My own.
Most analogue speedometers max out at about 200 – 240km/h and use about 270 degrees of rotation. Given that the speed limit in Australia is usually 100 – 110km/h this means that the entire scope of legal activity is conducted in less than 140 degrees, limiting notational accuracy.
The two cars that I own currently would not get anywhere near the top end of their speedometer. The first has a top speed of about 170km/h, but the speedometer goes up to 200. The second makes it to 200, but the speedometer goes to 240. I previously owned a car that would struggle to 110, but you wouldn’t know that from the speedometer. And, before you ask, the top speed was limited by gearing.
In the 1980s digital speedometers solved this problem by dealing only with the present. It didn’t matter what speed your car could achieve, you saw your current speed and that was it. Unfortunately when accelerating hard, it became hard to ‘hit’ a certain speed. With an analogue speedometer you could see the needle approaching your aimed at speed. Not so with digital.
Some speedometers have two sets of numbers, one for km/h and one for mph. So why not have two sets of numbers for low and high speed operation. The numbers could start at 0, with an entire rotation indicating 150, for example. A needle pointing at 100 would also be pointing at 250. The difference of 150km/h is large enough to avoid confusion – “I wonder whether I’m at 40 or 190?” These numbers mean that 0 – 100km/h covers 240 degrees of rotation.
There’s a major problem with this system: the needle that stops the speedometer reading dropping below zero. This needle also stops the speedometer covering more than 360 degrees. An easy fix – have it automatically retract when getting close (for example, at 270 degrees of rotation).
Does this exist already. I don’t know. However, I think this provides the best of both worlds – a high speed readout with low speed accuracy.
