In the UK, they used to put small engines in full-sized frames (maybe they still do). In the USA, small engines come in small frames. This does not work for bigger riders.The Grom looks on the small side. The Suzuki S40 single (650CC) is on the small side. I would love that 650 single in a larger frame, though. Say, a Sportster size, but built from aluminium, and with a single rear shock and single-sided swingarm to keep the weight down.