why do speedometers go as high as 140 – 160 mph but some average cars can’t go faster than 100 -120?
In: Technology
I believe the speedo is determined by engine rpm, transmission ratio in top gear and diff ratio. with no resistance, the engine at redline in top gear, the rear wheels should be that number.
Not sure how factual that is but my car has multiple different clusters with different red rpm numbers and speeds for different engine packages
I’d suspect it’s a holdover from mechanical gauges. Mechanical gauges are usually most accurate in the middle 1/3 of the range (e.x. a 0-120 gauge is most accurate in the 40-80 range).
With digital gauges this doesn’t matter because our speedometers are run by a sensor and motor so there’s no middle 1/3 benefit.
can you imagine if speedometers only went up to like 80MPH. then when you get pulled over and get asked “do you have any idea how fast you were going?” and you could honestly say “I have no idea officer.”
Assuming you’re in the US formal, then informal agreement to keep maximum acceptable speed limit range near the top. It helps you differentiate better than other angles.
Original version was a terrible implementation that actually had the limit at the end during the oil crysis. Important thing to note is your hand is often there in the way when driving. If you’re actually doing 160+ you won’t be looking down regardless
It seems like there may be a lot of speculation in this thread without any actual sources (e.g. “Because you can go downhill!”).
[The answer seems to be a mix of convention, marketing, and making things symmetrical and easy to read.](https://www.cnn.com/2022/09/10/business/speedometers-160-mph/index.html)
>Toyota spokesman Paul Hogard said the automaker wants speedometers to be easy to read, so there’s value in placing the typical operating speed of American cars, 45 mph to 70 mph, he said, at the top of the speedometer, which is the easiest place on the speedometer for the driver to read. To do this – while maintaining a visually-appealing, symmetrical speedometer – requires a gauge that displays well past operating speeds, he said.
One thing I haven’t seen mentioned that I’ve heard before is that it has to do with where the more commonly traveled speeds are placed. Most cars that have the round gauge on the right will have 60-80 mph somewhere close to the top, with the slower speeds of 0-40 closer to the middle. It isn’t as easy for your eyes to look down and a little ways to the right as it is to look down and slightly to the right.
Don’t know how much truth there is to that or how much it is taken into consideration, but it seems reasonable.
My parents had a 90’s suburban with a speedo that topped out at 80 mph. But the truck would definitely go faster than that. I suspect the choice of speedometer range is primarily a marketing/aesthetics thing and not a technical thing.
History lesson time, you little ones, gather ’round. There was a time, before mummy and daddy made you, that Congress (antonym of Progress) mandated 85 MPH speedometers, but consumers absolutely despised them. A few people could peg the speedometer, yet be able to estimate speed off the tachometer anyway, since the car was clearly running in the top gear, with a known ratio between the speedo and the tach. But mostly, it gave the impression to prospective customers that if 85 MPH was all the car could do, it was just wimpy and underpowered. It didn’t help that automakers were experimenting with high-mileage 6 and 4 cylinder cars at the same time. Congress eventually dropped the mandate, just as they backed off mandated 55 MPH highway speed limits and the automatic seat belts that would try to strangle you when you closed the door.
These things may be so far in the past that mere 5 year olds like yourselves don’t remember these things that were tried and failed. The 85 MPH speedometer law was enacted in 1979 and revoked in 1982. The law also required highlighting 55 MPH on the speedo, which was the mandated maximum speed limit at the time, in an effort to reduce gasoline consumption following big price hikes attributed to the Arab oil embargo.
You ypung whippersnappers probably weren’t alive when the Windfall Profit Tax was enacted because oil companies made out like bandits when gasoline prices rose like crazy and all their oil reserves were repriced to the new market reality. Nor could you remember gas rationing to about half a tank per fill-up or the even-odd rationing based on the last number in your license plate (very few people had vanity plates, and I’ve forgotten whether they were counted as odd or even). Families swapped cars so they could have one with an even plate and one with an odd plate.
One oul company: Shell, even tried to get Americans to buy gasoline in liters instead of gallons so they wouldn’t have to replace gas pumps to add a digit to the price per unit when oil prices got close to the plainly unbearable price of $1.00 per gallon. It’s a big factor in why the metric system is despised to this day. Highway signs of that era were starting to display distances to remote cities in both miles and kilometers until that time.
But in the end, Reagan illegally got the American hostages locked up in Iran for several extra months, so Jimmy Carter couldn’t take credit for negotiating their release, and it was sunrise in America again, and all was well ever after except for those damned polluting trees.
The main reasons are probably marketing and readability, but there’s another issue I haven’t seen mentioned yet: It makes sure that you’ll always know when you’re breaking the law, and by how much.
Imagine all speedometers maxed out at 80, but then they open a road where the speed limit is 85. You want to go 85 on this road, but…the thing maxes out at 80, so there’s no way to know if you’re *actually* traveling 80 or 85 or 90. So if you get pulled over you can honestly claim “I didn’t know how fast I was going!”
So it helps to make the max on the speedometer *much* higher than the current maximum speed limit. That way cautious drivers will always be able to go exactly the speed limit even if speed limits increase, and dangerous drivers won’t be able to pretend that they had no idea that they were driving at insane speeds.
Average car can def go more than 120 now. They’re limited. Usually by tires, but electronically limited.
Also, it’s perception. When you get into an econobox that goes to 110, it feels normal and expected. At 60mph that needle is past halfway so it feels different. Luxury cars not even sports cars often have higher speedometers for the perception of speed and capability when it’s probably limited to 120 anyways.
Take a Look at the Nissan GTR speedometer. 60mph is almost where 0 is on most cars. Aston Martin does reverse gauges I think. It’s all about perception IMO.
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