How to Read eBike Tire Specifications: Size, ETRTO, and PSI Explained

Choosing the right tire for your eBike isn’t just about finding the right size that “looks” about right. It involves decoding the numbers and markings printed on the sidewall of the tire, which represent size, structure, pressure range, and international standards. For cargo bikes and eBikes under varying loads and terrain, this knowledge is critical to ensuring safe, efficient, and long-lasting performance.

In this article, we’ll walk you through:

• How to read tire size (inch-based vs metric systems)
• What ETRTO numbers mean and why they matter
• Recommended tire pressure (PSI/bar) and how to adjust it
• Practical examples of common eBike and cargo bike tire sizes

Why Knowing Your Tire Size Matters

Your tires are the only part of your eBike that touches the ground. Get them wrong, and you may face:

• Poor performance: Sluggish acceleration, reduced range
• Safety hazards: Blowouts, rim failure, lack of traction
• Incompatibility: Tire won’t fit the rim, rubs the frame, or can’t maintain air pressure

Especially for cargo bikes, where load weight is much higher than standard bikes, tire specs directly affect load-bearing capability, braking distance, and road handling.

1. Inch-Based vs Metric Tire Sizing – Two Ways Ebike Tire Sizes Are Written

The Inch System (e.g., 26×2.0):

This traditional sizing method shows the outer tire diameter and the width in inches. For example:

• 26×2.0 means the tire has a 26-inch outer diameter and is 2.0 inches wide.
• 27.5×2.4 or 29×2.6 follow the same logic.

While intuitive, this system is inconsistent across brands because “26 inches” may not refer to the exact outer diameter due to differences in rim and bead seat.

The Metric/ETRTO System (e.g., 50-559):

This system, created by the European Tyre and Rim Technical Organisation (ETRTO), offers more precision. It shows:

• Tire width in millimetres (first number)
• Bead seat diameter (BSD) in millimetres (second number)

Example:

• 50-559: 50mm width, 559mm bead seat diameter (equivalent to 26×2.0)
• 55-406: 55mm width, 406mm BSD (often seen in 20″ cargo bikes)

Why ETRTO Matters:

• Ensures compatibility between tire and rim
• Avoids confusion between similar-looking but incompatible sizes
• Important when switching tire types (fat/slick/knobby)

If you’re buying from a serious bike shop or online store, ETRTO numbers help you avoid compatibility issues.

2. Common eBike & Cargo Bike Tire Sizes (Examples)

Knowing both size systems helps avoid mismatches when buying replacements or upgrades.

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3. Understanding PSI and Bar: Tire Pressure Explained

PSI stands for Pounds per Square Inch. It indicates how much air pressure the tire can safely hold.

Too low:

• Tire may feel soft and sluggish
• Higher risk of pinch flats (rim hits ground)
• Increases rolling resistance

Too high:

• Harsh ride
• Reduced grip
• Risk of blowout under heavy load or heat

Where to Find PSI

Your tire sidewall will show a range:

“Inflate to 45–65 PSI” or “Min 2.5 bar / Max 4.5 bar” (metric equivalent)

How Much PSI Do You Actually Need?

That depends on:

• Rider + Cargo weight: Heavier loads need higher PSI
• Tire width: Wider tires can use lower pressure safely
• Terrain: Lower PSI improves grip on loose terrain; higher PSI rolls better on asphalt
• Weather: Cold weather reduces internal pressure

Quick Guide (Approximate)

Always check the sidewall for the max rating, and use a quality gauge.

4. Bonus: Where to Find These Numbers

Tire specifications are molded into the sidewall rubber. Look for text like:

• ETRTO: e.g., 55-559
• Inch size: e.g., 26×2.0
• PSI range: e.g., Inflate to 35-65 PSI
• Brand/model: e.g., Schwalbe Marathon Plus

Why This Matters for Cargo Bikes

Cargo eBikes often carry 100kg+ including rider, cargo box, and load. That extra weight makes tire precision essential:

• Tire width affects comfort and stability
• Bead seat diameter ensures proper fit
• PSI affects rolling efficiency and motor strain

We’ve seen last-mile delivery fleets lose tire lifespan by 40% simply because they ran tires underinflated.

Don’t guess—measure, check the ETRTO, and monitor PSI weekly

Conclusion

Reading your eBike or cargo bike tire specifications is a fundamental skill that can save you from costly mistakes and unsafe riding conditions. By understanding both inch-based and ETRTO systems, and managing your PSI wisely, you ensure compatibility, comfort, and optimal performance.

Need help selecting tires for a specific eBike model or cargo setup? The Regen team is here to help—reach out to us for personalized recommendations and component matching support.

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