The sprocket included with the ZoomBicycles engine kit is designed to be coupled with a 36 spoke rear wheel. Some bicycle manufacturers offer wheels with 32 or fewer spokes (or in some cases, more than 36), and so the resulting hole pattern will not line up with the bolts. This will often result in bent or damaged spokes, and may cause issues down the line. For ease of installation, make sure the wheel has 36 spokes exactly.