Speed(o) awareness

I've just returned from a Speed Awareness driving course. I was caught speeding at 35mph in a 30mph zone by the latest smart road traffic camera. Speed is measured very accurately by sensors buried in the road, and a picture of the offence and calibration certificates are available on line. My Lambretta is 58 years old, as is the speedo, which is my only way of telling what speed I'm doing. How can I possibly know my speed when I don't know how accurate my speedo is? Since it was manufactured, it has never been tested or calibrated, unlike the speed cameras on our roads. Also, there doesn't seem to be any way of getting it tested. Speedos are never tested when the bike is serviced, and during an MoT it's not even checked to see if it works. Checking on a Dyno won't work as the front wheel is locked during the test. Asking friends is no good, as most of their speedos don't work. Updating to a SIP speedo is good, but it's left up to you to calibrate it. So my question is, how do I know how fast I'm travelling?

Hi John, If your speedo doesn’t work properly, then of course you are at risk of accruing speeding penalties. If you have no confidence in its accuracy, then perhaps attach a GPS unit (like a satnav or mobile phone) to the scooter and measure your speedo’s suggested speed against the actual speed as indicated by the GPS, thus knowing in future, for example, that when your speedo reads 30mph, you are actually doing 35mph… and so on. Failing that, buy an aftermarket unit like the SIP digital speedo, for example, and have that fitted. Dan