Before buying a hub-motor ebike conversion kit, check four frame measurements. You only need a ruler or tape measure — but make sure it is long enough.
1. Front and rear dropout width
- Front dropout: measure between the inner faces of the fork axle slots. Most Voilamart front kits fit about 100mm (100–103mm).
- Rear dropout: measure between the inner faces of the rear frame axle slots. Most Voilamart rear kits fit about 135mm (135–137mm).
- Fat-tire, beach-cruiser, and snow bikes may use wider dropouts, so measure them individually.
2. Wheel diameter
On a bare frame, measure from the dropout axle slot to the bottom bracket for the rear wheel, or to the fork bottom for the front wheel, then double that “half diameter”. On a complete bike, read the tire sidewall marking, which usually shows the wheel diameter and tire width together.
3. Maximum tire width
Measure the available width near the bottom bracket and fork bottom. If the tire is too wide, it will rub the frame or fork and the wheel will not spin freely.
4. Dropout space and axle fit
Check that the dropout opening can accept the hub-motor axle. Voilamart hub-motor axles are typically oval at about 10mm × 9mm.
Important before ordering
- A rear hub-motor wheel is only for the rear frame; a front hub-motor wheel is only for the front fork.
- Dropout width is mostly fixed and can only be adjusted slightly with spacers.
- Buying the wrong size costs time, even if the item can be returned.
Next, read how to choose the right ebike voltage before finalizing your kit.