeping very low rolling resistance. Tubeless has the lowest rolling resistance, but only slightly better than high-quality TPU tubes.
3. Tire dynamics
The choice of tire width (popular range 28c–32c) must follow the casing construction (the internal structural layer of the tire that defines strength and shape).
In a simple model, the tire is a system of a rubber spring (material) and an air spring (pressure).
- Energy loss vs flexibility: Tires with very high TPI (for example Vittoria Corsa Pro, Rene Herse) are very flexible. Their losses are so low that pressure is no longer the main limit for speed on smooth asphalt. A wider tire (for example 32c) at lower pressure creates a shorter but wider contact patch, which reduces sidewall bending and energy loss while also absorbing vibrations.
- Penalty for stiffness: Training tires with thicker casing (more stiff) need high pressure to reduce energy loss. Lowering pressure in these tires causes a big increase in rolling resistance, while high pressure creates losses through vibrations—especially on rough or uneven asphalt.
- Rider conclusions: A 28–30c tire remains the gold standard for aerodynamics while keeping low weight. Tire width alone is not the main factor for rolling resistance (rubber compound is more important), but a wider tire (for example 35c) has a larger frontal area, which reduces aerodynamic performance.
4. Pressure control and friction coefficient
Pressure is the main control parameter for safety and energy loss.
- Grip: Center Grip (middle of the tire) is much more sensitive to pressure changes than Edge Grip (side grip). At high pressure, the tire becomes more “pointed”, which reduces the contact area in a straight line.
- Cornering stability: At a lean angle of 35 degrees, lower pressure allows the tire to better follow the texture of the asphalt. For most modern road wheels, a 28–30c tire at 5.0–5.5 bar gives maximum contact area without risk of side instability. Even for heavier riders, up to 6.0 bar in a 28c tire is enough and improves grip while keeping low rolling resistance.
5. Summary: Setup configuration
To optimize rolling resistance, aerodynamics (CdA), comfort, grip, and puncture resistance, the wheel setup must match the road surface and your training or racing priorities.
- Scenario A
(Training – Road racing / mixed asphalt quality / changing weather):
28–32c tire (recommended: Pirelli P Zero Race / RS version, Continental Grand Prix 5000 S). System: Tubeless or TPU tubes, pressure 5.0–6.0 bar. This setup reduces energy loss from too stiff tires and gives maximum grip on wet asphalt. - Scenario B
(Perfect smooth asphalt / Time trial / Triathlon):
25–28c tire (for example Continental Grand Prix TT, Michelin Power TT, Vittoria Corsa Pro Speed). System: Tubeless or TPU. Pressure optimized for aerodynamics (higher, about 6.0 bar, but not above the point where vibrations become noticeable).
Final conclusions
Modern aerodynamic tests have disproved the “105% rule”, showing that air drag mainly depends on the individual rim shape, and any losses from using a wider tire are very small. Tests also show that an optimized tubeless system and classic latex tubes or modern TPU tubes are equally fast, while the traditional butyl tube creates the highest power loss (but it is the cheapest and easiest to use).
