Hi,

You need a simple computer that tells you how fast you are going.

Once you know your typical speed and gear its easy to convert that into cadence.

E.g, I know on my folder ~ 15 mph in top gear is ~ 80 rpm, it is quite easy to pedal
that fast on the flat. Flat, with wind behind me I can easily pedal ~ 18 mph, ~ 95 rpm.

It doesn't take long to have a very good idea how fast you are pedaling.

With the wind behind me on the flat I hit 28 mph in 5th on my road bike
and a quick calculation indicated that to get there I was doing ~ 120 rpm.

rgds, sreten.

50+ so my numbers are very realistic for most.