Folding Bike Tyre Sizes Guide

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Understanding folding bike tyre sizes

Folding bikes use specific tyre sizes that differ from regular bikes. Finding correct replacements requires understanding the sizing system. This guide explains ETRTO sizing, common folding bike tyre sizes, and how to find appropriate replacements for your folder.

How bicycle tyre sizing works

Two sizing systems exist:

Inch sizing (traditional, less accurate)

Format: 20 x 1.75 (diameter x width)

Problem: Same inch size may refer to different actual sizes. "20-inch" can mean 406mm, 451mm, or 419mm ETRTO.

ETRTO sizing (definitive, always accurate)

Format: 40-406 (width-diameter in mm)

The three-digit number (406) is the rim diameter. This is the definitive measurement. Always match this number when buying tyres.

Where to find size

Check current tyre sidewall. Look for format like:

  • 35-349 (16 x 1.35)
  • 47-406 (20 x 1.75)
  • 28-451 (20 x 1 1/8)

The three-digit ETRTO number (349, 406, 451) must match. Width (first number) can vary within frame clearance limits.

Common folding bike tyre sizes

16-inch wheels (Brompton, some compact folders)

ETRTO: 349mm

Common widths:

  • 35-349 (16 x 1.35): Standard Brompton
  • 40-349 (16 x 1.5): Slightly wider for comfort
  • 28-349 (16 x 1 1/8): Narrower for speed

Note: 349mm ETRTO is specific to 16-inch folders. Not interchangeable with other 16-inch sizes (305mm exists for some BMX bikes).

20-inch wheels (most Tern, Dahon, Decathlon folders)

ETRTO: 406mm (most common)

Common widths:

  • 40-406 (20 x 1.5): Standard for many folders
  • 47-406 (20 x 1.75): Wider for comfort/grip
  • 50-406 (20 x 2.0): Very wide, check frame clearance
  • 37-406 (20 x 1.35): Narrower for speed

ETRTO: 451mm (less common)

Some Tern and Dahon performance models use 451mm (not 406mm). Check carefully.

  • 28-451 (20 x 1 1/8): Common size for 451mm rims
  • 32-451 (20 x 1.25): Slightly wider

451mm and 406mm are NOT interchangeable despite both being "20-inch."

24-inch wheels (rare, some large folders)

ETRTO: 507mm

Less common in folders. If you have 24-inch, check ETRTO on sidewall.

Finding replacement tyres

Step 1: Identify current size

  1. Check tyre sidewall for ETRTO code (XX-XXX format)
  2. Note three-digit number (rim diameter - must match)
  3. Note two-digit number (tyre width - can vary within limits)
  4. Photograph sidewall if unsure

Step 2: Decide on width

Can you change width?

  • Yes, within frame clearance limits
  • Typically +/- 5-10mm width acceptable
  • Check clearance: spin wheel, verify 5mm+ gap to frame/mudguards
  • Wider = more comfort, grip, puncture protection
  • Narrower = lighter weight, less rolling resistance

Step 3: Choose tyre type

For commuting:

  • Puncture-resistant (Schwalbe Marathon, Continental Contact)
  • Reinforced sidewalls
  • Good wet grip
  • Higher price (£25-40 per tyre) but fewer punctures

For leisure/weekend:

  • Standard tyres adequate
  • Budget options fine (£10-20 per tyre)
  • Replace more frequently

For performance:

  • Lightweight tyres (Schwalbe Kojak, Marathon Racer)
  • Lower puncture protection
  • Faster rolling

Popular folding bike tyres

For Brompton (349mm)

  • Schwalbe Marathon: Excellent puncture protection, long life. £35-40 each.
  • Schwalbe Marathon Racer: Lighter, faster. Good protection. £30-35.
  • Schwalbe Kojak: Lightweight, fast. Less protection. £28-32.
  • Continental Contact: Good all-rounder. £25-30.

For 20-inch (406mm)

  • Schwalbe Marathon: Commuter standard. £30-38.
  • Kenda Kwest: Budget option. £12-18.
  • Continental Ride Tour: Good value. £18-25.
  • Schwalbe Big Apple: Very wide, comfortable. £35-40.

Changing folding bike tyres

Process is standard bicycle tyre change:

  1. Deflate tyre completely
  2. Use tyre levers to remove one side of tyre from rim
  3. Remove inner tube
  4. Check rim tape is intact (protects tube from spoke holes)
  5. Insert new/repaired tube (inflate slightly to give shape)
  6. Fit tyre onto rim (start opposite valve)
  7. Work tyre bead into rim (use levers carefully if tight)
  8. Ensure tube not pinched under tyre bead
  9. Inflate to correct pressure (check sidewall for range)

Tips

  • Remove wheel from bike for easier access
  • Start fitting tyre opposite valve
  • Check inside tyre for debris before refitting
  • Ensure direction arrows correct (if marked)
  • Use plastic levers (metal damages rims)

Where to buy folding bike tyres

  • Brompton official: Guaranteed fit for Bromptons, quality tyres
  • Local bike shops: Can advise on fit, check stock
  • Online retailers: Chain Reaction, Wiggle, Amazon (verify size carefully)
  • Decathlon: Budget options for their folders
  • Specialist folders shops: Often stock less common sizes

Always verify ETRTO size before purchasing. Returns difficult if wrong size ordered.

Extending tyre life

  • Maintain correct pressure (check weekly)
  • Remove embedded debris (glass, flints) promptly
  • Avoid kerbs and potholes
  • Store bike away from sunlight (UV degrades rubber)
  • Replace when tread worn or sidewalls cracked

Quality commuter tyres: 2,000-4,000 miles typical. Budget tyres: 1,000-2,000 miles.

Final tyre advice

Tyres are critical for safety and performance. Invest in quality tyres for commuting (puncture protection worth the cost). Budget tyres adequate for leisure use.

Always match ETRTO size exactly. Width can vary within frame clearance.

Keep spare inner tubes and tyre levers for roadside repairs.

Related: Servicing guide | Resources