The QR type hub is ideally suited to 20” wheel at 6V3W output or 26”/700C wheel at 6V2.4W output and perfect for rim brake. SP not only seeks to become No. 1 in specification, but also intends to closely monitor the quality of every single dynamo to ensure every dynamo is durable and reliable. SV-9, weight 309g, is for rim brake, suitable for all different sized wheel from 20” to 28”. It will certainly surprise you.