Why do car speedometers get marked higher than their top speeds?

174 viewsEngineeringOther

To start, I know that cars can go faster than typical speed limits because if you went on a freeway at 100km/h with a car that had the same top speed, you would essentially be pushing it to the limit constantly, which is not really good for the car.

My question is why do cars have their speedometers marked way higher than they can actually go? For example, my dad’s 2017 Toyota Yaris marks up to 220km/h but it could probably go no more than 150km/h tops, so could they not just mark the speedometer up to 150km/h because it’s not really going to go above that?

EDIT: FYI I live in Australia

In: Engineering

10 Answers

Anonymous 0 Comments

Because the off-the-shelf speedometer marking/housing probably costs 2 cents if they buy in bulk, and it would cost them 5 cents a unit to design a custom one and manufacture it themselves or 7 cents if they contract it out. Once you’re making millions of cars, the savings add up.

Anonymous 0 Comments

Traditionally old mechanical speedometers were more accurate in the centre of their range. You would often see a speedometer read 10-15 km/h wrong at the low speeds and although it was hard to test I presume this was the case for the high speeds as well. So you had to get a speedometer where the most common cruising speeds were in the middle of the range which meant it could go much higher. There was actually a US law in the early 80s requiring that speeds above 85mph were not marked but the speedometers were still the same as before.

Another reason is that it is much easier to see the top of the instrument dials when driving as this is much closer to the windscreen and therefore your sight line when driving. In some cars you can even see the top of the speedometer in your peripheral vision while looking at the road. So making sure the speed dial is pointing upwards makes it much easier to see. This is more prominent in old racing cars before they switched to digital dials as they would often turn the engine speed dial so the redline was at the top where they could better see it.

But as to the speed I bet you could get your Yaris up to higher speeds then 150 km/h if you tried hard enough. A long steep downhill could get you up to much higher speeds then on flat ground. And with different air pressures, different fuel, different temperatures, etc. the engine would perform differently and you could get more power out of it. Even things like bigger wheels could change the gear ratio and make you go faster.

Anonymous 0 Comments

In addition to the other comments, mountains exist, so good to know how fast you are going on the way down with a tail wind, rather than just burying the needle…

Anonymous 0 Comments

Most car manufacturers like a certain ‘look’ when you sit in them, they want the driver to know they’re sitting in a Toyota or a Kia … the instant they sit. One way to do thatvis to have the same gauges no matter what model car/truck/suv it is. As well, having only 1 style of gauge makes inventory easier. In 2017 toyota made a lot of cars and trucks that could easily go over 220.

Anonymous 0 Comments

My 96 Honda civic hatchback had a speedometer that went to 240 or something ridiculous.
It wouldn’t go that fast if you dropped it out of an airplane.

Anonymous 0 Comments

Because the top speed is tested on a flat road with not much wind. With a tailwind going downhill a car can reach much higher speeds.

I got a fiat doblo 95hp to 190km/h indicated going downhill with strong tailwind. It’s a freaking fridge but with the help of gravity and wind it was at 5000rpm, while max power is at 4000. I think the papers say top speed is 165.

Anonymous 0 Comments

A well designed analogue speedo is easiest to read when the needle is at a certain angle that is easy to recognize by only using peripheral vision. In Europe, most cars have speedos that point straight upward in the range between 120 to 140 kph, so you can easily control your highway speed without having to stare at the speedo for a couple of seconds. Euro speedos typically terminate at 240 to 260 kph, which puts 120 or 130 right in the middle of the scale.

Anonymous 0 Comments

The other people suggesting the positioning of an analogue needle being easier to read under certain conditions certainly is interesting, never heard of considered that before

But a more mundane answer is car manufacturers not only share parts between different models within a class, but also between classes and also between brands.

So often the poverty spec 1.2 Speedo will be on the higher end 2.0 model too… And even more so, the crappy little 1.2 hatchback might also share a Speedo with the 3.0 sedan… You sometimes even see switch great from a ford in an Aston Martin, as they are owned by the same parent company 

Anonymous 0 Comments

I used to be a product manager for a major automotive company. The reason now is purely for show.

Even now with digital dashes that simulate analog instruments, you’ll see sports sedans go up to 200mph or family vehicles show 160 – a number neither would be able to hit.

Even for cars that still have analog dashes, they are all unique and custom made for each model and on the backend actually digital/electronic. Sso it’s not a part commonality or accuracy issue at all – it’s purely to achieve the desired look that the product manager is going for.

Anonymous 0 Comments

They are likely to be common parts that are shared between various models/manufacturers for economy purposes.

Additionally, whilst in a practical normal use sense the Yaris you mentioned may only go to that speed, don’t forget modification of the vehicle/engine and specific conditions (for example, going downhill, un-laden etc) can affect the achievable speed.