ETRTO 5775: Tubeless Rim and Tire Standards

Introduction

Modern bicycles are assembled from highly interdependent components, where precise compatibility directly affects not only performance but, more importantly, rider safety. As a result, multiple international standards and technical frameworks have been established by organizations such as ETRTO to regulate rim and tire interoperability.

Details

With the continued evolution toward wider tires and the growing adoption of hookless rim systems, rim–tire compatibility has become increasingly critical for wheel and tire manufacturers. At the same time, expanding size options and mixed interpretations of standards have created confusion among brands and product engineers.

The European Tyre and Rim Technical Organisation (ETRTO) defines standardized guidelines for tire and rim compatibility across bicycles, motorcycles, and other vehicles. Based on ISO 5775, these standards provide a reference framework for designing interoperable and safe wheel systems.

This article outlines key principles of ETRTO 5775 related to tubeless rim and tire fit, helping wheel brands and OEM partners make more informed engineering and product development decisions.

Rim and Tire Fit: Understanding the System Relationship

In rim–tire compatibility, the most critical parameter is the internal rim width, also referred to as nominal rim width in ETRTO documentation. This measurement represents the distance between the rim hooks or sidewalls.

A tire mounted on rims with different internal widths will not maintain a fixed geometry. Instead, the tire casing deforms into different shapes depending on the rim width, inflation pressure, and construction. In practice, three general system behaviors can be observed:

System Configuration	Wide tire + narrow rim	Matched rim & tire (optimal range)	Narrow tire + wide rim
Tire Shape	Rounded / lightbulb profile	Controlled, balanced profile	Squared / over-expanded profile
Engineering Outcome	Reduced casing support	Best structural efficiency	Excessive casing tension
Considerations	Lower cornering stability, increased tread deformation	Optimal grip, rolling efficiency, and stability	Reduced impact absorption, compromised cornering control, increased exposure of rim walls.

The optimal configuration is not an absolute value but a tested compatibility range, typically defined within ETRTO recommendations and refined by individual manufacturers.

Recommended Rim Width Ranges for Tire Sizes

ETRTO provides recommended internal rim width ranges for corresponding tire widths. These ranges are designed to ensure safe bead retention and predictable tire deformation under load.

Source: ISO 5775-1:2023

While the exact optimal pairing depends on tire construction and intended use, most modern wheel designs target the upper-middle range of the recommended spectrum, balancing stability, comfort, and aerodynamic performance.

Rim Geometry and Bead Retention in Tubeless Systems

ETRTO 5775 (aligned with ISO 5775-2) defines critical geometric parameters that ensure reliable tire retention and safe operation in both hooked and hookless systems.

Bead Seat Diameter (BSD)

The Bead Seat Diameter defines the precise diameter at which the tire bead interfaces with the rim. It is fundamental to wheel sizing compatibility and determines standard dimensions such as 20”, 24”, 26”, 27.5” (650B), and 29” (700C).

Size	Nominal Diameter	Measured rim diameter (tolerance ±0.5mm)
20”	451	450.45
24”	507	506.95
26”	559	559
27.5”/650b	584	584.1
29”/700c	622	621.95
32”	686	N/A

BSD precision is essential:

If the BSD is too large, tire mounting becomes excessively tight and may exceed safe installation force.
If the BSD is too small, bead seating may become unstable, increasing the risk of air loss or improper retention.

G-Height (Bead Hook / Retention Height)

The G-height defines the vertical bead retention structure of the rim sidewall:

Hooked tubeless rims: 5.5 mm ± 0.5 mm
Hookless tubeless rims: 6.0 mm ± 0.5 mm

This parameter plays a key role in maintaining bead stability under pressure and lateral load.

However, bead retention performance is not governed by a single dimension alone. It is the combined result of multiple interacting factors, including:

BSD precision
bead seat profile geometry
tire bead construction
inflation pressure range

In practice, rim designers must balance tire compatibility, structural strength, and intended riding application when optimizing bead hook geometry. Rim design under ETRTO guidelines is not a fixed formula but a system of engineering compromises.

Each design decision must be validated through system-level testing with real tire models, rather than relying solely on nominal specifications.

OEM/ODM Engineering Support for Wheel Development

At NTP, every rim system is developed with a focus on structural safety, performance consistency, and application-specific requirements.

Our engineering team evaluates each project based on ETRTO compliance, material behavior, and intended use cases to ensure reliable real-world performance.

We provide full OEM/ODM support, including:

Custom rim geometry and carbon layup development
Application-specific optimization (road, gravel, MTB, downhill)
Prototype sampling and validation testing
Scalable mass production with strict quality control
Branding, packaging, and global logistics support

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