David Atkinson's advice...
As it came for the factory, the VBC Super was designed to have 8” wheels. If you have 10” wheels then something is amiss. Perhaps you have wheel rim extenders. That is, a metal annulus that allows you to bolt on 10” rims onto your 8” brake drums. If so not only won’t the brakes work as well as they should, but you will have trouble getting up to a decent speed if the transmission hasn’t been altered accordingly. Piaggio engineers got it pretty right across all their various models in terms of a balance of power, speed, fuel economy and exhaust noise. The choice of gear ratios was part of their considerations.
As a guide to typical performance, a stock Super with a good motor should easily reach 90 kms/hr on the flat and a little more. I’ve had my Super since new and on my way back from Sydney in 1969 I was able to pass many vehicles on the Hume. Of course in those days there were cars and trucks from the 1940-50s but it was a quick machine compared to many others in its day.
At higher speeds, a lot of engine power goes towards overcoming wind resistance. If your Super has a standard VBC gearbox then it may not have the power push along 10” wheels. The revs might be too low for the motor to get into a power band to cope with the very high gearing those 10” wheels give you. With 8” wheels, although the motor will be revving higher, it will be producing more power which will lead to a higher road speed. Do you know if the previous owner changed the gear ratios to match the 10” wheels?
All good - have sourced the correct 8" rims.