Crank length can make a big difference in how your Brompton feels, fits, and performs. Whether you’re tackling steep hills, riding long distances, or just looking for more comfort, the right crank size matters. Here’s how to decide.

Available Sizes 

We offer crank arms in six lengths:

• 155mm – Very short. Best for riders with shorter inseams or limited range of motion.

• 160mm – A good choice for shorter riders or those seeking high-cadence spinning.

• 165mm – Slightly shorter than stock, helps reduce knee and hip strain.

• 170mm – The Brompton standard. Works well for most riders.

• 172.5mm – Adds a bit more leverage. Best for taller riders.

• 175mm – Maximum leverage. Use with caution: increased risk of pedal strike on a Brompton.

What Crank Length Affects 

Crank arms are levers. Longer ones give more leverage, which can make climbing feel easier, while shorter ones reduce the range of motion required from your knees and hips. Here’s what that means in practice:

• Comfort: Shorter cranks keep your knees and hips in a more relaxed range of motion.

• Cadence: Short cranks make it easier to spin quickly and smoothly.

• Leverage: Long cranks give more mechanical advantage, but can stress joints.

• Clearance: Bromptons sit low. Longer cranks can increase pedal strike risk.

Anatomical Fit 

Crank length should match your body—especially your inseam. Here are some general guidelines:

• Inseam under 28” → consider 155mm or 160mm

• Inseam 28–30” → consider 160mm or 165mm

• Inseam 30–32” → 165mm or standard 170mm

• Inseam 32–34” → 170mm or 172.5mm

• Inseam over 34” → 172.5mm or possibly 175mm (if clearance allows)

These are not hard rules, but they’re a good place to start. Shorter riders typically benefit from shorter cranks, while taller riders may prefer the leverage of longer ones—provided it doesn’t impact comfort or pedal clearance.

Performance Considerations 

Crank length isn’t just about fit—it also affects how the bike rides:

• Climbing & Leverage: Longer cranks give more power per stroke, which can help on climbs, especially with high gearing.

• Cadence & Efficiency: Shorter cranks promote a faster, smoother pedal stroke, especially useful in stop-and-go urban riding.

• Acceleration: Shorter cranks can spin up faster; longer cranks deliver more torque.

If you’re a touring rider or ride with a loaded Brompton, you might appreciate the extra leverage of 172.5mm. But if you’re dealing with joint pain, or prioritize comfort and cadence, shorter cranks may be a better fit.

Accessibility & Comfort 

Shorter crank arms can greatly improve comfort for riders with:

• Knee or hip pain

• Limited range of motion

• Previous injuries or surgeries

They reduce the extremes of flexion at the top and bottom of your pedal stroke, making them ideal for anyone who wants to ride more comfortably—especially on longer trips or daily commutes.

Why Crank Length Matters More on a Brompton 

Bromptons are compact, and that affects everything—from fold clearance to pedal strike risk:

• Low bottom bracket = less ground clearance. That’s why we generally advise against cranks longer than 170mm.

• Fold compatibility. Some aftermarket cranks may interfere with Brompton’s fold. We only offer options that work cleanly.

• Shorter cranks improve tight cornering. You’re less likely to clip a pedal on a sharp turn.

Bottom Line: 

• Crank length affects comfort, cadence, leverage, and fit.

• Shorter cranks (155–165mm) suit shorter riders and those prioritizing comfort or recovery.

• Standard 170mm works for most people.

• Taller riders may benefit from 172.5mm or 175mm, but should be cautious of pedal clearance.

Still unsure? We’re happy to help you choose the right fit based on your inseam, riding style, and goals. Just reach out!

Ride what feels right. We’ll make sure it fits.