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Wheel & Tire Size Guide
For Lowrider, Cruiser, and BMX bikes • Practical sizing info adapted from industry standards and the ISO/ETRTO system.
1) Understanding Tire Size Markings
Most tires show something like 26 × 1.75 or 20 × 2.125. The first number is the nominal outer diameter, the second is the width. Modern fitment is determined by the ISO/ETRTO bead seat diameter (BSD).
“Brown’s Law” (practical rule): If two tires look mathematically equal but one uses decimals (1.75) and the other uses fractions (1 ¾), they’re usually not interchangeable.
2) Tire Sizing Systems
| System | Example | Units | Common Use |
|---|---|---|---|
| Fractional (inch) | 26 × 1 3/8 | Inches (fractions) | Vintage English/Schwinn roadsters |
| Decimal (inch) | 26 × 2.125 | Inches (decimals) | Cruiser, Lowrider, MTB, fat tire |
| French | 700C, 650B, 650C | mm + letter | Road, touring, gravel |
| ISO / ETRTO | 54-559 (≈26 × 2.125) | Width-mm / BSD-mm | Modern standard—match the BSD |
If the BSD (second ISO number) matches your rim’s BSD, the tire will seat on the rim.
3) Common Wheel Sizes for Lowrider & Cruiser Builds
| Nominal Size | ISO (BSD) | Typical Use |
|---|---|---|
| 20″ | 406 | BMX, Lowrider classics, juvenile |
| 22″ | 457 | BMX cruisers, stretched customs |
| 24″ | 507 | Cruiser, juvenile MTB |
| 26″ | 559 | Beach cruiser, Lowrider, MTB |
| 27.5″ | 584 | Modern MTB (“27.5”) |
| 700C / 29″ | 622 | Road, hybrid, 29er MTB |
| 16″ | 305 | Kids, folders, trikes |
| 12½″ | 203 | Mini bikes, scooters |
Marketing names like “29″” and “27.5″” often map to ISO 622 and 584 respectively.
4) Rim ↔ Tire Width Compatibility
Match tire width to rim inner width for safe handling and durability.
| Rim Inner Width (mm) | Recommended Tire Width (mm) |
|---|---|
| 13–15 | 18–25 |
| 17–19 | 25–32 |
| 20–23 | 28–37 |
| 25–28 | 32–44 |
| 30–35 | 40–57 |
| 35–50 | 47–60+ (cruiser & fat) |
- Leave ~10 mm clearance around the tire (20 mm if adding fenders).
- Too narrow a tire on a wide rim → pinch flats/rim damage.
- Too wide a tire on a narrow rim → squirmy handling and sidewall stress.
5) Quick Size Reference (Popular Builds)
| Sidewall Label | ISO / ETRTO | Typical Use |
|---|---|---|
| 20 × 1.75 | 47-406 | BMX / Lowrider |
| 20 × 2.125 | 54-406 | Fat BMX / Lowrider Classic look |
| 24 × 1.75 | 47-507 | Cruiser |
| 26 × 2.125 | 54-559 | Beach cruiser / Lowrider |
| 27.5 × 2.10 | 54-584 | MTB (“27.5”) |
| 700 × 28C | 28-622 | Road / City |
| 29 × 2.25 | 57-622 | 29er MTB |
6) How to Measure Your Rim/Tire
- Look for the ISO/ETRTO on the tire (e.g., 37-622).
- No label? Measure your rim’s bead seat diameter (BSD) inside the flanges and the inner rim width.
- Choose a tire with the same BSD and a width that matches the rim using the chart above.
Tip: Allow ~10 mm clearance all around the tire (20 mm with fenders) at the fork crown, seatstay bridge, and chainstays.
7) FAQ
Will 26 × 1.75 and 26 × 1 ¾ interchange?
Usually no. Fractional vs decimal markings can refer to different BSDs. Always verify the ISO/ETRTO numbers.
What do 27.5″ and 29″ really mean?
27.5″ generally maps to ISO 584; 29″ maps to ISO 622. Width varies by model.
How wide can I go on my rims?
Use the width chart above. For cruisers/fat looks, match wide tires with wider rims (e.g., 35–50 mm rims with 47–60 mm+ tires).
Any clearance rules of thumb?
Leave ~10 mm around the tire (20 mm if adding fenders). Check fork crown, seatstay bridge, chainstays, and brake reach.