E-Bike Tire Sidewall Numbers Explained: PSI, ETRTO, Load Ratings, Size

•10 min read•By E-Bike PSI
educationtire-selectionsafetyspecificationsbeginner

Your Tire's Secret Code

Every tire sidewall is covered in numbers, letters, and symbols. Most riders ignore them. That's dangerous—these markings tell you exactly what your tire can (and can't) handle.

Critical information printed on sidewall:

  • Maximum and minimum PSI
  • Tire size (multiple formats)
  • Load capacity
  • Speed rating
  • E-bike specific ratings
  • Construction type

This guide decodes every marking so you can make informed decisions about PSI, tire selection, and safety.

PSI Ratings (The Most Important Numbers)

Finding PSI Markings

Location: Printed on tire sidewall, usually near the bead.

Common formats:

  • INFLATE TO 30-50 PSI
  • 220-350 kPa (30-50 PSI)
  • 2.0-3.5 BAR (30-50 PSI)
  • MIN 30 PSI / MAX 50 PSI

All formats show same info: Minimum and maximum pressure.

What "MIN PSI" Means

Minimum PSI = Lowest safe pressure for tire structure.

Below minimum risks:

  • Tire rolls off rim (bead unseating)
  • Excessive tire flex (overheating, failure)
  • Pinch flats (tube pinched between tire and rim)
  • Voided warranty

Example: Tire says "MIN 20 PSI"

  • ✅ Safe: 22 PSI (above minimum)
  • ⚠️ Risky: 20 PSI (at minimum, no margin)
  • ❌ Dangerous: 18 PSI (below minimum)

Rule: Never go below printed minimum.

What "MAX PSI" Means

Maximum PSI = Highest safe pressure before structural failure.

Above maximum risks:

  • Tire blowout (casing ruptures)
  • Bead blows off rim
  • Harsh ride quality
  • Reduced traction
  • Voided warranty

Example: Tire says "MAX 50 PSI"

  • ✅ Safe: 45 PSI (below max, leaves heat buffer)
  • ⚠️ Risky: 50 PSI (at max, no margin for heat)
  • ❌ Dangerous: 53 PSI (over max, blowout risk)

Rule: Stay at least 3-5 PSI below maximum (allows for temperature increase during riding).

PSI vs kPa vs BAR

Three pressure units, same concept:

PSIkPaBARCommon Use
302072.07US standard
402762.76US standard
503453.45US standard
604144.14US standard

Conversions:

  • PSI to kPa: Multiply by 6.895 (30 PSI = 207 kPa)
  • PSI to BAR: Divide by 14.5 (30 PSI = 2.07 BAR)
  • kPa to PSI: Divide by 6.895 (207 kPa = 30 PSI)
  • BAR to PSI: Multiply by 14.5 (2.07 BAR = 30 PSI)

US riders: Use PSI. Most pumps and gauges default to PSI.

Tire Size Markings

Three Size Formats (Same Tire, Different Numbers)

Example tire can be marked:

  1. 27.5 x 2.4 (ISO/Common format)
  2. 650B x 2.4 (French designation for 27.5")
  3. 62-584 (ETRTO format)

All three describe the same tire. Let's decode each.

ISO/Common Format (27.5 x 2.4)

Format: [Wheel Diameter] x [Tire Width]

Example: 27.5 x 2.4

  • 27.5" = wheel diameter (also written as 650B)
  • 2.4" = tire width at widest point

Other common sizes:

  • 20 x 3.0 (Lectric XP, fat folders)
  • 26 x 4.0 (Fat tire e-bikes)
  • 27.5 x 2.2 (Standard e-bike)
  • 29 x 2.1 (Larger diameter trail bikes)
  • 700 x 35C (Road/hybrid format, also written 700x35c)

Note: 700C = approximately 29" diameter (road/hybrid standard).

ETRTO Format (62-584)

ETRTO = European Tire and Rim Technical Organization

Format: [Width]-[Bead Seat Diameter]

Example: 62-584

  • 62mm = tire width
  • 584mm = bead seat diameter (BSD)

Why ETRTO is better:

  • Precise (no ambiguity)
  • Matches tire to rim accurately
  • Used by manufacturers for compatibility

Common ETRTO sizes:

ETRTOISO SizeDescription
50-40620 x 2.0Compact wheel
75-40620 x 3.0Fat folder
100-55926 x 4.0Fat tire
57-58427.5 x 2.25Standard e-bike
62-58427.5 x 2.4Plus e-bike
37-622700 x 35CRoad/hybrid

When to use: Checking tire-to-rim compatibility. Bead seat diameter must match.

French Format (650B, 700C)

Old system, still used:

  • 650B = 27.5" diameter
  • 700C = 29" / road bike size

Not precise: Doesn't tell you tire width, only approximate diameter.

Ignore for e-bikes: Use ISO (27.5 x 2.4) or ETRTO (62-584) instead.

E-Bike Specific Markings

ECE-R75 Rating (European Standard)

Marking: E-25 or E-50 (sometimes just the number in a circle)

What it means:

  • E-25: Rated for 25 km/h (15.5 mph) — Class 1/2 minimum
  • E-50: Rated for 50 km/h (31 mph) — Recommended for Class 3

Why it matters:

  • E-bike rated tires have reinforced casings
  • Tested for motor torque and sustained speed
  • Required in Europe, optional in US (but recommended)

Look for E-50 if:

  • You ride Class 3 (28 mph)
  • You frequently hit 20-25 mph
  • You haul heavy cargo (stress similar to speed)

E-Bike Pictogram

Symbol: Bicycle with electric bolt, sometimes just "E-BIKE"

Meaning: Tire is designed/tested for e-bike use.

Advantages:

  • Thicker sidewalls (pinch flat resistance)
  • Heat-resistant rubber compounds
  • Higher load ratings
  • Better puncture protection

Not legally required in US, but smart choice.

"E-BIKE READY" vs "E-BIKE RATED"

E-Bike Ready: Marketing term, minimal testing E-Bike Rated (ECE-R75): Actual certification, tested to standard

Prefer: E-Bike Rated (look for E-50 marking).

Load Index and Capacity

Load Index Number (Rare on Bicycle Tires)

More common on motorcycle/moped tires, but some e-bike tires include it.

Format: Two or three-digit number (e.g., 62 or 125)

Example: 62 = 265 kg (584 lbs) max load per tire

For e-bikes: Usually not printed (overkill for bicycles). Ignore unless present.

Weight Limit Markings

Some cargo e-bike tires include explicit weight limits:

  • MAX LOAD 150 KG (330 lbs per tire)
  • CARGO RATED

Found on:

  • Schwalbe cargo tires (Pick-Up, Super Moto-X)
  • Some Kenda heavy-duty tires

If present: Respect the limit. Total bike + rider + cargo shouldn't exceed tire rating x 2.

Construction and Compound Markings

TPI (Threads Per Inch)

What it is: Casing density (how many threads in tire fabric).

Common TPI ratings:

  • 30-60 TPI: Budget/durable tires (thicker, heavier, more puncture resistant)
  • 60-120 TPI: Mid-range (balance of weight and durability)
  • 120+ TPI: Performance/lightweight (supple, less durable)

For e-bikes: 30-60 TPI is ideal (durability over weight savings).

Tire Casing Types

Markings:

  • KEVLAR: Kevlar beads (foldable tire, lighter)
  • WIRE: Steel wire beads (non-foldable, heavier, cheaper)
  • PLUS: Reinforced casing (thicker sidewalls)
  • PROTECTION: Puncture protection layer

E-bike recommendation: Look for "PLUS" or "PROTECTION" (durability matters).

Rubber Compound Codes

Examples:

  • ADDIX (Schwalbe): Rubber compound family
  • BLACK CHILI (Continental): Performance compound
  • DUAL COMPOUND: Two rubber types (hard center, soft edges)

Impact on PSI: Softer compounds grip better at lower PSI. Harder compounds need proper inflation for efficiency.

Tubeless Markings

Tubeless Ready (TLR, TR, UST)

Markings:

  • TLR = Tubeless Ready
  • TR = Tubeless Ready
  • UST = Universal System Tubeless (older standard)
  • TUBELESS = Generic tubeless compatible

What it means:

  • Tire bead designed to seal against rim
  • Airtight casing (no tube needed)
  • Can be run with tubes if desired

Not tubeless-ready: Can sometimes be converted with sealant/tape, but not ideal.

Hookless Compatible

Marking: HLC or HOOKLESS COMPATIBLE

What it means: Works with hookless rim designs (straight rim walls, no bead hooks).

PSI impact: Hookless rims have lower max PSI (often 72 PSI max, check rim spec).

Important: Not all tires work with hookless rims. Check compatibility.

Direction and Rotation Markings

Directional Arrows

Marking: Arrow on sidewall, labeled DIRECTION or ROTATION

Meaning: Tire has directional tread (must mount with arrow pointing forward).

Why it matters:

  • Wrong direction = reduced traction
  • Especially critical for knobby/aggressive tread

How to install: Arrow points forward when bike rolls forward.

"FRONT" and "REAR" Markings

Some tires are specific to front or rear.

Example: Schwalbe Magic Mary (front) vs Hans Dampf (rear).

Why: Tread pattern optimized for braking (rear) or steering (front).

If not marked: Tire can go either location.

Manufacturing Date Code

Week and Year of Manufacture

Format: Four-digit code (e.g., 2423)

  • First two digits = week of year (24)
  • Last two digits = year (23 = 2023)

Example: 2423 = 24th week of 2023 (June 2023)

Why it matters: Tires degrade over time. Replace if:

  • 3+ years old (regardless of tread)
  • 5+ years old (definitely replace, safety risk)

Where to find: Small numbers molded into sidewall, often near bead.

Safety and Certification Marks

ISO, ASTM, CE Marks

What they mean:

  • ISO: International standards compliance
  • ASTM: American Society for Testing and Materials
  • CE: European Conformity (safety standards)

All indicate: Tire passed minimum safety testing.

Absence doesn't mean unsafe, but presence is reassuring.

Country of Origin

Marking: MADE IN [COUNTRY]

Common countries:

  • Thailand (Schwalbe, others)
  • China (many brands)
  • Vietnam (growing)
  • Germany (high-end Schwalbe)

Quality varies by manufacturer, not country. Schwalbe Thailand = excellent. Generic China = variable.

Real-World Sidewall Reading Examples

Example 1: Standard E-Bike Commuter Tire

Sidewall reads:

SCHWALBE MARATHON PLUS
27.5 x 2.0 (50-584)
E-50
INFLATE TO 50-70 PSI
350-480 kPa / 3.5-4.8 BAR
SMARTGUARD / ENDURANCE / REFLEX
TPI 67
MADE IN THAILAND

Translation:

  • Size: 27.5" diameter, 2.0" width (ETRTO 50-584)
  • E-50 rated (good for Class 3, 28 mph)
  • PSI: 50-70 (run 50-65 for e-bike use, leave headroom)
  • Features: Puncture protection (SmartGuard), reflective sidewall (Reflex)
  • Quality: 67 TPI (durable), made in Thailand (high quality)

Example 2: Fat Tire E-Bike

Sidewall reads:

KENDA KRUSADE
26 x 4.0 (100-559)
E-BIKE READY
15-30 PSI
100-210 kPa
WIRE BEAD

Translation:

  • Size: 26" diameter, 4.0" width (ETRTO 100-559)
  • E-Bike Ready (marketing term, not certified E-50)
  • PSI: 15-30 (low pressure, good for comfort)
  • Wire bead (not foldable, heavier but cheaper)

Example 3: Tubeless Gravel Tire

Sidewall reads:

CONTINENTAL TERRA SPEED
27.5 x 2.2 (55-584)
TUBELESS READY
PROTECTION LAYER
40-65 PSI
FOLD / TUBELESS
BLACK CHILI COMPOUND

Translation:

  • Size: 27.5 x 2.2" (ETRTO 55-584)
  • Tubeless Ready (can run without tube)
  • PSI: 40-65 (firm for gravel speed)
  • Foldable (Kevlar bead, lighter)
  • Black Chili (Continental's performance compound)

Common Sidewall Marking Mistakes

Mistake 1: Ignoring MIN/MAX PSI

Problem: Inflating based on feel, not markings.

Result:

  • Below min = bead unseating, pinch flats
  • Above max = blowout risk

Fix: Always check and respect printed min/max.

Mistake 2: Mixing PSI Units

Problem: Pump shows BAR, gauge shows PSI, tire marked in kPa—confusion ensues.

Result: Inflating to wrong pressure (e.g., thinking 3.0 BAR = 30 PSI, actually = 43.5 PSI).

Fix: Convert to consistent unit (PSI for US). Use conversion table above.

Mistake 3: Ignoring E-Bike Rating

Problem: Using non-e-bike tire on Class 3 e-bike.

Result:

  • Tire not designed for sustained 25-28 mph
  • Premature wear, potential failure
  • No E-50 certification

Fix: For Class 3, look for E-50 marking. For Class 1/2, any quality tire okay.

Mistake 4: Not Checking Manufacturing Date

Problem: Buying 5-year-old "new" tire from shop shelf.

Result:

  • Rubber degraded from age
  • Reduced performance, safety risk
  • Wasted money

Fix: Check date code before buying. Avoid tires over 2 years old.

Using Sidewall Info to Calculate PSI

Our calculator uses tire size and PSI range from sidewalls to generate safe recommendations.

Open Calculator

Input tire size (from sidewall), your weight, and cargo. Calculator ensures recommendations stay within your tire's min/max PSI range.

Final tip: Take a photo of your tire sidewall with your phone. Store it in notes. When buying replacements or checking specs, you'll have all info handy. No more squinting at dirty sidewalls in bike shops.

Last updated: November 14, 2025

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