Folding e-bikes serve a specific transit-connected commuter: someone who takes a subway or train for part of the journey and needs the bike to fit in a bag, under a desk, or in a vehicle. The Brompton Electric C Line and Tern HSD P9 solve that problem differently — Brompton with the world's most compact fold, Tern with a larger but heavier-duty platform that also handles cargo. The comparison isn't purely about specs; it's about which lifestyle the bike fits.

Specs Comparison

The Fold: Size and Speed

Brompton's fold is the benchmark the entire industry compares to. The Electric C Line folds to 585 x 565 x 270mm — a package you can carry in one hand into a coffee shop, tuck under an office desk, and store in a coat closet. The fold takes approximately 20 seconds once you've learned the sequence: rear triangle folds in, handlebars fold down, pedals fold in. The folded bike stands on its own without a stand.

The Tern HSD P9 folds, but to a much larger package. The folded dimensions are approximately 740 x 1,010 x 480mm — it won't fit under most desks or in a coat closet. It's more appropriately described as a 'compact transport mode' bike: you can store it in the back of a car, take it on a train if space allows, and fit it in a larger space. It's not the same tool as the Brompton for true transit integration.

For riders whose commute involves subway systems where folded bikes are allowed in the car: the Brompton is the only practical choice. It literally fits in a bag. The Tern is more of a 'store at the station' or 'fit in the car' bike.

Motor and Performance

Brompton uses a front hub motor rated at 250W nominal with 40Nm of torque — modest specs that reflect the bike's purpose as a transit connector rather than a long-distance vehicle. The motor assist on the Electric C Line is smooth and natural, working primarily to flatten hills and maintain speed with less effort. You will still pedal this bike; the motor assists, it doesn't dominate.

The Tern HSD P9 uses a Bosch Performance Line mid-drive motor at 250W nominal and 65Nm — nearly twice the torque of the Brompton's front hub motor. The Bosch system handles the HSD P9's cargo capacity requirements appropriately: loaded with a child in a front seat and groceries in the rear, the P9 climbs hills at a usable pace. The Brompton under comparable load would require hard pedaling on anything over a 6% grade.

For a flat urban commute with minimal hills: Brompton's front hub motor is entirely adequate. For a commuter who also wants the bike to handle cargo, hills, or longer rides: Tern's Bosch mid-drive is the right tool.

Weight and Carry

The Brompton Electric C Line weighs approximately 16.6 kg (36.6 lbs) — heavier than Brompton's non-electric models due to the motor and battery, but still light enough to carry up stairs or into a building without extreme effort. The front hub motor design keeps weight distribution manageable.

The Tern HSD P9 weighs approximately 27.3 kg (60 lbs) — a significant difference. You do not carry this bike casually. It's meant to roll, not to be lifted. For apartment dwellers who need to bring the bike inside and there's no elevator: the Brompton wins substantially.

Brompton's 270Wh battery provides approximately 25-50 miles of assisted range depending on terrain and assist level — less than most commuter e-bikes but generally sufficient for the 5-15 mile transit-connected commutes Brompton targets. Tern's HSD P9 uses a Bosch PowerTube 400Wh battery for 30-60 miles of range.

Cargo, Accessories, and Price

The Tern HSD P9 is a cargo bike that happens to fold. The rear rack is rated to 27 kg (60 lbs), and Tern's ecosystem includes a child seat (Atlas Lug) that mounts at the front via a Yepp Maxi Fit adapter. You can realistically replace a car for school drop-off and grocery shopping on the HSD P9 in a way that isn't practical on the Brompton.

Brompton's accessory ecosystem is deep and refined: a front carrier bag system accepts bags from multiple Brompton-partnered brands, there's a travel bag for the folded bike, and the handlebar bag mounts without tools. The bike is designed around its folded use case in a way no other manufacturer matches.

Pricing: Brompton Electric C Line ranges from £2,795 / ~$3,400 USD depending on configuration. The Tern HSD P9 retails at approximately $3,099 USD. Given the Tern's Bosch mid-drive motor and cargo capacity, its pricing is genuinely competitive. The Brompton's premium reflects decades of engineering refinement on the unique fold mechanism and the brand's London manufacturing.

Best For

• Brompton Electric C Line Transit-connected commuters who need the smallest possible fold to integrate with subway, train, or small-space storage
• Tern HSD P9 Riders who want a folding bike that can also serve as a cargo and child-hauling platform

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