650B Geometry
Frame Sizing Guide
Find your perfect bamboo frame size in 3 minutes
Why Frame Size Matters
An ill-fitting frame isn't just uncomfortable — it changes how your bike handles and increases your risk of injury. Too large, and you'll be stretched out with poor leverage on climbs. Too small, and you'll feel cramped.
Two Key Measurements
Just two numbers determine your ideal frame size.
1. Your Height (Standing Measurement)
- Stand barefoot with your back against a wall
- Mark the top of your head on the wall
- Measure from floor to mark in centimetres
2. Your Inner Leg Length (Inseam)
This is the most important measurement for bike fit.
- Remove your shoes
- Stand with your back against a wall, feet 15cm apart
- Place a spirit level horizontally between your legs (as if you're sitting on a bike seat)
- Measure from the floor to the top of the level in centimetres
Pro tip: Have a friend help you take both measurements. It's easier and more accurate.
BBC Frame Size Chart
Find your size by matching your inseam to the chart below. Your inseam is the primary determinant — if you fall between sizes, use the height range as a secondary check.
| Size | Height Range | Inseam Range | Seat Tube | Top Tube |
|---|---|---|---|---|
| XS | 148–163 cm | 68–74 cm | 40 cm | 48 cm |
| S | 160–173 cm | 74–80 cm | 46 cm | 51 cm |
| M | 170–183 cm | 78–86 cm | 52 cm | 54 cm |
| L | 180–193 cm | 84–92 cm | 56 cm | 57 cm |
| XL | 190–203 cm | 90–100 cm | 60 cm | 60 cm |
| 2XL | 200+ cm | 98+ cm | 64 cm | 63 cm |
Frequently Asked Questions
I'm between two sizes. Which should I choose?
Answer: Use your inseam. If your inseam is exactly between two ranges, consider your riding style: want more comfort? Choose the larger frame. Want more speed? Choose the smaller frame. Unsure? Email us.
What if I have long arms and short legs (or vice versa)?
Answer: This is exactly why we offer so many sizes. Email us with your measurements and we'll recommend specific sizes that suit your proportions.
Can I size up or down based on riding type?
Answer: Yes, carefully. Size up for long-distance touring (more comfort). Size down for racing (more control). But start with your inseam-based size and adjust from there.
I've never built a bike. Does sizing still matter?
Answer: Absolutely. A poorly-sized frame is uncomfortable and potentially injurious, no matter how well it's built. Spend 3 minutes to measure properly.
What if my size isn't in stock?
Answer: We can often custom-build frames to unusual sizes. Contact us to discuss options.
Still Have Questions?
We're here to help. Get in touch — no measurement is too unusual.
Ready to Build?
Last updated: March 2026. Geometry specs subject to change based on current designs. Always measure yourself before ordering.